Per multicast flow Designated Forwarder Election for EVPN
draft-ietf-bess-evpn-per-mcast-flow-df-election-09

BESS WorkGroup                                              Ali. Sajassi
Internet-Draft                                         Mankamana. Mishra
Intended status: Standards Track                           Samir. Thoria
Expires: 11 January 2024                                   Cisco Systems
                                                          Jorge. Rabadan
                                                                   Nokia
                                                             John. Drake
                                                        Juniper Networks
                                                            10 July 2023

       Per multicast flow Designated Forwarder Election for EVPN
           draft-ietf-bess-evpn-per-mcast-flow-df-election-09

Abstract

   [RFC7432] describes mechanism to elect designated forwarder (DF) at
   the granularity of (ESI, EVI) which is per VLAN (or per group of
   VLANs in case of VLAN bundle or VLAN-aware bundle service).  However,
   the current level of granularity of per-VLAN is not adequate for some
   applications.[RFC8584] improves base line DF election by introducing
   HRW DF election.  [RFC9251] introduces applicability of EVPN to
   Multicast flows, routes to sync them and a default DF election.  This
   document is an extension to HRW base draft [RFC8584] and further
   enhances HRW algorithm for the Multicast flows to do DF election at
   the granularity of (ESI, VLAN, Mcast flow).

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 11 January 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  The DF Election Extended Community  . . . . . . . . . . . . .   4
   4.  HRW base per multicast flow EVPN DF election  . . . . . . . .   5
     4.1.  DF election for IGMP (S,G) membership request . . . . . .   6
     4.2.  DF election for IGMP (*,G) membership request . . . . . .   6
     4.3.  Default DF election procedure . . . . . . . . . . . . . .   7
   5.  Procedure to use per multicast flow DF election algorithm . .   7
   6.  Triggers for DF re-election . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  10
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   EVPN based All-Active multi-homing is becoming the basic building
   block for providing redundancy in next generation data center
   deployments as well as service provider access/aggregation networks.
   [RFC7432] defines the role of a designated forwarder as the node in
   the redundancy group that is responsible to forward Broadcast,
   Unknown unicast, Multicast (BUM) traffic on that Ethernet Segment (CE
   device or network) in All-Active multi-homing.

   The default DF election mechanism allows selecting a DF at the
   granularity of (ES, VLAN) or (ES, VLAN bundle) for BUM traffic.
   While [RFC8584] improve on the default DF election procedure, some
   service provider residential applications require a finer
   granularity, where whole multicast flows are delivered on a single
   VLAN.

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                               (Multicast sources)
                                        |
                                        |
                                      +---+
                                      |CE4|
                                      +---+
                                        |
                                        |
                                  +-----+-----+
                     +------------|   PE-1    |------------+
                     |            |           |            |
                     |            +-----------+            |
                     |                                     |
                     |                   EVPN              |
                     |                                     |
                     |                                     |
                     | (DF)                           (NDF)|
               +-----------+                        +-----------+
               |  |EVI-1|  |                        |  |EVI-1|  |
               |   PE-2    |------------------------|   PE-3    |
               +-----------+                        +-----------+
                      AC1  \                       / AC2
                            \                     /
                             \      ESI-1        /
                              \                 /
                               \               /
                               +---------------+
                               |    CE2        |
                               +---------------+
                                      |
                                      |
                             (Multiple receivers)

                   Figure 1: Multi-homing Network of EVPN
                             for IPTV deployments

   Consider the above topology, which shows a typical residential
   deployment scenario, where multiple receivers are behind an all-
   active multihoming segments.  All of the multicast traffic is
   provisioned on EVI-1.  Assume PE-2 get elected as DF.  According to
   [RFC7432], PE-2 will be responsible for forwarding multicast traffic
   to that Ethernet segment.

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   *  Forcing sole data plane forwarding responsibility on PE-2 is a
      limitation in the current DF election mechanism.  The topology at
      Figure 1 would always have only one of the PE to be elected as DF
      irrespective of which current DF election mechanism is in use
      defined in [RFC7432] or [RFC8584].

