PBB-EVPN ISID-based CMAC-Flush
draft-ietf-bess-pbb-evpn-isid-cmacflush-05

BESS Workgroup                                           J. Rabadan, Ed.
Internet-Draft                                              S. Sathappan
Intended status: Standards Track                              K. Nagaraj
Expires: 25 December 2022                                          Nokia
                                                               M. Miyake
                                                              T. Matsuda
                                                                Softbank
                                                            23 June 2022

                     PBB-EVPN ISID-based CMAC-Flush
               draft-ietf-bess-pbb-evpn-isid-cmacflush-05

Abstract

   Provider Backbone Bridging (PBB) can be combined with Ethernet VPN
   (EVPN) to deploy Ethernet Local Area Network (ELAN) services in large
   Multi-Protocol Label Switching (MPLS) networks (PBB-EVPN).  Single-
   Active Multi-homing and per-I-SID (per Service Instance Identifier)
   Load-Balancing can be provided to access devices and aggregation
   networks.  In order to speed up the network convergence in case of
   failures on Single-Active Multi-Homed Ethernet Segments, PBB-EVPN
   defines a flush mechanism for Customer MACs (CMAC-flush) that works
   for different Ethernet Segment Backbone MAC (BMAC) address allocation
   models.  This document complements those CMAC-flush procedures for
   cases in which no PBB-EVPN Ethernet Segments are defined (the
   attachment circuit is associated to a zero Ethernet Segment
   Identifier) and a Service Instance Identifier based (I-SID-based)
   CMAC-flush granularity is required.

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 25 December 2022.

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Copyright Notice

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology and Conventions . . . . . . . . . . . . . . .   4
   2.  Solution requirements . . . . . . . . . . . . . . . . . . . .   5
   3.  EVPN BGP Encoding for ISID-based CMAC-flush . . . . . . . . .   6
   4.  Solution description  . . . . . . . . . . . . . . . . . . . .   7
     4.1.  ISID-based CMAC-Flush activation procedures . . . . . . .   8
     4.2.  CMAC-Flush generation . . . . . . . . . . . . . . . . . .   8
     4.3.  CMAC-flush process upon receiving a CMAC-flush
           notification  . . . . . . . . . . . . . . . . . . . . . .   9
   5.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   [RFC7623] defines how Provider Backbone Bridging (PBB) can be
   combined with Ethernet VPN (EVPN) to deploy ELAN services in very
   large MPLS networks.  [RFC7623] also describes how Single-Active
   Multi-homing and per-I-SID Load-Balancing can be provided to access
   devices and aggregation networks.  When Access Ethernet/MPLS Networks
   exists, [I-D.ietf-bess-evpn-virtual-eth-segment] describes how
   virtual Ethernet Segments can be associated to a group of Ethernet
   Virtual Circuits (EVCs) or even Pseudowires (PWs).  In order to speed
   up the network convergence in case of failures on Single-Active
   Multi-Homed Ethernet Segments, [RFC7623] defines a CMAC-flush
   mechanism that works for different Ethernet Segment BMAC address

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   allocation models.

   In some cases, the administrative entities that manage the access
   devices or aggregation networks do not demand Multi-Homing Ethernet
   Segments (ES) from the PBB-EVPN provider, but simply multiple single-
   homed ES.  If that is the case, the PBB-EVPN network is no longer
   aware of the redundancy offered by the access administrative entity.
   Figure 1 shows an example where the PBB-EVPN network provides four
   different Attachment Circuits (ACs) for I-SID1, with those ACs not
   being part of any ES or vES (therefore they are referred to as null
   vES).

