Extensions to RT-Constrain in Hierarchical Route Reflection Scenarios
draft-dong-idr-rtc-hierarchical-rr-00

Network Working Group                                            J. Dong
Internet-Draft                                                   M. Chen
Intended status: Standards Track                     Huawei Technologies
Expires: December 21, 2014                                 June 19, 2014

 Extensions to RT-Constrain in Hierarchical Route Reflection Scenarios
                 draft-dong-idr-rtc-hierarchical-rr-00

Abstract

   The Route Target (RT) Constrain mechanism specified in RFC 4684 is
   used to build a route distribution graph in order to restrict the
   propagation of Virtual Private Network (VPN) routes.  In network
   scenarios where hierarchical route reflection (RR) is used, the
   existing RT-Constrain mechanism cannot build a correct route
   distribution graph.  This document refines the route distribution
   rules of RT-Constrain to address the hierarchical RR scenarios.

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].

Status of This Memo

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   This Internet-Draft will expire on December 21, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Proposed Solution . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The Route Target (RT) Constrain mechanism specified in RFC 4684 is
   used to build a route distribution graph in order to restrict the
   propagation of Virtual Private Network (VPN) routes.  In network
   scenarios where hierarchical route reflection (RR) is used, the
   existing RT-Constrain mechanism cannot build a correct route
   distribution graph.

                    +---------------------------------+
                    |              +----+             |
                    |        Clu-1 |RR-1|             |
                    |             /+----+\            |
                    |            /        \           |
                    |         +----+    +----+        |
                    |  Clu-2  |RR-2|    |RR-3|  Clu-3 |
                    |         +-/--+    +/--\+        |
                    |          /        /    \        |
                    |     +----+    +----+    +----+  |
                    |     |PE-1|    |PE-2|    |PE-3|  |
                    |     +----+    +----+    +----+  |
                    |       |          |         |    |
                    +-------|----------|---------|----+
                       RT-1 |     RT-1 |         | RT-1
                    +--------+   +--------+    +--------+
                    |  VPN-1 |   |  VPN-1 |    |  VPN-1 |
                    +--------+   +--------+    +--------+
                Figure 1. RT-Constrain with Hierarchical RR

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   As shown in Figure 1, hierarchical RRs are deployed in the network,
   RR-2 and RR-3 are route-reflectors of their connecting PEs, and are
   also the clients of RR-1.  If each PE advertises RT membership
   information of RT-1 to the upstream RR, after the best path
   selection, both RR-2 and RR-3 would create the CLUSTER_LIST
   attribute, prepend their local CLUSTER_ID and then advertise the best
   path to RR-1 and their clients respectively.

   On receipt of the RT-Constrain routes from RR-2 and RR-3, RR-1 will
   select one of the received routes as the best route, assume the route
   received from RR-2 is selected by RR-1 as the best path.  Then RR-1
   needs to advertise the best path to both RR-2 and RR-3 to create the
   route distribution graph of VPN-1.  RR-1 would prepend its CLUSTER_ID
   to the CLUSTER_LIST of the path, and according to the rules in
   Section 3.2 of [RFC4684], it sets the ORIGINATOR_ID to its own
   router-id, and the NEXT_HOP to the local address for the session.
   Then RR-1 would advertise this route to both RR-2 and RR-3.  On
   receipt of the RT-Constrain route from RR-1, RR-2 checks the
   CLUSTER_LIST and find its own CLUSTER_ID in the list, so this route
   will be ignored by RR-2.  As a result, RR-2 will not form the
   outbound filter of RT-1 towards RR-1, hence will not advertise VPN
   routes with RT-1 to RR-1.

2.  Proposed Solution

   The problem described in the above section is that the best path is
   sent back to the BGP speaker which advertised the path and get
   discarded due to the BGP loop detection mechanisms.  Since the
   advertisement of RT-Constrain route is to set up a route distribution
   graph and not to guide the data packet forwarding, all the available
   paths can be considered in setting up the route distribution graph,
   not just the best path.  Thus in addition to the rules specified in
   section 3.2 of [RFC4684], the following rule applies in the
   advertisement of RT-Constrain routes:

   o  When advertising an RT membership NLRI to a route-reflector
      client, if the best route as selected by the path selection
      procedure described in Section 9.1 of [RFC4271] is the path
      received from this client, and there are alternative paths
      received from other peers, the most disjoint alternative route
      SHOULD be advertised to that client; The most disjoint alternative
      path is the path whose CLUSTER_LIST and ORIGINATOR_ID attributes
      are different from the attributes of the best path.

   With this additional rule, RR-1 in Figure 1 would advertise to RR-2
   the RT-Constrain route received from RR-3, although the best route is
   received from RR-2.  Thus RR-2 will not discard the RT-constrain

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   route received from RR-1, and the route distribution graph can be set
   up completely.

3.  IANA Considerations

   This document makes no request of IANA.

4.  Security Considerations

   This document does not change the security properties of BGP based
   VPNs and [RFC4684].

5.  Acknowledgements

   The authors would like to thank Yaqun Xiao for the discussion about
   RT-Constrain in hierarchical RR scenario.

6.  Normative References

   [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.

   [RFC4684]  Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
              R., Patel, K., and J. Guichard, "Constrained Route
              Distribution for Border Gateway Protocol/MultiProtocol
              Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
              Private Networks (VPNs)", RFC 4684, November 2006.

Authors' Addresses

   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: jie.dong@huawei.com

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   Mach(Guoyi) Chen
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: mach.chen@huawei.com

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