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Extended Communities Derived from Route Targets

Document Type Active Internet-Draft (idr WG)
Authors Zhaohui (Jeffrey) Zhang , Jeffrey Haas , Keyur Patel
Last updated 2024-01-17
Replaces draft-zzhang-idr-rt-derived-community
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd Susan Hares
Shepherd write-up Show Last changed 2023-03-28
IESG IESG state I-D Exists
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idr                                                             Z. Zhang
Internet-Draft                                                   J. Haas
Intended status: Standards Track                        Juniper Networks
Expires: 20 July 2024                                           K. Patel
                                                         17 January 2024

            Extended Communities Derived from Route Targets


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

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 20 July 2024.

Copyright Notice

   Copyright (c) 2024 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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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Route Target Type/sub-type Conventions  . . . . . . . . . . .   3
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  EVPN EVI-RT Extended Community  . . . . . . . . . . . . .   4
     3.2.  Leaf Discovery with Controller Signaled BGP-MVPN  . . . .   4
     3.3.  Translated Route-target Extended Communities in
           [I-D.ietf-idr-legacy-rtc] . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Assignments  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

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.

   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

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   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 [RFC5701]).  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.  Route Target Type/sub-type Conventions

   It may be expected by some people that Route Targets are Extended
   Communities with sub-type 0x02 (or with Type 0x0002 in case of IPv6
   Address Specific Extended Community).  However, the only official
   specification are in [RFC7153] [RFC7432] and are only for the
   following types:

   *  Type 0x00 (Transitive Two-Octet AS-Specific EC)

   *  Type 0x01 (Transitive IPv4-Address-Specific EC)

   *  Type 0x02 (Transitive Four-Octet AS-Specific EC)

   *  Type 0x06 (EVPN AS-Specific EC)

   *  Type 0x0002 (Transitive IPv6-Address-Specific Route Target)

   *  Type 0x0011 (Transitive IPv6-Address-Specific EC, UUID-based Route

   While it may be desired to follow the unwritten convention and assign
   sub-type 0x02 for future Route Targets of future types of ECs, there
   is no guarantee of that.  For example, Type 0x0011 is assigned for
   UUID-based Route Target that imposes as an IPv6 Address Specific EC
   (even though UUID is not an IPv6 address).

   IANA has assigned sub-type 0x15 (or Type 0x0015 in case of IPv6
   Address Specific EC) to indicate an EC is derived from a Route Target
   that has sub-type 0x02 (or type 0x0002 in case of IPv6 Address
   Specific EC), and this document will further request another Type TBD
   (say, 0x0016) to derive from the UUID-based Route Target.

   All those can only be registered with the known types listed above.
   When a new type is defined and registered, the corresponding 0x02
   sub-type may be registered for Route Target purpose or for something

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   else, and there is no guarantee that the 0x15 sub-type will not be
   registered for something else as well (than for RT derivation).  As a
   result, the mapping between sub-type 0x02 and 0x15, type 0x0002 and
   0x0015, type 0x0011 and TBD are only defined for the known types
   listed above.

   Of course, when a new type is defined and registered, it is desired
   to proactively register sub-type 0x02 and 0x15 at the very beginning
   for Route Target and Route Target Derivation purposes, should the
   review process catch it.

3.  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

3.1.  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

   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.

3.2.  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
   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).

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3.3.  Translated Route-target Extended Communities in [I-D.ietf-idr-

   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

4.  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.

5.  IANA Assignments

   This document requests IANA to assign a new Type value (0x0016
   suggested) for "UUID-RT-derived-EC".

   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

   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.

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6.  Acknowledgements

   The authors thank Robert Raszuk for his valuable comments and

7.  References

7.1.  Normative References

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <>.

   [RFC5701]  Rekhter, Y., "IPv6 Address Specific BGP Extended Community
              Attribute", RFC 5701, DOI 10.17487/RFC5701, November 2009,

   [RFC7153]  Rosen, E. and Y. Rekhter, "IANA Registries for BGP
              Extended Communities", RFC 7153, DOI 10.17487/RFC7153,
              March 2014, <>.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <>.

7.2.  Informative References

              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,

              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-12, 30 December 2023,

              Mohapatra, P., Sreekantiah, A., Patel, K., Burjiz, B., and
              A. Lo, "Automatic Route Target Filtering for legacy PEs",

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              Work in Progress, Internet-Draft, draft-ietf-idr-legacy-
              rtc-08, 12 September 2017,

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks

   Jeff Haas
   Juniper Networks

   Keyur Patel

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