        <----G.8032--><--PBB-EVPN Network---><----MPLS---->
             Access          MPLS                Access
              Ring                               Network
        I-SID1    ESI +-----+         +-----+
        +----+    null| PE1 |---------| PE3 |
        |CE1 |--------|BMAC1|         |BMAC3| ESI null
        +----+  active|     |         |     |----+ PW
          |           +-----+         +-----+     \active
          |             |                 |        \  +----+
          |             |                 |         ==|CE3 |I-SID1
          |             |                 |        /  +----+
          |stb    ESI +-----+         +-----+     / PW
        +----+    null| PE2 |         | PE4 |----+ standby
        |CE2 |--------|BMAC2|         |BMAC4| ESI null
        +----+  active|     |---------|     |
        I-SID1        +-----+         +-----+

               Figure 1: PBB-EVPN and non-ES based redundancy

   In the example in Figure 1, CE1, CE2 and CE3 are attached to the same
   service, identified by I-SID1, in the PBB-EVPN PEs.  CE1 and CE2 are
   connected to the PEs via G.8032 Ethernet Ring Protection Switching,
   and their ACs to PE1 and PE2 are represented by a port and VLAN
   identifier.  CE3 is dual-homed to PE3 and PE4 through an active-
   standby PW, and its AC to the PEs is represented by a PW.  Each of
   the four PEs uses a dedicated BMAC address as source MAC address
   (BMAC1, BMAC2, BMAC3 and BMAC4, respectively) when encapsulating
   customer frames in PBB packets and forwarding those PBB packets to
   the remote PEs as per [RFC7623].  There are no multi-homed Ethernet
   Segments defined in the PBB-EVPN network of the example, that is why
   the four ACs in Figure 1 show the text "ES null", which means the
   Ethernet Segment Identifier on those ACs is zero.  Since there are no
   multi-homed ES defined, the PEs keep their ACs active as long as the
   physical connectivity is established and the CEs are responsible for
   managing the redundancy, avoiding loops and providing per-I-SID load
   balancing to the PBB-EVPN network.

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   For instance, CE2 will block its link to CE1 and CE3 will block its
   forwarding path to PE4.  In this situation, a failure in one of the
   redundant ACs will trigger the CEs to start using their redundant
   paths, however those failures will not trigger any CMAC-flush
   procedures in the PEs that implement [RFC7623], since the PEs are not
   using the PBB-EVPN multi-homing procedures.  For example, if the
   active PW from CE3 (to PE3) fails, PE3 will not issue any CMAC-flush
   message and therefore the remote PEs will continue pointing at PE3's
   BMAC to reach CE3's CMACs, until the CMACs age out in the I-SID1
   forwarding tables.

   [RFC7623] provides a CMAC-flush solution based on a shared BMAC
   update along with the MAC Mobility extended community where the
   sequence number is incremented.  However, the procedure is only used
   along with multi-homed Ethernet Segments.  Even if that procedure
   could be used for null Ethernet Segments, as in the example of
   Figure 1, the [RFC7623] CMAC-flush procedure would result in
   unnecessary flushing of unaffected I-SIDs on the remote PEs, and
   subsequent flooding of unknown unicast traffic in the network.

   This document describes an extension of the [RFC7623] CMAC-flush
   procedures, so that in the above failure example, PE3 can trigger a
   CMAC-flush notification that makes PE1, PE2 and PE4 flush all the
   CMACs associated to PE3's BMAC3 and (only) I-SID1.  This new CMAC-
   flush procedure explained in this document will be referred to as
   "PBB-EVPN I-SID-based CMAC-flush" and can be used in PBB-EVPN
   networks with null or non-null (virtual) Ethernet Segments.

1.1.  Terminology and Conventions

   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.

   AC: Attachment Circuit.

   B-Component: Backbone Component, as in [RFC7623].

   BMAC: Backbone MAC address.

   BMAC/0 route: an EVPN MAC/IP Advertisement route that uses a BMAC in
   the MAC address field and a zero Ethernet Tag ID.

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   BMAC/I-SID route: an EVPN MAC/IP Advertisement route that uses a BMAC
   in the MAC address field and an I-SID in the Ethernet Tag field, and
   it is used to notify remote PEs about the required CMAC-flush
   procedure for the CMACs associated with the advertised BMAC and
   I-SID.

   CE: Customer Edge router.

   CMAC: Customer MAC address.

