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Versions: 00 01 02 draft-ietf-idr-rtc-hierarchical-rr

Network Working Group                                            J. Dong
Internet-Draft                                                   M. Chen
Intended status: Standards Track                     Huawei Technologies
Expires: May 29, 2015                                          R. Raszuk
                                                           Mirantis Inc.
                                                       November 25, 2014


 Extensions to RT-Constrain in Hierarchical Route Reflection Scenarios
                 draft-dong-idr-rtc-hierarchical-rr-02

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 describes the problem scenario and
   proposes a solution to address the RT-Constrain issue in 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

   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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 29, 2015.







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Copyright Notice

   Copyright (c) 2014 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Proposed Solution . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Add-path Based Solution . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Another Possible Solution  . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The Route Target (RT) Constrain mechanism specified in [RFC4684] 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 advertisment rules of RT membership information as defined
   in section 3.2 of [RFC4684] cannot guarantee a correct route
   distribution graph.

   This document describes the problem scenario and proposes a solution
   to address the RT-Constrain issue in hierarchical RR scenarios.

2.  Problem Statement









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                    +---------------------------------+
                    |              +----+             |
                    |        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

   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, here 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.

3.  Proposed Solution







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3.1.  Add-path Based Solution

   During the discussion in the IDR working group, the add-path based
   solution is proposed.  It makes use of the add-path mechanism as
   defined in [I-D.ietf-idr-add-paths] for RTC route advertisement.  The
   solution is summerized as follows:

   o  The route-reflector clients which themselves are also route-
      reflectors SHOULD be identified, then BGP add-paths
      [I-D.ietf-idr-add-paths] SHOULD be enabled for RT membership NLRI
      on the BGP sessions between the higher layer RR and the lower
      layer RRs to ensure that sufficient RT-Constrain routes can be
      advertised by the higher layer RR to the lower layer RRs to pass
      BGP loop detection.  In this case normal BGP path advertisement
      rules as defined in [RFC4271] SHOULD be applied.  The number of
      RT-Constrain routes to be advertised is a local decision of
      operators.

   o  When advertising an RT membership NLRI to a route-reflector client
      which is not a lower layer RR, the advertisement rule as defined
      in section 3.2 of [RFC4684] SHOULD be applied.

   With the above advertisement rule, RR-1 in figure 1 SHOULD advertise
   to RR-2 the RT-Constrain routes received from both RR-2 and RR-3,
   then the RTC route from RR-3 will pass the BGP loop detection on RR-
   2, thus the route distribution graph can be set up correctly.

4.  IANA Considerations

   This document makes no request of IANA.

5.  Security Considerations

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

6.  Acknowledgements

   The authors would like to thank Yaqun Xiao for the discussion about
   RT-Constrain in hierarchical RR scenario.  Many people have made
   valuable comments and suggestions, including Susan Hares, Jeffrey
   Haas, Stephane Litkowski, Vitkovsky Adam, Xiaohu Xu, Uttaro James,
   Shyam Sethuram and Saikat Ray.








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7.  Normative References

   [I-D.ietf-idr-add-paths]
              Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", draft-ietf-idr-
              add-paths-10 (work in progress), October 2014.

   [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.

Appendix A.  Another Possible Solution

   This section provides another possible solution which was discussed
   among authors and IDR participants.

   Since the advertisement of RT-Constrain route is to set up a route
   distribution graph and not to guide the data packet forwarding,
   actually all the available RT-Constrain routes should be considered
   in setting up the route distribution graph, not just the best one.
   Thus the following advertisment rule for RT membership information is
   proposed to replace the rule i and ii in section 3.2 [RFC4684]:

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

   With the above advertisement 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 route received from RR-1, and the route distribution graph
   can be set up correctly.






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Authors' Addresses

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

   Email: jie.dong@huawei.com


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

   Email: mach.chen@huawei.com


   Robert Raszuk
   Mirantis Inc.
   615 National Ave. #100
   Mt View, CA  94043
   USA

   Email: robert@raszuk.net
























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