Context Label for MPLS EVPN
draft-wang-bess-evpn-context-label-00

BESS WG                                                      Yubao. Wang
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                        January 17, 2020
Expires: July 20, 2020

                      Context Label for MPLS EVPN
               draft-wang-bess-evpn-context-label-00.txt

Abstract

   EVPN is designed to provide a better VPLS service than [RFC4761] and
   [RFC4762],and EVPN indeed introduced many new features which couldn't
   be achieved in those old VPLS implementions.But EVPN didn't inherit
   all features of old VPLS, and a few issues arises for EVPN only.

   Some of these issues can be imputed to the MP2P nature of EVPN
   labels.The PW label in old VPLS is a label for P2P VC, so it contains
   more context than a identifier in dataplane for it's VSI instance.But
   the EVPN label just identifies it's VSI instnace and it can't stand
   for the ingress PE in dataplane.  So the following issues arises with
   MPLS EVPN service:

   MPLS EVPN statistics can't be done per ingress PE.

   MPLS EVPN can't support hub/spoke use case which the spoke PE can
   only connect to each other by the hub PE.

   MPLS EVPN can't support AR REPLICATOR.

   MPLS EVPN can't support anycast SR-MPLS tunnel on the SPE nodes.

   This document introduces a compound label stack to take advantage of
   both P2P VC and MP2P evpn labels.

Status of This Memo

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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 20, 2020.

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Table of Contents

   1.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Context VC Infrastructure . . . . . . . . . . . . . . . . . .   3
     2.1.  Context VC Signalling . . . . . . . . . . . . . . . . . .   4
       2.1.1.  Kompella Signalling for context VC  . . . . . . . . .   4
       2.1.2.  SR-MPLS signalling for context VC . . . . . . . . . .   4
   3.  Solutions . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Solution for spoke PE isolating on hub PE . . . . . . . .   5
     3.2.  Solution for per ingress statistics . . . . . . . . . . .   6
     3.3.  Solution for AR REPLICATOR in MPLS EVPN . . . . . . . . .   6
     3.4.  Solution for anycast tunnel usage on SPE  . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Problem Statement

   EVPN is designed to provide a better VPLS service than RFC4761/
   RFC4762, and EVPN indeed introduced many new features which couldn't
   be achieved in those old VPLS implemention.But EVPN didn't inherit
   all features of old VPLS, and a few issues arises for EVPN only.

   Some of these issues can be imputed to the MP2P nature of EVPN
   labels.The PW label in old VPLS is a label for P2P VC, so it contains
   more context than a identifier in dataplane for it's VSI instance.But
   the EVPN label just identifies it's VSI instnace and it can't stand

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   for the ingress PE in dataplane.  So the following issues arises with
   MPLS EVPN service:

   MPLS EVPN statistics can't be done per ingress PE.  All flows from
   remote PEs share the same statistics on egress PE, because they share
   the same EVPN label and the egress PE can't pick them out in the
   dataplane.

   MPLS EVPN can't support hub/spoke usecase, where the spoke PEs can
   only connect to each other through the hub PE.Especially when at
   least two of the spoke PEs are connected to a common route reflector.

   MPLS EVPN can't work as an AR-REPLICATOR.  Because the AR-REPLICATOR
   will apply replication for the ingress AR-LEAF too.but a packet shoud
   not be sent back to the AR-LEAF where it is received from.

   MPLS EVPN SPE cannot make use of SR-MPLS anycast tunnel because the
   two SPEs of the anycast tunnel will assign different EVPN labels for
   the same EVPN route.

   So this document introduces an compound label stack to take advantage
   of both P2P VC and MP2P evpn labels.

2.  Context VC Infrastructure

   In order to add as much context as old VPLS to EVPN data packet, We
   can construct a infrastructure by a full-mesh of context VCs among
   the EVPN PEs.

   Take the context VCs between PE-i and PE-j as an example, VC-ij is
   the context VC from PE-i to PE-j, and VC-ji is the context VC from
   PE-j to PE-i.  The VC-ij identifies the PE-i node on PE-j.  The VC-ji
   identifies PE-j node on PE-i.  The VC-label for VC-ij is called as
   L-ij, and the VC-label for VC-ji is called as L-ji.

   So the PE-i can push the L-ij in the EVPN data packet for PE-j to
   distinguish the packet of PE-i from other data packets.  Because the
   L-ij identifies the ingress PE of the data packet.  In other words,
   the context VC is dedicated to identifies the context for a data
   packet while the EVPN label still identifies the EVPN instance.

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             +---------------------------------+
             |  underlay ethernet header       |
             +---------------------------------+
             |  PSN tunnel label               |
             +---------------------------------+
             |  EVPN label                     |
             +---------------------------------+
             |  Context VC Label               |
             +---------------------------------+
             |  overlay ethernet or IP header  |
             +---------------------------------+

       Figure 1: Encapsulation of Context VC Label for EVPN Payload

   Note that typically a context VC can be shared by all the EVPN
   instances between it's ingress PE and egress PE.  In other words, we
   don't have to construct a dedicated mesh of context VCs for each
   specified EVPN service.  So we called the shared context VCs as a
   common infrastructure for those EVPN services.

2.1.  Context VC Signalling

   The VCs of a context VC infrastructure are set up by a context VC
   container, the container implements a VC signalling to set up the
   VCs.  There are two existing signalling protocol can be reused to set
   up context VCs for a context VC container.

2.1.1.  Kompella Signalling for context VC

   The signalling used by a Kompella VPLS instance per [RFC4761] can
   also be used by a context VC container.

