


Network Working Group                                        L. Ginsberg
Internet-Draft                                                S. Previdi
Intended status: Standards Track                                M. Shand
Expires: May 14, 2011                                      Cisco Systems
                                                       November 10, 2010


                Advertising Generic Information in IS-IS
                     draft-ietf-isis-genapp-04.txt

Abstract

   This draft describes the manner in which generic application
   information (i.e. information not directly related to the operation
   of the IS-IS protocol) should be advertised in IS-IS LSPs and defines
   guidelines which should be used when flooding such information.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 14, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Conventions used in this Document  . . . . . . . . . . . . . .  3
   2.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Encoding Format for GENINFO  . . . . . . . . . . . . . . . . .  3
     3.1.  GENINFO TLV  . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Use of sub-TLVs in GENINFO TLV . . . . . . . . . . . . . .  6
   4.  GENINFO Flooding Procedures  . . . . . . . . . . . . . . . . .  6
     4.1.  Leaking Procedures . . . . . . . . . . . . . . . . . . . .  7
     4.2.  Minimizing Update Confusion  . . . . . . . . . . . . . . .  7
     4.3.  Interpreting Attribute Information . . . . . . . . . . . .  8
   5.  Use of a Separate Protocol Instance  . . . . . . . . . . . . .  8
   6.  Applicability of GENINFO TLV . . . . . . . . . . . . . . . . .  9
   7.  Standardization Requirements . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   11. Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
































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1.  Conventions used in this Document

   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].


2.  Overview

   [ISO10589] defines the format of type-length-value (TLVs) which may
   be sent in IS-IS Protocol Data Units (PDUs).  The first octet of a
   TLV encodes the "type" or "codepoint" which provides a scope for the
   information and information format which follows.  The protocol is
   therefore limited to 256 different codepoints which may be assigned.
   This number has proved generous as regards the information required
   for correct operation of the Intermediate System to Internediate
   System (IS-IS) protocol.  However, the increasing use of IS-IS Link
   State Protocol Data Units (LSPs) for advertisement of generic
   information (GENINFO) not directly related to the operation of the
   IS-IS protocol places additional demands on the TLV encoding space
   which has the potential to consume a significant number of TLV
   codepoints.  This document therefore defines an encoding format for
   GENINFO which minimizes the consumption of TLV codepoints and also
   maximizes the flexibility of the formats which can be used to
   represent GENINFO.

   This document also discusses optimal behavior associated with the
   advertisement and flooding of LSPs containing GENINFO in order to
   avoid the advertisement of stale information and minimize the
   presence of duplicate or conflicting information when advertisements
   are updated.

   The manner in which the information contained in GENINFO TLVs is
   exchanged between an instance of the IS-IS protocol and the
   application which generates/consumes the GENINFO is outside the scope
   of this specification.

   In order to minimize the impact advertisement of GENINFO may have on
   the operation of routing, such advertisements MUST occur in the
   context of a non-zero instance of the IS-IS protocol as defined in
   [I-D.ietf-isis-mi] except where the rules for the use of the zero
   instance set out later in this document are followed.


3.  Encoding Format for GENINFO

   The encoding format defined below has the following goals regarding
   the advertisement of GENINFO in IS-IS LSPs:



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   o  Minimize the number of IS-IS top level and sub-TLV codepoints
      required

   o  Minimize the depth of sub-TLV levels required

   In order to support these goals, a new IANA registry is required.
   This registry will manage the assignment of IS-IS GENINFO Application
   Identifiers.  These numbers are unsigned 16 bit numbers ranging in
   value from 1 to 65535.  Application specific sub-TLV codepoints are
   unsigned 8 bit numbers ranging in value from 0 to 255.  The
   assignment of the sub-TLV codepoints is scoped by the Application
   Identifier.  Management of the application specific sub-TLV
   codepoints is outside the scope of this document.

3.1.  GENINFO TLV

   The GENINFO TLV supports the advertisement of application specific
   information which is not directly related to the operation of the
   IS-IS protocol.

