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Versions: 00 01 02 03 RFC 5566

Internet Draft                                         Lou Berger (LabN)
Category: Standards Track                     Russ White (Cisco Systems)
Expiration Date: October 6, 2009              Eric Rosen (Cisco Systems)

                                                           April 6, 2009

                BGP IPsec Tunnel Encapsulation Attribute

                draft-ietf-softwire-encaps-ipsec-03.txt

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Abstract


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

Table of Contents

    1      Introduction  ...........................................   3
    1.1    Conventions used in this document  ......................   3
    2      Tunnel Encapsulation Types  .............................   3
    3      Use of IPsec Tunnel Types  ..............................   4
    4      IPsec Tunnel Authenticator sub-TLV  .....................   4
    4.1    Use of the IPsec Tunnel Authenticator sub-TLV  ..........   5
    5      Security Considerations  ................................   6
    6      IANA Considerations  ....................................   7
    7      References  .............................................   7
    7.1    Normative References  ...................................   7
    7.2    Informative References  .................................   8
    8      Acknowledgments  ........................................   9
    9      Authors' Addresses  .....................................   9



























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1. Introduction

   The BGP [RFC4271] Encapsulation Subsequence Address Family
   Identifiers (SAFI) allows for the communication of tunnel information
   and 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 [V4NLRI-V6NH].  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].
   [SOFTWIRES] provides useful context for the use of the Encapsulation
   SAFI.

   The Encapsulation SAFI is defined in [ENCAPS-SAFI].  [ENCAPS-SAFI]
   also defines support for the GRE [RFC2784], L2TPv3 [RFC3931] and IP
   in IP [RFC2003] tunnel types.  This document builds on [ENCAPS-SAFI]
   and defines support for IPsec tunnels.  Support is defined for IP
   Authentication Header in Tunnel-mode (AH), [RFC4302], and for IP
   Encapsulating Security Payload in Tunnel-mode (ESP), [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 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].


2. Tunnel Encapsulation Types

   Per [ENCAPS-SAFI], 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 [ENCAPS-SAFI] for a discussion on the



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     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 [ENCAPS-SAFI] 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 a 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 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 which 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 which needs to be protected from
   traffic which 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
   IKEv2, [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, 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 [ENCAPS-SAFI].  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
   ([ENCAPS-SAFI]) 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



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   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 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 which 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].


4.1. Use of the IPsec Tunnel Authenticator sub-TLV

   If a 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



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   of the IPsec Tunnel Authenticator sub-TLV.  R2 MUST NOT attempt
   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 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 [ENCAPS-SAFI], any modification of the information that is
   used to form encapsulation headers, or to choose a tunnel type, or to
   choose a particular tunnel for a particular payload type, user data
   packets may end up 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.

   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 SAs 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 managment of such IPsec tunnels is outside the
   scope of this document.









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6. IANA Considerations

   IANA is requested to administer assignment of new namespaces and new
   values for namespaces defined in this document and reviewed in this
   section.

   Upon approval of this document, the IANA will make the assignment in
   the "BGP Tunnel Encapsulation Attribute Tunnel Types" and the "BGP
   Tunnel  Encapsulation Attribute Sub-TLVs" registries.

      Tunnel Type                                      Reference
      -----------                                      ---------
      Reserved:                                Type = 3 [This document]
      IPsec in Tunnel-mode:                    Type = 4 [This document]
      IP in IP tunnel
          with IPsec Transport Mode:           Type = 5 [This document]
      MPLS-in-IP tunnel
          with IPsec Transport Mode:           Type = 6 [This document]


      Tunnel Type  Sub-TLV Type                         Reference
      -----------  ------------                         ---------
        3,4,5,6    IPsec Tunnel Authenticator: Type = 3 [This document]


7. References

7.1. Normative References

   [ENCAPS-SAFI] Mohapatra, P., Rosen, E., "BGP Information SAFI
                 and BGP Tunnel Encapsulation Attribute", Work in
                 Progress, draft-ietf-softwire-encaps-safi-05.txt,
                 February 2009.

   [RFC4271]   Rekhter, Y., Ed. et al, "A Border Gateway Protocol 4
               (BGP-4)", RFC 4271, January 2006.

   [RFC4301]   Kent, S., Seo, K., "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.






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7.2. Informative References

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

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

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

   [RFC2784]   Farinacci, D., et al, "Generic Routing Encapsulation
               (GRE)", RFC 2784, March 2000.

   [RFC3931]   Lau, J., Ed., et al, "Layer Two Tunneling Protocol -
               Version 3 (L2TPv3)", RFC 3931, March 2005.

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

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

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

   [RFC4659]   De Clercq, J., et al, "BGP-MPLS IP Virtual Private
               Network (VPN) Extension for IPv6 VPN", RFC 4659,
               September 2006.

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

   [SOFTWIRES] Wu, J. et al, "Softwire Mesh Framework", Work in
               Progress, draft-ietf-softwire-mesh-framework-06.txt,
               February, 2009.

   [V4NLRI-V6NH] F. Le Faucheur, E. Rosen, "Advertising an IPv4 NLRI
                 with an IPv6 Next Hop", Work in Progress,
                 draft-ietf-idr-v4nlri-v6nh-01.txt, October 2007.












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8. Acknowledgments

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


9. 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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