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Versions: (draft-pmohapat-l3vpn-acceptown-community) 00 01 02 03 04 05 06 07 08

Network Working Group                                       James Uttaro
Internet Draft                                                      AT&T
Expiration Date: April 2009
                                                       Pradosh Mohapatra
                                                          David J. Smith
                                                     Cisco Systems, Inc.

                                                           Robert Raszuk
                                                            John Scudder
                                                  Juniper Networks, Inc.

                                                        October 05, 2008


          BGP ACCEPT_OWN Standards Action Community Attribute


                draft-ietf-l3vpn-acceptown-community-00.txt

Status of this Memo

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Abstract

   Under certain conditions it is desirable for a BGP route reflector to
   be able to modify the Route Target list of a VPN route that is
   distributed by the route reflector, enabling the route reflector to
   control how a route originated within one VRF is imported into other



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   VRFs.  This technique works effectively as long as the VRF that
   exports the route is not on the same PE as the VRF(s) that import the
   route. However, due to the constraints of the BGP protocol, it does
   not work if the two are on the same PE.

   This document describes a modification to the BGP protocol allowing
   this technique to work when the VRFs are on the same PE, allowing the
   technique to be used in a standard manner throughout an autonomous
   system.



Table of Contents

    1          Specification of Requirements  ......................   2
    2          Introduction  .......................................   3
    3          ACCEPT_OWN Community  ...............................   3
    3.1        Route Acceptance  ...................................   4
    3.2        Propagating ACCEPT_OWN Between Address Families  ....   4
    3.3        Configuration Control  ..............................   4
    4          Deployment Considerations  ..........................   5
    5          Other Applications  .................................   5
    6          Security Considerations  ............................   5
    7          IANA Considerations  ................................   5
    8          Appendix A - Extranet application (non-normative)  ..   6
    9          Acknowledgements  ...................................   7
   10          Normative References  ...............................   7
   11          Authors' Addresses  .................................   7
   12          Full Copyright Statement  ...........................   8
   13          Intellectual Property  ..............................   8






1. Specification of Requirements

   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

   In certain scenarios, a BGP speaker may maintain multiple "VPN
   Routing and Forwarding tables", or VRFs [RFC4364].  Under certain
   conditions it is desirable for a route reflector to be able to modify
   the Route Target (RT) list of a VPN route that is distributed by the
   route reflector, enabling the route reflector to control how a route
   originated within one VRF is imported into other VRFs.  Though it is
   possible to perform such policy control directly on the originator,
   it may be operationally cumbersome in an autonomous system with a
   large number of border routers having complex BGP policies.

   The technique of the route reflector modifying the RT list works
   effectively as long as the VRF that exports the route is not on the
   same PE as the VRF(s) that import the route. However, due to the
   constraints of the BGP protocol, it does not work if the two are on
   the same PE. This is because per the BGP specification [RFC4271], a
   BGP speaker rejects prefix advertisements received that were
   originated by itself. In an autonomous system with route reflectors,
   the route reflector attaches the ORIGINATOR_ID attribute to the
   UPDATE messages so that if such prefix advertisements reach the
   originator, the originator can reject them by simply checking the
   ORIGINATOR_ID attribute.  The BGP specification also mandates that a
   route should not be accepted from a peer when the NEXT_HOP attribute
   matches the receiver's own "IP address".

   This document proposes a modification to BGP's behavior by defining a
   new standards action community [RFC1997] value, in order to allow the
   technique of RT list modification by the route reflector to be used
   in a standard manner throughout an autonomous system, irrespective of
   whether the VRFs are on the same, or different PEs.


3. ACCEPT_OWN Community

   This memo defines a new standards action BGP community, ACCEPT_OWN, a
   new value to be assigned by IANA.  Processing of the ACCEPT_OWN
   community SHOULD be controlled by configuration.  The functionality
   SHOULD default to being disabled, as further specified in Section
   3.3.











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3.1. Route Acceptance

   A router MAY accept a route whose ORIGINATOR_ID or NEXT_HOP value
   matches that of the receiving speaker if all of the following are
   true:

     + Processing of the ACCEPT_OWN community is enabled by
       configuration.
     + The route in question carries the ACCEPT_OWN community.
     + The route in question was originated from a source VRF on the
       router (as determined by inspecting the Route Distinguisher).
     + The route in question is targeted to one or more destination VRFs
       on the router (as determined by inspecting the Route Target(s)).
     + At least one destination VRF is different from the source VRF.

   A route MUST never be accepted back into its source VRF, even if it
   carries one or more Route Targets (RTs) which match that VRF.


3.2. Propagating ACCEPT_OWN Between Address Families

   The ACCEPT_OWN community controls propagation of routes which can be
   associated with a source VRF by inspection of their Route
   Distinguisher and with a target VRF by inspection of their Route
   Target list (for example VPN routes with a SAFI of 128). As such, it
   SHOULD NOT be attached to any routes which cannot be associated with
   a source VRF.  This implies that when propagating routes into a VRF,
   the ACCEPT_OWN community should not be propagated.  Likewise, if a
   route carrying the ACCEPT_OWN community is received in an address
   family which does not allow the source VRF to be looked up, the
   ACCEPT_OWN community MUST be discarded. An OPTIONAL message may be
   logged in this case.