   Type   251
   Length # of octets in the value field (3 to 255)
   Value

                                        No. of octets
              +-----------------------+
              | Flags                 |     1
              +-----------------------+
              | Application ID        |     2
              +-----------------------+
              | Application           |
              | IP Address Info       |     0 to 20
              +-----------------------+
              | Additional Application|     0 to (252 -
              |  Specific Information |     len of IP Address info)
              +-----------------------+


            Flags

                  0 1 2 3 4 5 6 7
                 +-+-+-+-+-+-+-+-+
                 |  Rsvd |V|I|D|S|
                 +-+-+-+-+-+-+-+-+


                 The following bit flags are defined.




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                 S bit (0x01): If the S bit is set(1), the GENINFO TLV
                 MUST be flooded across the entire routing domain. If
                 the S bit is not set(0), the TLV MUST NOT be leaked
                 between levels. This bit MUST NOT be altered during the
                 TLV leaking.

                 D bit (0x02): When the GENINFO TLV is leaked from
                 level-2 to level-1, the D bit MUST be set. Otherwise
                 this bit MUST be clear. GENINFO TLVs with the D bit set
                 MUST NOT be leaked from level-1 to level-2. This is to
                 prevent TLV looping.

                 I bit (0x04): When the I bit is set the 4 octet IPv4
                 address associated with the application immediately
                 follows the Application ID.

                 V bit (0x08): When the V bit is set, the 16 octet IPv6
                 address associated with the application immediately
                 follows either the Application ID (if I bit is clear)
                 or the IPv4 address (if I bit is set).

            Application ID

                 An identifier assigned to this application via the IANA
                 registry defined later in this document.

            Application IPv4 Address Info

                 The IPv4 address associated with the application. This
                 is not necessarily an address of a router running the
                 IS-IS protocol.

            Application IPv6 Address Info

                 The IPv6 address associated with the application. This
                 is not necessarily an address of a router running the
                 IS-IS protocol.

            Additional Application Specific Information

                 Each application may define additional information to
                 be encoded in a GENINFO TLV following the fixed
                 information. Definition of such information is beyond
                 the scope of this document.







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3.2.  Use of sub-TLVs in GENINFO TLV

   [RFC5305] introduced the definition and use of sub-TLVs.  One of the
   advantages of using sub-TLVs rather than fixed encoding of
   information inside a TLV is to allow for the addition of new
   information in a backwards compatible manner i.e. just as with TLVs,
   implementations are required to ignore sub-TLVs which they do not
   understand.

   GENINFO TLVs MAY include sub-TLVs in the application specific
   information as deemed necessary and appropriate for each application.
   The scope of the codepoints used in such sub-TLVs is defined by the
   combination of the GENINFO TLV codepoint and the Application ID i.e.
   the sub-TLV codepoints are private to the application.  Such sub-TLVs
   are referred to as APPsub-TLVs.

   Additional levels of APPsub-TLVs may be required when there is
   variable information which is scoped by a specific APPsub-TLV.  These
   "nested" sub-TLVs MUST be encoded in the same manner as sub-TLVs i.e.
   with a one-octet Type field, a one-octet Length field, and zero or
   more octets of Value.


4.  GENINFO Flooding Procedures

   This section describes procedures which apply to the propagation of
   LSPs which contain GENINFO TLVs.  These procedures have been
   previously discussed in [RFC4971].  This section is intended to serve
   as a reference specification for future documents which define the
   use of GENINFO TLV(s) for a specific application - eliminating the
   need to repeat the definition of these procedures in the application
   specific documents.

   Each GENINFO TLV contains information regarding exactly one
   application instance as identified by the Application ID in the
   GENINFO TLV.  When it is necessary to advertise sets of information
   with the same Application ID which have different flooding scopes, a
   router MUST originate a minimum of one GENINFO TLV for each required
   flooding scope.  GENINFO TLVs which contain information having area/
   level scope will have the S bit clear.  These TLVs MUST NOT be leaked
   into another level.  GENINFO TLVs which contain information which has
   domain scope will have the S bit set.  These TLVs MUST be leaked into
   other IS-IS levels.  When a TLV is leaked from level-2 to level-1,
   the D bit MUST be set in the level-1 LSP advertisement.







