


Network Working Group                                       D. Farinacci
Internet-Draft                                                 V. Fuller
Intended status: Experimental                                   D. Meyer
Expires: August 15, 2012                                        D. Lewis
                                                           cisco Systems
                                                       February 12, 2012


                 Locator/ID Separation Protocol (LISP)
                           draft-ietf-lisp-22

Abstract

   This draft describes a network layer based protocol that enables
   separation of IP addresses into two new numbering spaces: Endpoint
   Identifiers (EIDs) and Routing Locators (RLOCs).  No changes are
   required to either host protocol stacks or to the "core" of the
   Internet infrastructure.  LISP can be incrementally deployed, without
   a "flag day", and offers traffic engineering, multi-homing, and
   mobility benefits to early adopters, even when there are relatively
   few LISP-capable sites.

   Design and development of LISP was largely motivated by the problem
   statement produced by the October 2006 IAB Routing and Addressing
   Workshop.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 15, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  5
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  8
   4.  Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 14
     4.1.  Packet Flow Sequence . . . . . . . . . . . . . . . . . . . 16
   5.  LISP Encapsulation Details . . . . . . . . . . . . . . . . . . 18
     5.1.  LISP IPv4-in-IPv4 Header Format  . . . . . . . . . . . . . 19
     5.2.  LISP IPv6-in-IPv6 Header Format  . . . . . . . . . . . . . 19
     5.3.  Tunnel Header Field Descriptions . . . . . . . . . . . . . 21
     5.4.  Dealing with Large Encapsulated Packets  . . . . . . . . . 25
       5.4.1.  A Stateless Solution to MTU Handling . . . . . . . . . 25
       5.4.2.  A Stateful Solution to MTU Handling  . . . . . . . . . 26
     5.5.  Using Virtualization and Segmentation with LISP  . . . . . 26
   6.  EID-to-RLOC Mapping  . . . . . . . . . . . . . . . . . . . . . 28
     6.1.  LISP IPv4 and IPv6 Control Plane Packet Formats  . . . . . 28
       6.1.1.  LISP Packet Type Allocations . . . . . . . . . . . . . 30
       6.1.2.  Map-Request Message Format . . . . . . . . . . . . . . 30
       6.1.3.  EID-to-RLOC UDP Map-Request Message  . . . . . . . . . 33
       6.1.4.  Map-Reply Message Format . . . . . . . . . . . . . . . 34
       6.1.5.  EID-to-RLOC UDP Map-Reply Message  . . . . . . . . . . 38
       6.1.6.  Map-Register Message Format  . . . . . . . . . . . . . 40
       6.1.7.  Map-Notify Message Format  . . . . . . . . . . . . . . 42
       6.1.8.  Encapsulated Control Message Format  . . . . . . . . . 43
     6.2.  Routing Locator Selection  . . . . . . . . . . . . . . . . 45
     6.3.  Routing Locator Reachability . . . . . . . . . . . . . . . 47
       6.3.1.  Echo Nonce Algorithm . . . . . . . . . . . . . . . . . 49
       6.3.2.  RLOC Probing Algorithm . . . . . . . . . . . . . . . . 50
     6.4.  EID Reachability within a LISP Site  . . . . . . . . . . . 51
     6.5.  Routing Locator Hashing  . . . . . . . . . . . . . . . . . 52
     6.6.  Changing the Contents of EID-to-RLOC Mappings  . . . . . . 53
       6.6.1.  Clock Sweep  . . . . . . . . . . . . . . . . . . . . . 54
       6.6.2.  Solicit-Map-Request (SMR)  . . . . . . . . . . . . . . 54
       6.6.3.  Database Map Versioning  . . . . . . . . . . . . . . . 56
   7.  Router Performance Considerations  . . . . . . . . . . . . . . 57
   8.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 58



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     8.1.  First-hop/Last-hop Tunnel Routers  . . . . . . . . . . . . 59
     8.2.  Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 59
     8.3.  ISP Provider-Edge (PE) Tunnel Routers  . . . . . . . . . . 60
     8.4.  LISP Functionality with Conventional NATs  . . . . . . . . 60
     8.5.  Packets Egressing a LISP Site  . . . . . . . . . . . . . . 61
   9.  Traceroute Considerations  . . . . . . . . . . . . . . . . . . 62
     9.1.  IPv6 Traceroute  . . . . . . . . . . . . . . . . . . . . . 63
     9.2.  IPv4 Traceroute  . . . . . . . . . . . . . . . . . . . . . 63
     9.3.  Traceroute using Mixed Locators  . . . . . . . . . . . . . 63
   10. Mobility Considerations  . . . . . . . . . . . . . . . . . . . 65
     10.1. Site Mobility  . . . . . . . . . . . . . . . . . . . . . . 65
     10.2. Slow Endpoint Mobility . . . . . . . . . . . . . . . . . . 65
     10.3. Fast Endpoint Mobility . . . . . . . . . . . . . . . . . . 65
     10.4. Fast Network Mobility  . . . . . . . . . . . . . . . . . . 67
     10.5. LISP Mobile Node Mobility  . . . . . . . . . . . . . . . . 67
   11. Multicast Considerations . . . . . . . . . . . . . . . . . . . 69
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 70
   13. Network Management Considerations  . . . . . . . . . . . . . . 72
   14. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 73
     14.1. LISP ACT and Flag Fields . . . . . . . . . . . . . . . . . 73
     14.2. LISP Address Type Codes  . . . . . . . . . . . . . . . . . 73
     14.3. LISP UDP Port Numbers  . . . . . . . . . . . . . . . . . . 73
     14.4. LISP Key ID Numbers  . . . . . . . . . . . . . . . . . . . 74
   15. Known Open Issues and Areas of Future Work . . . . . . . . . . 75
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 77
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 77
     16.2. Informative References . . . . . . . . . . . . . . . . . . 78
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 82
   Appendix B.  Document Change Log . . . . . . . . . . . . . . . . . 83
     B.1.  Changes to draft-ietf-lisp-22.txt  . . . . . . . . . . . . 83
     B.2.  Changes to draft-ietf-lisp-21.txt  . . . . . . . . . . . . 83
     B.3.  Changes to draft-ietf-lisp-20.txt  . . . . . . . . . . . . 83
     B.4.  Changes to draft-ietf-lisp-19.txt  . . . . . . . . . . . . 83
     B.5.  Changes to draft-ietf-lisp-18.txt  . . . . . . . . . . . . 83
     B.6.  Changes to draft-ietf-lisp-17.txt  . . . . . . . . . . . . 83
     B.7.  Changes to draft-ietf-lisp-16.txt  . . . . . . . . . . . . 83
     B.8.  Changes to draft-ietf-lisp-15.txt  . . . . . . . . . . . . 84
     B.9.  Changes to draft-ietf-lisp-14.txt  . . . . . . . . . . . . 84
     B.10. Changes to draft-ietf-lisp-13.txt  . . . . . . . . . . . . 84
     B.11. Changes to draft-ietf-lisp-12.txt  . . . . . . . . . . . . 85
     B.12. Changes to draft-ietf-lisp-11.txt  . . . . . . . . . . . . 86
     B.13. Changes to draft-ietf-lisp-10.txt  . . . . . . . . . . . . 87
     B.14. Changes to draft-ietf-lisp-09.txt  . . . . . . . . . . . . 88
     B.15. Changes to draft-ietf-lisp-08.txt  . . . . . . . . . . . . 88
     B.16. Changes to draft-ietf-lisp-07.txt  . . . . . . . . . . . . 90
     B.17. Changes to draft-ietf-lisp-06.txt  . . . . . . . . . . . . 91
     B.18. Changes to draft-ietf-lisp-05.txt  . . . . . . . . . . . . 92
     B.19. Changes to draft-ietf-lisp-04.txt  . . . . . . . . . . . . 93



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     B.20. Changes to draft-ietf-lisp-03.txt  . . . . . . . . . . . . 95
     B.21. Changes to draft-ietf-lisp-02.txt  . . . . . . . . . . . . 95
     B.22. Changes to draft-ietf-lisp-01.txt  . . . . . . . . . . . . 95
     B.23. Changes to draft-ietf-lisp-00.txt  . . . . . . . . . . . . 96
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 97














































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1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].














































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2.  Introduction

   This document describes the Locator/Identifier Separation Protocol
   (LISP), which provides a set of functions for routers to exchange
   information used to map from non globally routeable Endpoint
   Identifiers (EIDs) to routeable Routing Locators (RLOCs).  It also
   defines a mechanism for these LISP routers to encapsulate IP packets
   addressed with EIDs for transmission across the< Internet that uses
   RLOCs for routing and forwarding.

   Creation of LISP was initially motivated by discussions during the
   IAB-sponsored Routing and Addressing Workshop held in Amsterdam in
   October, 2006 (see [RFC4984]).  A key conclusion of the workshop was
   that the Internet routing and addressing system was not scaling well
   in the face of the explosive growth of new sites; one reason for this
   poor scaling is the increasing number of multi-homed and other sites
   that cannot be addressed as part of topologically- or provider-based
   aggregated prefixes.  Additional work that more completely described
   the problem statement may be found in [RADIR].

   A basic observation, made many years ago in early networking research
   such as that documented in [CHIAPPA] and [RFC4984], is that using a
   single address field for both identifying a device and for
   determining where it is topologically located in the network requires
   optimization along two conflicting axes: for routing to be efficient,
   the address must be assigned topologically; for collections of
   devices to be easily and effectively managed, without the need for
   renumbering in response to topological change (such as that caused by
   adding or removing attachment points to the network or by mobility
   events), the address must explicitly not be tied to the topology.

   The approach that LISP takes to solving the routing scalability
   problem is to replace IP addresses with two new types of numbers:
   Routing Locators (RLOCs), which are topologically assigned to network
   attachment points (and are therefore amenable to aggregation) and
   used for routing and forwarding of packets through the network; and
   Endpoint Identifiers (EIDs), which are assigned independently from
   the network topology, are used for numbering devices, and are
   aggregated along administrative boundaries.  LISP then defines
   functions for mapping between the two numbering spaces and for
   encapsulating traffic originated by devices using non-routeable EIDs
   for transport across a network infrastructure that routes and
   forwards using RLOCs.  Both RLOCs and EIDs are syntactically-
   identical to IP addresses; it is the semantics of how they are used
   that differs.

   This document describes the protocol that implements these functions.
   The database which stores the mappings between EIDs and RLOCs is



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   explicitly a separate "module" to facilitate experimentation with a
   variety of approaches.  One database design that is being developed
   for experimentation as part of the LISP working group work is [ALT].
   Others that have been described include [CONS], [EMACS], [NERD].
   Finally, [LISP-MS], documents a general-purpose service interface for
   accessing a mapping database; this interface is intended to make the
   mapping database modular so that different approaches can be tried
   without the need to modify installed LISP capable devices in LISP
   sites.

   This experimental specification has areas that require additional
   experience and measurement.  It is NOT RECOMMENDED for deployment
   beyond experimental situations.  Results of experimentation may lead
   to modifications and enhancements of protocol mechanisms defined in
   this document.  See Section 15 for specific, known issues that are in
   need of further work during development, implementation, and
   experimentation.

   An examination of the implications of LISP on Internet traffic,
   applications, routers, and security is for future study.  This
   analysis will explain what role LISP can play in scalable routing and
   will also look at scalability and levels of state required for
   encapsulation, decapsulation, liveness, and so on.




























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3.  Definition of Terms

   Provider Independent (PI) Addresses:   PI addresses are an address
      block assigned from a pool where blocks are not associated with
      any particular location in the network (e.g. from a particular
      service provider), and is therefore not topologically aggregatable
      in the routing system.

   Provider Assigned (PA) Addresses:   PA addresses are an address block
      assigned to a site by each service provider to which a site
      connects.  Typically, each block is sub-block of a service
      provider Classless Inter-Domain Routing (CIDR) [RFC4632] block and
      is aggregated into the larger block before being advertised into
      the global Internet.  Traditionally, IP multihoming has been
      implemented by each multi-homed site acquiring its own, globally-
      visible prefix.  LISP uses only topologically-assigned and
      aggregatable address blocks for RLOCs, eliminating this
      demonstrably non-scalable practice.

   Routing Locator (RLOC):   A RLOC is an IPv4 [RFC0791] or IPv6
      [RFC2460] address of an egress tunnel router (ETR).  A RLOC is the
      output of an EID-to-RLOC mapping lookup.  An EID maps to one or
      more RLOCs.  Typically, RLOCs are numbered from topologically-
      aggregatable blocks that are assigned to a site at each point to
      which it attaches to the global Internet; where the topology is
      defined by the connectivity of provider networks, RLOCs can be
      thought of as PA addresses.  Multiple RLOCs can be assigned to the
      same ETR device or to multiple ETR devices at a site.

   Endpoint ID (EID):   An EID is a 32-bit (for IPv4) or 128-bit (for
      IPv6) value used in the source and destination address fields of
      the first (most inner) LISP header of a packet.  The host obtains
      a destination EID the same way it obtains an destination address
      today, for example through a Domain Name System (DNS) [RFC1034]
      lookup or Session Invitation Protocol (SIP) [RFC3261] exchange.
      The source EID is obtained via existing mechanisms used to set a
      host's "local" IP address.  An EID used on the public Internet
      must have the same properties as any other IP address used in that
      manner; this means, among other things, that it must be globally
      unique.  An EID is allocated to a host from an EID-prefix block
      associated with the site where the host is located.  An EID can be
      used by a host to refer to other hosts.  EIDs MUST NOT be used as
      LISP RLOCs.  Note that EID blocks MAY be assigned in a
      hierarchical manner, independent of the network topology, to
      facilitate scaling of the mapping database.  In addition, an EID
      block assigned to a site may have site-local structure
      (subnetting) for routing within the site; this structure is not
      visible to the global routing system.  In theory, the bit string



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      that represents an EID for one device can represent an RLOC for a
      different device.  As the architecture is realized, if a given bit
      string is both an RLOC and an EID, it must refer to the same
      entity in both cases.  When used in discussions with other
      Locator/ID separation proposals, a LISP EID will be called a
      "LEID".  Throughout this document, any references to "EID" refers
      to an LEID.

   EID-prefix:   An EID-prefix is a power-of-two block of EIDs which are
      allocated to a site by an address allocation authority.  EID-
      prefixes are associated with a set of RLOC addresses which make up
      a "database mapping".  EID-prefix allocations can be broken up
      into smaller blocks when an RLOC set is to be associated with the
      larger EID-prefix block.  A globally routed address block (whether
      PI or PA) is not inherently an EID-prefix.  A globally routed
      address block MAY be used by its assignee as an EID block.  The
      converse is not supported.  That is, a site which receives an
      explicitly allocated EID-prefix may not use that EID-prefix as a
      globally routed prefix.  This would require coordination and
      cooperation with the entities managing the mapping infrastructure.
      Once this has been done, that block could be removed from the
      globally routed IP system, if other suitable transition and access
      mechanisms are in place.  Discussion of such transition and access
      mechanisms can be found in [INTERWORK] and [LISP-DEPLOY].

   End-system:   An end-system is an IPv4 or IPv6 device that originates
      packets with a single IPv4 or IPv6 header.  The end-system
      supplies an EID value for the destination address field of the IP
      header when communicating globally (i.e. outside of its routing
      domain).  An end-system can be a host computer, a switch or router
      device, or any network appliance.

   Ingress Tunnel Router (ITR):   An ITR is a router that resides in a
      LISP site.  Packets sent by sources inside of the LISP site to
      destinations outside of the site are candidates for encapsulation
      by the ITR.  The ITR treats the IP destination address as an EID
      and performs an EID-to-RLOC mapping lookup.  The router then
      prepends an "outer" IP header with one of its globally-routable
      RLOCs in the source address field and the result of the mapping
      lookup in the destination address field.  Note that this
      destination RLOC MAY be an intermediate, proxy device that has
      better knowledge of the EID-to-RLOC mapping closer to the
      destination EID.  In general, an ITR receives IP packets from site
      end-systems on one side and sends LISP-encapsulated IP packets
      toward the Internet on the other side.






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      Specifically, when a service provider prepends a LISP header for
      Traffic Engineering purposes, the router that does this is also
      regarded as an ITR.  The outer RLOC the ISP ITR uses can be based
      on the outer destination address (the originating ITR's supplied
      RLOC) or the inner destination address (the originating hosts
      supplied EID).

   TE-ITR:   A TE-ITR is an ITR that is deployed in a service provider
      network that prepends an additional LISP header for Traffic
      Engineering purposes.

   Egress Tunnel Router (ETR):   An ETR is a router that accepts an IP
      packet where the destination address in the "outer" IP header is
      one of its own RLOCs.  The router strips the "outer" header and
      forwards the packet based on the next IP header found.  In
      general, an ETR receives LISP-encapsulated IP packets from the
      Internet on one side and sends decapsulated IP packets to site
      end-systems on the other side.  ETR functionality does not have to
      be limited to a router device.  A server host can be the endpoint
      of a LISP tunnel as well.

   TE-ETR:   A TE-ETR is an ETR that is deployed in a service provider
      network that strips an outer LISP header for Traffic Engineering
      purposes.

   xTR:   A xTR is a reference to an ITR or ETR when direction of data
      flow is not part of the context description. xTR refers to the
      router that is the tunnel endpoint.  Used synonymously with the
      term "Tunnel Router".  For example, "An xTR can be located at the
      Customer Edge (CE) router", meaning both ITR and ETR functionality
      is at the CE router.

   LISP Router:   A LISP router is a router that performs the functions
      of any or all of ITR, ETR, PITR, or PETR.

   EID-to-RLOC Cache:   The EID-to-RLOC cache is a short-lived, on-
      demand table in an ITR that stores, tracks, and is responsible for
      timing-out and otherwise validating EID-to-RLOC mappings.  This
      cache is distinct from the full "database" of EID-to-RLOC
      mappings, it is dynamic, local to the ITR(s), and relatively small
      while the database is distributed, relatively static, and much
      more global in scope.

   EID-to-RLOC Database:   The EID-to-RLOC database is a global
      distributed database that contains all known EID-prefix to RLOC
      mappings.  Each potential ETR typically contains a small piece of
      the database: the EID-to-RLOC mappings for the EID prefixes
      "behind" the router.  These map to one of the router's own,



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      globally-visible, IP addresses.  The same database mapping entries
      MUST be configured on all ETRs for a given site.  In a steady
      state the EID-prefixes for the site and the locator-set for each
      EID-prefix MUST be the same on all ETRs.  Procedures to enforce
      and/or verify this are outside the scope of this document.  Note
      that there MAY be transient conditions when the EID-prefix for the
      site and locator-set for each EID-prefix may not be the same on
      all ETRs.  This has no negative implications since a partial set
      of locators can be used.

   Recursive Tunneling:   Recursive tunneling occurs when a packet has
      more than one LISP IP header.  Additional layers of tunneling MAY
      be employed to implement traffic engineering or other re-routing
      as needed.  When this is done, an additional "outer" LISP header
      is added and the original RLOCs are preserved in the "inner"
      header.  Any references to tunnels in this specification refers to
      dynamic encapsulating tunnels and they are never statically
      configured.

   Reencapsulating Tunnels:   Reencapsulating tunneling occurs when an
      ETR removes a LISP header, then acts as an ITR to prepend another
      LISP header.  Doing this allows a packet to be re-routed by the
      re-encapsulating router without adding the overhead of additional
      tunnel headers.  Any references to tunnels in this specification
      refers to dynamic encapsulating tunnels and they are never
      statically configured.  When using multiple mapping database
      systems, care must be taken to not create reencapsulation loops
      through misconfiguration.

   LISP Header:   a term used in this document to refer to the outer
      IPv4 or IPv6 header, a UDP header, and a LISP-specific 8-octet
      header that follows the UDP header, an ITR prepends or an ETR
      strips.