   *  The problem may also manifest itself in a different way.  For
      example, AC1 happens to use 80% of its available bandwidth to
      forward unicast data.  And now there is need to serve multicast
      receivers where it would require more than 20% of AC1 bandwidth.
      In this case, AC1 becomes oversubscribed and multicast traffic
      drop would be observed even though there is already another link
      (AC2) present in network which can be used more efficiently load
      balance the multicast traffic.

   In this document, we propose an extension to the HRW base draft to
   allow DF election at the granularity of (ESI, VLAN, Mcast flow) which
   would allow multicast flows to be better distributed among redundancy
   group PEs to share the load.

2.  Terminology

   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 [RFC2119] .

   With respect to EVPN, this document follows the terminology that has
   been defined in [RFC7432] and [RFC4601] for multicast terminology.

3.  The DF Election Extended Community

   [RFC8584] defines an extended community, which would be used for PEs
   in redundancy group to reach a consensus as to which DF election
   procedure is desired.  A PE can notify other participating PEs in
   redundancy group about its willingness to support Per multicast flow
   base DF election capability by signaling a DF election extended
   community along with Ethernet-Segment Route (Type-4).  The current
   proposal extends the existing extended community defined in
   [RFC8584].  This draft defines new a DF type.

   *  DF type (1 octet) - Encodes the DF Election algorithm values
      (between 0 and 255) that the advertising PE desires to use for the
      ES.  This document requests two new types in the DF type field:

      -  Type 4: HRW base per (S,G) multicast flow DF election
         (explained in this document)

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      -  Type 5: HRW base per (*,G) multicast flow DF election
         (explained in this document)

   *  The [RFC8584] describes encoding of capabilities associated to the
      DF election algorithm using Bitmap field.  When these capabilities
      bits are set along with the DF type-4 and type-5, they need to be
      interpreted in context of this new DF type-4 and type-5.  For
      example, consider a scenario where all PEs in the same redundancy
      group (same ES) can support both AC-DF, DF type-4 and DF type-5
      and receive such indications from the other PEs in the ES.  In
      this scenario, if a VLAN is not active in a PE, then the DF
      election procedure on all PEs in the ES should factor that in and
      exclude that PE in the DF election per multicast flow.

   *  A PE SHOULD attach the DF election Extended Community to ES route
      and Extended Community MUST be sent if the ES is locally
      configured for DF type Per Multicast flow DF election.  Only one
      DF Election Extended community can be sent along with an ES route.

   *  When a PE receives the ES Routes from all the other PEs for the
      ES, it checks if all of other PEs have advertised their desire to
      proceed by Per multicast flow DF election.  If all peering PEs
      have done so, it performs DF election based on Per multicast flow
      procedure.  But if:

      -  There is at least one PE which advertised route-4 ( AD per ES
         Route) which does not indicate its capability to perform Per
         multicast flow DF election.  OR

      -  There is at least one PE signaling single active in the AD per
         ES route

      it MUST be considered as an indication to support of only Default
      DF election [RFC7432] and DF election procedure in [RFC7432] MUST
      be used.

4.  HRW base per multicast flow EVPN DF election

   This document is an extension of [RFC8584], so this draft does not
   repeat the description of HRW algorithm itself.

   EVPN PE does the discovery of redundancy groups based on [RFC7432].
   If redundancy group consists of N peering EVPN PE nodes, after the
   discovery all PEs build an unordered list of IP address of all the
   nodes in the redundancy group.  The procedure defined in this draft
   does not require the list of PEs to be ordered.  Address [i] denotes
   the IP address of the [i]th EVPN PE in redundancy group where (0 < i
   <= N ).

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4.1.  DF election for IGMP (S,G) membership request

   The DF is the PE who has maximum weight for (S, G, V, Es) where

   *  S - Multicast Source

   *  G - Multicast Group

   *  V - VLAN ID.

   *  Es - Ethernet Segment Identifier

   Address[i] is address of the ith PE.  The PEs IP address length does
   not matter as only the lower-order 31 bits are modulo significant.