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4.1.  Leaking Procedures

   When leaking GENINFO TLVs downward from Level-2 into Level-1, if the
   originator of the TLV is a Level-1 router in another area, it is
   possible that multiple copies of the same TLV may be received from
   multiple L2 routers in the originating area.  A router performing
   downward leaking MUST check for such duplication by comparing the
   contents of the TLVs.  The set of LSPs generated by a router for a
   given level MUST NOT contain two or more copies of the same GENINFO
   TLV.

   In order to prevent the use of stale GENINFO information, a system
   MUST NOT use a GENINFO TLV present in an LSP of a system which is not
   currently reachable via Level-x paths, where "x" is the level (1 or
   2) associated with the LSP in which the GENINFO TLV appears.  Note
   that leaking a GENINFO TLV is one of the uses which is prohibited
   under these conditions.  The following example illustrates what might
   occur in the absence of this restriction.

   Example: If Level-1 router A generates a GENINFO TLV and floods it to
   two L1/L2 routers S and T, they will flood it into the Level-2 sub-
   domain.  Now suppose the Level-1 area partitions, such that A and S
   are in one partition and T is in another.  IP routing will still
   continue to work, but if A now issues a revised version of the
   GENINFO TLV, or decides to stop advertising it, S will follow suit,
   but T will continue to advertise the old version until the LSP times
   out.

   Routers in other areas have to choose whether to trust T's copy of
   A's GENINFO TLV or S's copy of A's information and they have no
   reliable way to choose.  By making sure that T stops leaking A's
   information, this removes the possibility that other routers will use
   stale information from A.

4.2.  Minimizing Update Confusion

   If an update to a TLV is advertised in an LSP with a different number
   than the LSP associated with the old advertisement, the possibility
   exists that other systems can temporarily have either 0 copies of a
   particular advertisement or 2 copies of a particular advertisement,
   depending on the order in which new copies of the LSP which had the
   old advertisement and the LSP which has the new advertisement arrive
   at other systems.

   Whenever possible, an implementation SHOULD advertise the update to a
   GENINFO TLV in the LSP with the same number as the advertisement
   which it replaces.  Where this is not possible, the two affected LSPs
   SHOULD be flooded as an atomic action.



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   Systems which receive an update to an existing GENINFO TLV can
   minimize the potential disruption associated with the update by
   employing a holddown time prior to processing the update so as to
   allow for the receipt of multiple LSPs associated with the same
   update prior to beginning processing.

4.3.  Interpreting Attribute Information

   Where a receiving system has two copies of a GENINFO TLV with the
   same Application ID, attribute information in the two TLVs which does
   not conflict MUST be considered additive.  When information in the
   two GENINFO TLVs conflicts i.e there are different settings for a
   given attribute, the procedure used to choose which copy shall be
   used is undefined.


5.  Use of a Separate Protocol Instance

   The use of the IS-IS flooding mechanism as a means of reliably and
   efficiently propagating information is understandably attractive.
   However, it is prudent to remember that the primary purpose of that
   mechanism is to flood information necessary for the correct operation
   of the IS-IS protocol.  Flooding of information not directly related
   to the use of the IS-IS protocol in support of routing degrades the
   operation of the protocol.  Degradation occurs because the frequency
   of LSP updates is increased and because the processing of non-routing
   information in each router consumes resources whose primary
   responsibility is to efficiently respond to reachability changes in
   the network.

   Advertisement of GENINFO therefore MUST occur in the context of a
   non-zero instance of the IS-IS protocol as defined in
   [I-D.ietf-isis-mi] except when the use in the zero instance is
   defined in a Standards Track RFC.

   The use of a separate instance of the protocol allows both the
   flooding and the processing of the non-routing information to be
   decoupled from the information necessary to support correct routing
   of data in the network.  The flooding and processing of non-routing
   information can then be prioritized appropriately.