   Address Family Identifier (AFI):   a term used to describe an address
      encoding in a packet.  An address family currently pertains to an
      IPv4 or IPv6 address.  See [AFI]/[AFI-REGISTRY] and [RFC3232] for
      details.  An AFI value of 0 used in this specification indicates
      an unspecified encoded address where the length of the address is
      0 octets following the 16-bit AFI value of 0.

   Negative Mapping Entry:   A negative mapping entry, also known as a
      negative cache entry, is an EID-to-RLOC entry where an EID-prefix
      is advertised or stored with no RLOCs.  That is, the locator-set
      for the EID-to-RLOC entry is empty or has an encoded locator count
      of 0.  This type of entry could be used to describe a prefix from
      a non-LISP site, which is explicitly not in the mapping database.
      There are a set of well defined actions that are encoded in a



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      Negative Map-Reply (Section 6.1.5).

   Data Probe:   A data-probe is a LISP-encapsulated data packet where
      the inner header destination address equals the outer header
      destination address used to trigger a Map-Reply by a decapsulating
      ETR.  In addition, the original packet is decapsulated and
      delivered to the destination host if the destination EID is in the
      EID-prefix range configured on the ETR.  Otherwise, the packet is
      discarded.  A Data Probe is used in some of the mapping database
      designs to "probe" or request a Map-Reply from an ETR; in other
      cases, Map-Requests are used.  See each mapping database design
      for details.  When using Data Probes, by sending Map-Requests on
      the underlying routing system, EID-prefixes must be advertised.
      However, this is discouraged if the core is to scale by having
      less EID-prefixes stored in the core router's routing tables.

   Proxy ITR (PITR):   A PITR is defined and described in [INTERWORK], a
      PITR acts like an ITR but does so on behalf of non-LISP sites
      which send packets to destinations at LISP sites.

   Proxy ETR (PETR):   A PETR is defined and described in [INTERWORK], a
      PETR acts like an ETR but does so on behalf of LISP sites which
      send packets to destinations at non-LISP sites.

   Route-returnability:  is an assumption that the underlying routing
      system will deliver packets to the destination.  When combined
      with a nonce that is provided by a sender and returned by a
      receiver, this limits off-path data insertion.  A route-
      returnability check is verified when a message is sent with a
      nonce, another message is returned with the same nonce, and the
      destination of the original message appears as the source of the
      returned message.

   LISP site:  is a set of routers in an edge network that are under a
      single technical administration.  LISP routers which reside in the
      edge network are the demarcation points to separate the edge
      network from the core network.

   Client-side:  a term used in this document to indicate a connection
      initiation attempt by an EID.  The ITR(s) at the LISP site are the
      first to get involved in obtaining database map cache entries by
      sending Map-Request messages.

   Server-side:  a term used in this document to indicate a connection
      initiation attempt is being accepted for a destination EID.  The
      ETR(s) at the destination LISP site are the first to send Map-
      Replies to the source site initiating the connection.  The ETR(s)
      at this destination site can obtain mappings by gleaning



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      information from Map-Requests, Data-Probes, or encapsulated
      packets.

   Locator Status Bits (LSBs):  Locator status bits are present in the
      LISP header.  They are used by ITRs to inform ETRs about the up/
      down status of all ETRs at the local site.  These bits are used as
      a hint to convey up/down router status and not path reachability
      status.  The LSBs can be verified by use of one of the Locator
      Reachability Algorithms described in Section 6.3.

   Anycast Address:  a term used in this document to refer to the same
      IPv4 or IPv6 address configured and used on multiple systems at
      the same time.  An EID or RLOC can be an anycast address in each
      of their own address spaces.





































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4.  Basic Overview

   One key concept of LISP is that end-systems (hosts) operate the same
   way they do today.  The IP addresses that hosts use for tracking
   sockets, connections, and for sending and receiving packets do not
   change.  In LISP terminology, these IP addresses are called Endpoint
   Identifiers (EIDs).

   Routers continue to forward packets based on IP destination
   addresses.  When a packet is LISP encapsulated, these addresses are
   referred to as Routing Locators (RLOCs).  Most routers along a path
   between two hosts will not change; they continue to perform routing/
   forwarding lookups on the destination addresses.  For routers between
   the source host and the ITR as well as routers from the ETR to the
   destination host, the destination address is an EID.  For the routers
   between the ITR and the ETR, the destination address is an RLOC.

   Another key LISP concept is the "Tunnel Router".  A tunnel router
   prepends LISP headers on host-originated packets and strips them
   prior to final delivery to their destination.  The IP addresses in
   this "outer header" are RLOCs.  During end-to-end packet exchange
   between two Internet hosts, an ITR prepends a new LISP header to each
   packet and an egress tunnel router strips the new header.  The ITR
   performs EID-to-RLOC lookups to determine the routing path to the
   ETR, which has the RLOC as one of its IP addresses.

   Some basic rules governing LISP are:

   o  End-systems (hosts) only send to addresses which are EIDs.  They
      don't know addresses are EIDs versus RLOCs but assume packets get
      to their intended destinations.  In a system where LISP is
      deployed, LISP routers intercept EID addressed packets and assist
      in delivering them across the network core where EIDs cannot be
      routed.  The procedure a host uses to send IP packets does not
      change.

   o  EIDs are always IP addresses assigned to hosts.

   o  LISP routers mostly deal with Routing Locator addresses.  See
      details later in Section 4.1 to clarify what is meant by "mostly".

   o  RLOCs are always IP addresses assigned to routers; preferably,
      topologically-oriented addresses from provider CIDR (Classless
      Inter-Domain Routing) blocks.

   o  When a router originates packets it may use as a source address
      either an EID or RLOC.  When acting as a host (e.g. when
      terminating a transport session such as SSH, TELNET, or SNMP), it



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      may use an EID that is explicitly assigned for that purpose.  An
      EID that identifies the router as a host MUST NOT be used as an
      RLOC; an EID is only routable within the scope of a site.  A
      typical BGP configuration might demonstrate this "hybrid" EID/RLOC
      usage where a router could use its "host-like" EID to terminate
      iBGP sessions to other routers in a site while at the same time
      using RLOCs to terminate eBGP sessions to routers outside the
      site.

   o  Packets with EIDs in them are not expected to be delivered end-to-
      end in the absence of an EID-to-RLOC mapping operation.  They are
      expected to be used locally for intra-site communication or to be
      encapsulated for inter-site communication.

   o  EID prefixes are likely to be hierarchically assigned in a manner
      which is optimized for administrative convenience and to
      facilitate scaling of the EID-to-RLOC mapping database.  The
      hierarchy is based on a address allocation hierarchy which is
      independent of the network topology.

   o  EIDs may also be structured (subnetted) in a manner suitable for
      local routing within an autonomous system.

   An additional LISP header MAY be prepended to packets by a TE-ITR
   when re-routing of the path for a packet is desired.  A potential
   use-case for this would be an ISP router that needs to perform
   traffic engineering for packets flowing through its network.  In such
   a situation, termed Recursive Tunneling, an ISP transit acts as an
   additional ingress tunnel router and the RLOC it uses for the new
   prepended header would be either a TE-ETR within the ISP (along
   intra-ISP traffic engineered path) or a TE-ETR within another ISP (an
   inter-ISP traffic engineered path, where an agreement to build such a
   path exists).

   In order to avoid excessive packet overhead as well as possible
   encapsulation loops, this document mandates that a maximum of two
   LISP headers can be prepended to a packet.  For initial LISP
   deployments, it is assumed two headers is sufficient, where the first
   prepended header is used at a site for Location/Identity separation
   and second prepended header is used inside a service provider for
   Traffic Engineering purposes.

   Tunnel Routers can be placed fairly flexibly in a multi-AS topology.
   For example, the ITR for a particular end-to-end packet exchange
   might be the first-hop or default router within a site for the source
   host.  Similarly, the egress tunnel router might be the last-hop
   router directly-connected to the destination host.  Another example,
   perhaps for a VPN service out-sourced to an ISP by a site, the ITR



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   could be the site's border router at the service provider attachment
   point.  Mixing and matching of site-operated, ISP-operated, and other
   tunnel routers is allowed for maximum flexibility.  See Section 8 for
   more details.

4.1.  Packet Flow Sequence

   This section provides an example of the unicast packet flow with the
   following conditions:

   o  Source host "host1.abc.example.com" is sending a packet to
      "host2.xyz.example.com", exactly what host1 would do if the site
      was not using LISP.

   o  Each site is multi-homed, so each tunnel router has an address
      (RLOC) assigned from the service provider address block for each
      provider to which that particular tunnel router is attached.

   o  The ITR(s) and ETR(s) are directly connected to the source and
      destination, respectively, but the source and destination can be
      located anywhere in LISP site.

   o  Map-Requests can be sent on the underlying routing system
      topology, to a mapping database system, or directly over an
      alternative topology [ALT].  A Map-Request is sent for an external
      destination when the destination is not found in the forwarding
      table or matches a default route.

   o  Map-Replies are sent on the underlying routing system topology.

   Client host1.abc.example.com wants to communicate with server
   host2.xyz.example.com:

   1.  host1.abc.example.com wants to open a TCP connection to
       host2.xyz.example.com.  It does a DNS lookup on
       host2.xyz.example.com.  An A/AAAA record is returned.  This
       address is the destination EID.  The locally-assigned address of
       host1.abc.example.com is used as the source EID.  An IPv4 or IPv6
       packet is built and forwarded through the LISP site as a normal
       IP packet until it reaches a LISP ITR.

   2.  The LISP ITR must be able to map the destination EID to an RLOC
       of one of the ETRs at the destination site.  The specific method
       used to do this is not described in this example.  See [ALT] or
       [CONS] for possible solutions.

   3.  The ITR will send a LISP Map-Request.  Map-Requests SHOULD be
       rate-limited.



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   4.  When an alternate mapping system is not in use, the Map-Request
       packet is routed through the underlying routing system.
       Otherwise, the Map-Request packet is routed on an alternate
       logical topology, for example the [ALT] database mapping system.
       In either case, when the Map-Request arrives at one of the ETRs
       at the destination site, it will process the packet as a control
       message.

   5.  The ETR looks at the destination EID of the Map-Request and
       matches it against the prefixes in the ETR's configured EID-to-
       RLOC mapping database.  This is the list of EID-prefixes the ETR
       is supporting for the site it resides in.  If there is no match,
       the Map-Request is dropped.  Otherwise, a LISP Map-Reply is
       returned to the ITR.

   6.  The ITR receives the Map-Reply message, parses the message (to
       check for format validity) and stores the mapping information
       from the packet.  This information is stored in the ITR's EID-to-
       RLOC mapping cache.  Note that the map cache is an on-demand
       cache.  An ITR will manage its map cache in such a way that
       optimizes for its resource constraints.

   7.  Subsequent packets from host1.abc.example.com to
       host2.xyz.example.com will have a LISP header prepended by the
       ITR using the appropriate RLOC as the LISP header destination
       address learned from the ETR.  Note the packet MAY be sent to a
       different ETR than the one which returned the Map-Reply due to
       the source site's hashing policy or the destination site's
       locator-set policy.

   8.  The ETR receives these packets directly (since the destination
       address is one of its assigned IP addresses), checks the validity
       of the addresses, strips the LISP header, and forwards packets to
       the attached destination host.

   In order to defer the need for a mapping lookup in the reverse
   direction, an ETR MAY create a cache entry that maps the source EID
   (inner header source IP address) to the source RLOC (outer header
   source IP address) in a received LISP packet.  Such a cache entry is
   termed a "gleaned" mapping and only contains a single RLOC for the
   EID in question.  More complete information about additional RLOCs
   SHOULD be verified by sending a LISP Map-Request for that EID.  Both
   ITR and the ETR may also influence the decision the other makes in
   selecting an RLOC.  See Section 6 for more details.







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5.  LISP Encapsulation Details

   Since additional tunnel headers are prepended, the packet becomes
   larger and can exceed the MTU of any link traversed from the ITR to
   the ETR.  It is RECOMMENDED in IPv4 that packets do not get
   fragmented as they are encapsulated by the ITR.  Instead, the packet
   is dropped and an ICMP Too Big message is returned to the source.

   This specification RECOMMENDS that implementations provide support
   for one of the proposed fragmentation and reassembly schemes.  Two
   existing schemes are detailed in Section 5.4.

   Since IPv4 or IPv6 addresses can be either EIDs or RLOCs, the LISP
   architecture supports IPv4 EIDs with IPv6 RLOCs (where the inner
   header is in IPv4 packet format and the other header is in IPv6
   packet format) or IPv6 EIDs with IPv4 RLOCs (where the inner header
   is in IPv6 packet format and the other header is in IPv4 packet
   format).  The next sub-sections illustrate packet formats for the
   homogeneous case (IPv4-in-IPv4 and IPv6-in-IPv6) but all 4
   combinations MUST be supported.































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5.1.  LISP IPv4-in-IPv4 Header Format



        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version|  IHL  |Type of Service|          Total Length         |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |         Identification        |Flags|      Fragment Offset    |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   OH  |  Time to Live | Protocol = 17 |         Header Checksum       |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                    Source Routing Locator                     |
    \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                 Destination Routing Locator                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4341        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   L   |N|L|E|V|I|flags|            Nonce/Map-Version                  |
   I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   S / |                 Instance ID/Locator Status Bits               |
   P   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version|  IHL  |Type of Service|          Total Length         |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |         Identification        |Flags|      Fragment Offset    |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   IH  |  Time to Live |    Protocol   |         Header Checksum       |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                           Source EID                          |
    \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                         Destination EID                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




5.2.  LISP IPv6-in-IPv6 Header Format



        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version| Traffic Class |           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   |   |         Payload Length        | Next Header=17|   Hop Limit   |
   v   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
   O   +                                                               +
   u   |                                                               |
   t   +                     Source Routing Locator                    +
   e   |                                                               |
   r   +                                                               +
       |                                                               |
   H   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   d   |                                                               |
   r   +                                                               +
       |                                                               |
   ^   +                  Destination Routing Locator                  +
   |   |                                                               |
    \  +                                                               +
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4341        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   L   |N|L|E|V|I|flags|            Nonce/Map-Version                  |
   I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   S / |                 Instance ID/Locator Status Bits               |
   P   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version| Traffic Class |           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /   |         Payload Length        |  Next Header  |   Hop Limit   |
   v   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
   I   +                                                               +
   n   |                                                               |
   n   +                          Source EID                           +
   e   |                                                               |
   r   +                                                               +
       |                                                               |
   H   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   d   |                                                               |
   r   +                                                               +
       |                                                               |
   ^   +                        Destination EID                        +
   \   |                                                               |
    \  +                                                               +
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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5.3.  Tunnel Header Field Descriptions

   Inner Header (IH):  The inner header is the header on the datagram
      received from the originating host.  The source and destination IP
      addresses are EIDs, [RFC0791], [RFC2460].

   Outer Header: (OH)  The outer header is a new header prepended by an
      ITR.  The address fields contain RLOCs obtained from the ingress
      router's EID-to-RLOC cache.  The IP protocol number is "UDP (17)"
      from [RFC0768].  The setting of the DF bit Flags field is
      according to rules in Section 5.4.1 and Section 5.4.2.

   UDP Header:  The UDP header contains an ITR selected source port when
      encapsulating a packet.  See Section 6.5 for details on the hash
      algorithm used to select a source port based on the 5-tuple of the
      inner header.  The destination port MUST be set to the well-known
      IANA assigned port value 4341.

   UDP Checksum:  The UDP checksum field SHOULD be transmitted as zero
      by an ITR for either IPv4 [RFC0768] or IPv6 encapsulation
      [UDP-TUNNELS] [UDP-ZERO].  When a packet with a zero UDP checksum
      is received by an ETR, the ETR MUST accept the packet for
      decapsulation.  When an ITR transmits a non-zero value for the UDP
      checksum, it MUST send a correctly computed value in this field.
      When an ETR receives a packet with a non-zero UDP checksum, it MAY
      choose to verify the checksum value.  If it chooses to perform
      such verification, and the verification fails, the packet MUST be
      silently dropped.  If the ETR chooses not to perform the
      verification, or performs the verification successfully, the
      packet MUST be accepted for decapsulation.  The handling of UDP
      checksums for all tunneling protocols, including LISP, is under
      active discussion within the IETF.  When that discussion
      concludes, any necessary changes will be made to align LISP with
      the outcome of the broader discussion.

   UDP Length:  The UDP length field is set for an IPv4 encapsulated
      packet to be the sum of the inner header IPv4 Total Length plus
      the UDP and LISP header lengths.  For an IPv6 encapsulated packet,
      the UDP length field is the sum of the inner header IPv6 Payload
      Length, the size of the IPv6 header (40 octets), and the size of
      the UDP and LISP headers.

   N: The N bit is the nonce-present bit.  When this bit is set to 1,
      the low-order 24-bits of the first 32-bits of the LISP header
      contains a Nonce.  See Section 6.3.1 for details.  Both N and V
      bits MUST NOT be set in the same packet.  If they are, a
      decapsulating ETR MUST treat the "Nonce/Map-Version" field as
      having a Nonce value present.



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   L: The L bit is the Locator Status Bits field enabled bit.  When this
      bit is set to 1, the Locator Status Bits in the second 32-bits of
      the LISP header are in use.


     x 1 x x 0 x x x
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |N|L|E|V|I|flags|            Nonce/Map-Version                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Locator Status Bits                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   E: The E bit is the echo-nonce-request bit.  This bit MUST be ignored
      and has no meaning when the N bit is set to 0.  When the N bit is
      set to 1 and this bit is set to 1, means an ITR is requesting for
      the nonce value in the Nonce field to be echoed back in LISP
      encapsulated packets when the ITR is also an ETR.  See
      Section 6.3.1 for details.

   V: The V bit is the Map-Version present bit.  When this bit is set to
      1, the N bit MUST be 0.  Refer to Section 6.6.3 for more details.
      This bit indicates that the LISP header is encoded in this case
      as:


     0 x 0 1 x x x x
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |N|L|E|V|I|flags|  Source Map-Version   |   Dest Map-Version    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Instance ID/Locator Status Bits               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   I: The I bit is the Instance ID bit.  See Section 5.5 for more
      details.  When this bit is set to 1, the Locator Status Bits field
      is reduced to 8-bits and the high-order 24-bits are used as an
      Instance ID.  If the L-bit is set to 0, then the low-order 8 bits
      are transmitted as zero and ignored on receipt.  The format of the
      LISP header would look like in this case:













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     x x x x 1 x x x
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |N|L|E|V|I|flags|            Nonce/Map-Version                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Instance ID                   |     LSBs      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   flags:  The flags field is a 3-bit field is reserved for future flag
      use.  It MUST be set to 0 on transmit and MUST be ignored on
      receipt.

   LISP Nonce:  The LISP nonce field is a 24-bit value that is randomly
      generated by an ITR when the N-bit is set to 1.  Nonce generation
      algorithms are an implementation matter but are required to
      generate different nonces when sending to different destinations.
      However, the same nonce can be used for a period of time to the
      same destination.  The nonce is also used when the E-bit is set to
      request the nonce value to be echoed by the other side when
      packets are returned.  When the E-bit is clear but the N-bit is
      set, a remote ITR is either echoing a previously requested echo-
      nonce or providing a random nonce.  See Section 6.3.1 for more
      details.