   1.  Weight

       *  The weight of PE(i) to (S,G,VLAN ID, Es) is calculated by
          function, weight (S,G,V, Es, Address(i)), where (0 < i <= N),
          PE(i) is the PE at ordinal i.

       *  Weight (S,G,V, Es, Address(i)) = (1103515245.
          ((1103515245.Address(i) + 12345) XOR D(S,G,V,ESI))+12345) (mod
          2^31)

       *  In case of tie, the PE whose IP address is numerically least
          is chosen.

   2.  Digest

       *  D(S,G,V, Es) = CRC_32(S,G,V, Es)

       *  Here D(S,G,V,Es) is the 31-bit digest (CRC_32 and discarding
          the MSB) of the Source IP, Group IP, Vlan ID and Es.  The CRC
          MUST proceed as if the architecture is in network byte order
          (big-endian).

4.2.  DF election for IGMP (*,G) membership request

   The DF is the PE who has maximum weight for (G, V, Es) where

   *  G - Multicast Group

   *  V - VLAN ID.

   *  Es - Ethernet Segment Identifier

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   Address[i] is address of the ith PE.  The PEs IP address length does
   not matter as only the lower-order 31 bits are modulo significant.

   1.  Weight

       *  The weight of PE(i) to (G,VLAN ID, Es) is calculated by
          function, weight (G,V, Es, Address(i)), where (0 < i <= N),
          PE(i) is the PE at ordinal i.

       *  Weight (G,V, Es, Address(i)) = (1103515245.
          ((1103515245.Address(i) + 12345) XOR D(G,V,ESI))+12345) (mod
          2^31)

       *  In case of tie, the PE whose IP address is numerically least
          is chosen.

   2.  Digest

       *  D(G,V, Es) = CRC_32(G,V, Es)

       *  Here D(G,V,Es) is the 31-bit digest (CRC_32 and discarding the
          MSB) of the Group IP, Vlan ID and Es.  The CRC MUST proceed as
          if the architecture is in network byte order (big-endian).

4.3.  Default DF election procedure

   Per multicast DF election procedure would be applicable only when
   host behind Attachment Circuit (of the Es) start sending IGMP
   membership requests.  Membership requests are synced using procedure
   defined in [RFC9251], and each of the PE in redundancy group can use
   per flow DF election and create DF state per multicast flow.  The HRW
   DF election "Type 1" procedure defined in [RFC8584] MUST be used for
   the Es DF election and SHOULD be performed on Es even before learning
   multicast membership request state.  This default election procedure
   MUST be used at port level but will be overwritten by Per flow DF
   election as and when new membership request state are learnt.

5.  Procedure to use per multicast flow DF election algorithm

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                                     Multicast  Source
                                             |
                                             |
                                             |
                                             |
                                         +---------+
                          +--------------+  PE-4   +--------------+
                          |              |         |              |
                          |              +---------+              |
                          |                                       |
                          |              EVPN CORE                |
                          |                                       |
                          |                                       |
                          |                                       |
                      +---------+        +---------+         +---------+
                      |  PE-1   +--------+   PE-2  +---------+   PE-3  |
                      |  EVI-1  |        |  EVI-1  |         | EVI-1   |
                      +---------+        +---------+         +---------+
                           |__________________|___________________|
                         AC-1    ESI-1        | AC-2               AC-3
                                         +---------+
                                         |  CE-1   |
                                         |         |
                                         +---------+
                                              |
                                              |
                                              |
                                              |
                                      Multicast Receivers

                      Figure-2 : Multihomed network

   Figure-2 shows multihomed network.  Where EVPN PE-1, PE-2, PE-3 are
   multihomed to CE-1.  Multiple multicast receivers are behind all
   active multihoming segment.

   1.  PEs connected to the same Ethernet segment can automatically
       discover each other through exchange of the Ethernet Segment
       Route.  This draft does not change any of this procedure, it
       still uses the procedure defined in [RFC7432].

   2.  Each of the PEs in redundancy group advertise Ethernet segment
       route with extended community indicating their ability to
       participate in per multicast flow DF election procedure.  Since
       Per multicast flow would not be applicable unless PE learns about
       membership request from receiver, there is a need to have the
       default DF election among PEs in redundancy group for BUM

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       traffic.  Until multicast membership state are learnt, we use the
       the DF election procedure in Section 4.3, namely HRW per (v,Es)
       as defined in [RFC8584] .

