Context Label for MPLS EVPN
draft-wang-bess-evpn-context-label-01

BESS WG                                                          Y. Wang
Internet-Draft                                                   B. Song
Intended status: Standards Track                         ZTE Corporation
Expires: December 9, 2020                                   June 7, 2020

                      Context Label for MPLS EVPN
                 draft-wang-bess-evpn-context-label-01

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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any

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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 December 9, 2020.

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Table of Contents

   1.  Terminology and Acronyms  . . . . . . . . . . . . . . . . . .   3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Context VC Infrastructure . . . . . . . . . . . . . . . . . .   4
     3.1.  The Shared Context VCs  . . . . . . . . . . . . . . . . .   4
       3.1.1.  Signalling for Shared Context VCs . . . . . . . . . .   5
     3.2.  The per-EVI Context VCs . . . . . . . . . . . . . . . . .   6
       3.2.1.  Signalling for per-EVI Context VCs  . . . . . . . . .   6
   4.  Solutions . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Solution for spoke PE isolating on hub PE . . . . . . . .   7
     4.2.  Solution for per ingress statistics . . . . . . . . . . .   8
       4.2.1.  Signalling using Context Label Space ID Extended
               Community . . . . . . . . . . . . . . . . . . . . . .   8
       4.2.2.  Signalling using Label of Context-Label-Space
               Extended Community  . . . . . . . . . . . . . . . . .   9
     4.3.  Solution for AR REPLICATOR in MPLS EVPN . . . . . . . . .   9
     4.4.  Solution for anycast tunnel usage on SPE  . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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1.  Terminology and Acronyms

   This document uses the following acronyms and terms:

   BUM - Broadcast, Unknown unicast, and Multicast.

   CE - Customer Edge equipment.

   OPE - Originating PE - the original Router of an EVPN route.

   PE - Provider Edge equipment.

   ORIP - Originating Router's IP address.

   PTA - PMSI Tunnel Attribute.

   IR - Ingress Replication.

   AR - Assisted Replication.

   IR PTA - PMSI Tunnel Attribute with tunnel-type = IR.

   AR PTA - PMSI Tunnel Attribute with tunnel-type = AR.

   IRL - Ingress Replication List, the list for Ingress-Replication BUM
   packets forwarding.

   LS - Label Space.

   CLS - Context Label Space.

2.  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 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

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   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.

3.  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.

   There are two styles of context VC in this draft.  One style is named
   as shared context VC, the other style is named per-EVI context VC.

3.1.  The Shared Context VCs

   The shared context VCs are dedicated to identify the context for a
   data packet while the EVPN label still identifies the EVPN instance.
   Note that typically a shared 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.

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3.1.1.  Signalling for Shared Context VCs

   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.

3.1.1.1.  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.

3.1.1.2.  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.

   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.

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

    Figure 1: 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.

3.2.  The per-EVI Context VCs

   The per-EVI context VCs are used to identify both the context
   (typically the ingress-PE) and the EVPN instance for a data packet at
   the same time.  In other words, we have to construct a dedicated set
   of per-EVI context VCs for each specified EVPN service.

3.2.1.  Signalling for per-EVI Context VCs

   The IMET route per [RFC7432] have a corresponding route-type in MVPN.
   It is, in effect, the Intra-AS I-PMSI route per [RFC6514].  But an
   IMET route with Ingress Replication (IR) tunnel type PMSI Tunnel
   Attribute (PTA) doesn't need a responding Leaf A-D route.  The Leaf
   A-D route per [I-D.ietf-bess-evpn-bum-procedure-updates] is required
   for P2MP PTA only.  In this draft, we use the Leaf A-D route with IR-
   PTA to construct per-EVI context-VCs.

3.2.1.1.  Construct Leaf A-D Route for IR

   PE1 will construct a Leaf A-D route with IR-PTA for EVI1 in response
   to an IMET route R1 with IR-PTA.  The IMET route R1 is received from
   PE2 previously.  The key fields of the IMET route is included in the
   "Route Type specific" fields of the Leaf A-D route (say R2) along
   with the ORIP of PE1 itself.  We call the ORIP of PE1 itself as the
   Leaf A-D route's "self-ORIP" in order to distinguish it from the
   "Route Type specific" ORIP.  So the key fields of the Leaf A-D route
   is per <EVI1,PE2> basis.