   LISP Locator Status Bits (LSBs):  When the L-bit is also set, the
      locator status bits field in the LISP header is set by an ITR to
      indicate to an ETR the up/down status of the Locators in the
      source site.  Each RLOC in a Map-Reply is assigned an ordinal
      value from 0 to n-1 (when there are n RLOCs in a mapping entry).
      The Locator Status Bits are numbered from 0 to n-1 from the least
      significant bit of field.  The field is 32-bits when the I-bit is
      set to 0 and is 8 bits when the I-bit is set to 1.  When a Locator
      Status Bit is set to 1, the ITR is indicating to the ETR the RLOC
      associated with the bit ordinal has up status.  See Section 6.3
      for details on how an ITR can determine the status of the ETRs at
      the same site.  When a site has multiple EID-prefixes which result
      in multiple mappings (where each could have a different locator-
      set), the Locator Status Bits setting in an encapsulated packet
      MUST reflect the mapping for the EID-prefix that the inner-header
      source EID address matches.  If the LSB for an anycast locator is
      set to 1, then there is at least one RLOC with that address the
      ETR is considered 'up'.

   When doing ITR/PITR encapsulation:

   o  The outer header Time to Live field (or Hop Limit field, in case
      of IPv6) SHOULD be copied from the inner header Time to Live
      field.




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   o  The outer header Type of Service field (or the Traffic Class
      field, in the case of IPv6) SHOULD be copied from the inner header
      Type of Service field (with one exception, see below).

   When doing ETR/PETR decapsulation:

   o  The inner header Time to Live field (or Hop Limit field, in case
      of IPv6) SHOULD be copied from the outer header Time to Live
      field, when the Time to Live field of the outer header is less
      than the Time to Live of the inner header.  Failing to perform
      this check can cause the Time to Live of the inner header to
      increment across encapsulation/decapsulation cycle.  This check is
      also performed when doing initial encapsulation when a packet
      comes to an ITR or PITR destined for a LISP site.

   o  The inner header Type of Service field (or the Traffic Class
      field, in the case of IPv6) SHOULD be copied from the outer header
      Type of Service field (with one exception, see below).

   Note if an ETR/PETR is also an ITR/PITR and choose to reencapsulate
   after decapsulating, the net effect of this is that the new outer
   header will carry the same Time to Live as the old outer header minus
   1.

   Copying the TTL serves two purposes: first, it preserves the distance
   the host intended the packet to travel; second, and more importantly,
   it provides for suppression of looping packets in the event there is
   a loop of concatenated tunnels due to misconfiguration.  See
   Section 9.3 for TTL exception handling for traceroute packets.

   The ECN field occupies bits 6 and 7 of both the IPv4 Type of Service
   field and the IPv6 Traffic Class field [RFC3168].  The ECN field
   requires special treatment in order to avoid discarding indications
   of congestion [RFC3168].  ITR encapsulation MUST copy the 2-bit ECN
   field from the inner header to the outer header.  Re-encapsulation
   MUST copy the 2-bit ECN field from the stripped outer header to the
   new outer header.  If the ECN field contains a congestion indication
   codepoint (the value is '11', the Congestion Experienced (CE)
   codepoint), then ETR decapsulation MUST copy the 2-bit ECN field from
   the stripped outer header to the surviving inner header that is used
   to forward the packet beyond the ETR.  These requirements preserve
   Congestion Experienced (CE) indications when a packet that uses ECN
   traverses a LISP tunnel and becomes marked with a CE indication due
   to congestion between the tunnel endpoints.







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5.4.  Dealing with Large Encapsulated Packets

   This section proposes two mechanisms to deal with packets that exceed
   the path MTU between the ITR and ETR.

   It is left to the implementor to decide if the stateless or stateful
   mechanism should be implemented.  Both or neither can be used since
   it is a local decision in the ITR regarding how to deal with MTU
   issues, and sites can interoperate with differing mechanisms.

   Both stateless and stateful mechanisms also apply to Reencapsulating
   and Recursive Tunneling.  So any actions below referring to an ITR
   also apply to an TE-ITR.

5.4.1.  A Stateless Solution to MTU Handling

   An ITR stateless solution to handle MTU issues is described as
   follows:

   1.  Define H to be the size, in octets, of the outer header an ITR
       prepends to a packet.  This includes the UDP and LISP header
       lengths.

   2.  Define L to be the size, in octets, of the maximum sized packet
       an ITR can send to an ETR without the need for the ITR or any
       intermediate routers to fragment the packet.

   3.  Define an architectural constant S for the maximum size of a
       packet, in octets, an ITR must receive so the effective MTU can
       be met.  That is, S = L - H.

   When an ITR receives a packet from a site-facing interface and adds H
   octets worth of encapsulation to yield a packet size greater than L
   octets, it resolves the MTU issue by first splitting the original
   packet into 2 equal-sized fragments.  A LISP header is then prepended
   to each fragment.  The size of the encapsulated fragments is then
   (S/2 + H), which is less than the ITR's estimate of the path MTU
   between the ITR and its correspondent ETR.

   When an ETR receives encapsulated fragments, it treats them as two
   individually encapsulated packets.  It strips the LISP headers then
   forwards each fragment to the destination host of the destination
   site.  The two fragments are reassembled at the destination host into
   the single IP datagram that was originated by the source host.  Note
   that reassembly can happen at the ETR if the encapsulated packet was
   fragmented at or after the ITR.

   This behavior is performed by the ITR when the source host originates



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   a packet with the DF field of the IP header is set to 0.  When the DF
   field of the IP header is set to 1, or the packet is an IPv6 packet
   originated by the source host, the ITR will drop the packet when the
   size is greater than L, and sends an ICMP Too Big message to the
   source with a value of S, where S is (L - H).

   When the outer header encapsulation uses an IPv4 header, an
   implementation SHOULD set the DF bit to 1 so ETR fragment reassembly
   can be avoided.  An implementation MAY set the DF bit in such headers
   to 0 if it has good reason to believe there are unresolvable path MTU
   issues between the sending ITR and the receiving ETR.

   This specification RECOMMENDS that L be defined as 1500.

5.4.2.  A Stateful Solution to MTU Handling

   An ITR stateful solution to handle MTU issues is described as follows
   and was first introduced in [OPENLISP]:

   1.  The ITR will keep state of the effective MTU for each locator per
       mapping cache entry.  The effective MTU is what the core network
       can deliver along the path between ITR and ETR.

   2.  When an IPv6 encapsulated packet or an IPv4 encapsulated packet
       with DF bit set to 1, exceeds what the core network can deliver,
       one of the intermediate routers on the path will send an ICMP Too
       Big message to the ITR.  The ITR will parse the ICMP message to
       determine which locator is affected by the effective MTU change
       and then record the new effective MTU value in the mapping cache
       entry.

   3.  When a packet is received by the ITR from a source inside of the
       site and the size of the packet is greater than the effective MTU
       stored with the mapping cache entry associated with the
       destination EID the packet is for, the ITR will send an ICMP Too
       Big message back to the source.  The packet size advertised by
       the ITR in the ICMP Too Big message is the effective MTU minus
       the LISP encapsulation length.

   Even though this mechanism is stateful, it has advantages over the
   stateless IP fragmentation mechanism, by not involving the
   destination host with reassembly of ITR fragmented packets.

5.5.  Using Virtualization and Segmentation with LISP

   When multiple organizations inside of a LISP site are using private
   addresses [RFC1918] as EID-prefixes, their address spaces MUST remain
   segregated due to possible address duplication.  An Instance ID in



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   the address encoding can aid in making the entire AFI based address
   unique.  See IANA Considerations Section 14.2 for details for
   possible address encodings.

   An Instance ID can be carried in a LISP encapsulated packet.  An ITR
   that prepends a LISP header, will copy a 24-bit value, used by the
   LISP router to uniquely identify the address space.  The value is
   copied to the Instance ID field of the LISP header and the I-bit is
   set to 1.

   When an ETR decapsulates a packet, the Instance ID from the LISP
   header is used as a table identifier to locate the forwarding table
   to use for the inner destination EID lookup.

   For example, a 802.1Q VLAN tag or VPN identifier could be used as a
   24-bit Instance ID.



































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6.  EID-to-RLOC Mapping

6.1.  LISP IPv4 and IPv6 Control Plane Packet Formats

   The following UDP packet formats are used by the LISP control-plane.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version|  IHL  |Type of Service|          Total Length         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Identification        |Flags|      Fragment Offset    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Time to Live | Protocol = 17 |         Header Checksum       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    Source Routing Locator                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 Destination Routing Locator                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |           Source Port         |         Dest Port             |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                         LISP Message                          |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version| Traffic Class |           Flow Label                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Payload Length        | Next Header=17|   Hop Limit   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                     Source Routing Locator                    +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |



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       +                  Destination Routing Locator                  +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |           Source Port         |         Dest Port             |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                         LISP Message                          |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The LISP UDP-based messages are the Map-Request and Map-Reply
   messages.  When a UDP Map-Request is sent, the UDP source port is
   chosen by the sender and the destination UDP port number is set to
   4342.  When a UDP Map-Reply is sent, the source UDP port number is
   set to 4342 and the destination UDP port number is copied from the
   source port of either the Map-Request or the invoking data packet.
   Implementations MUST be prepared to accept packets when either the
   source port or destination UDP port is set to 4342 due to NATs
   changing port number values.

   The UDP Length field will reflect the length of the UDP header and
   the LISP Message payload.

   The UDP Checksum is computed and set to non-zero for Map-Request,
   Map-Reply, Map-Register and ECM control messages.  It MUST be checked
   on receipt and if the checksum fails, the packet MUST be dropped.

   The format of control messages includes the UDP header so the
   checksum and length fields can be used to protect and delimit message
   boundaries.
















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6.1.1.  LISP Packet Type Allocations

   This section will be the authoritative source for allocating LISP
   Type values and for defining LISP control message formats.  Current
   allocations are:


       Reserved:                          0    b'0000'
       LISP Map-Request:                  1    b'0001'
       LISP Map-Reply:                    2    b'0010'
       LISP Map-Register:                 3    b'0011'
       LISP Map-Notify:                   4    b'0100'
       LISP Encapsulated Control Message: 8    b'1000'


6.1.2.  Map-Request Message Format



        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=1 |A|M|P|S|p|s|    Reserved     |   IRC   | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Source-EID-AFI        |   Source EID Address  ...     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         ITR-RLOC-AFI 1        |    ITR-RLOC Address 1  ...    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              ...                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         ITR-RLOC-AFI n        |    ITR-RLOC Address n  ...    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |   Reserved    | EID mask-len  |        EID-prefix-AFI         |
   Rec +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                       EID-prefix  ...                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Map-Reply Record  ...                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Packet field descriptions:






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   Type:   1 (Map-Request)

   A: This is an authoritative bit, which is set to 0 for UDP-based Map-
      Requests sent by an ITR.  Set to 1 when an ITR wants the
      destination site to return the Map-Reply rather than the mapping
      database system.

   M: This is the map-data-present bit, when set, it indicates a Map-
      Reply Record segment is included in the Map-Request.

   P: This is the probe-bit which indicates that a Map-Request SHOULD be
      treated as a locator reachability probe.  The receiver SHOULD
      respond with a Map-Reply with the probe-bit set, indicating the
      Map-Reply is a locator reachability probe reply, with the nonce
      copied from the Map-Request.  See Section 6.3.2 for more details.

   S: This is the Solicit-Map-Request (SMR) bit.  See Section 6.6.2 for
      details.

   p: This is the PITR bit.  This bit is set to 1 when a PITR sends a
      Map-Request.

   s: This is the SMR-invoked bit.  This bit is set to 1 when an xTR is
      sending a Map-Request in response to a received SMR-based Map-
      Request.

   Reserved:  It MUST be set to 0 on transmit and MUST be ignored on
      receipt.

   IRC:  This 5-bit field is the ITR-RLOC Count which encodes the
      additional number of (ITR-RLOC-AFI, ITR-RLOC Address) fields
      present in this message.  At least one (ITR-RLOC-AFI, ITR-RLOC-
      Address) pair MUST be encoded.  Multiple ITR-RLOC Address fields
      are used so a Map-Replier can select which destination address to
      use for a Map-Reply.  The IRC value ranges from 0 to 31.  For a
      value of 0, there is 1 ITR-RLOC address encoded, and for a value
      of 1, there are 2 ITR-RLOC addresses encoded and so on up to 31
      which encodes a total of 32 ITR-RLOC addresses.

   Record Count:  The number of records in this Map-Request message.  A
      record is comprised of the portion of the packet that is labeled
      'Rec' above and occurs the number of times equal to Record Count.
      For this version of the protocol, a receiver MUST accept and
      process Map-Requests that contain one or more records, but a
      sender MUST only send Map-Requests containing one record.  Support
      for requesting multiple EIDs in a single Map-Request message will
      be specified in a future version of the protocol.




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   Nonce:  An 8-octet random value created by the sender of the Map-
      Request.  This nonce will be returned in the Map-Reply.  The
      security of the LISP mapping protocol depends critically on the
      strength of the nonce in the Map-Request message.  The nonce
      SHOULD be generated by a properly seeded pseudo-random (or strong
      random) source.  See [RFC4086] for advice on generating security-
      sensitive random data.

   Source-EID-AFI:  Address family of the "Source EID Address" field.

   Source EID Address:  This is the EID of the source host which
      originated the packet which is caused the Map-Request.  When Map-
      Requests are used for refreshing a map-cache entry or for RLOC-
      probing, an AFI value 0 is used and this field is of zero length.

   ITR-RLOC-AFI:  Address family of the "ITR-RLOC Address" field that
      follows this field.

   ITR-RLOC Address:  Used to give the ETR the option of selecting the
      destination address from any address family for the Map-Reply
      message.  This address MUST be a routable RLOC address of the
      sender of the Map-Request message.

   EID mask-len:  Mask length for EID prefix.

   EID-prefix-AFI:  Address family of EID-prefix according to [AFI]

   EID-prefix:  4 octets if an IPv4 address-family, 16 octets if an IPv6
      address-family.  When a Map-Request is sent by an ITR because a
      data packet is received for a destination where there is no
      mapping entry, the EID-prefix is set to the destination IP address
      of the data packet.  And the 'EID mask-len' is set to 32 or 128
      for IPv4 or IPv6, respectively.  When an xTR wants to query a site
      about the status of a mapping it already has cached, the EID-
      prefix used in the Map-Request has the same mask-length as the
      EID-prefix returned from the site when it sent a Map-Reply
      message.

   Map-Reply Record:  When the M bit is set, this field is the size of a
      single "Record" in the Map-Reply format.  This Map-Reply record
      contains the EID-to-RLOC mapping entry associated with the Source
      EID.  This allows the ETR which will receive this Map-Request to
      cache the data if it chooses to do so.








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6.1.3.  EID-to-RLOC UDP Map-Request Message

   A Map-Request is sent from an ITR when it needs a mapping for an EID,
   wants to test an RLOC for reachability, or wants to refresh a mapping
   before TTL expiration.  For the initial case, the destination IP
   address used for the Map-Request is the data packet's destination
   address (i.e. the destination-EID) which had a mapping cache lookup
   failure.  For the latter two cases, the destination IP address used
   for the Map-Request is one of the RLOC addresses from the locator-set
   of the map cache entry.  The source address is either an IPv4 or IPv6
   RLOC address depending if the Map-Request is using an IPv4 versus
   IPv6 header, respectively.  In all cases, the UDP source port number
   for the Map-Request message is an ITR/PITR selected 16-bit value and
   the UDP destination port number is set to the well-known destination
   port number 4342.  A successful Map-Reply, which is one that has a
   nonce that matches an outstanding Map-Request nonce, will update the
   cached set of RLOCs associated with the EID prefix range.

   One or more Map-Request (ITR-RLOC-AFI, ITR-RLOC-Address) fields MUST
   be filled in by the ITR.  The number of fields (minus 1) encoded MUST
   be placed in the IRC field.  The ITR MAY include all locally
   configured locators in this list or just provide one locator address
   from each address family it supports.  If the ITR erroneously
   provides no ITR-RLOC addresses, the Map-Replier MUST drop the Map-
   Request.

   Map-Requests can also be LISP encapsulated using UDP destination port
   4342 with a LISP type value set to "Encapsulated Control Message",
   when sent from an ITR to a Map-Resolver.  Likewise, Map-Requests are
   LISP encapsulated the same way from a Map-Server to an ETR.  Details
   on encapsulated Map-Requests and Map-Resolvers can be found in
   [LISP-MS].

   Map-Requests MUST be rate-limited.  It is RECOMMENDED that a Map-
   Request for the same EID-prefix be sent no more than once per second.

   An ITR that is configured with mapping database information (i.e. it
   is also an ETR) MAY optionally include those mappings in a Map-
   Request.  When an ETR configured to accept and verify such
   "piggybacked" mapping data receives such a Map-Request and it does
   not have this mapping in the map-cache, it MAY originate a "verifying
   Map-Request", addressed to the map-requesting ITR and the ETR MAY add
   a map-cache entry.  If the ETR has a map-cache entry that matches the
   "piggybacked" EID and the RLOC is in the locator-set for the entry,
   then it may send the "verifying Map-Request" directly to the
   originating Map-Request source.  If the RLOC is not in the locator-
   set, then the ETR MUST send the "verifying Map-Request" to the
   "piggybacked" EID.  Doing this forces the "verifying Map-Request" to



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   go through the mapping database system to reach the authoritative
   source of information about that EID, guarding against RLOC-spoofing
   in in the "piggybacked" mapping data.

6.1.4.  Map-Reply Message Format



        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=2 |P|E|S|          Reserved               | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                          Record  TTL                          |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   R   | Locator Count | EID mask-len  | ACT |A|      Reserved         |
   e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   c   | Rsvd  |  Map-Version Number   |       EID-prefix-AFI          |
   o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   r   |                          EID-prefix                           |
   d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
   | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | o |        Unused Flags     |L|p|R|           Loc-AFI             |
   | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  \|                             Locator                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Packet field descriptions:

   Type:   2 (Map-Reply)

   P: This is the probe-bit which indicates that the Map-Reply is in
      response to a locator reachability probe Map-Request.  The nonce
      field MUST contain a copy of the nonce value from the original
      Map-Request.  See Section 6.3.2 for more details.

   E: Indicates that the ETR which sends this Map-Reply message is
      advertising that the site is enabled for the Echo-Nonce locator
      reachability algorithm.  See Section 6.3.1 for more details.






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   S: This is the Security bit.  When set to 1 the following
      authentication information will be appended to the end of the Map-
      Reply.  The detailed format of the Authentication Data Content is
      for further study.


     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    AD Type    |       Authentication Data Content . . .       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reserved:  It MUST be set to 0 on transmit and MUST be ignored on
      receipt.

   Record Count:  The number of records in this reply message.  A record
      is comprised of that portion of the packet labeled 'Record' above
      and occurs the number of times equal to Record count.

   Nonce:  A 24-bit value set in a Data-Probe packet or a 64-bit value
      from the Map-Request is echoed in this Nonce field of the Map-
      Reply.  When a 24-bit value is supplied, it resides in the low-
      order 64 bits of the nonce field.

   Record TTL:  The time in minutes the recipient of the Map-Reply will
      store the mapping.  If the TTL is 0, the entry SHOULD be removed
      from the cache immediately.  If the value is 0xffffffff, the
      recipient can decide locally how long to store the mapping.

   Locator Count:  The number of Locator entries.  A locator entry
      comprises what is labeled above as 'Loc'.  The locator count can
      be 0 indicating there are no locators for the EID-prefix.

   EID mask-len:  Mask length for EID prefix.

   ACT:  This 3-bit field describes negative Map-Reply actions.  In any
      other message type, these bits are set to 0 and ignored on
      receipt.  These bits are used only when the 'Locator Count' field
      is set to 0.  The action bits are encoded only in Map-Reply
      messages.  The actions defined are used by an ITR or PITR when a
      destination EID matches a negative mapping cache entry.
      Unassigned values should cause a map-cache entry to be created
      and, when packets match this negative cache entry, they will be
      dropped.  The current assigned values are:







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      (0) No-Action:  The map-cache is kept alive and no packet
         encapsulation occurs.