   ES, vES and ESI: Ethernet Segment, virtual Ethernet Segment and
   Ethernet Segment Identifier.

   EVI: EVPN Instance.

   EVPN: Ethernet Virtual Private Networks, as in [RFC7432].

   G.8032: Ethernet Ring Protection.

   I-Component: Service Instance Component, as in [RFC7623].

   I-SID: Service Instance Identifier.

   MAC-VRF: A Virtual Routing and Forwarding table for MAC addresses.

   PBB-EVPN: Provider-Backbone-Bridging and EVPN, as in [RFC7623].

   PE: Provider Edge router.

   RD: Route Distinguisher.

   RT: Route Target.

   Familiarity with the terminology in [RFC7623] is expected.

2.  Solution requirements

   The following requirements are followed by the CMAC-flush solution
   described in this document:

   a.  The solution solves black-hole scenarios in case of failures on
       null ES ACs (Attachment Circuits not associated to ES, that is,
       ESI=0) when the access device/network is responsible for the
       redundancy.

   b.  This extension works with Single-Active non-null ES and virtual
       ES, irrespective of the PE BMAC address assignment (dedicated
       per-ES BMAC or shared BMAC, as in [RFC7623]).

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   c.  In case of failure on the egress PE, the solution provides a
       CMAC-flush notification at BMAC and I-SID granularity level.

   d.  The solution provides a reliable CMAC-flush notification in PBB-
       EVPN networks that use Route-Reflectors (RRs), without causing
       "double flushing" or no flushing for certain I-SIDs due to the
       notification messages being aggregated at the RR.

   e.  The solution coexists in [RFC7623] networks where there are PEs
       that do not support this specification.

   f.  The solution SHOULD be enabled/disabled by an administrative
       option on a per-PE and per-I-SID basis.

3.  EVPN BGP Encoding for ISID-based CMAC-flush

   The solution does not use any new BGP attributes but reuses the MAC
   Mobility extended community as an indication of CMAC-flush (as in
   [RFC7623]) and encodes the I-SID in the Ethernet Tag field of the
   EVPN MAC/IP advertisement route.  As a reference, Figure 2 shows the
   MAC Mobility extended community and the EVPN MAC/IP advertisement
   route that are used specified in [RFC7432] and used in this document
   as a CMAC-flush notification message.

   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type=0x06     | Sub-Type=0x03 |   Flags       |   Reserved=0  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Sequence Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               +---------------------------------------+
               |  RD                                   |
               +---------------------------------------+
               |  ESI = 0                              |
               +---------------------------------------+
               |  Ethernet Tag ID = I-SID              |
               +---------------------------------------+
               |  MAC Address Length = 48              |
               +---------------------------------------+
               |  BMAC Address                         |
               +---------------------------------------+
               |  IP Address Length = 0                |
               +---------------------------------------+
               |  MPLS Label1                          |
               +---------------------------------------+

        Figure 2: CMAC-Flush notification encoding: BMAC/ISID route

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   Where:

   *  The route's RD and RT are the ones corresponding to its EVI.
      Alternatively to the EVI's RT, the route MAY be tagged with an RT
      auto-derived from the Ethernet Tag (I-SID) instead.  [RFC7623]
      describes how the EVPN MAC/IP Advertisement routes can be
      advertised along with the EVI RT or an RT that is derived from the
      I-SID.

   *  The Ethernet Tag encodes the I-SID for which the PE that receives
      the route must flush the CMACs upon reception of the route.

   *  The MAC address field encodes the BMAC Address for which the PE
      that receives the route must flush the CMACs upon reception of the
      route.

   *  The MAC Mobility extended community is used as in [RFC7623], where
      a delta in the sequence number between two updates for the same
      BMAC/I-SID will be interpreted as a CMAC-flush notification for
      the corresponding BMAC and I-SID.

   All the other fields are set and used as defined in [RFC7623].  This
   document will refer to this route as the BMAC/I-SID route, as opposed
   to the [RFC7623] BMAC/0 route (BMAC route sent with Ethernet Tag ID =
   0).

