





Network Working Group                                          L. Berger
Request for Comments: 5566                                          LabN
Category: Standards Track                                       R. White
                                                                E. Rosen
                                                           Cisco Systems
                                                               June 2009


                BGP IPsec Tunnel Encapsulation Attribute

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   The BGP Encapsulation Subsequent Address Family Identifier (SAFI)
   provides a method for the dynamic exchange of encapsulation
   information and for the indication of encapsulation protocol types to
   be used for different next hops.  Currently, support for Generic
   Routing Encapsulation (GRE), Layer 2 Tunneling Protocol (L2TPv3), and
   IP in IP tunnel types are defined.  This document defines support for
   IPsec tunnel types.













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Table of Contents

   1. Introduction ....................................................2
      1.1. Conventions Used in This Document ..........................2
   2. Tunnel Encapsulation Types ......................................3
   3. Use of IPsec Tunnel Types .......................................3
   4. IPsec Tunnel Authenticator sub-TLV ..............................4
      4.1. Use of the IPsec Tunnel Authenticator sub-TLV ..............5
   5. Security Considerations .........................................5
   6. IANA Considerations .............................................6
   7. References ......................................................7
      7.1. Normative References .......................................7
      7.2. Informative References .....................................7
   8. Acknowledgments .................................................8

1.  Introduction

   The BGP [RFC4271] Encapsulation Subsequent Address Family Identifier
   (SAFI) allows for the communication of tunnel information and for the
   association of this information to a BGP next hop.  The Encapsulation
   SAFI can be used to support the mapping of prefixes to next hops and
   tunnels of the same address family, IPv6 prefixes to IPv4 next hops
   and tunnels using [RFC4798], and IPv4 prefixes to IPv6 next hops and
   tunnels using [RFC5549].  The Encapsulation SAFI can also be used to
   support the mapping of VPN prefixes to tunnels when VPN prefixes are
   advertised per [RFC4364] or [RFC4659].  [RFC5565] provides useful
   context for the use of the Encapsulation SAFI.

   The Encapsulation SAFI is defined in [RFC5512].  [RFC5512] also
   defines support for the GRE [RFC2784], L2TPv3 [RFC3931], and IP in IP
   [RFC2003] tunnel types.  This document builds on [RFC5512] and
   defines support for IPsec tunnels.  Support is defined for IP
   Authentication Header (AH) in tunnel mode [RFC4302] and for IP
   Encapsulating Security Payload (ESP) in tunnel mode [RFC4303].  The
   IPsec architecture is defined in [RFC4301].  Support for IP in IP
   [RFC2003] and MPLS-in-IP [RFC4023] protected by IPsec Transport Mode
   is also defined.

   The Encapsulation Network Layer Reachability Information (NLRI)
   Format is not modified by this document.

1.1.  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].





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2.  Tunnel Encapsulation Types

   Per [RFC5512], tunnel type is indicated in the Tunnel Encapsulation
   attribute.  This document defines the following tunnel type values:

     - Transmit tunnel endpoint: Tunnel Type = 3

     - IPsec in Tunnel-mode: Tunnel Type = 4 [RFC4302], [RFC4303]

     - IP in IP Tunnel with IPsec Transport Mode: Tunnel Type = 5
       [RFC2003], [RFC4303]

     - MPLS-in-IP Tunnel with IPsec Transport Mode: Tunnel Type = 6
       [RFC4023]

       Note, see Section 4.3 of [RFC5512] for a discussion on the
       advertisement and use of multiple tunnel types.

       Note, the specification in [RFC4023] for MPLS-in-IP tunnels with
       IPsec Transport mode applies as well to IP in IP tunnels.

   This document does not specify the use of the sub-TLV types defined
   in [RFC5512] with these tunnel types.  See below for the definition
   of a specific sub-TLV for use with the defined tunnel types.

3.  Use of IPsec Tunnel Types

   The IPsec tunnel types are defined above with the values 4, 5, and 6.
   If R1 is a BGP speaker that receives an Encapsulation SAFI update
   from another BGP speaker, R2, then if R1 has any data packets for
   which R2 is the BGP next hop, R1 MUST initiate an IPsec SA (security
   association) of the specified "tunnel type", and all such data
   packets MUST be sent through that SA.

   Let R1 and R2 be two BGP speakers that may send data packets through
   R3, such that the data packets from R1 and from R2 may be received by
   R3 over the same interface.  In this case, when R3 sends an
   Encapsulation SAFI that indicates an IPsec tunnel type to R2, then R3
   SHOULD also send an update specifying an Encapsulation SAFI with an
   IPsec tunnel type to R1.  That is, on a given interface, if IPsec is
   required for any data packets, it SHOULD be required for all.  This
   eliminates dependence on the IPsec selector mechanisms to correctly
   distinguish traffic that needs to be protected from traffic that does
   not.