      (1) Natively-Forward:  The packet is not encapsulated or dropped
         but natively forwarded.

      (2) Send-Map-Request:  The packet invokes sending a Map-Request.

      (3) Drop:  A packet that matches this map-cache entry is dropped.
         An ICMP Unreachable message SHOULD be sent.

   A: The Authoritative bit, when sent is always set to 1 by an ETR.
      When a Map-Server is proxy Map-Replying [LISP-MS] for a LISP site,
      the Authoritative bit is set to 0.  This indicates to requesting
      ITRs that the Map-Reply was not originated by a LISP node managed
      at the site that owns the EID-prefix.

   Map-Version Number:  When this 12-bit value is non-zero the Map-Reply
      sender is informing the ITR what the version number is for the
      EID-record contained in the Map-Reply.  The ETR can allocate this
      number internally but MUST coordinate this value with other ETRs
      for the site.  When this value is 0, there is no versioning
      information conveyed.  The Map-Version Number can be included in
      Map-Request and Map-Register messages.  See Section 6.6.3 for more
      details.

   EID-prefix-AFI:  Address family of EID-prefix according to [AFI].

   EID-prefix:  4 octets if an IPv4 address-family, 16 octets if an IPv6
      address-family.

   Priority:  each RLOC is assigned a unicast priority.  Lower values
      are more preferable.  When multiple RLOCs have the same priority,
      they MAY be used in a load-split fashion.  A value of 255 means
      the RLOC MUST NOT be used for unicast forwarding.

   Weight:  when priorities are the same for multiple RLOCs, the weight
      indicates how to balance unicast traffic between them.  Weight is
      encoded as a relative weight of total unicast packets that match
      the mapping entry.  For example if there are 4 locators in a
      locator set, where the weights assigned are 30, 20, 20, and 10,
      the first locator will get 37.5% of the traffic, the 2nd and 3rd
      locators will get 25% of traffic and the 4th locator will get
      12.5% of the traffic.  If all weights for a locator-set are equal,
      receiver of the Map-Reply will decide how to load-split traffic.
      See Section 6.5 for a suggested hash algorithm to distribute load



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      across locators with same priority and equal weight values.

   M Priority:  each RLOC is assigned a multicast priority used by an
      ETR in a receiver multicast site to select an ITR in a source
      multicast site for building multicast distribution trees.  A value
      of 255 means the RLOC MUST NOT be used for joining a multicast
      distribution tree.  For more details, see [MLISP].

   M Weight:  when priorities are the same for multiple RLOCs, the
      weight indicates how to balance building multicast distribution
      trees across multiple ITRs.  The weight is encoded as a relative
      weight (similar to the unicast Weights) of total number of trees
      built to the source site identified by the EID-prefix.  If all
      weights for a locator-set are equal, the receiver of the Map-Reply
      will decide how to distribute multicast state across ITRs.  For
      more details, see [MLISP].

   Unused Flags:  set to 0 when sending and ignored on receipt.

   L: when this bit is set, the locator is flagged as a local locator to
      the ETR that is sending the Map-Reply.  When a Map-Server is doing
      proxy Map-Replying [LISP-MS] for a LISP site, the L bit is set to
      0 for all locators in this locator-set.

   p: when this bit is set, an ETR informs the RLOC-probing ITR that the
      locator address, for which this bit is set, is the one being RLOC-
      probed and MAY be different from the source address of the Map-
      Reply.  An ITR that RLOC-probes a particular locator, MUST use
      this locator for retrieving the data structure used to store the
      fact that the locator is reachable.  The "p" bit is set for a
      single locator in the same locator set.  If an implementation sets
      more than one "p" bit erroneously, the receiver of the Map-Reply
      MUST select the first locator.  The "p" bit MUST NOT be set for
      locator-set records sent in Map-Request and Map-Register messages.

   R: set when the sender of a Map-Reply has a route to the locator in
      the locator data record.  This receiver may find this useful to
      know if the locator is up but not necessarily reachable from the
      receiver's point of view.  See also Section 6.4 for another way
      the R-bit may be used.

   Locator:  an IPv4 or IPv6 address (as encoded by the 'Loc-AFI' field)
      assigned to an ETR.  Note that the destination RLOC address MAY be
      an anycast address.  A source RLOC can be an anycast address as
      well.  The source or destination RLOC MUST NOT be the broadcast
      address (255.255.255.255 or any subnet broadcast address known to
      the router), and MUST NOT be a link-local multicast address.  The
      source RLOC MUST NOT be a multicast address.  The destination RLOC



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      SHOULD be a multicast address if it is being mapped from a
      multicast destination EID.

6.1.5.  EID-to-RLOC UDP Map-Reply Message

   A Map-Reply returns an EID-prefix with a prefix length that is less
   than or equal to the EID being requested.  The EID being requested is
   either from the destination field of an IP header of a Data-Probe or
   the EID record of a Map-Request.  The RLOCs in the Map-Reply are
   globally-routable IP addresses of all ETRs for the LISP site.  Each
   RLOC conveys status reachability but does not convey path
   reachability from a requesters perspective.  Separate testing of path
   reachability is required, See Section 6.3 for details.

   Note that a Map-Reply may contain different EID-prefix granularity
   (prefix + length) than the Map-Request which triggers it.  This might
   occur if a Map-Request were for a prefix that had been returned by an
   earlier Map-Reply.  In such a case, the requester updates its cache
   with the new prefix information and granularity.  For example, a
   requester with two cached EID-prefixes that are covered by a Map-
   Reply containing one, less-specific prefix, replaces the entry with
   the less-specific EID-prefix.  Note that the reverse, replacement of
   one less-specific prefix with multiple more-specific prefixes, can
   also occur but not by removing the less-specific prefix rather by
   adding the more-specific prefixes which during a lookup will override
   the less-specific prefix.

   When an ETR is configured with overlapping EID-prefixes, a Map-
   Request with an EID that longest matches any EID-prefix MUST be
   returned in a single Map-Reply message.  For instance, if an ETR had
   database mapping entries for EID-prefixes:

     10.0.0.0/8
     10.1.0.0/16
     10.1.1.0/24
     10.1.2.0/24

   A Map-Request for EID 10.1.1.1 would cause a Map-Reply with a record
   count of 1 to be returned with a mapping record EID-prefix of
   10.1.1.0/24.

   A Map-Request for EID 10.1.5.5, would cause a Map-Reply with a record
   count of 3 to be returned with mapping records for EID-prefixes
   10.1.0.0/16, 10.1.1.0/24, and 10.1.2.0/24.

   Note that not all overlapping EID-prefixes need to be returned, only
   the more specifics (note in the second example above 10.0.0.0/8 was
   not returned for requesting EID 10.1.5.5) entries for the matching



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   EID-prefix of the requesting EID.  When more than one EID-prefix is
   returned, all SHOULD use the same Time-to-Live value so they can all
   time out at the same time.  When a more specific EID-prefix is
   received later, its Time-to-Live value in the Map-Reply record can be
   stored even when other less specifics exist.  When a less specific
   EID-prefix is received later, its map-cache expiration time SHOULD be
   set to the minimum expiration time of any more specific EID-prefix in
   the map-cache.  This is done so the integrity of the EID-prefix set
   is wholly maintained so no more-specific entries are removed from the
   map-cache while keeping less-specific entries.

   Map-Replies SHOULD be sent for an EID-prefix no more often than once
   per second to the same requesting router.  For scalability, it is
   expected that aggregation of EID addresses into EID-prefixes will
   allow one Map-Reply to satisfy a mapping for the EID addresses in the
   prefix range thereby reducing the number of Map-Request messages.

   Map-Reply records can have an empty locator-set.  A negative Map-
   Reply is a Map-Reply with an empty locator-set.  Negative Map-Replies
   convey special actions by the sender to the ITR or PITR which have
   solicited the Map-Reply.  There are two primary applications for
   Negative Map-Replies.  The first is for a Map-Resolver to instruct an
   ITR or PITR when a destination is for a LISP site versus a non-LISP
   site.  And the other is to source quench Map-Requests which are sent
   for non-allocated EIDs.

   For each Map-Reply record, the list of locators in a locator-set MUST
   appear in the same order for each ETR that originates a Map-Reply
   message.  The locator-set MUST be sorted in order of ascending IP
   address where an IPv4 locator address is considered numerically 'less
   than' an IPv6 locator address.

   When sending a Map-Reply message, the destination address is copied
   from the one of the ITR-RLOC fields from the Map-Request.  The ETR
   can choose a locator address from one of the address families it
   supports.  For Data-Probes, the destination address of the Map-Reply
   is copied from the source address of the Data-Probe message which is
   invoking the reply.  The source address of the Map-Reply is one of
   the local IP addresses chosen to allow uRPF checks to succeed in the
   upstream service provider.  The destination port of a Map-Reply
   message is copied from the source port of the Map-Request or Data-
   Probe and the source port of the Map-Reply message is set to the
   well-known UDP port 4342.

6.1.5.1.  Traffic Redirection with Coarse EID-Prefixes

   When an ETR is misconfigured or compromised, it could return coarse
   EID-prefixes in Map-Reply messages it sends.  The EID-prefix could



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   cover EID-prefixes which are allocated to other sites redirecting
   their traffic to the locators of the compromised site.

   To solve this problem, there are two basic solutions that could be
   used.  The first is to have Map-Servers proxy-map-reply on behalf of
   ETRs so their registered EID-prefixes are the ones returned in Map-
   Replies.  Since the interaction between an ETR and Map-Server is
   secured with shared-keys, it is easier for an ETR to detect
   misbehavior.  The second solution is to have ITRs and PITRs cache
   EID-prefixes with mask-lengths that are greater than or equal to a
   configured prefix length.  This limits the damage to a specific width
   of any EID-prefix advertised, but needs to be coordinated with the
   allocation of site prefixes.  These solutions can be used
   independently or at the same time.

   At the time of this writing, other approaches are being considered
   and researched.

6.1.6.  Map-Register Message Format

   The usage details of the Map-Register message can be found in
   specification [LISP-MS].  This section solely defines the message
   format.

   The message is sent in UDP with a destination UDP port of 4342 and a
   randomly selected UDP source port number.

   The Map-Register message format is:























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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=3 |P|            Reserved               |M| Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            Key ID             |  Authentication Data Length   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                     Authentication Data                       ~
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                          Record  TTL                          |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   R   | Locator Count | EID mask-len  | ACT |A|      Reserved         |
   e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   c   | Rsvd  |  Map-Version Number   |        EID-prefix-AFI         |
   o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   r   |                          EID-prefix                           |
   d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
   | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | o |        Unused Flags     |L|p|R|           Loc-AFI             |
   | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  \|                             Locator                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Packet field descriptions:

   Type:   3 (Map-Register)

   P: This is the proxy-map-reply bit, when set to 1 an ETR sends a Map-
      Register message requesting for the Map-Server to proxy Map-Reply.
      The Map-Server will send non-authoritative Map-Replies on behalf
      of the ETR.  Details on this usage can be found in [LISP-MS].

   Reserved:  It MUST be set to 0 on transmit and MUST be ignored on
      receipt.

   M: This is the want-map-notify bit, when set to 1 an ETR is
      requesting for a Map-Notify message to be returned in response to
      sending a Map-Register message.  The Map-Notify message sent by a
      Map-Server is used to an acknowledge receipt of a Map-Register
      message.





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   Record Count:  The number of records in this Map-Register message.  A
      record is comprised of that portion of the packet labeled 'Record'
      above and occurs the number of times equal to Record count.

   Nonce:  This 8-octet Nonce field is set to 0 in Map-Register
      messages.  Since the Map-Register message is authenticated, the
      nonce field is not currently used for any security function but
      may be in the future as part of an anti-replay solution.

   Key ID:  A configured ID to find the configured Message
      Authentication Code (MAC) algorithm and key value used for the
      authentication function.  See Section 14.4 for codepoint
      assignments.

   Authentication Data Length:  The length in octets of the
      Authentication Data field that follows this field.  The length of
      the Authentication Data field is dependent on the Message
      Authentication Code (MAC) algorithm used.  The length field allows
      a device that doesn't know the MAC algorithm to correctly parse
      the packet.

   Authentication Data:  The message digest used from the output of the
      Message Authentication Code (MAC) algorithm.  The entire Map-
      Register payload is authenticated with this field preset to 0.
      After the MAC is computed, it is placed in this field.
      Implementations of this specification MUST include support for
      HMAC-SHA-1-96 [RFC2404] and support for HMAC-SHA-256-128 [RFC6234]
      is RECOMMENDED.

   The definition of the rest of the Map-Register can be found in the
   Map-Reply section.

6.1.7.  Map-Notify Message Format

   The usage details of the Map-Notify message can be found in
   specification [LISP-MS].  This section solely defines the message
   format.

   The message is sent inside a UDP packet with source and destination
   UDP ports equal to 4342.

   The Map-Notify message format is:









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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=4 |              Reserved                 | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            Key ID             |  Authentication Data Length   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                     Authentication Data                       ~
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                          Record  TTL                          |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   R   | Locator Count | EID mask-len  | ACT |A|      Reserved         |
   e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   c   | Rsvd  |  Map-Version Number   |         EID-prefix-AFI        |
   o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   r   |                          EID-prefix                           |
   d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
   | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | o |        Unused Flags     |L|p|R|           Loc-AFI             |
   | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  \|                             Locator                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Packet field descriptions:

   Type:   4 (Map-Notify)

   The Map-Notify message has the same contents as a Map-Register
   message.  See Map-Register section for field descriptions.

6.1.8.  Encapsulated Control Message Format

   An Encapsulated Control Message (ECM) is used to encapsulate control
   packets sent between xTRs and the mapping database system described
   in [LISP-MS].










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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |                       IPv4 or IPv6 Header                     |
   OH  |                      (uses RLOC addresses)                    |
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4342        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   LH  |Type=8 |S|                  Reserved                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |                       IPv4 or IPv6 Header                     |
   IH  |                  (uses RLOC or EID addresses)                 |
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = yyyy        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   LCM |                      LISP Control Message                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Packet header descriptions:

   OH:   The outer IPv4 or IPv6 header which uses RLOC addresses in the
      source and destination header address fields.

   UDP:   The outer UDP header with destination port 4342.  The source
      port is randomly allocated.  The checksum field MUST be non-zero.

   LH:   Type 8 is defined to be a "LISP Encapsulated Control Message"
      and what follows is either an IPv4 or IPv6 header as encoded by
      the first 4 bits after the reserved field.

   S:   This is the Security bit.  When set to 1 the field following the
      Reserved field will have the following format.  The detailed
      format of the Authentication Data Content is for further study.












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     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    AD Type    |       Authentication Data Content . . .       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IH:   The inner IPv4 or IPv6 header which can use either RLOC or EID
      addresses in the header address fields.  When a Map-Request is
      encapsulated in this packet format the destination address in this
      header is an EID.

   UDP:   The inner UDP header where the port assignments depends on the
      control packet being encapsulated.  When the control packet is a
      Map-Request or Map-Register, the source port is ITR/PITR selected
      and the destination port is 4342.  When the control packet is a
      Map-Reply, the source port is 4342 and the destination port is
      assigned from the source port of the invoking Map-Request.  Port
      number 4341 MUST NOT be assigned to either port.  The checksum
      field MUST be non-zero.

   LCM:   The format is one of the control message formats described in
      this section.  At this time, only Map-Request messages are allowed
      to be encapsulated.  And in the future, PIM Join-Prune messages
      [MLISP] might be allowed.  Encapsulating other types of LISP
      control messages are for further study.  When Map-Requests are
      sent for RLOC-probing purposes (i.e the probe-bit is set), they
      MUST NOT be sent inside Encapsulated Control Messages.

6.2.  Routing Locator Selection

   Both client-side and server-side may need control over the selection
   of RLOCs for conversations between them.  This control is achieved by
   manipulating the Priority and Weight fields in EID-to-RLOC Map-Reply
   messages.  Alternatively, RLOC information MAY be gleaned from
   received tunneled packets or EID-to-RLOC Map-Request messages.

   The following enumerates different scenarios for choosing RLOCs and
   the controls that are available:

   o  Server-side returns one RLOC.  Client-side can only use one RLOC.
      Server-side has complete control of the selection.

   o  Server-side returns a list of RLOC where a subset of the list has
      the same best priority.  Client can only use the subset list
      according to the weighting assigned by the server-side.  In this
      case, the server-side controls both the subset list and load-
      splitting across its members.  The client-side can use RLOCs
      outside of the subset list if it determines that the subset list



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      is unreachable (unless RLOCs are set to a Priority of 255).  Some
      sharing of control exists: the server-side determines the
      destination RLOC list and load distribution while the client-side
      has the option of using alternatives to this list if RLOCs in the
      list are unreachable.

   o  Server-side sets weight of 0 for the RLOC subset list.  In this
      case, the client-side can choose how the traffic load is spread
      across the subset list.  Control is shared by the server-side
      determining the list and the client determining load distribution.
      Again, the client can use alternative RLOCs if the server-provided
      list of RLOCs are unreachable.

   o  Either side (more likely on the server-side ETR) decides not to
      send a Map-Request.  For example, if the server-side ETR does not
      send Map-Requests, it gleans RLOCs from the client-side ITR,
      giving the client-side ITR responsibility for bidirectional RLOC
      reachability and preferability.  Server-side ETR gleaning of the
      client-side ITR RLOC is done by caching the inner header source
      EID and the outer header source RLOC of received packets.  The
      client-side ITR controls how traffic is returned and can alternate
      using an outer header source RLOC, which then can be added to the
      list the server-side ETR uses to return traffic.  Since no
      Priority or Weights are provided using this method, the server-
      side ETR MUST assume each client-side ITR RLOC uses the same best
      Priority with a Weight of zero.  In addition, since EID-prefix
      encoding cannot be conveyed in data packets, the EID-to-RLOC cache
      on tunnel routers can grow to be very large.

   o  A "gleaned" map-cache entry, one learned from the source RLOC of a
      received encapsulated packet, is only stored and used for a few
      seconds, pending verification.  Verification is performed by
      sending a Map-Request to the source EID (the inner header IP
      source address) of the received encapsulated packet.  A reply to
      this "verifying Map-Request" is used to fully populate the map-
      cache entry for the "gleaned" EID and is stored and used for the
      time indicated from the TTL field of a received Map-Reply.  When a
      verified map-cache entry is stored, data gleaning no longer occurs
      for subsequent packets which have a source EID that matches the
      EID-prefix of the verified entry.

   RLOCs that appear in EID-to-RLOC Map-Reply messages are assumed to be
   reachable when the R-bit for the locator record is set to 1.  When
   the R-bit is set to 0, an ITR or PITR MUST NOT encapsulate to the
   RLOC.  Neither the information contained in a Map-Reply or that
   stored in the mapping database system provides reachability
   information for RLOCs.  Note that reachability is not part of the
   mapping system and is determined using one or more of the Routing



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   Locator Reachability Algorithms described in the next section.

6.3.  Routing Locator Reachability

   Several mechanisms for determining RLOC reachability are currently
   defined:

   1.  An ETR may examine the Locator Status Bits in the LISP header of
       an encapsulated data packet received from an ITR.  If the ETR is
       also acting as an ITR and has traffic to return to the original
       ITR site, it can use this status information to help select an
       RLOC.

   2.  An ITR may receive an ICMP Network or ICMP Host Unreachable
       message for an RLOC it is using.  This indicates that the RLOC is
       likely down.  Note, trusting ICMP messages may not be desirable
       but neither is ignoring them completely.  Implementations are
       encouraged to follow current best practices in treating these
       conditions.

   3.  An ITR which participates in the global routing system can
       determine that an RLOC is down if no BGP RIB route exists that
       matches the RLOC IP address.