   Note that this BMAC/I-SID route will be accepted and reflected by any
   [RFC7432] RR, since no new attributes or values are used.  A PE
   receiving the route will process the received BMAC/I-SID update only
   in case of supporting the procedures described in this document.

4.  Solution description

   Figure 1 will be used in the description of the solution.  CE1, CE2
   and CE3 are connected to ACs associated to I-SID1, where no (Multi-
   Homed) Ethernet Segments have been enabled, and the ACs and PWs are
   in active or standby state as per Figure 1.

   Enabling or disabling I-SID-based CMAC-flush SHOULD be an
   administrative choice on the system that MAY be configured per I-SID
   (I-Component).  When enabled on a PE:

   a.  The PE will be able to generate BMAC/I-SID routes as CMAC-Flush
       notifications for the remote PEs.

   b.  The PE will be able to process BMAC/I-SID routes received from
       remote PEs.

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   When I-SID-based CMAC-flush is disabled, the PE will follow the
   [RFC7623] procedures for CMAC-flush.

   This CMAC-flush specification is described in three sets of
   procedures:

   *  I-SID-based CMAC-flush activation

   *  CMAC-flush notification generation upon AC failures

   *  CMAC-flush process upon receiving a CMAC-flush notification

4.1.  ISID-based CMAC-Flush activation procedures

   The following behavior MUST be followed by the PBB-EVPN PEs following
   this specification.  Figure 1 is used as a reference.

   *  As in [RFC7623], each PE advertises a shared BMAC in a BMAC/0
      route (with BMAC1, BMAC2, BMAC3 and BMAC4 in the MAC address
      field, respectively).  This is the BMAC that each PE will use as
      BMAC SA (Source Address) when encapsulating the frames received on
      any local single-homed AC.  Each PE will import the received
      BMAC/0 routes from the remote PEs and will install the BMACs in
      its B-component MAC-VRF.  For instance, PE1 will advertise BMAC1/0
      and will install BMAC2, BMAC3 and BMAC4 in its MAC-VRF.

   *  Assuming I-SID-based CMAC-flush is activated for I-SID 1, the PEs
      will advertise the shared BMAC with I-SID 1 encoded in the
      Ethernet Tag. That is, PE1 will advertise BMAC1/1 and will receive
      BMAC2/1, BMAC3/1 and BMAC4/1.  The receiving PEs MUST use these
      BMAC/I-SID routes only for CMAC-flush procedures and they MUST NOT
      be used them to add/withdraw any BMAC entry in the MAC-VRFs.  As
      per [RFC7623], only BMAC/0 routes can be used to add/withdraw
      BMACs in the MAC-VRFs.

   *  The above procedure MAY also be used for dedicated BMACs (BMACs
      allocated per Ethernet Segment).

4.2.  CMAC-Flush generation

   If, for instance, there is a failure on PE1's AC, PE1 will generate
   an update including BMAC1/1 along with the MAC Mobility extended
   community where the Sequence Number has been incremented.  The
   reception of the BMAC1/1 with a delta in the sequence number will
   trigger the CMAC-flush procedures on the receiving PEs.

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   *  An AC going operationally down MUST generate a BMAC/I-SID with a
      higher Sequence Number.  If the AC going down makes the entire
      local I-SID go operationally down, the PE will withdraw the BMAC/
      I-SID route for the I-SID.

   *  An AC going operationally up SHOULD NOT generate any BMAC/I-SID
      update, unless it activates its corresponding I-SID, in which case
      the PE will advertise the BMAC/I-SID route.

   *  An AC receiving a G.8032 flush notification or a flush message in
      any other protocol from the access network MAY propagate it to the
      remote PEs by generating a BMAC/I-SID route update with higher
      Sequence Number.

4.3.  CMAC-flush process upon receiving a CMAC-flush notification

   A PE receiving a CMAC-flush notification will follow these
   procedures:

   *  A received BMAC/I-SID route (with non-zero I-SID) MUST NOT add/
      remove any BMAC to/from the MAC-VRF.

