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

Network Working Group                                          J. Uttaro
Internet-Draft                                                      AT&T
Intended status: Standards Track                            P. Mohapatra
Expires: February 1, 2013                                       D. Smith
                                                           Cisco Systems
                                                               R. Raszuk
                                                            NTT MCL Inc.
                                                              J. Scudder
                                                        Juniper Networks
                                                           July 31, 2012


                   BGP ACCEPT_OWN Community Attribute
              draft-ietf-l3vpn-acceptown-community-05.txt

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
   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.

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
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   This Internet-Draft will expire on February 1, 2013.

Copyright Notice




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

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   it for publication as an RFC or to translate it into languages other
   than English.



























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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 4
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . . . 4
   2.  ACCEPT_OWN Community  . . . . . . . . . . . . . . . . . . . . . 4
     2.1.  Route Acceptance  . . . . . . . . . . . . . . . . . . . . . 5
     2.2.  Propagating ACCEPT_OWN Between Address Families . . . . . . 5
     2.3.  Configuration Control . . . . . . . . . . . . . . . . . . . 5
   3.  Decision Process  . . . . . . . . . . . . . . . . . . . . . . . 6
   4.  Deployment Considerations . . . . . . . . . . . . . . . . . . . 6
   5.  Other Applications  . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Local Extranet Application (non-informative) . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8


































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1.  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 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.

1.1.  Requirements Language

   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 RFC 2119 [RFC2119].


2.  ACCEPT_OWN Community

   This memo defines a new BGP community, ACCEPT_OWN, whose value as
   assigned by IANA is 0xFFFF0001.  Processing of the ACCEPT_OWN
   community SHOULD be controlled by configuration.  The functionality
   SHOULD default to being disabled, as further specified in
   Section 2.3.




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2.1.  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:

   o  Processing of the ACCEPT_OWN community is enabled by
      configuration.

   o  The route in question carries the ACCEPT_OWN community.

   o  The route in question was originated from a source VRF on the
      router (as determined by inspecting the Route Distinguisher).

   o  The route in question is targeted to one or more destination VRFs
      on the router (as determined by inspecting the Route Target(s)).

   o  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.

2.2.  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.

2.3.  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 2.1.
   The router SHOULD still apply the propagation rules detailed in
   Section 2.2.







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3.  Decision Process

   If a BGP speaker supports ACCEPT_OWN and is configured for the
   extensions defined in this document, the following step is inserted
   after the LOCAL_PREF comparison step in BGP decision process:

      When comparing a pair of routes for a BGP destination, the route
      attached with ACCEPT_OWN community is preferred over the route
      that does not have the community.

   In all other respects, the decision process remains unchanged.  This
   extra step MUST only be invoked during the best path selection
   process of VPN-IP routes [RFC4364] (i.e. it MUST NOT be invoked for
   the best path selection of "imported" IP routes in a VRF).  The
   purpose of the extra step is to allow the paths advertised by the
   route reflector with ACCEPT_OWN community to be selected as best over
   other paths that the BGP speaker may have received, hence enabling
   the applications ACCEPT_OWN is designed for.


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.







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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 has assigned the value 0xFFFF0001 from BGP well-known
   communities registry for ACCEPT_OWN community.  No additional IANA
   action is required.


8.  Acknowledgments

   The authors would like to thank Yakov Rekhter, Jim Guichard, Clarence
   Filsfils, John Mullooly, Jeff Haas, Pranav Mehta, and Tamas Mondal
   for their valuable comments and suggestions.  The decision process
   changes were suggested by Pranav Mehta to solve the remote extranet
   problem.


9.  Normative References

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

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

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

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


Appendix A.  Local Extranet Application (non-informative)

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







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

                      Figure 1: Extranet Application

   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.


Authors' Addresses

   James Uttaro
   AT&T
   200 S. Laurel Avenue
   Middletown, NJ  07748
   USA

   Email: uttaro@att.com






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   Pradosh Mohapatra
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: pmohapat@cisco.com


   David J. Smith
   Cisco Systems
   111 Wood Avenue South
   Iselin, NJ  08830
   USA

   Email: djsmith@cisco.com


   Robert Raszuk
   NTT MCL Inc.
   101 S Ellsworth Avenue Suite 350
   San Mateo, CA  94401
   US

   Email: robert@raszuk.net


   John Scudder
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA  94089
   USA

   Email: jgs@juniper.net

















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