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   The MPLS label field in the IR-PTA of the Leaf A-D route is allocated
   per <EVI1,PE2> basis in per-platform label space.  So the per-EVI
   context VC can identify the EVI1 too.

   Note that PE1 may already advertise an IMET route R3 to PE2 before
   the advertisement of above Leaf A-D route.  Note that the MPLS label
   field in the IR-PTA of R2 (Leaf A-D) may be the same label in the IR-
   PTA of R3 (IMET) either.  In such case, the IR-PTA is included in the
   Leaf A-D route along with a "Context Label Space (CLS) ID Extended
   Community" per [I-D.ietf-bess-mvpn-evpn-aggregation-label].  The ID-
   type field of the CLS-ID EC is 0, the ID-Value field of the CLS-ID EC
   is a label of "Shared Context VC" Label.

3.2.1.2.  Construct Ingress Replication List by Leaf A-D Route

   PE2 receives the responding Leaf A-D route (say R2) of the IMET route
   R1 which is previously advertised by itself, and PE2 preiously
   received an IMET route R3 with the same ORIP as the self-ORIP of R2 .
   Given that R1,R2 and R3 both have a IR-PTA, PE2 SHOULD use R2 to
   construct the Ingress Replication List (IRL) item for PE1 instead,
   and R3 will not used to construct the IRL-item for PE1 from then on.

   Note that when R2 included a CLS-ID EC, the ID-value of the CLS-ID EC
   will be used as outgoing label by the IRL-item.  It will be used as
   the context label of the MPLS label of the IR-PTA.

4.  Solutions

4.1.  Solution for spoke PE isolating on hub PE

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

                      Figure 2: 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.

   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

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   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.

4.2.  Solution for per ingress statistics

   The EVPN label is allocated from per-platform label space, and it
   identifies the EVPN instance as per [RFC7432].  But it also
   identifies a context label space LS1.

4.2.1.  Signalling using Context Label Space ID Extended Community

   The signalling in Section 3.2.1.1 with CLS-ID EC will be used.

   But the ID-value in CLS-ID EC is the EVPN Label, and the IR-PTA label
   of the Leaf A-D route will be allocated in LS1 per TPE basis, and it
   is actually the context VC label.  So the context VC label need to be
   pushed to the label stack before the EVPN Label.  Such encapsulation
   is illustrated as the following figure:

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

       Figure 3: Encapsulation of Context VC Label for EVPN Payload

   Note that the Context VC Label here is not the CLS-ID of the EVPN
   Label.  But the EVPN label is the CLS-ID of the Context VC Label.
   And the label space LS1 may be actually the per-platform label space.

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4.2.2.  Signalling using Label of Context-Label-Space Extended Community

   Note that when the label space LS1 is actually the per-platform label
   space, and PE1 send a Leaf A-D route with CLS-ID EC to PE2, but PE2
   don't recognize the CLS-ID EC, then PE2 will encapsulate the context
   VC label without the EVPN label.  This will cause packet drop.

   So we introduce a new EC called Label of CLS (LoCLS) EC, the LoCLS EC
   has the same format as the CLS-ID EC except for a different code-
   point of it's "sub-type" field.  The ID-Value of the LoCLS EC is a
   MPLS label in a context label space identified by the PTA label.  And
   the MPLS label in LoCLS EC will be pushed to the label stack before
   the PTA label by the ingress PE.  Typically, the MPLS label of the
   LoCLS EC is a downstream assigned label, which means that it will be
   used as outgoing label by the PE receiving the LoCLS EC, not as
   incomming label.

