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Versions: 00                                                            
Network Working Group                                            H. Wang
Internet-Draft                                                   F. Duan
Intended status: Informational                       Huawei Technologies
Expires: 26 April 2022                                   23 October 2021


         Multicast VPN Upstream Designated Forwarder Selection
             draft-wang-bess-mvpn-upstream-df-selection-00

Abstract

   This document defines Multicast Virtual Private Network (VPN)
   extensions and procedures that allow fast failover for upstream
   failures by allowing upstream Provider Edges (PEs) to determine a
   single forwarder for a VPN multicast flow, without the downstream
   PEs' duplication prevention.  The fast failover is accomplished by
   using Virtual Router Redundancy Protocol (VRRP) [RFC5798] or similar
   technologies for the upstream PEs to determine a single desinated
   fowarder.  Also, this document introduces a new BGP Extended
   Community called "Upstream Forwarder Selection", carried by BGP VPN
   route so that the upstream PEs can inform downstream PEs the election
   behavior.  The downstream PEs, accordingly, send C-multicast routes
   to both the primary and standby upstream PEs and forward the
   multicast flow comming from both sides to the CEs.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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 https://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."




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   This Internet-Draft will expire on 26 April 2022.

Copyright Notice

   Copyright (c) 2021 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 (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Upstream Designated Forwarder Selection . . . . . . . . . . .   3
     3.1.  Upstream Designated Forwarder Selection by VRRP . . . . .   4
     3.2.  Other Feasible Selection Technologies . . . . . . . . . .   4
   4.  Upstream Forwarder Selection Extended Community . . . . . . .   4
   5.  Downstream PE Behavior  . . . . . . . . . . . . . . . . . . .   5
     5.1.  Standby C-multicast Route Advertisment  . . . . . . . . .   5
     5.2.  Anycast Reverse Path Forwarding Checking  . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   MVPN [RFC6513] and [RFC6514] defines the MVPN architecture and MVPN
   protocol specification which include the basic procedures for
   selecting the Upstream Multicast Hop.  Further [RFC9026] defines some
   extension that allow fast failover for upstream failures by allowing
   downstream PEs to consider the status of Provider-Tunnels (P-tunnels)
   when selecting the Upstream PE for a VPN multicast flow.  However,
   there are some problems when deploying the "hot root standby"
   mechanism described in [RFC9026].

   First, all the ingress PEs, regardless of the primary or standby
   role, forward (C-S,C-G) flow to other PEs though a P-tunnel, forcing
   the egress PEs to discard all but one, which will cause the steady
   traffic redundancy throughout the backbone network.



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   Second, an efficient and accurate method for the downstream PEs to
   determine the "status" of a P-tunnel is required, which is somewhat
   complicated in some cases, as mentioned in Section 3.1.8 of [RFC9026]

   This document proposes a different "warm root standby" procedure
   mentioned in Section 4.2 of [RFC9026].  The procedures include a) an
   upstream designated forwarder election between multi homing ingress
   PEs, and b) the downstream PEs' advertising Primary and Standby BGP
   C-multicast route and accepting traffic from any of both sides.

   Section 3 describes procedures allowing multi homing ingress PEs to
   determine "locally" a single forwarder to avoid duplicate packets
   sending through the backbone, without the egress PEs' primary or
   standby UMH selection.

   Section 4 describes an optional BGP Extended Community called
   "Upstream Forwarder Selection", which is carried by BGP VPN routes
   (SAFI 128 or 129), to inform the downstream PEs the selection
   behavior describes in Section 3.

   Section 5 describes the downstream PEs' behavior in this case.  The
   downstream PEs advertise C-multicast Source Tree Join route to both
   the primary and secondary Upstream PEs (carrying, as Route Target
   extended communities, the values of the VRF Route Import Extended
   Community of each VPN route from each Upstream PE).  The Upstream
   Forwarder Selection Extended Community indicates that the packet
   duplication prevention will be accomplished by the upstream PEs and
   that any of the traffic from both the primary and secondary upstream
   PEs would be acceptable to be forwarded to the CEs.

2.  Terminology

   Readers of this document are assumed to be familiar with the
   terminology and concepts of the documents listed as Normative
   References.

3.  Upstream Designated Forwarder Selection


   Section 9.1.2 of [RFC6513] describes a "single forwarder selection"
   to ensure that duplicate packets not sending through the backbone.
   This document proposes a deployment of VRRP or some similar
   technology to enable dual or multi homing ingress PEs to determine a
   designated forwarder.







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3.1.  Upstream Designated Forwarder Selection by VRRP


   VRRP specifies an election protocol that dynamically assigns
   responsibility for a virtual router to one of the VRRP routers on a
   LAN.  The VRRP router controlling the IPv4 or IPv6 address(es)
   associated with a virtual router is called the Master, and it
   forwards packets sent to these IPv4 or IPv6 addresses.  Similarly,
   the role of the VRRP routers associated with a virtual router can
   also be that of the upstream PEs in MVPN dual homing upstream PEs
   deployment.