   3.  When a receiver starts sending membership requests for (s1,g1),
       where s1 is multicast source address and g1 is multicast group
       address, CE-1 could hash membership request (IGMP join) to any of
       the PEs in redundancy group.  Let's consider it is hashed to PE-
       2.  [RFC9251] defines a procedure to sync IGMP join state among
       redundancy group of PEs.  Now each of the PE would have
       information about membership request (s1,g1) and each of them run
       DF election procedure Section 4.1 to elect DF among participating
       PEs in redundancy group.  Consider PE-2 gets elected as DF for
       multicast flow (s1,g1).

       1.  PE-1 forwarding state would be nDF for flow (s1,g1) and DF
           for rest other BUM traffic.

       2.  PE-2 forwarding state would be DF for flow (s1,g1) and nDF
           for rest other BUM traffic.

       3.  PE-3 forwarding state would be nDF for flow (s1,g1) and rest
           other BUM traffic.

   4.  As and when new multicast membership request comes, same
       procedure as above would continue.

   5.  If Section 3 has DF type 4, For membership request (S,G) it MUST
       use Section 4.1 to elect DF among participating PEs.  And
       membership request (*,G) MUST use Section 4.2 to elect DF among
       participating PEs.

6.  Triggers for DF re-election

   There are multiple triggers which can cause DF re-election.  Some of
   the triggers could be

   1.  Local ES going down due to physical failure or configuration
       change triggers DF re-election at peering PE.

   2.  Detection of new PE through ES route.

   3.  AC going up / down

   4.  ESI change

   5.  Remote PE removed / Down

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   6.  Local configuration change of DF election Type and peering PE
       consensus on new DF Type

   This document does not provide any new mechanism to handle DF re-
   election procedure.  It uses the existing mechanism defined in
   [RFC7432].  Whenever either of the triggers occur, a DF re-election
   would be done. and all of the flows would be redistributed among
   existing PEs in redundancy group for ES.

7.  Security Considerations

   The same Security Considerations described in [RFC7432] are valid for
   this document.

8.  IANA Considerations

   Allocation of DF type in DF extended community for EVPN.

9.  Acknowledgement

   Authors would like to acknowledge helpful comments and contributions
   of Luc Andre Burdet.

10.  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>.

   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601,
              DOI 10.17487/RFC4601, August 2006,
              <https://www.rfc-editor.org/info/rfc4601>.

   [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, <https://www.rfc-editor.org/info/rfc7432>.

   [RFC8584]  Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
              J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
              VPN Designated Forwarder Election Extensibility",
              RFC 8584, DOI 10.17487/RFC8584, April 2019,
              <https://www.rfc-editor.org/info/rfc8584>.

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   [RFC9251]  Sajassi, A., Thoria, S., Mishra, M., Patel, K., Drake, J.,
              and W. Lin, "Internet Group Management Protocol (IGMP) and
              Multicast Listener Discovery (MLD) Proxies for Ethernet
              VPN (EVPN)", RFC 9251, DOI 10.17487/RFC9251, June 2022,
              <https://www.rfc-editor.org/info/rfc9251>.

Authors' Addresses

   Ali Sajassi
   Cisco Systems
   821 Alder Drive,
   MILPITAS, CALIFORNIA 95035
   United States
   Email: sajassi@cisco.com

   Mankamana Mishra
   Cisco Systems
   821 Alder Drive,
   MILPITAS, CALIFORNIA 95035
   United States
   Email: mankamis@cisco.com

   Samir Thoria
   Cisco Systems
   821 Alder Drive,
   MILPITAS, CALIFORNIA 95035
   United States
   Email: sthoria@cisco.com

   Jorge Rabadan
   Nokia
   777 E. Middlefield Road
   Mountain View, CA 94043
   United States
   Email: jorge.rabadan@nokia.com

   John Drake
   Juniper Networks
   Email: jdrake@juniper.net

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