3.3. Configuration Control

   ACCEPT_OWN handling SHOULD be controlled by configuration, and SHOULD
   default to being disabled.  When ACCEPT_OWN is disabled by
   configuration (either explicitly or by default), the router MUST NOT
   apply the special route acceptance rules detailed in Section 3.1.
   The router SHOULD still apply the propagation rules detailed in
   Section 3.2.









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4. Deployment Considerations

   The ACCEPT_OWN community as described in this document is useful
   within a single autonomous system which uses a single layer of route
   reflectors.  Its use with hierarchical route reflectors would require
   further specification and is out of scope for this document.
   Likewise, its use across multiple autonomous systems is out of scope
   for this document.


5. Other Applications

   This approach may also be relevant to other scenarios where a BGP
   speaker maintains multiple routing contexts using an approach
   different from that of [RFC4364], as long as the specific approach in
   use has the property that the BGP speaker originates and receives
   routes within a particular context.  In such a case, "VRF" in this
   document should be understood to mean whatever construct provides a
   routing context in the specific technology under consideration.
   Likewise, "Route Distinguisher" should be understood to mean whatever
   construct allows a route's originator to associate that route with
   its source context, and "Route Target" should be understood to mean
   whatever construct allows a route to be targeted for import into a
   context other than its source.


6. Security Considerations

   ACCEPT_OWN as described above permits a router's own route prefix to
   be advertised to a different VRF on that router. In this respect,
   such a route is similar to any other BGP route and shares the same
   set of security vulnerabilities and concerns. No new fundamental
   security issues are introduced by ACCEPT_OWN.


7. IANA Considerations

   IANA shall assign a new code point from BGP standards action
   communities for ACCEPT_OWN.












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8. Appendix A - Extranet application (non-normative)

   One of the applications for this behavior is auto-configuration of
   extranets within MPLS VPN networks. Consider the following topology:


   CE1 --------+
               |
              (VRF 1, RD 1, RT 1)
                       PE1 ................... RR
              (VRF 2, RD 2, RT 2)
               |
   CE2 --------+


   Within the above topology, PE1 receives a prefix X from CE1. Prefix X
   is installed in VRF 1 and is advertised to the route reflector with
   route distinguisher (RD) 1 and route target (RT) 1 as configured on
   PE1. The requirement is to import prefix X into VRF 2 and advertise
   it to CE2 in support of extranet VPN connectivity between CE1/VRF1
   and CE2/VRF2. Current BGP mechanisms for MPLS VPNs [RFC4364] require
   changing the import RT value and/or import policy for VRF 2 on PE1.
   This is operationally cumbersome in a network with a large number of
   border routers having complex BGP policies.

   Alternatively, using the new ACCEPT_OWN community value, the route
   reflector can simply re-advertise prefix X back to PE1 with RT 2
   appended. In this way, PE1 will accept prefix X despite its
   ORIGINATOR_ID or NEXT_HOP value, import it into VRF 2 as a result of
   RT 2, and will then determine the correct adjacency rewrite within
   VRF 1 based on the RD value (1) and the prefix. Note that the RT 1
   value originally attached to the route will simply be ignored since
   associated with the source VRF 1. The same operation needs also to
   happen in the reverse direction (VRF 1 learning a route from VRF 2)
   to achieve establishment of an extranet VPN strictly via the route
   reflector without changing the BGP policy of PE1 in any way.

   A router performing such an extranet application can accept a route
   with its own ORIGINATOR_ID or NEXT_HOP value only if the VRF in which
   the router originated the route is different than the VRF in which
   the router accepts the re-advertised route.










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9. Acknowledgements

   The authors would like to thank Yakov Rekhter, Jim Guichard, Clarence
   Filsfils, John Mullooly, and Jeff Haas for their valuable comments
   and suggestions.


10. Normative References

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

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

   [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
   Attribute", RFC 1997, August 1996.

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


11. Authors' Addresses


      James Uttaro
      AT&T
      200 S. Laurel Avenue
      Middletown, NJ 07748
      Email: uttaro@att.com



      Pradosh Mohapatra
      Cisco Systems, Inc.
      170 Tasman Drive
      San Jose, CA  95134
      Email: pmohapat@cisco.com



      David J. Smith
      Cisco Systems, Inc.
      111 Wood Avenue South
      Iselin, NJ  08830
      E-mail: dasmith@cisco.com





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      Robert Raszuk
      Juniper Networks
      1194 North Mathilda Avenue
      Sunnyvale, California 94089
      USA
      Email: raszuk@juniper.net



      John Scudder
      Juniper Networks
      1194 North Mathilda Avenue
      Sunnyvale, California 94089
      USA
      Email: jgs@juniper.net



12. Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
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   Copies of IPR disclosures made to the IETF Secretariat and any



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   assurances of licenses to be made available, or the result of an
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