Extensions to RT-Constrain in Hierarchical Route Reflection Scenarios
draft-ietf-idr-rtc-hierarchical-rr-04

Network Working Group                                            J. Dong
Internet-Draft                                                   M. Chen
Intended status: Standards Track                     Huawei Technologies
Expires: 5 September 2024                                      R. Raszuk
                                                                  Arrcus
                                                            4 March 2024

 Extensions to RT-Constrain in Hierarchical Route Reflection Scenarios
                 draft-ietf-idr-rtc-hierarchical-rr-04

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 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.

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
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   This Internet-Draft will expire on 5 September 2024.

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Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Potential Solutions . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Add-path Based Solution . . . . . . . . . . . . . . . . .   4
     3.2.  Disjoint Alternate Path Solution  . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   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 route.  Then
   RR-1 needs to advertise the best RT-Constrain route 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 it will not advertise the
   VPN routes of VPN-1 to RR-1.

3.  Potential Solutions

   This document specifies 2 potential solutions for the RTC issue in
   hierarchical RR scenario.  In a later revision, one solution will to
   be selected based on the decision of the IDR working group.

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3.1.  Add-path Based Solution

   This section provides one possible solution which is based on the
   add-path mechanism defined in [RFC7911].  It makes use of the add-
   path mechanism for RTC route advertisement between the hierarchical
   RRs.  The solution is summerized as follows:

   *  The route-reflector clients which themselves are also route-
      reflectors SHOULD be identified, then BGP add-paths [RFC7911]
      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 with add-path mechanism is a local decision of
      operators.  To ensure that sufficient RT-Constrain routes are
      advertised to build the distribution graph, the recommended add-
      path number is the maximum number of the BGP client sessions in
      the same cluster plus 1.

   *  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.

3.2.  Disjoint Alternate Path Solution

   This section specifies another possible solution which proposes some
   modification to the intra-AS advertisement rule of RTC route.

   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 of [RFC4684]:

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   *  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, which is the most
   disjoint alternative route compared with the best route received from
   RR-2.  In this way, RR-2 will not discard the RT-constrain route
   received from RR-1, and 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 of RT-
   Constrain issue in hierarchical RR scenario.  Many people have made
   valuable comments and suggestions, including Susan Hares, Jeffrey
   Haas, Stephane Litkowski, Vitkovský Adam, Xiaohu Xu, Uttaro James,
   Shyam Sethuram, Saikat Ray and Bruno Decraene.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

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   [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, DOI 10.17487/RFC4684,
              November 2006, <https://www.rfc-editor.org/info/rfc4684>.

7.2.  Informative References

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <https://www.rfc-editor.org/info/rfc7911>.

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
   Arrcus
   Email: robert@raszuk.net

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