   4.  An ITR may receive an ICMP Port Unreachable message from a
       destination host.  This occurs if an ITR attempts to use
       interworking [INTERWORK] and LISP-encapsulated data is sent to a
       non-LISP-capable site.

   5.  An ITR may receive a Map-Reply from an ETR in response to a
       previously sent Map-Request.  The RLOC source of the Map-Reply is
       likely up since the ETR was able to send the Map-Reply to the
       ITR.

   6.  When an ETR receives an encapsulated packet from an ITR, the
       source RLOC from the outer header of the packet is likely up.

   7.  An ITR/ETR pair can use the Locator Reachability Algorithms
       described in this section, namely Echo-Noncing or RLOC-Probing.

   When determining Locator up/down reachability by examining the
   Locator Status Bits from the LISP encapsulated data packet, an ETR
   will receive up to date status from an encapsulating ITR about
   reachability for all ETRs at the site.  CE-based ITRs at the source
   site can determine reachability relative to each other using the site
   IGP as follows:





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   o  Under normal circumstances, each ITR will advertise a default
      route into the site IGP.

   o  If an ITR fails or if the upstream link to its PE fails, its
      default route will either time-out or be withdrawn.

   Each ITR can thus observe the presence or lack of a default route
   originated by the others to determine the Locator Status Bits it sets
   for them.

   RLOCs listed in a Map-Reply are numbered with ordinals 0 to n-1.  The
   Locator Status Bits in a LISP encapsulated packet are numbered from 0
   to n-1 starting with the least significant bit.  For example, if an
   RLOC listed in the 3rd position of the Map-Reply goes down (ordinal
   value 2), then all ITRs at the site will clear the 3rd least
   significant bit (xxxx x0xx) of the Locator Status Bits field for the
   packets they encapsulate.

   When an ETR decapsulates a packet, it will check for any change in
   the Locator Status Bits field.  When a bit goes from 1 to 0, the ETR
   if acting also as an ITR, will refrain from encapsulating packets to
   an RLOC that is indicated as down.  It will only resume using that
   RLOC if the corresponding Locator Status Bit returns to a value of 1.
   Locator Status Bits are associated with a locator-set per EID-prefix.
   Therefore, when a locator becomes unreachable, the Locator Status Bit
   that corresponds to that locator's position in the list returned by
   the last Map-Reply will be set to zero for that particular EID-
   prefix.

   When ITRs at the site are not deployed in CE routers, the IGP can
   still be used to determine the reachability of Locators provided they
   are injected into the IGP.  This is typically done when a /32 address
   is configured on a loopback interface.

   When ITRs receive ICMP Network or Host Unreachable messages as a
   method to determine unreachability, they will refrain from using
   Locators which are described in Locator lists of Map-Replies.
   However, using this approach is unreliable because many network
   operators turn off generation of ICMP Unreachable messages.

   If an ITR does receive an ICMP Network or Host Unreachable message,
   it MAY originate its own ICMP Unreachable message destined for the
   host that originated the data packet the ITR encapsulated.

   Also, BGP-enabled ITRs can unilaterally examine the RIB to see if a
   locator address from a locator-set in a mapping entry matches a
   prefix.  If it does not find one and BGP is running in the Default
   Free Zone (DFZ), it can decide to not use the locator even though the



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   Locator Status Bits indicate the locator is up.  In this case, the
   path from the ITR to the ETR that is assigned the locator is not
   available.  More details are in [LOC-ID-ARCH].

   Optionally, an ITR can send a Map-Request to a Locator and if a Map-
   Reply is returned, reachability of the Locator has been determined.
   Obviously, sending such probes increases the number of control
   messages originated by tunnel routers for active flows, so Locators
   are assumed to be reachable when they are advertised.

   This assumption does create a dependency: Locator unreachability is
   detected by the receipt of ICMP Host Unreachable messages.  When an
   Locator has been determined to be unreachable, it is not used for
   active traffic; this is the same as if it were listed in a Map-Reply
   with priority 255.

   The ITR can test the reachability of the unreachable Locator by
   sending periodic Requests.  Both Requests and Replies MUST be rate-
   limited.  Locator reachability testing is never done with data
   packets since that increases the risk of packet loss for end-to-end
   sessions.

   When an ETR decapsulates a packet, it knows that it is reachable from
   the encapsulating ITR because that is how the packet arrived.  In
   most cases, the ETR can also reach the ITR but cannot assume this to
   be true due to the possibility of path asymmetry.  In the presence of
   unidirectional traffic flow from an ITR to an ETR, the ITR SHOULD NOT
   use the lack of return traffic as an indication that the ETR is
   unreachable.  Instead, it MUST use an alternate mechanisms to
   determine reachability.

6.3.1.  Echo Nonce Algorithm

   When data flows bidirectionally between locators from different
   sites, a data-plane mechanism called "nonce echoing" can be used to
   determine reachability between an ITR and ETR.  When an ITR wants to
   solicit a nonce echo, it sets the N and E bits and places a 24-bit
   nonce [RFC4086] in the LISP header of the next encapsulated data
   packet.

   When this packet is received by the ETR, the encapsulated packet is
   forwarded as normal.  When the ETR next sends a data packet to the
   ITR, it includes the nonce received earlier with the N bit set and E
   bit cleared.  The ITR sees this "echoed nonce" and knows the path to
   and from the ETR is up.

   The ITR will set the E-bit and N-bit for every packet it sends while
   in echo-nonce-request state.  The time the ITR waits to process the



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   echoed nonce before it determines the path is unreachable is variable
   and a choice left for the implementation.

   If the ITR is receiving packets from the ETR but does not see the
   nonce echoed while being in echo-nonce-request state, then the path
   to the ETR is unreachable.  This decision may be overridden by other
   locator reachability algorithms.  Once the ITR determines the path to
   the ETR is down it can switch to another locator for that EID-prefix.

   Note that "ITR" and "ETR" are relative terms here.  Both devices MUST
   be implementing both ITR and ETR functionality for the echo nonce
   mechanism to operate.

   The ITR and ETR may both go into echo-nonce-request state at the same
   time.  The number of packets sent or the time during which echo nonce
   requests are sent is an implementation specific setting.  However,
   when an ITR is in echo-nonce-request state, it can echo the ETR's
   nonce in the next set of packets that it encapsulates and then
   subsequently, continue sending echo-nonce-request packets.

   This mechanism does not completely solve the forward path
   reachability problem as traffic may be unidirectional.  That is, the
   ETR receiving traffic at a site may not be the same device as an ITR
   which transmits traffic from that site or the site to site traffic is
   unidirectional so there is no ITR returning traffic.

   The echo-nonce algorithm is bilateral.  That is, if one side sets the
   E-bit and the other side is not enabled for echo-noncing, then the
   echoing of the nonce does not occur and the requesting side may
   regard the locator unreachable erroneously.  An ITR SHOULD only set
   the E-bit in a encapsulated data packet when it knows the ETR is
   enabled for echo-noncing.  This is conveyed by the E-bit in the Map-
   Reply message.

   Note that other locator reachability mechanisms are being researched
   and can be used to compliment or even override the Echo Nonce
   Algorithm.  See next section for an example of control-plane probing.

6.3.2.  RLOC Probing Algorithm

   RLOC Probing is a method that an ITR or PITR can use to determine the
   reachability status of one or more locators that it has cached in a
   map-cache entry.  The probe-bit of the Map-Request and Map-Reply
   messages are used for RLOC Probing.

   RLOC probing is done in the control-plane on a timer basis where an
   ITR or PITR will originate a Map-Request destined to a locator
   address from one of its own locator addresses.  A Map-Request used as



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   an RLOC-probe is NOT encapsulated and NOT sent to a Map-Server or on
   the ALT like one would when soliciting mapping data.  The EID record
   encoded in the Map-Request is the EID-prefix of the map-cache entry
   cached by the ITR or PITR.  The ITR may include a mapping data record
   for its own database mapping information which contains the local
   EID-prefixes and RLOCs for its site.  RLOC-probes are sent
   periodically using a jittered timer interval.

   When an ETR receives a Map-Request message with the probe-bit set, it
   returns a Map-Reply with the probe-bit set.  The source address of
   the Map-Reply is set according to the procedure described in
   Section 6.1.5.  The Map-Reply SHOULD contain mapping data for the
   EID-prefix contained in the Map-Request.  This provides the
   opportunity for the ITR or PITR, which sent the RLOC-probe to get
   mapping updates if there were changes to the ETR's database mapping
   entries.

   There are advantages and disadvantages of RLOC Probing.  The greatest
   benefit of RLOC Probing is that it can handle many failure scenarios
   allowing the ITR to determine when the path to a specific locator is
   reachable or has become unreachable, thus providing a robust
   mechanism for switching to using another locator from the cached
   locator.  RLOC Probing can also provide rough RTT estimates between a
   pair of locators which can be useful for network management purposes
   as well as for selecting low delay paths.  The major disadvantage of
   RLOC Probing is in the number of control messages required and the
   amount of bandwidth used to obtain those benefits, especially if the
   requirement for failure detection times are very small.

   Continued research and testing will attempt to characterize the
   tradeoffs of failure detection times versus message overhead.

6.4.  EID Reachability within a LISP Site

   A site may be multihomed using two or more ETRs.  The hosts and
   infrastructure within a site will be addressed using one or more EID
   prefixes that are mapped to the RLOCs of the relevant ETRs in the
   mapping system.  One possible failure mode is for an ETR to lose
   reachability to one or more of the EID prefixes within its own site.
   When this occurs when the ETR sends Map-Replies, it can clear the
   R-bit associated with its own locator.  And when the ETR is also an
   ITR, it can clear its locator-status-bit in the encapsulation data
   header.

   It is recognized there are no simple solutions to the site
   partitioning problem because it is hard to know which part of the
   EID-prefix range is partitioned.  And which locators can reach any
   sub-ranges of the EID-prefixes.  This problem is under investigation



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   with the expectation that experiments will tell us more.  Note, this
   is not a new problem introduced by the LISP architecture.  The
   problem exists today when a multi-homed site uses BGP to advertise
   its reachability upstream.

6.5.  Routing Locator Hashing

   When an ETR provides an EID-to-RLOC mapping in a Map-Reply message to
   a requesting ITR, the locator-set for the EID-prefix may contain
   different priority values for each locator address.  When more than
   one best priority locator exists, the ITR can decide how to load
   share traffic against the corresponding locators.

   The following hash algorithm may be used by an ITR to select a
   locator for a packet destined to an EID for the EID-to-RLOC mapping:

   1.  Either a source and destination address hash can be used or the
       traditional 5-tuple hash which includes the source and
       destination addresses, source and destination TCP, UDP, or SCTP
       port numbers and the IP protocol number field or IPv6 next-
       protocol fields of a packet a host originates from within a LISP
       site.  When a packet is not a TCP, UDP, or SCTP packet, the
       source and destination addresses only from the header are used to
       compute the hash.

   2.  Take the hash value and divide it by the number of locators
       stored in the locator-set for the EID-to-RLOC mapping.

   3.  The remainder will yield a value of 0 to "number of locators
       minus 1".  Use the remainder to select the locator in the
       locator-set.

   Note that when a packet is LISP encapsulated, the source port number
   in the outer UDP header needs to be set.  Selecting a hashed value
   allows core routers which are attached to Link Aggregation Groups
   (LAGs) to load-split the encapsulated packets across member links of
   such LAGs.  Otherwise, core routers would see a single flow, since
   packets have a source address of the ITR, for packets which are
   originated by different EIDs at the source site.  A suggested setting
   for the source port number computed by an ITR is a 5-tuple hash
   function on the inner header, as described above.

   Many core router implementations use a 5-tuple hash to decide how to
   balance packet load across members of a LAG.  The 5-tuple hash
   includes the source and destination addresses of the packet and the
   source and destination ports when the protocol number in the packet
   is TCP or UDP.  For this reason, UDP encoding is used for LISP
   encapsulation.



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6.6.  Changing the Contents of EID-to-RLOC Mappings

   Since the LISP architecture uses a caching scheme to retrieve and
   store EID-to-RLOC mappings, the only way an ITR can get a more up-to-
   date mapping is to re-request the mapping.  However, the ITRs do not
   know when the mappings change and the ETRs do not keep track of which
   ITRs requested its mappings.  For scalability reasons, we want to
   maintain this approach but need to provide a way for ETRs change
   their mappings and inform the sites that are currently communicating
   with the ETR site using such mappings.

   When adding a new locator record in lexicographic order to the end of
   a locator-set, it is easy to update mappings.  We assume new mappings
   will maintain the same locator ordering as the old mapping but just
   have new locators appended to the end of the list.  So some ITRs can
   have a new mapping while other ITRs have only an old mapping that is
   used until they time out.  When an ITR has only an old mapping but
   detects bits set in the loc-status-bits that correspond to locators
   beyond the list it has cached, it simply ignores them.  However, this
   can only happen for locator addresses that are lexicographically
   greater than the locator addresses in the existing locator-set.

   When a locator record is inserted in the middle of a locator-set, to
   maintain lexicographic order, the SMR procedure in Section 6.6.2 is
   used to inform ITRs and PITRs of the new locator-status-bit mappings.

   When a locator record is removed from a locator-set, ITRs that have
   the mapping cached will not use the removed locator because the xTRs
   will set the loc-status-bit to 0.  So even if the locator is in the
   list, it will not be used.  For new mapping requests, the xTRs can
   set the locator AFI to 0 (indicating an unspecified address), as well
   as setting the corresponding loc-status-bit to 0.  This forces ITRs
   with old or new mappings to avoid using the removed locator.

   If many changes occur to a mapping over a long period of time, one
   will find empty record slots in the middle of the locator-set and new
   records appended to the locator-set.  At some point, it would be
   useful to compact the locator-set so the loc-status-bit settings can
   be efficiently packed.

   We propose here three approaches for locator-set compaction, one
   operational and two protocol mechanisms.  The operational approach
   uses a clock sweep method.  The protocol approaches use the concept
   of Solicit-Map-Requests and Map-Versioning.







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6.6.1.  Clock Sweep

   The clock sweep approach uses planning in advance and the use of
   count-down TTLs to time out mappings that have already been cached.
   The default setting for an EID-to-RLOC mapping TTL is 24 hours.  So
   there is a 24 hour window to time out old mappings.  The following
   clock sweep procedure is used:

   1.  24 hours before a mapping change is to take effect, a network
       administrator configures the ETRs at a site to start the clock
       sweep window.

   2.  During the clock sweep window, ETRs continue to send Map-Reply
       messages with the current (unchanged) mapping records.  The TTL
       for these mappings is set to 1 hour.

   3.  24 hours later, all previous cache entries will have timed out,
       and any active cache entries will time out within 1 hour.  During
       this 1 hour window the ETRs continue to send Map-Reply messages
       with the current (unchanged) mapping records with the TTL set to
       1 minute.

   4.  At the end of the 1 hour window, the ETRs will send Map-Reply
       messages with the new (changed) mapping records.  So any active
       caches can get the new mapping contents right away if not cached,
       or in 1 minute if they had the mapping cached.  The new mappings
       are cached with a time to live equal to the TTL in the Map-Reply.

6.6.2.  Solicit-Map-Request (SMR)

   Soliciting a Map-Request is a selective way for ETRs, at the site
   where mappings change, to control the rate they receive requests for
   Map-Reply messages.  SMRs are also used to tell remote ITRs to update
   the mappings they have cached.

   Since the ETRs don't keep track of remote ITRs that have cached their
   mappings, they do not know which ITRs need to have their mappings
   updated.  As a result, an ETR will solicit Map-Requests (called an
   SMR message) from those sites to which it has been sending
   encapsulated data to for the last minute.  In particular, an ETR will
   send an SMR an ITR to which it has recently sent encapsulated data.

   An SMR message is simply a bit set in a Map-Request message.  An ITR
   or PITR will send a Map-Request when they receive an SMR message.
   Both the SMR sender and the Map-Request responder MUST rate-limited
   these messages.  Rate-limiting can be implemented as a global rate-
   limiter or one rate-limiter per SMR destination.




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   The following procedure shows how a SMR exchange occurs when a site
   is doing locator-set compaction for an EID-to-RLOC mapping:

   1.  When the database mappings in an ETR change, the ETRs at the site
       begin to send Map-Requests with the SMR bit set for each locator
       in each map-cache entry the ETR caches.

   2.  A remote ITR which receives the SMR message will schedule sending
       a Map-Request message to the source locator address of the SMR
       message or to the mapping database system.  A newly allocated
       random nonce is selected and the EID-prefix used is the one
       copied from the SMR message.  If the source locator is the only
       locator in the cached locator-set, the remote ITR SHOULD send a
       Map-Request to the database mapping system just in case the
       single locator has changed and may no longer be reachable to
       accept the Map-Request.

   3.  The remote ITR MUST rate-limit the Map-Request until it gets a
       Map-Reply while continuing to use the cached mapping.  When Map
       Versioning is used, described in Section 6.6.3, an SMR sender can
       detect if an ITR is using the most up to date database mapping.

   4.  The ETRs at the site with the changed mapping will reply to the
       Map-Request with a Map-Reply message that has a nonce from the
       SMR-invoked Map-Request.  The Map-Reply messages SHOULD be rate
       limited.  This is important to avoid Map-Reply implosion.

   5.  The ETRs, at the site with the changed mapping, record the fact
       that the site that sent the Map-Request has received the new
       mapping data in the mapping cache entry for the remote site so
       the loc-status-bits are reflective of the new mapping for packets
       going to the remote site.  The ETR then stops sending SMR
       messages.

   Experimentation is in progress to determine the appropriate rate-
   limit parameters.

   For security reasons an ITR MUST NOT process unsolicited Map-Replies.
   To avoid map-cache entry corruption by a third-party, a sender of an
   SMR-based Map-Request MUST be verified.  If an ITR receives an SMR-
   based Map-Request and the source is not in the locator-set for the
   stored map-cache entry, then the responding Map-Request MUST be sent
   with an EID destination to the mapping database system.  Since the
   mapping database system is more secure to reach an authoritative ETR,
   it will deliver the Map-Request to the authoritative source of the
   mapping data.

   When an ITR receives an SMR-based Map-Request for which it does not



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   have a cached mapping for the EID in the SMR message, it MAY not send
   a SMR-invoked Map-Request.  This scenario can occur when an ETR sends
   SMR messages to all locators in the locator-set it has stored in its
   map-cache but the remote ITRs that receive the SMR may not be sending
   packets to the site.  There is no point in updating the ITRs until
   they need to send, in which case, they will send Map-Requests to
   obtain a map-cache entry.

6.6.3.  Database Map Versioning

   When there is unidirectional packet flow between an ITR and ETR, and
   the EID-to-RLOC mappings change on the ETR, it needs to inform the
   ITR so encapsulation can stop to a removed locator and start to a new
   locator in the locator-set.

   An ETR, when it sends Map-Reply messages, conveys its own Map-Version
   number.  This is known as the Destination Map-Version Number.  ITRs
   include the Destination Map-Version Number in packets they
   encapsulate to the site.  When an ETR decapsulates a packet and
   detects the Destination Map-Version Number is less than the current
   version for its mapping, the SMR procedure described in Section 6.6.2
   occurs.

   An ITR, when it encapsulates packets to ETRs, can convey its own Map-
   Version number.  This is known as the Source Map-Version Number.
   When an ETR decapsulates a packet and detects the Source Map-Version
   Number is greater than the last Map-Version Number sent in a Map-
   Reply from the ITR's site, the ETR will send a Map-Request to one of
   the ETRs for the source site.

   A Map-Version Number is used as a sequence number per EID-prefix.  So
   values that are greater, are considered to be more recent.  A value
   of 0 for the Source Map-Version Number or the Destination Map-Version
   Number conveys no versioning information and an ITR does no
   comparison with previously received Map-Version Numbers.