      Virtual Router -- pair of dual homing upstream PEs

      Virtual Router Master -- the primary upstream PE

      Virtual Router Backup -- the standby upstream PE

   The method of mapping the role of a VRRP router to that of a MVPN
   upstream PE is more likely an administrative measure and could be
   implemented as configurable policies.  Both the primary and standby
   PEs install VRF PIM state corresponding to BGP Source Tree Join route
   and send C-Join messages to the CE toward C-S.  Whereas only the
   primary upstream PE (Virtual Router Master according to VRRP)
   forwards (C-S,C-G) flow to downstream PEs through a P-tunnel.


3.2.  Other Feasible Selection Technologies


   VRRP is just an example of the feasible choices for the dual homing
   upstream PEs' single forwarder selection.  Other private
   implementations or similar designated forwarder selection
   technologies could also be optional for further study.  However, a
   feasible technology should has the ability of being deployed per VRF
   and being associated with one Multicast VPN instance.


4.  Upstream Forwarder Selection Extended Community


   This document defines a new BGP Extended Community called "Upstream
   Forwarder Selection".

   The Upstream Forwarder Selection is an IP-address-specific Extended
   Community, of an extended type, and is transitive across AS
   boundaries [RFC4360].




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   An upstream PE constructs Upstream Forwarder Selection as follows,
   regardless of the role of the selection result:

      The Global Administrator field of the Upstream Forwarder Selection
      SHOULD be set to a virtual IP address (or similar identity) of the
      upstream PEs (such as the VRRP Virtual IP address when using
      VRRP), which is identical between primary and standby PEs.

      The Local Administrator field of the Upstream Forwarder Selection
      SHOULD be set to a master or backup status determined by the
      election which is different between primary and standby PEs.

   Similar with the carrying of the VRF Route Import Extended Community
   imposed in Section 7 of [RFC6514], the multi homing PEs MUST also
   include in the BGP Updates message that carries the (unicast) VPN
   route the Upstream Forwarder Selection Extended Community that has
   the value of DF election result associated with this VRF.


5.  Downstream PE Behavior


5.1.  Standby C-multicast Route Advertisment


   The Standby BGP C-multicast route advertisement described in
   Section 4 of [RFC9026] is still necessary.  One downstream PE needs
   to determine a secondary UMH, originates and sends C-multicast routes
   with RTs that identify both the Primary and Standby Upstream PEs.
   However, because of the duplication prevention being accomplished by
   the upstream DF selection described above, carrying the new Standby
   PE BGP Communities with C-multicast routes is no longer a
   indispensable requirement.


5.2.  Anycast Reverse Path Forwarding Checking


   Multicast VPN specifications [RFC6513] impose that a downstream PE
   only forwards to CEs the packets coming from the expected Upstream PE
   (Section 9.1.1 of [RFC6513]).

   When performing the UMH selection, if a route in the set of VPN-IP
   eligible UMH routes carries the Upstream Forwarder Selection Extended
   Community, the Upstream PE determined from the route should be
   considered a potentially valid Upstream PE.  In most cases, there
   should be two of that routes for one (C-S,C-G) flow, indicateing the
   primary and standby upstream PEs.  As a result, the downstream PE



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   accepts the (C-S,C-G) flow from any of both sides and forward it to
   CEs.  It is a kind of "anycast" reverse path forwarding (RPF)
   checking.  Eventually, it is the upstream single forwarder selection
   mechanism that ensures the duplicate packets not passing through the
   backbone network, as described in Section 3.


6.  Security Considerations

   This document introduces no new security considerations beyond those
   already specified in [RFC6513] and [RFC6514].


7.  IANA Considerations

   This document contains no actions for IANA.


8.  Acknowledgements

   The authors wish to thank Jingrong Xie, for his reviews, comments and
   suggestions.


9.  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>.

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

   [RFC5798]  Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
              Version 3 for IPv4 and IPv6", RFC 5798,
              DOI 10.17487/RFC5798, March 2010,
              <https://www.rfc-editor.org/info/rfc5798>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <https://www.rfc-editor.org/info/rfc6513>.

   [RFC6514]  Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
              Encodings and Procedures for Multicast in MPLS/BGP IP
              VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
              <https://www.rfc-editor.org/info/rfc6514>.



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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC9026]  Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed.,
              "Multicast VPN Fast Upstream Failover", RFC 9026,
              DOI 10.17487/RFC9026, April 2021,
              <https://www.rfc-editor.org/info/rfc9026>.

Authors' Addresses

   Heng Wang
   Huawei Technologies

   Email: wangheng21@huawei.com


   Fanghong Duan
   Huawei Technologies

   Email: duanfanghong@huawei.com






























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