BESS WG                                                          Y. Wang
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                           21 March 2022
Expires: 22 September 2022


    Centerlized EVPN Prefix Advertisement for Common Prefixes behind
                             Different CEs
            draft-wang-bess-center-rt5-for-common-prefix-00

Abstract

   In Section 5.8 of [I-D.wang-bess-evpn-arp-nd-synch-without-irb],
   centerlized RT-5 advertisement are used for common prefixes behind
   different CEs, This draft describes the requirements for such
   scenarios.  Then this draft reuse the procedures defined in
   Section 6.2.2 of [I-D.wz-bess-evpn-vpws-as-vrf-ac] to support this
   scenario.

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Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.











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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  ECMP for Centerlized RT-5 Advertisement . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Basic Control Plane Procedures  . . . . . . . . . . . . .   5
       3.1.1.  Centerlized CE-BGP  . . . . . . . . . . . . . . . . .   5
       3.1.2.  RT-2E Advertisement from PE1/PE2 to DGW1  . . . . . .   6
       3.1.3.  RT-5G Advertisement from DGW1 to PE1/PE2/PE3/DGW1'  .   6
       3.1.4.  RT-2E Advertisement between PE1 and PE2 . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   In Figure 1, Both R1 and R2 advertise their prefixes to DGW1
   according to Section 5 of
   [I-D.wang-bess-evpn-arp-nd-synch-without-irb].  Subnet SN1 can only
   be reached through R1, so we say SN1 is R1's exlusive prefix.  Then
   subnet SN2 is R2's exlusive prefix, because SN2 can only be reached
   throug R2.  But subnet SN21 can be reached either through R1, or
   through R2, thus we say SN21 is a common prefix of R1 and R2.

   When there are both exlusive prefixes and common prefixes behind some
   CEs, some special requirements should be considered, especially when
   some of these CEs will not aware which prefixes are the common
   prefixes.  This draft describes the requirements and solutions
   related to these scenarios .

1.1.  ECMP for Centerlized RT-5 Advertisement

   R1 and R2 both establish a single CE-BGP session with DGW1.  These
   CE-BGP session can be called the centerlized CE-BGP session.




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   SN21 is a common prefix of R1 and R2, when R4 send traffic to a host
   inside subnet SN21, DGW1' should load-balance that traffic between
   PE1, PE2 and PE3.

            +--------------------->----------------------+
            |                   CE-BGP                   |
            |              PE3                           |
            |             +----------+                   |
            |             | +------+ | ------>           | CE-BGP
         R2 |             | |      | | RT-2R             | SN21,SN2
        +-------+         | | VPNx | | 20.2(MAC34)       | NH=20.2
        |       |  P3.1   | |      | | MAC34             |
        | ...................(20.9)| |                   |
        | .     |         | +------+ |                   |  DGW1'
   SN2--| .     |         +----------+               +---|---------+
        | .     |            ^           <---------- |   V         |
        | .     |            | RT-2       RT-5       | +---------+ |
        |(20.2) |            | 20.2       SN21       | |  VPNx   | |
        | .     |            | ESI34      GW-IP=20.2 | |         |....R4
    +---| .     |            |                       | |(z.z.z.z)| |
    |   | .     |         +----------+ ------>       | |         | |
    |   | .     |         | +------+ | RT-2R         | +---------+ |
    |   | ...................(20.9)| | 20.2          |             |
    |   |       |  P4.1   | |      | | MAC34         +-------------+
    |   +-------+         | |      | |
   SN21               PE1 | | VPNx | | ------>
    |    R1               | |      | | RT-2R
    |   +-------+         | |      | | 10.2
    |   |       |  P1.1   | |      | | MAC21
    |   | ...................(10.9)| |                      DGW1
    |   | .     |         | +------+ |               +-------------+
    |   | .     |         +----------+               |             |
    +---| .     |            ^           <---------- | +---------+ |
        | .     |            | RT-2       RT-5       | |         | |
        |(10.2) |            | 10.2       SN21       | |  VPNx   | |
        | .     |            | ESI21      GW-IP=10.2 | |         |....R3
        | .     |            |                       | |(z.z.z.z)| |
   SN1--| .     |         +----------+ ------>       | +---------+ |
        | .     |         | +------+ | RT-2R         |   ^         |
        | ...................(10.9)| | 10.2          |   |         |
        |       |  P2.1   | |      | | MAC21         +---|---------+
        +-------+         | | VPNx | |                   |
            |             | |      | |                   | CE-BGP
            |             | +------+ |                   | SN21,SN1
            |             +----------+                   | NH=10.2
            |              PE2                           |
            |                   CE-BGP                   |
            +--------------------->----------------------+



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             Figure 1: Centerlized RT-5 for common CE-Prefixes

   Note that we just use centerlized CE-BGP session to discover CE-
   prefixes, but we still expect a distributed Layer 3 forwarding
   framework.