   A Map-Version Number can be included in Map-Register messages as
   well.  This is a good way for the Map-Server can assure that all ETRs
   for a site registering to it will be Map-Version number synchronized.

   See [VERSIONING] for a more detailed analysis and description of
   Database Map Versioning.









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7.  Router Performance Considerations

   LISP is designed to be very hardware-based forwarding friendly.  A
   few implementation techniques can be used to incrementally implement
   LISP:

   o  When a tunnel encapsulated packet is received by an ETR, the outer
      destination address may not be the address of the router.  This
      makes it challenging for the control plane to get packets from the
      hardware.  This may be mitigated by creating special FIB entries
      for the EID-prefixes of EIDs served by the ETR (those for which
      the router provides an RLOC translation).  These FIB entries are
      marked with a flag indicating that control plane processing should
      be performed.  The forwarding logic of testing for particular IP
      protocol number value is not necessary.  There are a few proven
      cases where no changes to existing deployed hardware were needed
      to support the LISP data-plane.

   o  On an ITR, prepending a new IP header consists of adding more
      octets to a MAC rewrite string and prepending the string as part
      of the outgoing encapsulation procedure.  Routers that support GRE
      tunneling [RFC2784] or 6to4 tunneling [RFC3056] may already
      support this action.

   o  A packet's source address or interface the packet was received on
      can be used to select a VRF (Virtual Routing/Forwarding).  The
      VRF's routing table can be used to find EID-to-RLOC mappings.

   For performance issues related to map-cache management, see section
   Section 12.





















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8.  Deployment Scenarios

   This section will explore how and where ITRs and ETRs can be deployed
   and will discuss the pros and cons of each deployment scenario.  For
   a more detailed deployment recommendation, refer to [LISP-DEPLOY].

   There are two basic deployment trade-offs to consider: centralized
   versus distributed caches and flat, recursive, or re-encapsulating
   tunneling.  When deciding on centralized versus distributed caching,
   the following issues should be considered:

   o  Are the tunnel routers spread out so that the caches are spread
      across all the memories of each router?  A centralized cache is
      when an ITR keeps a cache for all the EIDs it is encapsulating to.
      The packet takes a direct path to the destination locator.  A
      distributed cache is when an ITR needs help from other re-
      encapsulating routers because it does not store all the cache
      entries for the EIDs is it encapsulating to.  So the packet takes
      a path through re-encapsulating routers that have a different set
      of cache entries.

   o  Should management "touch points" be minimized by choosing few
      tunnel routers, just enough for redundancy?

   o  In general, using more ITRs doesn't increase management load,
      since caches are built and stored dynamically.  On the other hand,
      more ETRs does require more management since EID-prefix-to-RLOC
      mappings need to be explicitly configured.

   When deciding on flat, recursive, or re-encapsulation tunneling, the
   following issues should be considered:

   o  Flat tunneling implements a single tunnel between source site and
      destination site.  This generally offers better paths between
      sources and destinations with a single tunnel path.

   o  Recursive tunneling is when tunneled traffic is again further
      encapsulated in another tunnel, either to implement VPNs or to
      perform Traffic Engineering.  When doing VPN-based tunneling, the
      site has some control since the site is prepending a new tunnel
      header.  In the case of TE-based tunneling, the site may have
      control if it is prepending a new tunnel header, but if the site's
      ISP is doing the TE, then the site has no control.  Recursive
      tunneling generally will result in suboptimal paths but at the
      benefit of steering traffic to resource available parts of the
      network.





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   o  The technique of re-encapsulation ensures that packets only
      require one tunnel header.  So if a packet needs to be rerouted,
      it is first decapsulated by the ETR and then re-encapsulated with
      a new tunnel header using a new RLOC.

   The next sub-sections will survey where tunnel routers can reside in
   the network.

8.1.  First-hop/Last-hop Tunnel Routers

   By locating tunnel routers close to hosts, the EID-prefix set is at
   the granularity of an IP subnet.  So at the expense of more EID-
   prefix-to-RLOC sets for the site, the caches in each tunnel router
   can remain relatively small.  But caches always depend on the number
   of non-aggregated EID destination flows active through these tunnel
   routers.

   With more tunnel routers doing encapsulation, the increase in control
   traffic grows as well: since the EID-granularity is greater, more
   Map-Requests and Map-Replies are traveling between more routers.

   The advantage of placing the caches and databases at these stub
   routers is that the products deployed in this part of the network
   have better price-memory ratios then their core router counterparts.
   Memory is typically less expensive in these devices and fewer routes
   are stored (only IGP routes).  These devices tend to have excess
   capacity, both for forwarding and routing state.

   LISP functionality can also be deployed in edge switches.  These
   devices generally have layer-2 ports facing hosts and layer-3 ports
   facing the Internet.  Spare capacity is also often available in these
   devices as well.

8.2.  Border/Edge Tunnel Routers

   Using customer-edge (CE) routers for tunnel endpoints allows the EID
   space associated with a site to be reachable via a small set of RLOCs
   assigned to the CE routers for that site.  This is the default
   behavior envisioned in the rest of this specification.

   This offers the opposite benefit of the first-hop/last-hop tunnel
   router scenario: the number of mapping entries and network management
   touch points are reduced, allowing better scaling.

   One disadvantage is that less of the network's resources are used to
   reach host endpoints thereby centralizing the point-of-failure domain
   and creating network choke points at the CE router.




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   Note that more than one CE router at a site can be configured with
   the same IP address.  In this case an RLOC is an anycast address.
   This allows resilience between the CE routers.  That is, if a CE
   router fails, traffic is automatically routed to the other routers
   using the same anycast address.  However, this comes with the
   disadvantage where the site cannot control the entrance point when
   the anycast route is advertised out from all border routers.  Another
   disadvantage of using anycast locators is the limited advertisement
   scope of /32 (or /128 for IPv6) routes.

8.3.  ISP Provider-Edge (PE) Tunnel Routers

   Use of ISP PE routers as tunnel endpoint routers is not the typical
   deployment scenario envisioned in the specification.  This section
   attempts to capture some of reasoning behind this preference of
   implementing LISP on CE routers.

   Use of ISP PE routers as tunnel endpoint routers gives an ISP, rather
   than a site, control over the location of the egress tunnel
   endpoints.  That is, the ISP can decide if the tunnel endpoints are
   in the destination site (in either CE routers or last-hop routers
   within a site) or at other PE edges.  The advantage of this case is
   that two tunnel headers can be avoided.  By having the PE be the
   first router on the path to encapsulate, it can choose a TE path
   first, and the ETR can decapsulate and re-encapsulate for a tunnel to
   the destination end site.

   An obvious disadvantage is that the end site has no control over
   where its packets flow or the RLOCs used.  Other disadvantages
   include the difficulty in synchronizing path liveness updates between
   CE and PE routers.

   As mentioned in earlier sections a combination of these scenarios is
   possible at the expense of extra packet header overhead, if both site
   and provider want control, then recursive or re-encapsulating tunnels
   are used.

8.4.  LISP Functionality with Conventional NATs

   LISP routers can be deployed behind Network Address Translator (NAT)
   devices to provide the same set of packet services hosts have today
   when they are addressed out of private address space.

   It is important to note that a locator address in any LISP control
   message MUST be a globally routable address and therefore SHOULD NOT
   contain [RFC1918] addresses.  If a LISP router is configured with
   private addresses, they MUST be used only in the outer IP header so
   the NAT device can translate properly.  Otherwise, EID addresses MUST



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   be translated before encapsulation is performed.  Both NAT
   translation and LISP encapsulation functions could be co-located in
   the same device.

   More details on LISP address translation can be found in [INTERWORK].

8.5.  Packets Egressing a LISP Site

   When a LISP site is using two ITRs for redundancy, the failure of one
   ITR will likely shift outbound traffic to the second.  This second
   ITR's cache may not not be populated with the same EID-to-RLOC
   mapping entries as the first.  If this second ITR does not have these
   mappings, traffic will be dropped while the mappings are retrieved
   from the mapping system.  The retrieval of these messages may
   increase the load of requests being sent into the mapping system.
   Deployment and experimentation will determine whether this issue
   requires more attention.


































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9.  Traceroute Considerations

   When a source host in a LISP site initiates a traceroute to a
   destination host in another LISP site, it is highly desirable for it
   to see the entire path.  Since packets are encapsulated from ITR to
   ETR, the hop across the tunnel could be viewed as a single hop.
   However, LISP traceroute will provide the entire path so the user can
   see 3 distinct segments of the path from a source LISP host to a
   destination LISP host:


      Segment 1 (in source LISP site based on EIDs):

          source-host ---> first-hop ... next-hop ---> ITR

      Segment 2 (in the core network based on RLOCs):

          ITR ---> next-hop ... next-hop ---> ETR

      Segment 3 (in the destination LISP site based on EIDs):

          ETR ---> next-hop ... last-hop ---> destination-host

   For segment 1 of the path, ICMP Time Exceeded messages are returned
   in the normal manner as they are today.  The ITR performs a TTL
   decrement and test for 0 before encapsulating.  So the ITR hop is
   seen by the traceroute source has an EID address (the address of
   site-facing interface).

   For segment 2 of the path, ICMP Time Exceeded messages are returned
   to the ITR because the TTL decrement to 0 is done on the outer
   header, so the destination of the ICMP messages are to the ITR RLOC
   address, the source RLOC address of the encapsulated traceroute
   packet.  The ITR looks inside of the ICMP payload to inspect the
   traceroute source so it can return the ICMP message to the address of
   the traceroute client as well as retaining the core router IP address
   in the ICMP message.  This is so the traceroute client can display
   the core router address (the RLOC address) in the traceroute output.
   The ETR returns its RLOC address and responds to the TTL decrement to
   0 like the previous core routers did.

   For segment 3, the next-hop router downstream from the ETR will be
   decrementing the TTL for the packet that was encapsulated, sent into
   the core, decapsulated by the ETR, and forwarded because it isn't the
   final destination.  If the TTL is decremented to 0, any router on the
   path to the destination of the traceroute, including the next-hop
   router or destination, will send an ICMP Time Exceeded message to the
   source EID of the traceroute client.  The ICMP message will be



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   encapsulated by the local ITR and sent back to the ETR in the
   originated traceroute source site, where the packet will be delivered
   to the host.

9.1.  IPv6 Traceroute

   IPv6 traceroute follows the procedure described above since the
   entire traceroute data packet is included in ICMP Time Exceeded
   message payload.  Therefore, only the ITR needs to pay special
   attention for forwarding ICMP messages back to the traceroute source.

9.2.  IPv4 Traceroute

   For IPv4 traceroute, we cannot follow the above procedure since IPv4
   ICMP Time Exceeded messages only include the invoking IP header and 8
   octets that follow the IP header.  Therefore, when a core router
   sends an IPv4 Time Exceeded message to an ITR, all the ITR has in the
   ICMP payload is the encapsulated header it prepended followed by a
   UDP header.  The original invoking IP header, and therefore the
   identity of the traceroute source is lost.

   The solution we propose to solve this problem is to cache traceroute
   IPv4 headers in the ITR and to match them up with corresponding IPv4
   Time Exceeded messages received from core routers and the ETR.  The
   ITR will use a circular buffer for caching the IPv4 and UDP headers
   of traceroute packets.  It will select a 16-bit number as a key to
   find them later when the IPv4 Time Exceeded messages are received.
   When an ITR encapsulates an IPv4 traceroute packet, it will use the
   16-bit number as the UDP source port in the encapsulating header.
   When the ICMP Time Exceeded message is returned to the ITR, the UDP
   header of the encapsulating header is present in the ICMP payload
   thereby allowing the ITR to find the cached headers for the
   traceroute source.  The ITR puts the cached headers in the payload
   and sends the ICMP Time Exceeded message to the traceroute source
   retaining the source address of the original ICMP Time Exceeded
   message (a core router or the ETR of the site of the traceroute
   destination).

   The signature of a traceroute packet comes in two forms.  The first
   form is encoded as a UDP message where the destination port is
   inspected for a range of values.  The second form is encoded as an
   ICMP message where the IP identification field is inspected for a
   well-known value.

9.3.  Traceroute using Mixed Locators

   When either an IPv4 traceroute or IPv6 traceroute is originated and
   the ITR encapsulates it in the other address family header, you



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   cannot get all 3 segments of the traceroute.  Segment 2 of the
   traceroute can not be conveyed to the traceroute source since it is
   expecting addresses from intermediate hops in the same address format
   for the type of traceroute it originated.  Therefore, in this case,
   segment 2 will make the tunnel look like one hop.  All the ITR has to
   do to make this work is to not copy the inner TTL to the outer,
   encapsulating header's TTL when a traceroute packet is encapsulated
   using an RLOC from a different address family.  This will cause no
   TTL decrement to 0 to occur in core routers between the ITR and ETR.










































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10.  Mobility Considerations

   There are several kinds of mobility of which only some might be of
   concern to LISP.  Essentially they are as follows.

10.1.  Site Mobility

   A site wishes to change its attachment points to the Internet, and
   its LISP Tunnel Routers will have new RLOCs when it changes upstream
   providers.  Changes in EID-RLOC mappings for sites are expected to be
   handled by configuration, outside of the LISP protocol.

10.2.  Slow Endpoint Mobility

   An individual endpoint wishes to move, but is not concerned about
   maintaining session continuity.  Renumbering is involved.  LISP can
   help with the issues surrounding renumbering [RFC4192] [LISA96] by
   decoupling the address space used by a site from the address spaces
   used by its ISPs.  [RFC4984]

10.3.  Fast Endpoint Mobility

   Fast endpoint mobility occurs when an endpoint moves relatively
   rapidly, changing its IP layer network attachment point.  Maintenance
   of session continuity is a goal.  This is where the Mobile IPv4
   [RFC5944] and Mobile IPv6 [RFC6275] [RFC4866] mechanisms are used,
   and primarily where interactions with LISP need to be explored.

   The problem is that as an endpoint moves, it may require changes to
   the mapping between its EID and a set of RLOCs for its new network
   location.  When this is added to the overhead of mobile IP binding
   updates, some packets might be delayed or dropped.

   In IPv4 mobility, when an endpoint is away from home, packets to it
   are encapsulated and forwarded via a home agent which resides in the
   home area the endpoint's address belongs to.  The home agent will
   encapsulate and forward packets either directly to the endpoint or to
   a foreign agent which resides where the endpoint has moved to.
   Packets from the endpoint may be sent directly to the correspondent
   node, may be sent via the foreign agent, or may be reverse-tunneled
   back to the home agent for delivery to the mobile node.  As the
   mobile node's EID or available RLOC changes, LISP EID-to-RLOC
   mappings are required for communication between the mobile node and
   the home agent, whether via foreign agent or not.  As a mobile
   endpoint changes networks, up to three LISP mapping changes may be
   required:





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   o  The mobile node moves from an old location to a new visited
      network location and notifies its home agent that it has done so.
      The Mobile IPv4 control packets the mobile node sends pass through
      one of the new visited network's ITRs, which needs an EID-RLOC
      mapping for the home agent.

   o  The home agent might not have the EID-RLOC mappings for the mobile
      node's "care-of" address or its foreign agent in the new visited
      network, in which case it will need to acquire them.

   o  When packets are sent directly to the correspondent node, it may
      be that no traffic has been sent from the new visited network to
      the correspondent node's network, and the new visited network's
      ITR will need to obtain an EID-RLOC mapping for the correspondent
      node's site.

   In addition, if the IPv4 endpoint is sending packets from the new
   visited network using its original EID, then LISP will need to
   perform a route-returnability check on the new EID-RLOC mapping for
   that EID.

   In IPv6 mobility, packets can flow directly between the mobile node
   and the correspondent node in either direction.  The mobile node uses
   its "care-of" address (EID).  In this case, the route-returnability
   check would not be needed but one more LISP mapping lookup may be
   required instead:

   o  As above, three mapping changes may be needed for the mobile node
      to communicate with its home agent and to send packets to the
      correspondent node.

   o  In addition, another mapping will be needed in the correspondent
      node's ITR, in order for the correspondent node to send packets to
      the mobile node's "care-of" address (EID) at the new network
      location.

   When both endpoints are mobile the number of potential mapping
   lookups increases accordingly.

   As a mobile node moves there are not only mobility state changes in
   the mobile node, correspondent node, and home agent, but also state
   changes in the ITRs and ETRs for at least some EID-prefixes.

   The goal is to support rapid adaptation, with little delay or packet
   loss for the entire system.  Also IP mobility can be modified to
   require fewer mapping changes.  In order to increase overall system
   performance, there may be a need to reduce the optimization of one
   area in order to place fewer demands on another.



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   In LISP, one possibility is to "glean" information.  When a packet
   arrives, the ETR could examine the EID-RLOC mapping and use that
   mapping for all outgoing traffic to that EID.  It can do this after
   performing a route-returnability check, to ensure that the new
   network location does have a internal route to that endpoint.
   However, this does not cover the case where an ITR (the node assigned
   the RLOC) at the mobile-node location has been compromised.

   Mobile IP packet exchange is designed for an environment in which all
   routing information is disseminated before packets can be forwarded.
   In order to allow the Internet to grow to support expected future
   use, we are moving to an environment where some information may have
   to be obtained after packets are in flight.  Modifications to IP
   mobility should be considered in order to optimize the behavior of
   the overall system.  Anything which decreases the number of new EID-
   RLOC mappings needed when a node moves, or maintains the validity of
   an EID-RLOC mapping for a longer time, is useful.

10.4.  Fast Network Mobility

   In addition to endpoints, a network can be mobile, possibly changing
   xTRs.  A "network" can be as small as a single router and as large as
   a whole site.  This is different from site mobility in that it is
   fast and possibly short-lived, but different from endpoint mobility
   in that a whole prefix is changing RLOCs.  However, the mechanisms
   are the same and there is no new overhead in LISP.  A map request for
   any endpoint will return a binding for the entire mobile prefix.

   If mobile networks become a more common occurrence, it may be useful
   to revisit the design of the mapping service and allow for dynamic
   updates of the database.

   The issue of interactions between mobility and LISP needs to be
   explored further.  Specific improvements to the entire system will
   depend on the details of mapping mechanisms.  Mapping mechanisms
   should be evaluated on how well they support session continuity for
   mobile nodes.

10.5.  LISP Mobile Node Mobility

   A mobile device can use the LISP infrastructure to achieve mobility
   by implementing the LISP encapsulation and decapsulation functions
   and acting as a simple ITR/ETR.  By doing this, such a "LISP mobile
   node" can use topologically-independent EID IP addresses that are not
   advertised into and do not impose a cost on the global routing
   system.  These EIDs are maintained at the edges of the mapping system
   (in LISP Map-Servers and Map-Resolvers) and are provided on demand to
   only the correspondents of the LISP mobile node.



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   Refer to the LISP Mobility Architecture specification [LISP-MN] for
   more details.

















































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11.  Multicast Considerations

   A multicast group address, as defined in the original Internet
   architecture is an identifier of a grouping of topologically
   independent receiver host locations.  The address encoding itself
   does not determine the location of the receiver(s).  The multicast
   routing protocol, and the network-based state the protocol creates,
   determines where the receivers are located.

   In the context of LISP, a multicast group address is both an EID and
   a Routing Locator.  Therefore, no specific semantic or action needs
   to be taken for a destination address, as it would appear in an IP
   header.  Therefore, a group address that appears in an inner IP
   header built by a source host will be used as the destination EID.
   The outer IP header (the destination Routing Locator address),
   prepended by a LISP router, will use the same group address as the
   destination Routing Locator.

   Having said that, only the source EID and source Routing Locator
   needs to be dealt with.  Therefore, an ITR merely needs to put its
   own IP address in the source Routing Locator field when prepending
   the outer IP header.  This source Routing Locator address, like any
   other Routing Locator address MUST be globally routable.