   When constructing the Leaf A-D route, the IR-PTA label is the EVPN
   Label, as per [RFC7432].  But the ID-value in LoCLS ES is a label
   which is allocated in LS1 per TPE basis, and it is actually the
   context VC label.  So the context VC label need to be pushed to the
   label stack before EVPN Label (which identifies LS1) on ingress PEs.

   Note that when PE1 send a Leaf A-D route with LoCLS EC to PE2, but
   PE2 don't recognize the LoCLS EC, then PE2 will encapsulate the EVPN
   label without the inner context label.  This will work as well as
   [RFC7432], although the per-ingress statistics can't be applied.

   Note that the LoCLS ECs (for different EVIs) received from the same
   TPE will be the same label, So we can select a single EVI to use the
   Leaf A-D route with LoCLS EC.  This EVI is called as administrating
   EVI (admin-EVI).  The context VC label carried in the Leaf A-D routes
   of the admin-EVI will be used for the IMET routes with the same ORIP
   in all other ordinary EVIs in such case.  Note that all other
   ordinary EVIs don't use the Leaf A-D routes with IR-PTA, they use
   ordinary IMET routes instead.  The admin-EVI need to be configured on
   all EVPN-PEs in such case.

4.3.  Solution for AR REPLICATOR in MPLS EVPN

                     LEAF1--------REPLICATOR1--------RNVE1
                                      /
                     LEAF2-----------/

                   Figure 4: AR REPLICATOR in MPLS EVPN

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   When REPLICATOR1 node recieves an IMET Route with AR-role = AR-LEAF
   from LEAF1 node, REPLICATOR1 SHOLD respond to it with an Leaf A-D
   route with AR-PTA.  The MPLS label field of the AR-PTA (say AR-PTA
   Label) will be allocated following the same rules as the IR-PTA Label
   in Section 3.2.1.1.  When ALEAF1 receives above Leaf A-D route, the
   Leaf A-D route is treated as a Replicator-AR route for the same ORIP,
   and then the control-plane procedures works following
   [I-D.ietf-bess-evpn-optimized-ir].  When REPLICATOR1 receives data
   packets from the AR-PTA Label, REPLICATOR1 will do source-squelching
   for LEAF1 which means that these data packets will not be forwarded
   back to LEAF1.

   Note that the old Replicator-AR route which is in terms of IMET route
   will not be used by MPLS EVPN AR-REPLICATOR.  Because that the Leaf
   A-D routes will take it's place per AR-LEAF basis.  But the old
   Regular-IR route can still be used by MPLS EVPN AR-REPLICATORs.

4.4.  Solution for anycast tunnel usage on SPE

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

                     Figure 5: 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 6: 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.

5.  Security Considerations

   This section will be added in future versions.

6.  IANA Considerations

   The IANA considerations for LoCLS EC in Section 4.2.2 will be added
   in future versions.

7.  Acknowledgements

   The authors would like to thank the following for their comments and
   review of this document:

   Benchong Xu.

8.  Normative References

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   [I-D.ietf-bess-evpn-bum-procedure-updates]
              Zhang, Z., Lin, W., Rabadan, J., Patel, K., and A.
              Sajassi, "Updates on EVPN BUM Procedures", draft-ietf-
              bess-evpn-bum-procedure-updates-08 (work in progress),
              November 2019.

   [I-D.ietf-bess-evpn-optimized-ir]
              Rabadan, J., Sathappan, S., Lin, W., Katiyar, M., and A.
              Sajassi, "Optimized Ingress Replication solution for
              EVPN", draft-ietf-bess-evpn-optimized-ir-06 (work in
              progress), October 2018.

   [I-D.ietf-bess-mvpn-evpn-aggregation-label]
              Zhang, Z., Rosen, E., Lin, W., Li, Z., and I. Wijnands,
              "MVPN/EVPN Tunnel Aggregation with Common Labels", draft-
              ietf-bess-mvpn-evpn-aggregation-label-03 (work in
              progress), October 2019.

   [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>.

   [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>.

   [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>.

   [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>.

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Authors' Addresses

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

   Email: yubao.wang2008@hotmail.com

   Bing Song
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: song.bing@zte.com.cn

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