1.2.  Terminology

   Most of the terminology used in this documents comes from [RFC7432]
   and [RFC9136] except for the following:

   * L3 EVI:  An EVPN instance spanning the Provider Edge (PE) devices
     participating in that EVPN which contains VRF ACs and maybe
     contains IRB interfaces or IRC interfaces.

   * CE-BGP:  The BGP session between PE and CE.  Note that CE-BGP route
     doesn't have a RD or Route-Target.

   * RMAC:  Router's MAC, which is signaled in the Router's MAC extended
     community.

   * RT-2R:  When a MAC/IP Advertisement Route is used in the context of
     an IP-VRF, it is called as a RT-2R in this draft.

   * RT-5E:  An EVPN Prefix Advertisement Route with a non-reserved ESI.

   * RT-5G:  An EVPN Prefix Advertisement Route with a zero ESI and a
     non-zero GW-IP.

   * RT-5L:  An EVPN Prefix Advertisement Route with both zero ESI and
     zero GW-IP, but a valid MPLS label.

   * Internal Remote PE:  When PEx is called as an EVPN route ERy's
     internal remote PE, that is saying that, PEx is on the ES which is
     identified by ERy's ESI field.  When ERy's SOI is not zero, that is
     aslo saying that PEx has been attached to the ethernet tag which is
     identified by the <ESI, SOI>.

   * External Remote PE:  When PEx is called as an EVPN route ERy's
     external remote PE, that is saying that, PEx is not on the ES which
     is identified by ERy's ESI field.  When ERy's SOI is not zero, PEx
     may aslo be a PE which has not been attached to the ethernet tag
     which is identified by the <ESI, SOI>.

   * CE-Prefix:  When an IP prefix can be reached through CEx from PEy,
     that IP prefix is called as PEy's CE-prefix behind CEx in this
     draft.  PEy's CE-prefix behind CEx is also called as PEy's CE-
     prefix for short in this draft.



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   * Common CE-Prefix:  When an CE-Prefix can be reached through either
     CEy or CEz from PEy, in this draft, it is called as a common CE-
     Prefix of CEy and CEz,from the viewpoint of PEy.

   * Exclusive CE-Prefix:  When an CE-Prefix of PEy can be reached
     through CEy, and it can't be reached through other CEs of PEy, it
     is called as an exlusive CE-Prefix of CEy, from the viewpoint of
     PEy.

   * SNGW:  Sub-Net-specific Gate Way IP address, the SNGW of a subnet
     is an IP address which is used by the hosts of that subnet to be
     the nexthop of the default route of these host.

   * Overlay nexthop :  The CE-Prefix's nexthop IP address which is in
     the address-space of the L3 EVI.

   * Original Overlay nexthop :  The overlay nexthop which is advertised
     by the CE through a PE-CE route protocol.

2.  Requirements

   Before advertise SN1/SN2/SN21 to DGWs, R1 and R2 don't have to know
   which prefix is their common prefix, and which prefix is their
   exclusive prefix.

3.  Solution

3.1.  Basic Control Plane Procedures

3.1.1.  Centerlized CE-BGP

   The CE-BGP session between R1 and DGW1 is established between 10.2
   and z.z.z.z.  The IP address 10.2 is called the uplink interface
   address of R1 in this document.  The IP address z.z.z.z is called the
   centerlized loopback address of VPNx in this document.  The IP
   address 10.9 is called the downlink VRF-interface address of PE1/PE2
   in this document.

   R1 advertises a BGP route for a prefix (say "SN21") behind it to DGW1
   via that CE-BGP session.  The nexthop for SN21 is R1's uplink
   interface address (say 10.2).

   R2 advertises a BGP route for a prefix (say "SN21") behind it to
   DGW1' via that CE-BGP session.  The nexthop for SN21 is R2's uplink
   interface address (say 20.2).






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   Note that the data packets from R1(R2) to the centerlized loopback
   address may be routed following the default route on R1(R2).  Thus
   DGW1 doesn't need to use the CE-BGP session to advertise prefixes of
   VPNx to R1(R2).

3.1.2.  RT-2E Advertisement from PE1/PE2 to DGW1

   When PE1 and PE2 learns the ARP entry of 10.2, it advertises a RT-2R
   route to DGW1 (and DGW1').

   When PE1 and PE3 learns the ARP entry of 20.2, it advertises a RT-2R
   route to DGW1 (and DGW1').