   Security policy has the granularity of BGP speaker to BGP speaker.
   The required security policies must be configured into the BGP
   speakers.  Policies for each SA will typically be established using



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   IKEv2 (Internet Key Exchange) [RFC4306], with either public-key or
   pre-shared key authentication.  The SA MAY also be configured via
   manual techniques.  Manual configuration specification and
   considerations are defined in [RFC4301], [RFC4302], and [RFC4303]
   (and includes keys, Security Parameter Index (SPI) numbers, IPsec
   protocol, integrity/encryption algorithms, and sequence number mode).

4.  IPsec Tunnel Authenticator sub-TLV

   This document defines a new sub-TLV for use with the Tunnel
   Encapsulation attribute defined in [RFC5512].  The new sub-TLV is
   referred to as the "IPsec Tunnel Authenticator sub-TLV", and one or
   more of the sub-TLVs MAY be included in any Encapsulation SAFI NLRI
   [RFC5512] indicating a tunnel type defined in this document.  Support
   for the IPsec Tunnel Authenticator sub-TLV MUST be implemented
   whenever the tunnel types defined in this document are implemented.
   However, its use is OPTIONAL, and is a matter of policy.

   The sub-TLV type of the IPsec Tunnel Authenticator sub-TLV is 3.  The
   sub-TLV length is variable.  The structure of the sub-TLV is as
   follows:

     - Authenticator Type: two octets

       This document defines authenticator type 1, "SHA-1 hash of public
       key", as defined in Section 3.7 of RFC 4306.

     - Value: (variable)

       A value used to authenticate the BGP speaker that generated this
       NLRI.  The length of this field is not encoded explicitly, but
       can be calculated as (sub-TLV length - 2).

       In the case of authenticator type 1, this field contains the
       20-octet value of the hash.

   A BGP speaker that sends the IPsec Tunnel Authenticator sub-TLV with
   authenticator type 1 MUST be configured with a private key / public
   key pair, the public key being the key whose hash is sent in the
   value field of the sub-TLV.  The BGP speaker MUST either (a) be able
   to generate a self-signed certificate for the public key, or else (b)
   be configured with a certificate for the public key.

   When the IPsec Tunnel Authenticator sub-TLV is used, it is highly
   RECOMMENDED that the integrity of the BGP session itself be
   protected.  This is usually done by using the TCP MD5 option
   [RFC2385].




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4.1.  Use of the IPsec Tunnel Authenticator sub-TLV

   If an IPsec Tunnel Authenticator sub-TLV with authenticator type 1 is
   present in the Encapsulation SAFI update, then R1 (as defined above
   in Section 3) MUST use IKEv2 [RFC4306] to obtain a certificate from
   R2 (as defined above in Section 3), and R2 MUST send a certificate
   for the public key whose hash occurred in the value field of the
   IPsec Tunnel Authenticator sub-TLV.  R1 MUST NOT attempt to establish
   an SA to R2 UNLESS the public key in the certificate hashes to the
   same value that occurs in one of the IPsec Tunnel Authenticator sub-
   TLVs.

   R2 MUST also perform the reciprocal processing.  Specifically, when
   establishing an SA from R1 and R1 has advertised the IPsec Tunnel
   Authenticator sub-TLV with authenticator type 1, R2 MUST use IKEv2
   [RFC4306] to obtain a certificate from R1, and R1 MUST send a
   certificate for the public key whose hash occurred in the value field
   of the IPsec Tunnel Authenticator sub-TLV.  R2 MUST NOT attempt to
   establish an SA to R1 UNLESS the public key in the certificate hashes
   to the same value that occurs in one of the IPsec Tunnel
   Authenticator sub-TLVs.

   Note that the "Transmit tunnel endpoint" tunnel type (value = 3) may
   be used by a BGP speaker that does not want to be the receiving
   endpoint of an IPsec tunnel but only the transmitting endpoint.

5.  Security Considerations

   This document uses IP-based tunnel technologies to support data plane
   transport.  Consequently, the security considerations of those tunnel
   technologies apply.  This document defines support for IPsec AH
   [RFC4302] and ESP [RFC4303].  The security considerations from those
   documents as well as [RFC4301] apply to the data plane aspects of
   this document.