   *  An update of a previously received BMAC/I-SID route with a delta
      Sequence Number, MUST flush all the CMACs associated to that I-SID
      and BMAC.  CMACs associated to the same I-SID but different BMAC
      MUST NOT be flushed.

   *  A received BMAC/I-SID withdraw (with non-zero I-SID) MUST flush
      all the CMACs associated to that BMAC and I-SID.

   Note that the CMAC-flush procedures described in [RFC7623] for BMAC/0
   routes are still valid and a PE receiving [RFC7623] CMAC-flush
   notification messages MUST observe the behavior specified in
   [RFC7623].

5.  Conclusions

   The I-SID-based CMAC-flush solution described in this document has
   the following benefits:

   a.  The solution solves black-hole scenarios in case of failures on
       null ES ACs, since the CMAC-flush procedures are independent of
       the Ethernet Segment definition.

   b.  This extension can also be used with Single-Active non-null ES
       and virtual ES, irrespective of the PE BMAC address assignment
       (dedicated per-ES BMAC or shared BMAC).

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   c.  It provides a CMAC-flush notification at BMAC and I-SID
       granularity level, therefore flushing a minimum number of CMACs
       and reducing the amount of unknown unicast flooding in the
       network.

   d.  It provides a reliable CMAC-flush notification in PBB-EVPN
       networks that use RRs.  RRs will propagate the CMAC-flush
       notifications for all the affected I-SIDs and irrespective of the
       order in which the notifications make it to the RR.

   e.  The solution can coexist in a network with systems supporting or
       not supporting this specification.

6.  Security Considerations

   Security considerations described in [RFC7623] apply to this
   document.

   In addition, this document suggests additional procedures, that can
   be activated on a per I-SID basis, and generate additional EVPN MAC/
   IP Advertisement routes in the network.  The format of these
   additional EVPN MAC/IP Advertisement routes is backwards compatible
   with [RFC7623] procedures and should not create any issues on
   receiving PEs not following this specification, however, the
   additional routes may consume extra memory and processing resources
   on the receiving PEs.  Because of that, it is RECOMMENDED to activate
   this feature only when necessary (when multi-homed networks or
   devices are attached to the PBB-EVPN PEs), and not by default in any
   PBB-EVPN PE.

7.  IANA Considerations

8.  Acknowledgments

   The authors want to thank Vinod Prabhu, Sriram Venkateswaran, Laxmi
   Padakanti, Ranganathan Boovaraghavan for their review and
   contributions.

9.  Contributors

10.  References

10.1.  Normative References

   [RFC7623]  Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
              Henderickx, "Provider Backbone Bridging Combined with
              Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
              September 2015, <https://www.rfc-editor.org/info/rfc7623>.

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   [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>.

   [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>.

   [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>.

10.2.  Informative References

   [I-D.ietf-bess-evpn-virtual-eth-segment]
              Sajassi, A., Brissette, P., Schell, R., Drake, J. E., and
              J. Rabadan, "EVPN Virtual Ethernet Segment", Work in
              Progress, Internet-Draft, draft-ietf-bess-evpn-virtual-
              eth-segment-07, 6 July 2021,
              <https://www.ietf.org/archive/id/draft-ietf-bess-evpn-
              virtual-eth-segment-07.txt>.

Authors' Addresses

   Jorge Rabadan (editor)
   Nokia
   520 Almanor Avenue
   Sunnyvale, CA 94085
   United States of America
   Email: jorge.rabadan@nokia.com

   Senthil Sathappan
   Nokia
   520 Almanor Avenue
   Sunnyvale, CA 94085
   United States of America
   Email: senthil.sathappan@nokia.com

   Kiran Nagaraj
   Nokia
   520 Almanor Avenue
   Sunnyvale, CA 94085
   United States of America
   Email: kiran.nagaraj@nokia.com

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   M. Miyake
   Softbank
   Email: masahiro.miyake@g.softbank.co.jp

   T. Matsuda
   Softbank
   Email: taku.matsuda@g.softbank.co.jp

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