Extended Communities Derived from Route Targets
draft-zzhang-idr-rt-derived-community-03

idr                                                             Z. Zhang
Internet-Draft                                                   J. Haas
Intended status: Standards Track                        Juniper Networks
Expires: 30 June 2023                                           K. Patel
                                                                  Arrcus
                                                        27 December 2022

            Extended Communities Derived from Route Targets
                draft-zzhang-idr-rt-derived-community-03

Abstract

   This document specifies a way to derive an Extended Community from a
   Route Target and describes some example use cases.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 30 June 2023.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  EVPN EVI-RT Extended Community  . . . . . . . . . . . . .   3
     2.2.  Leaf Discovery with Controller Signaled BGP-MVPN  . . . .   3
     2.3.  Translated Route-target Extended Communities in
           [I-D.ietf-idr-legacy-rtc] . . . . . . . . . . . . . . . .   4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Assignments  . . . . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Consider a VPN with 10 PEs.  A Route Target (say RT1) [RFC4360] is
   configured for the VPN and all PEs will import VPN routes with RT1
   attached.  The RT is an Extended Community (say EC1), with its sub-
   type being 0x02.  While RT1 and EC1 have the same encoding, typically
   when we mention a Route Target, its property of being able to control
   the route propagation and importation is implied.  When we just
   mention an Extended Community, that property is not implied.

   Now consider that another BGP route needs to be imported by some but
   not all those PEs.  The route could be of any SAFI/type (does not
   need to be a VPN prefix), but it needs to be associated with the VPN
   on those importing PEs.  The exact meaning of "association" here does
   not matter, but the key is that those PEs need to know that the route
   is related to that VPN.

   To control the propagation to and importation by those PEs, a
   different Route Target (say RT3) is attached to the route.  For those
   PE to associate the route with the VPN, an Extended Community (say
   EC2) is attached.  Even though RT1/EC1 is already associated with the
   VPN, EC2 needs to be different from RT1/EC1, because if EC1 was used,
   the route would be propagated to and imported by all the 10 PEs.  EC2
   cannot be the same as RT3 either, because there could be other routes
   to be propagated to and imported by those same set of PEs yet those
   other routes are not related to the VPN.

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   While EC2 can be any Extended Community (that is not a RT) configured
   on the originating and receiving PEs to map it to the VPN, it is
   convenient if EC2 is derived from the RT1/EC1, e.g. the sub-type of
   RT1/EC1 is changed to a new known value while everything else remains
   the same.  We call this a Route Target derived Extended Community, or
   RT-derived EC.  A new sub-type is assigned specifically for this
   purpose (see IANA considerations).

   This document only specifies a way to derive an Extended Community
   from a Route Target Extended Community using IANA-assigned Extended
   Community sub-types (or Extended Community Type in case of IPv6-
   Address-Specific Extended Community).  Any protocol/feature that can
   take advantages of the convenience of generic derivation may use
   them, or not use them at its own discretion, and how they are used is
   outside the scope of this document.

2.  Use Cases

   The following are a few examples of use cases.  To reiterate, these
   are example scenarios where generic RT-derived ECs could be used
   (when the routes to which they are attached provide enough context).
   It is not the intention of this document to mandate that it must be
   used.

2.1.  EVPN EVI-RT Extended Community

   Section 9.5 "EVI-RT Extended Community" of
   [I-D.ietf-bess-evpn-igmp-mld-proxy] describes a situation similar to
   the above.  As a solution, four EVPN specific EVI-RT ECs are defined,
   each mapping to a type of Route Target for the corresponding EVPN
   instance.

   As a theoretical alternative, a RT-derived EC described in this
   document could be used instead - just derive a generic EC from the
   EVI RT.  Note that this document does not attempt to change the
   existing procedures in [I-D.ietf-bess-evpn-igmp-mld-proxy], but
   merely use it for illustration purposes.