   Use of a separate protocol instance to advertise GENINFO does not
   eliminate the need to use prudence in the frequency with which such
   information is updated.  One of the most egregious oversights is a
   failure to appropriately dampen changes in the information to be
   advertised, which can lead to flooding storms.  Documents which
   specify the use of the mechanisms defined here MUST define the
   expected rate of change of the information to be advertised.



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   If desirable, independent control of the flooding scope for
   information related to two different applications can be achieved by
   utilizing separate non-zero protocol instances for each
   application.[I-D.ietf-isis-mi].


6.  Applicability of GENINFO TLV

   The GENINFO TLV supports the advertisement of application specific
   information in IS-IS LSPs which is not directly related to the
   operation of the IS-IS protocol.  Information advertised in the
   GENINFO TLV MUST NOT alter basic IS-IS protocol operation including
   (but not limited to) the establishment of adjacencies, the update
   process, and the decision process.


7.  Standardization Requirements

   GENINFO is intended to advertise information on behalf of
   applications whose operations have been defined in a public
   specification as discussed in [RFC5226].

   The public specification MUST include:

   o  a description of the sub-TLV allocation policy

   o  discussion of security issues

   o  discussion of the rate of change of the information being
      advertised

   o  justification for the use of GENINFO


8.  Security Considerations

   The introduction and use of the new TLV codepoint for GENINFO in and
   of itself raises no new security issues for IS-IS.

   It is possible that information advertised in a GENINFO TLV by a
   given Application MAY introduce new security issues.  The public
   specification which defines the use of GENINFO by that Application
   MUST include a discussion of the security issues.  Where appropriate,
   it is recommended that either [RFC5304] or [RFC5310] be used.







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9.  IANA Considerations

   This document defines a new IS-IS TLV that needs to be reflected in
   the IS-IS TLV code-point registry:

   Type        Description                            IIH   LSP   SNP
   ----        -----------------------------------    ---   ---   ---
   251         Generic Information                     n     y     n

   This document also defines a new registry.  The new registry will
   manage the assignment of Application Identifiers which may be used in
   the Generic Information TLV.  These identifiers are unsigned 16 bit
   numbers ranging in value from 1 to 65535.  The value 0 is reserved.
   Registration procedure is "Expert Review" as defined in [RFC5226].
   The expert MUST verify that the public specification which defines
   the use of GENINFO for the application adequately discusses all
   points mentioned in Section 7 of this document.

   The following information MUST be specified in the registry:

   o  ID Value (1-65535)

   o  Description

   o  Allowed in Instance zero (Y/N)

   o  Reference Specification


10.  Acknowledgements

   The authors would like to thank JP Vasseur and David Ward for
   providing the need to produce this document and Tony Li for making
   sure it was done with appropriate wisdom and prudence.


11.  Normative References

   [I-D.ietf-isis-mi]
              Previdi, S., Ginsberg, L., Shand, M., Ward, D., and A.
              Roy, "IS-IS Multi-Instance", draft-ietf-isis-mi-03 (work
              in progress), July 2010.

   [ISO10589]
              International Organization for Standardization,
              "Intermediate system to Intermediate system intra-domain
              routeing information exchange protocol for use in
              conjunction with the protocol for providing the



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              connectionless-mode Network Service (ISO 8473)", ISO/
              IEC 10589:2002, Second Edition, Nov 2002.

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

   [RFC4971]  Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
              System to Intermediate System (IS-IS) Extensions for
              Advertising Router Information", RFC 4971, July 2007.

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

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, October 2008.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, October 2008.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, February 2009.


Authors' Addresses

   Les Ginsberg
   Cisco Systems
   510 McCarthy Blvd.
   Milpitas, Ca.  95035
   USA

   Email: ginsberg@cisco.com


   Stefano Previdi
   Cisco Systems
   Via Del Serafico 200
   00142 - Roma,
   Italy

   Email: sprevidi@cisco.com








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   Mike Shand
   Cisco Systems
   250, Longwater Avenue.
   Reading, Berks  RG2 6GB
   UK

   Email: mshand@cisco.com












































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