   Therefore, an EID-to-RLOC mapping does not need to be performed by an
   ITR when a received data packet is a multicast data packet or when
   processing a source-specific Join (either by IGMPv3 or PIM).  But the
   source Routing Locator is decided by the multicast routing protocol
   in a receiver site.  That is, an EID to Routing Locator translation
   is done at control-time.

   Another approach is to have the ITR not encapsulate a multicast
   packet and allow the host built packet to flow into the core even if
   the source address is allocated out of the EID namespace.  If the
   RPF-Vector TLV [RFC5496] is used by PIM in the core, then core
   routers can RPF to the ITR (the Locator address which is injected
   into core routing) rather than the host source address (the EID
   address which is not injected into core routing).

   To avoid any EID-based multicast state in the network core, the first
   approach is chosen for LISP-Multicast.  Details for LISP-Multicast
   and Interworking with non-LISP sites is described in specification
   [MLISP].








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12.  Security Considerations

   It is believed that most of the security mechanisms will be part of
   the mapping database service when using control plane procedures for
   obtaining EID-to-RLOC mappings.  For data plane triggered mappings,
   as described in this specification, protection is provided against
   ETR spoofing by using Return-Routability (see Section 3) mechanisms
   evidenced by the use of a 24-bit Nonce field in the LISP
   encapsulation header and a 64-bit Nonce field in the LISP control
   message.

   The nonce, coupled with the ITR accepting only solicited Map-Replies
   provides a basic level of security, in many ways similar to the
   security experienced in the current Internet routing system.  It is
   hard for off-path attackers to launch attacks against these LISP
   mechanisms, as they do not have the nonce values.  Sending a large
   number of packets to accidentally find the right nonce value is
   possible, but would already by itself be a denial-of-service attack.
   On-path attackers can perform far more serious attacks, but on-path
   attackers can launch serious attacks in the current Internet as well,
   including eavesdropping, blocking or redirecting traffic.  See more
   discussion on this topic in Section 6.1.5.1.

   LISP does not rely on a PKI or a more heavy weight authentication
   system.  These systems challenge the scalability of LISP which was a
   primary design goal.

   DoS attack prevention will depend on implementations rate-limiting
   Map-Requests and Map-Replies to the control plane as well as rate-
   limiting the number of data-triggered Map-Replies.

   An incorrectly implemented or malicious ITR might choose to ignore
   the priority and weights provided by the ETR in its Map-Reply.  This
   traffic steering would be limited to the traffic that is sent by this
   ITR's site, and no more severe than if the site initiated a bandwidth
   DoS attack on (one of) the ETR's ingress links.  The ITR's site would
   typically gain no benefit from not respecting the weights, and would
   likely to receive better service by abiding by them.

   To deal with map-cache exhaustion attempts in an ITR/PITR, the
   implementation should consider putting a maximum cap on the number of
   entries stored with a reserve list for special or frequently accessed
   sites.  This should be a configuration policy control set by the
   network administrator who manages ITRs and PITRs.  When overlapping
   EID-prefixes occur across multiple map-cache entries, the integrity
   of the set must be wholly maintained.  So if a more-specific entry
   cannot be added due to reaching the maximum cap, then none of the
   less specifics should be stored in the map-cache.



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   Given that the ITR/PITR maintains a cache of EID-to-RLOC mappings,
   cache sizing and maintenance is an issue to be kept in mind during
   implementation.  It is a good idea to have instrumentation in place
   to detect thrashing of the cache.  Implementation experimentation
   will be used to determine which cache management strategies work
   best.  In general, it is difficult to defend against cache trashing
   attacks.  It should be noted that an undersized cache in an ITR/PITR
   not only causes adverse affect on the site or region they support,
   but may also cause increased Map-Request load on the mapping system.

   "Piggybacked" mapping data discussed in Section 6.1.3 specifies how
   to handle such mappings and includes the possibility for an ETR to
   temporarily accept such a mapping before verification when running in
   "trusted" environments.  In such cases, there is a potential threat
   that a fake mapping could be inserted (even if only for a short
   period) into a map-cache.  As noted in Section 6.1.3, an ETR MUST be
   specifically configured to run in such a mode and might usefully only
   consider some specific ITRs as also running in that same trusted
   environment.

   There is a security risk implicit in the fact that ETRs generate the
   EID prefix to which they are responding.  An ETR can claim a shorter
   prefix than it is actually responsible for.  Various mechanisms to
   ameliorate or resolve this issue will be examined in the future,
   [LISP-SEC].

   Spoofing of inner header addresses of LISP encapsulated packets is
   possible like with any tunneling mechanism.  ITRs MUST verify the
   source address of a packet to be an EID that belongs to the site's
   EID-prefix range prior to encapsulation.  An ETR must only
   decapsulate and forward datagrams with an inner header destination
   that matches one of its EID-prefix ranges.  If, upon receipt and
   decapsulation, the destination EID of a datagram does not match one
   of the ETR's configured EID-prefixes, the ETR MUST drop the datagram.
   If a LISP encapsulated packet arrives at an ETR, it SHOULD compare
   the inner header source EID address and the outer header source RLOC
   address with the mapping that exists in the mapping database.  Then
   when spoofing attacks occur, the outer header source RLOC address can
   be used to trace back the attack to the source site, using existing
   operational tools.

   This experimental specification does not address automated key
   management (AKM).  BCP 107 provides guidance in this area.  In
   addition, at the time of this writing, substantial work is being
   undertaken to improve security of the routing system [KARP], [RPKI],
   [BGP-SEC], [LISP-SEC].  Future work on LISP should address BCP-107 as
   well as other open security considerations, which may require changes
   to this specification.



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13.  Network Management Considerations

   Considerations for Network Management tools exist so the LISP
   protocol suite can be operationally managed.  The mechanisms can be
   found in [LISP-MIB] and [LISP-LIG].














































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14.  IANA Considerations

   This section provides guidance to the Internet Assigned Numbers
   Authority (IANA) regarding registration of values related to the LISP
   specification, in accordance with BCP 26 and RFC 5226 [RFC5226].

   There are four name spaces in LISP that require registration:

   o  LISP IANA registry allocations should not be made for purposes
      unrelated to LISP routing or transport protocols.

   o  The following policies are used here with the meanings defined in
      BCP 26: "Specification Required", "IETF Review", "Experimental
      Use", "First Come First Served".

14.1.  LISP ACT and Flag Fields

   New ACT values (Section 6.1.4) can be allocated through IETF review
   or IESG approval.  Four values have already been allocated by this
   specification (Section 6.1.4).

   In addition, the LISP protocol has a number of flag and reserved
   fields, such as the LISP header flags field (Section 5.3).  New bits
   for flags can be taken into use from these fields through IETF review
   or IESG approval, but these need not be managed by IANA.

14.2.  LISP Address Type Codes

   LISP Address [LCAF] type codes have a range from 0 to 255.  New type
   codes MUST be allocated consecutively starting at 0.  Type Codes 0 -
   127 are to be assigned by IETF review or IESG approval.

   Type Codes 128 - 255 are available on a First Come First Served
   policy.

   This registry, initially empty, is constructed for future-use
   experimental work of LCAF values.  See [LCAF] for details for other
   possible unapproved address encodings.  The unapproved LCAF encodings
   are an area for further study and experimentation.

14.3.  LISP UDP Port Numbers

   The IANA registry has allocated UDP port numbers 4341 and 4342 for
   LISP data-plane and control-plane operation, respectively.







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14.4.  LISP Key ID Numbers

   The following Key ID values are defined by this specification as used
   in any packet type that references a Key ID field:


       Name                 Number          Defined in
       -----------------------------------------------
       None                 0               n/a
       HMAC-SHA-1-96        1               [RFC2404]
       HMAC-SHA-256-128     2               [RFC6234]








































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15.  Known Open Issues and Areas of Future Work

   As an experimental specification, this work is, by definition,
   incomplete.  Specific areas where additional experience and work are
   needed include:

   o  At present, only [ALT] is defined for implementing a database of
      EID-to-RLOC mapping information.  Additional research on other
      mapping database systems is strongly encouraged.

   o  Failure and recovery of LISP site partitioning (see Section 6.4),
      in the presence of redundant configuration (see Section 8.5) needs
      further research and experimentation.

   o  The characteristics of map-cache management under exceptional
      conditions, such as denial-of-service attacks are not fully
      understood.  Further experience is needed to determine whether
      current caching methods are practical or in need of further
      development.  In particular, the performance, scaling and security
      characteristics of the map-cache will be discovered as part of
      this experiment.  Performance metrics to be observed are packet
      reordering associated with the LISP data probe and loss of the
      first packet in a flow associated with map-caching.  The impact of
      these upon TCP will be observed.  See Section 12 for additional
      thoughts and considerations.

   o  Preliminary work has been done to ensure that sites employing LISP
      can interconnect with the rest of the Internet.  This work is
      documented in [INTERWORK], but further experimentation and
      experience is needed.

   o  At present, no mechanism for automated key management for message
      authentication is defined.  Addressing automated key management is
      necessary before this specification could be developed into a
      standards track RFC.  See Section 12 for further details regarding
      security considerations.

   o  In order to maintain security and stability, Internet Protocols
      typically isolate the control and data planes.  Therefore, user
      activity cannot cause control plane state to be created or
      destroyed.  LISP does not maintain this separation.  The degree to
      which the loss of separation impacts security and stability is a
      topic for experimental observation.

   o  LISP allows for different mapping database systems to be used.
      While only one [ALT] is currently well-defined, each mapping
      database will likely have some impact on the security of the EID-
      to-RLOC mappings.  How each mapping database system's security



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      properties impact on LISP overall is for further study.

   o  An examination of the implications of LISP on Internet traffic,
      applications, routers, and security is needed.  This will help to
      understand the consequences for network stability, routing
      protocol function, routing scalability, migration and backward
      compatibility, and implementation scalability (as influenced by
      additional protocol components, additional state, and additional
      processing for encapsulation, decapsulation, liveness).

   o  Experiments need to verify that LISP produces no significant
      change in the behavior of protocols run between end-systems over a
      LISP infrastructure versus being run directly between those same
      end-systems.

   o  Experiments need to verify that the issues raised in the Critique
      section of [RFC6115] are either insignificant or have been
      addressed by updates to the LISP protocol.

   Other LISP documents may also include open issues and areas for
   future work.






























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16.  References

16.1.  Normative References

   [ALT]      Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
              Alternative Topology (LISP-ALT)",
              draft-ietf-lisp-alt-09.txt (work in progress).

   [LISP-MS]  Farinacci, D. and V. Fuller, "LISP Map Server",
              draft-ietf-lisp-ms-12.txt (work in progress).

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2404]  Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
              ESP and AH", RFC 2404, November 1998.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, September 2001.

   [RFC3232]  Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by
              an On-line Database", RFC 3232, January 2002.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, August 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.




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   [RFC5496]  Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
              Forwarding (RPF) Vector TLV", RFC 5496, March 2009.

   [RFC5944]  Perkins, C., "IP Mobility Support for IPv4, Revised",
              RFC 5944, November 2010.

   [RFC6115]  Li, T., "Recommendation for a Routing Architecture",
              RFC 6115, February 2011.

   [RFC6234]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.

   [RFC6275]  Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
              in IPv6", RFC 6275, July 2011.

   [UDP-TUNNELS]
              Eubanks, M. and P. Chimento, "UDP Checksums for Tunneled
              Packets", draft-eubanks-chimento-6man-01.txt (work in
              progress), October 2010.

   [UDP-ZERO]
              Fairhurst, G. and M. Westerland, "IPv6 UDP Checksum
              Considerations", draft-ietf-6man-udpzero-04.txt (work in
              progress), October 2011.

   [VERSIONING]
              Iannone, L., Saucez, D., and O. Bonaventure, "LISP Mapping
              Versioning", draft-ietf-lisp-map-versioning-05.txt (work
              in progress).

16.2.  Informative References

   [AFI]      IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
              NUMBERS
              http://www.iana.org/assignments/address-family-numbers.

   [AFI-REGISTRY]
              IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
              NUMBER registry http://www.iana.org/assignments/
              address-family-numbers/
              address-family-numbers.xml#address-family-numbers-1.

   [BGP-SEC]  Lepinski, M., "An Overview of BGPSEC",
              draft-lepinski-bgpsec-overview-00.txt (work in progress),
              March 2011.

   [CHIAPPA]  Chiappa, J., "Endpoints and Endpoint names: A Proposed
              Enhancement to the Internet Architecture", Internet-



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              Draft http://www.chiappa.net/~jnc/tech/endpoints.txt.

   [CONS]     Farinacci, D., Fuller, V., and D. Meyer, "LISP-CONS: A
              Content distribution Overlay Network  Service for LISP",
              draft-meyer-lisp-cons-04.txt (work in progress).

   [EMACS]    Brim, S., Farinacci, D., Meyer, D., and J. Curran, "EID
              Mappings Multicast Across Cooperating Systems for LISP",
              draft-curran-lisp-emacs-00.txt (work in progress).

   [INTERWORK]
              Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking LISP with IPv4 and IPv6",
              draft-ietf-lisp-interworking-02.txt (work in progress).

   [KARP]     Lebovitz, G. and M. Bhatia, "Keying and Authentication for
              Routing Protocols (KARP)Design Guidelines",
              draft-ietf-karp-design-guide-06.txt (work in progress),
              October 2011.

   [LCAF]     Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
              Address Format", draft-farinacci-lisp-lcaf-06.txt (work in
              progress).

   [LISA96]   Lear, E., Katinsky, J., Coffin, J., and D. Tharp,
              "Renumbering: Threat or Menace?", Usenix .

   [LISP-DEPLOY]
              Jakab, L., Coras, F., Domingo-Pascual, J., and D. Lewis,
              "LISP Network Element Deployment Considerations",
              draft-ietf-lisp-deployment-02.txt (work in progress).

   [LISP-LIG]
              Farinacci, D. and D. Meyer, "LISP Internet Groper (LIG)",
              draft-ietf-lisp-lig-06.txt (work in progress).

   [LISP-MAIN]
              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-farinacci-lisp-12.txt (work in progress).

   [LISP-MIB]
              Schudel, G., Jain, A., and V. Moreno, "LISP MIB",
              draft-ietf-lisp-mib-02.txt (work in progress).

   [LISP-MN]  Farinacci, D., Fuller, V., Lewis, D., and D. Meyer, "LISP
              Mobility Architecture", draft-meyer-lisp-mn-06.txt (work
              in progress).



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   [LISP-SEC]
              Maino, F., Ermagon, V., Cabellos, A., Sausez, D., and O.
              Bonaventure, "LISP-Security (LISP-SEC)",
              draft-ietf-lisp-sec-00.txt (work in progress).

   [LOC-ID-ARCH]
              Meyer, D. and D. Lewis, "Architectural Implications of
              Locator/ID  Separation",
              draft-meyer-loc-id-implications-02.txt (work in progress).

   [MLISP]    Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas,
              "LISP for Multicast Environments",
              draft-ietf-lisp-multicast-10.txt (work in progress).

   [NERD]     Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
              draft-lear-lisp-nerd-08.txt (work in progress).

   [OPENLISP]
              Iannone, L. and O. Bonaventure, "OpenLISP Implementation
              Report", draft-iannone-openlisp-implementation-01.txt
              (work in progress).

   [RADIR]    Narten, T., "Routing and Addressing Problem Statement",
              draft-narten-radir-problem-statement-05.txt (work in
              progress).

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              March 2000.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              September 2005.

   [RFC4866]  Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route
              Optimization for Mobile IPv6", RFC 4866, May 2007.




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   [RFC4984]  Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
              Workshop on Routing and Addressing", RFC 4984,
              September 2007.

   [RPKI]     Lepinski, M., "An Infrastructure to Support Secure
              Internet Routing", draft-ietf-sidr-arch-13.txt (work in
              progress), February 2011.












































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Appendix A.  Acknowledgments

   An initial thank you goes to Dave Oran for planting the seeds for the
   initial ideas for LISP.  His consultation continues to provide value
   to the LISP authors.

   A special and appreciative thank you goes to Noel Chiappa for
   providing architectural impetus over the past decades on separation
   of location and identity, as well as detailed review of the LISP
   architecture and documents, coupled with enthusiasm for making LISP a
   practical and incremental transition for the Internet.

   The authors would like to gratefully acknowledge many people who have
   contributed discussion and ideas to the making of this proposal.
   They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller,
   Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston,
   David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley,
   Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler,
   Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi
   Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Terry
   Manderson, Roger Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van
   Beijnum, Roland Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien
   Saucez, Damian Lezama, Attilla De Groot, Parantap Lahiri, David
   Black, Roque Gagliano, Isidor Kouvelas, Jesper Skriver, Fred Templin,
   Margaret Wasserman, Sam Hartman, Michael Hofling, Pedro Marques, Jari
   Arkko, Gregg Schudel, Srinivas Subramanian, Amit Jain, Xu Xiaohu,
   Dhirendra Trivedi, Yakov Rekhter, John Scudder, John Drake, Dimitri
   Papadimitriou, Ross Callon, Selina Heimlich, Job Snijders, Vina
   Ermagan, Albert Cabellos, Fabio Maino, Victor Moreno, Chris White,
   Clarence Filsfils, and Alia Atlas.

   This work originated in the Routing Research Group (RRG) of the IRTF.
   The individual submission [LISP-MAIN] was converted into this IETF
   LISP working group draft.

   The LISP working group would like to give a special thanks to Jari
   Arkko, the Internet Area AD at the time the set of LISP documents
   were being prepared for IESG last call, for his meticulous review and
   detail commentary on the 7 working group last call drafts progressing
   toward experimental RFCs.











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Appendix B.  Document Change Log

B.1.  Changes to draft-ietf-lisp-22.txt

   o  Posted February 2012 to reflect final DISCUSS comments from Adrian
      Farrel.

B.2.  Changes to draft-ietf-lisp-21.txt

   o  Posted February 2012 to reflect DISCUSS comments from Adrian
      Farrel, Stewart Bryant, and Wesley Eddy.

B.3.  Changes to draft-ietf-lisp-20.txt

   o  Posted January 2012 for resolution to Adrian Farrel's security
      comments as well as additions to the end of section 2, Elwyn
      Davies Gen-Art comments, and Ralph Droms' IANA and EID definition
      comments.

B.4.  Changes to draft-ietf-lisp-19.txt

   o  Posted January 2012 for Stephen Farrell's comment resolution.

B.5.  Changes to draft-ietf-lisp-18.txt

   o  Posted December 2011 after reflecting comments from IANA.

   o  Create reference to sections 5.4.1 and 5.4.2 about DF bit setting
      from section 5.3.

   o  Inserted two references for Route-Returnability and on-path
      attacks in Security Considerations section.

B.6.  Changes to draft-ietf-lisp-17.txt

   o  Posted December 2011 after IETF last call comments.

   o  Make Map-Notify port assignment be 4342 in both source and
      destination ports.  This change was agreed on and put in [LISP-MS]
      but was not updated in this spec.

B.7.  Changes to draft-ietf-lisp-16.txt

   o  Posted October 2011 after AD review by Jari.







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B.8.  Changes to draft-ietf-lisp-15.txt

   o  Posted July 2011.  Fixing IDnits errors.

   o  Change description on how to select a source address for RLOC-
      probe Map-Replies to refer to the "EID-to-RLOC Map-Reply Message"
      section.