2.2.  Leaf Discovery with Controller Signaled BGP-MVPN

   In Section 2 "Alternative to BGP-MVPN" of
   [I-D.ietf-bess-bgp-multicast-controller], BGP MCAST-TREE SAFI
   signaling can be used for a controller to program multicast
   forwarding state in VRFs of ingress/egress PEs, instead of relying on
   distributed BGP-MVPN signaling.  For the controller to learn egress
   PEs of a VPN customer multicast tree (so that it can build/find a
   corresponding provider tunnel), egress PEs signal leaf information to
   the controller via Leaf Auto-Discovery routes.  The routes carry a

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   Route Target for the controller (so that only the controller receives
   them), and an EC derived from the VPN's Route Target (so that the
   controller knows which VPN they are for).

2.3.  Translated Route-target Extended Communities in [I-D.ietf-idr-
      legacy-rtc]

   In Section 3.1 of [I-D.ietf-idr-legacy-rtc], a similar mechanism is
   described, as quoted below:

     "The translation of the IRTs is necessary in order to refrain from
     importing "route-filter" VRF routes into VPN VRFs that would
     import the same route-targets.  The translation of the IRTS is
     done as follows.  For a given IRT, the equivalent translated RT
     (TRT) is constructed by means of swapping the value of the high-
     order octet of the Type field for the IRT (as defined in
     [RFC4360])."

3.  Security Considerations

   This document specifies a way to derive an Extended Community from a
   Route Target Extended Community and does not specify how derived
   Extended Communities are used.  As a result, this document does not
   need security considerations.  Any potential security concerns need
   be addressed by documents that specify the actual usage.

4.  IANA Assignments

   IANA has assign a new sub-type "RT-derived-EC" with value 0x15 in the
   following registries:

   *  Transitive Two-Octet AS-Specific Extended Community Sub-Types

   *  Transitive Four-Octet AS-Specific Extended Community Sub-Types

   *  Transitive IPv4-Address-Specific Extended Community Sub-Types

   *  Non-Transitive Opaque Extended Community Sub-Types

   *  EVPN Extended Community Sub-Types

   IANA has also assigned a new type "RT-derived-EC" with value 0x0015
   in the following registry:

   *  Transitive IPv6-Address-Specific Extended Community Types

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   If and when additional Extended Community types are defined with a
   Route Target sub-type, the "RT-derived-EC" sub-type may also be
   registered for those new types, preferably with the same value.

5.  References

5.1.  Normative References

   [RFC4360]  Sangli, S., Tappan, D., Rekhter, Y., and RFC Publisher,
              "BGP Extended Communities Attribute", RFC 4360,
              DOI 10.17487/RFC4360, February 2006,
              <https://www.rfc-editor.org/info/rfc4360>.

5.2.  Informative References

   [I-D.ietf-bess-evpn-igmp-mld-proxy]
              Sajassi, A., Thoria, S., Mishra, M. P., Drake, J., and W.
              Lin, "Internet Group Management Protocol (IGMP) and
              Multicast Listener Discovery (MLD) Proxies for Ethernet
              VPN (EVPN)", Work in Progress, Internet-Draft, draft-ietf-
              bess-evpn-igmp-mld-proxy-21, 22 March 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-
              igmp-mld-proxy-21.txt>.

   [I-D.ietf-bess-bgp-multicast-controller]
              Zhang, Z. J., Raszuk, R., Pacella, D., and A. Gulko,
              "Controller Based BGP Multicast Signaling", Work in
              Progress, Internet-Draft, draft-ietf-bess-bgp-multicast-
              controller-09, 11 April 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-bgp-
              multicast-controller-09.txt>.

   [I-D.ietf-idr-legacy-rtc]
              Mohapatra, P., Sreekantiah, A., Patel, K., Burjiz, B., and
              A. Lo, "Automatic Route Target Filtering for legacy PEs",
              Work in Progress, Internet-Draft, draft-ietf-idr-legacy-
              rtc-08, 12 September 2017,
              <https://www.ietf.org/archive/id/draft-ietf-idr-legacy-
              rtc-08.txt>.

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks
   Email: zzhang@juniper.net

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   Jeff Haas
   Juniper Networks
   Email: jhaas@juniper.net

   Keyur Patel
   Arrcus
   Email: keyur@arrcus.com

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