   Different from the Kompella VPLS instance, a context VC container
   only use the signalling to set up the context VCs.  They are the same
   in signalling but different in dataplane.  Take the PW between PE-i
   and PE-j as an example, it is constructed by VC-ij and VC-ji, and
   none of the two context VCs will identify a MAC-VRF.  In other words
   the PW is a context PW.

   Note that the context VC containers don't have a MAC-VRF or a MAC-
   table, they are just containers for context VC.

2.1.2.  SR-MPLS signalling for context VC

   SR-MPLS signalling is very similar to the singleton pattern of
   Kompella VPLS, in spite of their different data plane and service
   procedure.  The SID is similar to the VE-ID, the SRGB is similar to
   the label block.

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   So the constructed LSPs of the SR-MPLS signalling can be
   reinterpreted as context VCs in another label space named S.  These
   context VCs use the same label values as those SR-LSPs but they are
   constructed at the same time in different label spaces.  Take the VC-
   ij as an example, its label value L-ij is the same as the SID label
   for PE-i in PE-j's SRGB.  But the VC-ij are constructed in the
   context label space S which is identified by a static label. it is
   not constructed in the same label space with that SID label.

   The context VC signalling may be [RFC8665], [RFC8666], [RFC8667].
   The context VC may be established along with SR-LSPs.

            +---------------------------------+
            |  underlay ethernet header       |
            +---------------------------------+
            |  PSN tunnel label               |
            +---------------------------------+
            |  EVPN label                     |
            +---------------------------------+
            |  Static Label for Label Space S |
            +---------------------------------+
            |  Context VC Label               |
            +---------------------------------+
            |  overlay ethernet or IP header  |
            +---------------------------------+

    Figure 2: Encapsulation of Context VC Label in Context Label Space

   Note that the static label S is the context label for L-ij, while the
   L-ij is the context label for the data packet.

3.  Solutions

3.1.  Solution for spoke PE isolating on hub PE

              PEs1--------RR1--------PEh---------RR2--------PEs3
                          /
              PEs2-------/

                     Figure 3: Hub PE and Spoke PEs

   Now take above use case for example, there are three spoke PEs and
   one hub PE.  The spoke PEs are PEs1, PEs2 and PEs3.  The hub PE is
   PEh.  Two of the spoke PEs (PEs1 and PEs2) are connected to the same
   RR group and the third one connects to another RR group.

   Although we can advertise different EVPN labels for different RR
   groups, we can't advertise different EVPN labels for PEs1 and PEs2.

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   But PEh can request PEs1 or PEs2 to push the label of the context VC
   from it to PEh.  Benefit from the context VC label, PEh can
   distinguish where the packet from, in other words, PEh can decide
   where the packet can't be sent to.

   The signaling for the hub PE to request the spoke PE to push the
   context VC label will be added in future versions.

   Note that although PEs1 and PEs2 can receive EVPN routes from each
   other they won't import these routes because of the hub/spoke
   behaviors.

3.2.  Solution for per ingress statistics

   This section will be added in future versions.

3.3.  Solution for AR REPLICATOR in MPLS EVPN

   This section will be added in future versions.

3.4.  Solution for anycast tunnel usage on SPE

                         /--------SPE1-------\
                       TPE1                   TPE2
                         \--------SPE2-------/

                       Figure 4: SPE with Anycast Tunnel

   Now take above use case for example, the two SPEs are the egress
   nodes of an anycast SR-MPLS tunnel.  The anycast SR-MPLS tunnel is
   used to transport flows from TPE1 to either SPE1 or SPE2 according to
   load balancing procedures.  So SPE1 and SPE2 have to advertise the
   same EVPN label independently for a given EVPN route.

   In fact, SPE1 and SPE2 can simply inherit the EVPN label from TPE2,
   and they advertise it to TPE1 along with a context VC label.  The
   context VC label is for the context VC from TPE2 to SPE1 or SPE2.  We
   can make the VC labels from TPE2 to SPE1 and SPE2 have the same value
   through configuring.

   And the label stack on the anycast SR-MPLS tunnel is constructed as
   the following:

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                +---------------------------------+
                |  underlay ethernet header       |
                +---------------------------------+
                |  Anycast SR-MPLS tunnel label   |
                +---------------------------------+
                |  Static Label for Label Space S |
                +---------------------------------+
                |  Context VC Label               |
                +---------------------------------+
                |  EVPN label                     |
                +---------------------------------+
                |  overlay ethernet or IP header  |
                +---------------------------------+

        Figure 5: Encapsulation of Context VC Label for EVPN Label

   Note that the context VC is also constructed in a context label
   space, the label space is identified by a static label.  And the
   context label space is identified by the same label on all PEs of the
   service domain. so the label stacks on the anycast tunnel are the
   same for SPE1 and SPE2.

   SPE1/SPE2 will perform ILM lookup for the EVPN label in the label
   space identified by the context VC label.

4.  Security Considerations

   This section will be added in future versions.

5.  IANA Considerations

   There is no IANA consideration.

6.  Normative References

   [RFC4761]  Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
              LAN Service (VPLS) Using BGP for Auto-Discovery and
              Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
              <https://www.rfc-editor.org/info/rfc4761>.

   [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>.

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   [RFC8665]  Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
              H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", RFC 8665,
              DOI 10.17487/RFC8665, December 2019,
              <https://www.rfc-editor.org/info/rfc8665>.

   [RFC8666]  Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
              for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
              December 2019, <https://www.rfc-editor.org/info/rfc8666>.

   [RFC8667]  Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
              Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
              Extensions for Segment Routing", RFC 8667,
              DOI 10.17487/RFC8667, December 2019,
              <https://www.rfc-editor.org/info/rfc8667>.

Author's Address

   Yubao Wang
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: wang.yubao2@zte.com.cn

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