   As with [RFC5512], any modification of the information that is used
   to form encapsulation headers, to choose a tunnel type, or to choose
   a particular tunnel for a particular payload type may lead to user
   data packets getting misrouted, misdelivered, and/or dropped.
   Misdelivery is less of an issue when IPsec is used, as such
   misdelivery is likely to result in a failure of authentication or
   decryption at the receiver.  Furthermore, in environments where
   authentication of BGP speakers is desired, the IPsec Tunnel
   Authenticator sub-TLV defined in Section 4 may be used.







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   More broadly, the security considerations for the transport of IP
   reachability information using BGP are discussed in [RFC4271] and
   [RFC4272], and are equally applicable for the extensions described in
   this document.

   If the integrity of the BGP session is not itself protected, then an
   imposter could mount a denial-of-service attack by establishing
   numerous BGP sessions and forcing an IPsec SA to be created for each
   one.  However, as such an imposter could wreak havoc on the entire
   routing system, this particular sort of attack is probably not of any
   special importance.

   It should be noted that a BGP session may itself be transported over
   an IPsec tunnel.  Such IPsec tunnels can provide additional security
   to a BGP session.  The management of such IPsec tunnels is outside
   the scope of this document.

6.  IANA Considerations

   IANA administers the assignment of new namespaces and new values for
   namespaces defined in this document and reviewed in this section.

   IANA has made the following assignments in the "BGP Tunnel
   Encapsulation Attribute Tunnel Types" registry.

   Value  Name                                        Reference
   -----  ----                                        ---------
     3    Transmit tunnel endpoint                    [RFC5566]

     4    IPsec in Tunnel-mode                        [RFC5566]

     5    IP in IP tunnel
             with IPsec Transport Mode                [RFC5566]

     6    MPLS-in-IP tunnel
             with IPsec Transport Mode                [RFC5566]

   IANA has made the following assignment in the "BGP Tunnel
   Encapsulation Attribute Sub-TLVs" registry.

   Value  Name                                        Reference
   -----  ----                                        ---------
     3    IPsec Tunnel Authenticator                  [RFC5566]








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7.  References

7.1.  Normative References

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

   [RFC4271]   Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
               Border Gateway Protocol 4 (BGP-4)", RFC 4271, January
               2006.

   [RFC4301]   Kent, S. and K. Seo, "Security Architecture for the
               Internet Protocol", RFC 4301, December 2005.

   [RFC4302]   Kent, S., "IP Authentication Header", RFC 4302, December
               2005.

   [RFC4303]   Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
               4303, December 2005.

   [RFC4306]   Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
               Protocol", RFC 4306, December 2005.

   [RFC5512]   Mohapatra, P. and E. Rosen, "The BGP Encapsulation
               Subsequent Address Family Identifier (SAFI) and the BGP
               Tunnel Encapsulation Attribute", RFC 5512, April 2009.

7.2.  Informative References

   [RFC2003]   Perkins, C., "IP Encapsulation within IP", RFC 2003,
               October 1996.

   [RFC2385]   Heffernan, A., "Protection of BGP Sessions via the TCP
               MD5 Signature Option", RFC 2385, August 1998.

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

   [RFC3931]   Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
               "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC
               3931, March 2005.

   [RFC4023]   Worster, T., Rekhter, Y., and E. Rosen, Ed.,
               "Encapsulating MPLS in IP or Generic Routing
               Encapsulation (GRE)", RFC 4023, March 2005.





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   [RFC4272]   Murphy, S., "BGP Security Vulnerabilities Analysis", RFC
               4272, January 2006.

   [RFC4364]   Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
               Networks (VPNs)", RFC 4364, February 2006.

   [RFC4659]   De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
               "BGP-MPLS IP Virtual Private Network (VPN) Extension for
               IPv6 VPN", RFC 4659, September 2006.

   [RFC4798]   De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
               "Connecting IPv6 Islands over IPv4 MPLS Using IPv6
               Provider Edge Routers (6PE)", RFC 4798, February 2007.

   [RFC5549]   Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
               Layer Reachability Information with an IPv6 Next Hop",
               RFC 5549, May 2009.

   [RFC5565]   Wu, J., Cui, Y., Metz, C. and E. Rosen, "Softwire Mesh
               Framework", RFC 5565, June 2009.

8.  Acknowledgments

   The authors wish to thank Sam Hartman and Tero Kivinen for their help
   with the security-related issues.

Authors' Addresses

   Lou Berger
   LabN Consulting, L.L.C.
   Phone: +1-301-468-9228
   EMail: lberger@labn.net

   Russ White
   Cisco Systems
   EMail: riw@cisco.com

   Eric C. Rosen
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough, MA, 01719
   EMail: erosen@cisco.com









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