3.1.3.  RT-5G Advertisement from DGW1 to PE1/PE2/PE3/DGW1'

   When DGW1 receives the SN21 from the CE-BGP session.  The nexthop for
   SN21 is 10.2.  So DGW1 advertises a RT-5G route to PE1/PE2/PE3 for
   SN21.  The GW-IP value of the RT-5G route for SN21 is 10.2.

   When DGW1' receives the SN21 from the CE-BGP session.  The nexthop
   for SN21 is 20.2.  So DGW1 advertises a RT-5G route to PE1/PE2/PE3
   for SN21.  The GW-IP value of the RT-5G route for SN21 is 20.2.

   DGW1 and DGW1' may be the same device, in such case DGW1 should use
   the ADD-PATH of [RFC7911] to advertise two GW-IPs for the same
   prefixe SN21.

   Note that when other PEs receive these RT-5 route for SN21, the ECMP
   behavior is already defined in Section 4.1 of [RFC9136] as the
   following:

        *  Based on the BD-10 Route Target in DGW1 and DGW2, the IP
           Prefix route is also imported, and SN1/24 is added to the IP-
           VRF with Overlay Index IP2 pointing at the local BD-10.  In
           this example, it is assumed that the RT-5 from NVE2 is
           preferred over the RT-5 from NVE3.  If both routes were
           equally preferable and ECMP enabled, SN1/24 would also be
           added to the routing table with Overlay Index IP3.

                 Figure 2: ECMP for GW-IP based RT-5

3.1.4.  RT-2E Advertisement between PE1 and PE2

   The RT-2R routes advertisement between PE1 and PE2 is used to sync
   subnet 10.0's ARP entries to each other in order to avoid ARP
   missing.  The ESI Value of these two RT-2R routes is ESI21.





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   The RT-2R routes advertisement between PE1 and PE3 is used to sync
   subnet 20.0's ARP entries to each other in order to avoid ARP
   missing.  The ESI Value of these two RT-2R routes is ESI34.

4.  Security Considerations

   TBD.

5.  IANA Considerations

   There is no IANA consideration needed.

6.  Normative References

   [I-D.wang-bess-evpn-arp-nd-synch-without-irb]
              Wang, Y. and Z. Zhang, "ARP/ND Synching And IP Aliasing
              without IRB", Work in Progress, Internet-Draft, draft-
              wang-bess-evpn-arp-nd-synch-without-irb-08, 1 September
              2021, <https://datatracker.ietf.org/doc/html/draft-wang-
              bess-evpn-arp-nd-synch-without-irb-08>.

   [I-D.wz-bess-evpn-vpws-as-vrf-ac]
              Wang, Y. and Z. Zhang, "EVPN VPWS as VRF Attachment
              Circuit", Work in Progress, Internet-Draft, draft-wz-bess-
              evpn-vpws-as-vrf-ac-02, 28 August 2021,
              <https://datatracker.ietf.org/doc/html/draft-wz-bess-evpn-
              vpws-as-vrf-ac-02>.

   [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>.

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <https://www.rfc-editor.org/info/rfc7911>.

   [RFC8214]  Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
              Rabadan, "Virtual Private Wire Service Support in Ethernet
              VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
              <https://www.rfc-editor.org/info/rfc8214>.

   [RFC8365]  Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
              Uttaro, J., and W. Henderickx, "A Network Virtualization
              Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
              DOI 10.17487/RFC8365, March 2018,
              <https://www.rfc-editor.org/info/rfc8365>.



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   [RFC9135]  Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
              Rabadan, "Integrated Routing and Bridging in Ethernet VPN
              (EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
              <https://www.rfc-editor.org/info/rfc9135>.

   [RFC9136]  Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
              A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
              (EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
              <https://www.rfc-editor.org/info/rfc9136>.

7.  Informative References

   [I-D.sajassi-bess-evpn-ip-aliasing]
              Sajassi, A., Badoni, G., Warade, P., Pasupula, S.,
              Krattiger, L., Drake, J., and J. Rabadan, "EVPN Support
              for L3 Fast Convergence and Aliasing/Backup Path", Work in
              Progress, Internet-Draft, draft-sajassi-bess-evpn-ip-
              aliasing-04, 7 March 2022,
              <https://datatracker.ietf.org/doc/html/draft-sajassi-bess-
              evpn-ip-aliasing-04>.

Author's Address

   Yubao Wang
   ZTE Corporation
   No. 68 of Zijinghua Road, Yuhuatai Distinct
   Nanjing
   China
   Email: wang.yubao2@zte.com.cn






















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