B.9.  Changes to draft-ietf-lisp-14.txt

   o  Post working group last call and pre-IESG last call review.

   o  Indicate that an ICMP Unreachable message should be sent when a
      packet matches a drop-based negative map-cache entry.

   o  Indicate how a map-cache set of overlapping EID-prefixes must
      maintain integrity when the map-cache maximum cap is reached.

   o  Add Joel's description for the definition of an EID, that the bit
      string value can be an RLOC for another device in abstract but the
      architecture allows it to be an EID of one device and the same
      value as an RLOC for another device.

   o  In the "Tunnel Encapsulation Details" section, indicate that 4
      combinations of encapsulation are supported.

   o  Add what ETR should do for a Data-Probe when received for a
      destination EID outside of its EID-prefix range.  This was added
      in the Data Probe definition section.

   o  Added text indicating that more-specific EID-prefixes must not be
      removed when less-specific entries stay in the map-cache.  This is
      to preserve the integrity of the EID-prefix set.

   o  Add clarifying text in the Security Considerations section about
      how an ETR must not decapsulate and forward a packet that is not
      for its configured EID-prefix range.

B.10.  Changes to draft-ietf-lisp-13.txt

   o  Posted June 2011 to complete working group last call.

   o  Tracker item 87.  Put Yakov suggested wording in the EID-prefix
      definition section to reference [INTERWORK] and [LISP-DEPLOY]
      about discussion on transition and access mechanisms.

   o  Change "ITRs" to "ETRs" in the Locator Status Bit definition
      section and data packet description section per Damien's comment.



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   o  Remove the normative reference to [LISP-SEC] when describing the
      S-bit in the ECM and Map-Reply headers.

   o  Tracker item 54.  Added text from John Scudder in the "Packets
      Egressing a LISP Site" section.

   o  Add sentence to the "Reencapsulating Tunnel" definition about how
      reencapsulation loops can occur when not coordinating among
      multiple mapping database systems.

   o  Remove "In theory" from a sentence in the Security Considerations
      section.

   o  Remove Security Area Statement title and reword section with
      Eliot's provided text.  The text was agreed upon by LISP-WG chairs
      and Security ADs.

   o  Remove word "potential" from the over-claiming paragraph of the
      Security Considerations section per Stephen's request.

   o  Wordsmithing and other editorial comments from Alia.

B.11.  Changes to draft-ietf-lisp-12.txt

   o  Posted April 2011.

   o  Tracker item 87.  Provided rewording how an EID-prefix can be
      reused in the definition section of "EID-prefix".

   o  Tracker item 95.  Change "eliminate" to "defer" in section 4.1.

   o  Tracker item 110.  Added that the Mapping Protocol Data field in
      the Map-Reply message is only used when needed by the particular
      Mapping Database System.

   o  Tracker item 111.  Indicate that if an LSB that is associated with
      an anycast address, that there is at least one RLOC that is up.

   o  Tracker item 108.  Make clear the R-bit does not define RLOC path
      reachability.

   o  Tracker item 107.  Indicate that weights are relative to each
      other versus requiring an addition of up to 100%.

   o  Tracker item 46.  Add a sentence how LISP products should be sized
      for the appropriate demand so cache thrashing is avoided.





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   o  Change some references of RFC 5226 to [AFI] per Luigi.

   o  Per Luigi, make reference to "EID-AFI" consistent to "EID-prefix-
      AFI".

   o  Tracker item 66.  Indicate that appending locators to a locator-
      set is done when the added locators are lexicographically greater
      than the previous ones in the set.

   o  Tracker item 87.  Once again reword the definition of the EID-
      prefix to reflect recent comments.

   o  Tracker item 70.  Added text to security section on what the
      implications could be if an ITR does not obey priority and weights
      from a Map-Reply message.

   o  Tracker item 54.  Added text to the new section titled "Packets
      Egressing a LISP Site" to describe the implications when two or
      more ITRs exist at a site where only one ITR is used for egress
      traffic and when there is a shift of traffic to the others, how
      the map-cache will need to be populated in those new egress ITRs.

   o  Tracker item 33.  Make more clear in the Routing Locator Selection
      section what an ITR should do when it sees an R-bit of 0 in a
      locator-record of a Map-Reply.

   o  Tracker item 33.  Add paragraph to the EID Reachability section
      indicating that site partitioning is under investigation.

   o  Tracker item 58.  Added last paragraph of Security Considerations
      section about how to protect inner header EID address spoofing
      attacks.

   o  Add suggested Sam text to indicate that all security concerns need
      not be addressed for moving document to Experimental RFC status.
      Put this in a subsection of the Security Considerations section.

B.12.  Changes to draft-ietf-lisp-11.txt

   o  Posted March 30, 2011.

   o  Change IANA URL.  The URL we had pointed to a general protocol
      numbers page.

   o  Added the "s" bit to the Map-Request to allow SMR-invoked Map-
      Requests to be sent to a MN ETR via the map-server.





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   o  Generalize text for the definition of Reencapsuatling tunnels.

   o  Add paragraph suggested by Joel to explain how implementation
      experimentation will be used to determine the proper cache
      management techniques.

   o  Add Yakov provided text for the definition of "EID-to-RLOC
      "Database".

   o  Add reference in Section 8, Deployment Scenarios, to the
      draft-jakab-lisp-deploy-02.txt draft.

   o  Clarify sentence about no hardware changes needed to support LISP
      encapsulation.

   o  Add paragraph about what is the procedure when a locator is
      inserted in the middle of a locator-set.

   o  Add a definition for Locator Status Bits so we can emphasize they
      are used as a hint for router up/down status and not path
      reachability.

   o  Change "BGP RIB" to "RIB" per Clarence's comment.

   o  Fixed complaints by IDnits.

   o  Add subsection to Security Considerations section indicating how
      EID-prefix overclaiming in Map-Replies is for further study and
      add a reference to LISP-SEC.

B.13.  Changes to draft-ietf-lisp-10.txt

   o  Posted March 2011.

   o  Add p-bit to Map-Request so there is documentary reasons to know
      when a PITR has sent a Map-Request to an ETR.

   o  Add Map-Notify message which is used to acknowledge a Map-Register
      message sent to a Map-Server.

   o  Add M-bit to the Map-Register message so an ETR that wants an
      acknowledgment for the Map-Register can request one.

   o  Add S-bit to the ECM and Map-Reply messages to describe security
      data that can be present in each message.  Then refer to
      [LISP-SEC] for expansive details.





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   o  Add Network Management Considerations section and point to the MIB
      and LIG drafts.

   o  Remove the word "simple" per Yakov's comments.

B.14.  Changes to draft-ietf-lisp-09.txt

   o  Posted October 2010.

   o  Add to IANA Consideration section about the use of LCAF Type
      values that accepted and maintained by the IANA registry and not
      the LCAF specification.

   o  Indicate that implementations should be able to receive LISP
      control messages when either UDP port is 4342, so they can be
      robust in the face of intervening NAT boxes.

   o  Add paragraph to SMR section to indicate that an ITR does not need
      to respond to an SMR-based Map-Request when it has no map-cache
      entry for the SMR source's EID-prefix.

B.15.  Changes to draft-ietf-lisp-08.txt

   o  Posted August 2010.

   o  In section 6.1.6, remove statement about setting TTL to 0 in Map-
      Register messages.

   o  Clarify language in section 6.1.5 about Map-Replying to Data-
      Probes or Map-Requests.

   o  Indicate that outer TTL should only be copied to inner TTL when it
      is less than inner TTL.

   o  Indicate a source-EID for RLOC-probes are encoded with an AFI
      value of 0.

   o  Indicate that SMRs can have a global or per SMR destination rate-
      limiter.

   o  Add clarifications to the SMR procedures.

   o  Add definitions for "client-side" and 'server-side" terms used in
      this specification.

   o  Clear up language in section 6.4, last paragraph.





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   o  Change ACT of value 0 to "no-action".  This is so we can RLOC-
      probe a PETR and have it return a Map-Reply with a locator-set of
      size 0.  The way it is spec'ed the map-cache entry has action
      "dropped".  Drop-action is set to 3.

   o  Add statement about normalizing locator weights.

   o  Clarify R-bit definition in the Map-Reply locator record.

   o  Add section on EID Reachability within a LISP site.

   o  Clarify another disadvantage of using anycast locators.

   o  Reworded Abstract.

   o  Change section 2.0 Introduction to remove obsolete information
      such as the LISP variant definitions.

   o  Change section 5 title from "Tunneling Details" to "LISP
      Encapsulation Details".

   o  Changes to section 5 to include results of network deployment
      experience with MTU.  Recommend that implementations use either
      the stateful or stateless handling.

   o  Make clarification wordsmithing to Section 7 and 8.

   o  Identify that if there is one locator in the locator-set of a map-
      cache entry, that an SMR from that locator should be responded to
      by sending the the SMR-invoked Map-Request to the database mapping
      system rather than to the RLOC itself (which may be unreachable).

   o  When describing Unicast and Multicast Weights indicate the the
      values are relative weights rather than percentages.  So it
      doesn't imply the sum of all locator weights in the locator-set
      need to be 100.

   o  Do some wordsmithing on copying TTL and TOS fields.

   o  Numerous wordsmithing changes from Dave Meyer.  He fine toothed
      combed the spec.

   o  Removed Section 14 "Prototype Plans and Status".  We felt this
      type of section is no longer appropriate for a protocol
      specification.

   o  Add clarification text for the IRC description per Damien's
      commentary.



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   o  Remove text on copying nonce from SMR to SMR-invoked Map- Request
      per Vina's comment about a possible DoS vector.

   o  Clarify (S/2 + H) in the stateless MTU section.

   o  Add text to reflect Damien's comment about the description of the
      "ITR-RLOC Address" field in the Map-Request. that the list of RLOC
      addresses are local addresses of the Map-Requester.

B.16.  Changes to draft-ietf-lisp-07.txt

   o  Posted April 2010.

   o  Added I-bit to data header so LSB field can also be used as an
      Instance ID field.  When this occurs, the LSB field is reduced to
      8-bits (from 32-bits).

   o  Added V-bit to the data header so the 24-bit nonce field can also
      be used for source and destination version numbers.

   o  Added Map-Version 12-bit value to the EID-record to be used in all
      of Map-Request, Map-Reply, and Map-Register messages.

   o  Added multiple ITR-RLOC fields to the Map-Request packet so an ETR
      can decide what address to select for the destination of a Map-
      Reply.

   o  Added L-bit (Local RLOC bit) and p-bit (Probe-Reply RLOC bit) to
      the Locator-Set record of an EID-record for a Map-Reply message.
      The L-bit indicates which RLOCs in the locator-set are local to
      the sender of the message.  The P-bit indicates which RLOC is the
      source of a RLOC-probe Reply (Map-Reply) message.

   o  Add reference to the LISP Canonical Address Format [LCAF] draft.

   o  Made editorial and clarification changes based on comments from
      Dhirendra Trivedi.

   o  Added wordsmithing comments from Joel Halpern on DF=1 setting.

   o  Add John Zwiebel clarification to Echo Nonce Algorithm section
      6.3.1.

   o  Add John Zwiebel comment about expanding on proxy-map-reply bit
      for Map-Register messages.

   o  Add NAT section per Ron Bonica comments.




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   o  Fix IDnits issues per Ron Bonica.

   o  Added section on Virtualization and Segmentation to explain the
      use if the Instance ID field in the data header.

   o  There are too many P-bits, keep their scope to the packet format
      description and refer to them by name every where else in the
      spec.

   o  Scanned all occurrences of "should", "should not", "must" and
      "must not" and uppercased them.

   o  John Zwiebel offered text for section 4.1 to modernize the
      example.  Thanks Z!

   o  Make it more clear in the definition of "EID-to-RLOC Database"
      that all ETRs need to have the same database mapping.  This
      reflects a comment from John Scudder.

   o  Add a definition "Route-returnability" to the Definition of Terms
      section.

   o  In section 9.2, add text to describe what the signature of
      traceroute packets can look like.

   o  Removed references to Data Probe for introductory example.  Data-
      probes are still part of the LISP design but not encouraged.

   o  Added the definition for "LISP site" to the Definition of Terms"
      section.

B.17.  Changes to draft-ietf-lisp-06.txt

   Editorial based changes:

   o  Posted December 2009.

   o  Fix typo for flags in LISP data header.  Changed from "4" to "5".

   o  Add text to indicate that Map-Register messages must contain a
      computed UDP checksum.

   o  Add definitions for PITR and PETR.

   o  Indicate an AFI value of 0 is an unspecified address.

   o  Indicate that the TTL field of a Map-Register is not used and set
      to 0 by the sender.  This change makes this spec consistent with



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      [LISP-MS].

   o  Change "... yield a packet size of L octets" to "... yield a
      packet size greater than L octets".

   o  Clarify section 6.1.5 on what addresses and ports are used in Map-
      Reply messages.

   o  Clarify that LSBs that go beyond the number of locators do not to
      be SMRed when the locator addresses are greater lexicographically
      than the locator in the existing locator-set.

   o  Add Gregg, Srini, and Amit to acknowledgment section.

   o  Clarify in the definition of a LISP header what is following the
      UDP header.

   o  Clarify "verifying Map-Request" text in section 6.1.3.

   o  Add Xu Xiaohu to the acknowledgment section for introducing the
      problem of overlapping EID-prefixes among multiple sites in an RRG
      email message.

   Design based changes:

   o  Use stronger language to have the outer IPv4 header set DF=1 so we
      can avoid fragment reassembly in an ETR or PETR.  This will also
      make IPv4 and IPv6 encapsulation have consistent behavior.

   o  Map-Requests should not be sent in ECM with the Probe bit is set.
      These type of Map-Requests are used as RLOC-probes and are sent
      directly to locator addresses in the underlying network.

   o  Add text in section 6.1.5 about returning all EID-prefixes in a
      Map-Reply sent by an ETR when there are overlapping EID-prefixes
      configure.

   o  Add text in a new subsection of section 6.1.5 about dealing with
      Map-Replies with coarse EID-prefixes.

B.18.  Changes to draft-ietf-lisp-05.txt

   o  Posted September 2009.

   o  Added this Document Change Log appendix.

   o  Added section indicating that encapsulated Map-Requests must use
      destination UDP port 4342.



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   o  Don't use AH in Map-Registers.  Put key-id, auth-length, and auth-
      data in Map-Register payload.

   o  Added Jari to acknowledgment section.

   o  State the source-EID is set to 0 when using Map-Requests to
      refresh or RLOC-probe.

   o  Make more clear what source-RLOC should be for a Map-Request.

   o  The LISP-CONS authors thought that the Type definitions for CONS
      should be removed from this specification.

   o  Removed nonce from Map-Register message, it wasn't used so no need
      for it.

   o  Clarify what to do for unspecified Action bits for negative Map-
      Replies.  Since No Action is a drop, make value 0 Drop.

B.19.  Changes to draft-ietf-lisp-04.txt

   o  Posted September 2009.

   o  How do deal with record count greater than 1 for a Map-Request.
      Damien and Joel comment.  Joel suggests: 1) Specify that senders
      compliant with the current document will always set the count to
      1, and note that the count is included for future extensibility.
      2) Specify what a receiver compliant with the draft should do if
      it receives a request with a count greater than 1.  Presumably, it
      should send some error back?

   o  Add Fred Templin in acknowledgment section.

   o  Add Margaret and Sam to the acknowledgment section for their great
      comments.

   o  Say more about LAGs in the UDP section per Sam Hartman's comment.

   o  Sam wants to use MAY instead of SHOULD for ignoring checksums on
      ETR.  From the mailing list: "You'd need to word it as an ITR MAY
      send a zero checksum, an ETR MUST accept a 0 checksum and MAY
      ignore the checksum completely.  And of course we'd need to
      confirm that can actually be implemented.  In particular, hardware
      that verifies UDP checksums on receive needs to be checked to make
      sure it permits 0 checksums."

   o  Margaret wants a reference to
      http://www.ietf.org/id/draft-eubanks-chimento-6man-00.txt.



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   o  Fix description in Map-Request section.  Where we describe Map-
      Reply Record, change "R-bit" to "M-bit".

   o  Add the mobility bit to Map-Replies.  So PITRs don't probe so
      often for MNs but often enough to get mapping updates.

   o  Indicate SHA1 can be used as well for Map-Registers.

   o  More Fred comments on MTU handling.

   o  Isidor comment about spec'ing better periodic Map-Registers.  Will
      be fixed in draft-ietf-lisp-ms-02.txt.

   o  Margaret's comment on gleaning: "The current specification does
      not make it clear how long gleaned map entries should be retained
      in the cache, nor does it make it clear how/ when they will be
      validated.  The LISP spec should, at the very least, include a
      (short) default lifetime for gleaned entries, require that they be
      validated within a short period of time, and state that a new
      gleaned entry should never overwrite an entry that was obtained
      from the mapping system.  The security implications of storing
      "gleaned" entries should also be explored in detail."

   o  Add section on RLOC-probing per working group feedback.

   o  Change "loc-reach-bits" to "loc-status-bits" per comment from
      Noel.

   o  Remove SMR-bit from data-plane.  Dino prefers to have it in the
      control plane only.

   o  Change LISP header to allow a "Research Bit" so the Nonce and LSB
      fields can be turned off and used for another future purpose.  For
      Luigi et al versioning convergence.

   o  Add a N-bit to the data header suggested by Noel.  Then the nonce
      field could be used when N is not 1.

   o  Clarify that when E-bit is 0, the nonce field can be an echoed
      nonce or a random nonce.  Comment from Jesper.

   o  Indicate when doing data-gleaning that a verifying Map-Request is
      sent to the source-EID of the gleaned data packet so we can avoid
      map-cache corruption by a 3rd party.  Comment from Pedro.

   o  Indicate that a verifying Map-Request, for accepting mapping data,
      should be sent over the ALT (or to the EID).




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   o  Reference IPsec RFC 4302.  Comment from Sam and Brian Weis.

   o  Put E-bit in Map-Reply to tell ITRs that the ETR supports echo-
      noncing.  Comment by Pedro and Dino.

   o  Jesper made a comment to loosen the language about requiring the
      copy of inner TTL to outer TTL since the text to get mixed-AF
      traceroute to work would violate the "MUST" clause.  Changed from
      MUST to SHOULD in section 5.3.

B.20.  Changes to draft-ietf-lisp-03.txt

   o  Posted July 2009.

   o  Removed loc-reach-bits longword from control packets per Damien
      comment.

   o  Clarifications in MTU text from Roque.

   o  Added text to indicate that the locator-set be sorted by locator
      address from Isidor.

   o  Clarification text from John Zwiebel in Echo-Nonce section.

B.21.  Changes to draft-ietf-lisp-02.txt

   o  Posted July 2009.

   o  Encapsulation packet format change to add E-bit and make loc-
      reach-bits 32-bits in length.

   o  Added Echo-Nonce Algorithm section.

   o  Clarification how ECN bits are copied.

   o  Moved S-bit in Map-Request.

   o  Added P-bit in Map-Request and Map-Reply messages to anticipate
      RLOC-Probe Algorithm.

   o  Added to Mobility section to reference [LISP-MN].

B.22.  Changes to draft-ietf-lisp-01.txt

   o  Posted 2 days after draft-ietf-lisp-00.txt in May 2009.

   o  Defined LEID to be a "LISP EID".




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   o  Indicate encapsulation use IPv4 DF=0.

   o  Added negative Map-Reply messages with drop, native-forward, and
      send-map-request actions.

   o  Added Proxy-Map-Reply bit to Map-Register.

B.23.  Changes to draft-ietf-lisp-00.txt

   o  Posted May 2009.

   o  Rename of draft-farinacci-lisp-12.txt.

   o  Acknowledgment to RRG.





































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Authors' Addresses

   Dino Farinacci
   cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: dino@cisco.com


   Vince Fuller
   cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: vaf@cisco.com


   Dave Meyer
   cisco Systems
   170 Tasman Drive
   San Jose, CA
   USA

   Email: dmm@cisco.com


   Darrel Lewis
   cisco Systems
   170 Tasman Drive
   San Jose, CA
   USA

   Email: darlewis@cisco.com















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