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BESS WG                                                         Z. Zhang
Internet-Draft                                                   Y. Wang
Intended status: Standards Track                               G. Mirsky
Expires: September 6, 2019                               ZTE Corporation
                                                           March 5, 2019


   Bidirectional Forwarding Detection (BFD) for EVPN Ethernet Segment
                           Failover Use Case
                   draft-zwm-bess-es-failover-00.txt

Abstract

   This document introduces a method for fast switchover of Designated
   Forwarder for Ethernet Segment failover by using Bidirectional
   Forwarding Detection protocol.

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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   This Internet-Draft will expire on September 6, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Proposal  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   [RFC7432] introduces Ethernet Virtual Private Network (EVPN)
   technology.  Designated Forwarder (DF) election procedures for multi-
   homing Ethernet Segments has been described in it.  When PE (provider
   edge) receives BUM (Broadcast, Unknown Unicast and Multicast) flows,
   only DF forwards the BUM flows to CE (customer edge).  Non-DFs do not
   forward the BUM flows in order to avoid duplication.  If the link
   between DF and CE fails, another PE will forward the BUM flows after
   it is elected as DF.

   [I-D.ietf-bess-evpn-df-election-framework] defines the DF election
   framework, including that Backup Designated Forwarder (BDF) can be
   elected as the next best for the role.  But before the BDF is elected
   as DF, the BUM flows are discarded after the link between DF and CE
   fails.

                                          +-----+
                               +-----X----+ PE1 |
                               |          +--+--+
                               |
                             +-+--+
                             | CE |
                             +-+--+
                               |
                               |          +--+--+
                               +----------+ PE2 |
                                          +-----+

   For example, CE is multihomed to PE1 and PE2.  PE1 is elected as DF.
   All BUM flows are forwarded by PE1 when the link between PE1 and CE
   is operational.  When the link between PE1 and CE fails, the BUM
   flows are discarded until PE2 is elected as DF.

   This document will use terminology defined in [RFC7432] and
   [I-D.jain-bess-evpn-lsp-ping].





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2.  Proposal

   In order to avoid the BUM packet loss on BDF after the link between
   DF and CE fails, a data-plane detection function is needed for DF
   fast switchover.  [RFC5884] provides mechanisms for using LSP Ping to
   bootstrap a BFD session.  [I-D.jain-bess-evpn-lsp-ping] introduces
   four new Target FEC Stack sub-TLVs that are included in the LSP-Ping
   Echo Request packet.  This document uses the mechanisms defined in
   [RFC5884] and the EVPN Ethernet Auto-Discovery (AD) sub-TLV defined
   in [I-D.jain-bess-evpn-lsp-ping] to provide DF fast switchover by
   data-plane failure detection.

   An LSP-Ping Echo Request message which carries EVPN AD Sub-TLV
   associated with the DF-CE Ethernet Segment Identifier (ESI) is used
   to bootstrap the BFD session between BDF and DF.  After the BFD
   session is built, when the ES fault occurs on DF-CE link, BDF detects
   the fault by the state change BFD control packet sent by DF, or BDF
   detects the fault when the detection timer expires.  Then BDF becomes
   DF and will forward the BUM flows to CE.

3.  Specification

   [I-D.jain-bess-evpn-lsp-ping] section 4.3 defines an Ethernet AD sub-
   TLV as a new Target FEC Stack sub-TLV.  It is carried in the LSP-Ping
   Echo Request message.  BDF generates an LSP-Ping Echo Request message
   which carries the associated ES AD sub-TLV.  And BDF sends the
   message with a local discriminator assigned by BDF for this BFD
   session to DF.  DF responds with the BFD control packet with 'Your
   discriminator' set to the discriminator value received in the Echo
   request message from the BDF.  BDF can demultiplex the BFD session
   based on the received 'Your Discriminator' field.

   After the BFD session is established, when the link between DF and CE
   fails, DF MUST send a BFD control packet with the value of State
   field set to AdminDown through the established BFD session to BDF.
   If DF is not operational, BDF also detects the failure when the BFD
   detection time expires.  Then BDF becomes DF immediately and forwards
   the BUM flows to CE.

   When the ES between 'old' DF and CE recovers, the BFD session MAY be
   reused or a new BFD session can be established for the ES failover
   monitor.

   For the same example in last section, PE2 generates an LSP-Ping Echo
   Request message which carries the associated ES AD sub-TLV and sends
   the message with an assigned local discriminator to DF.  PE1 responds
   with a BFD control packet with 'Your discriminator' set to the




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   received discriminator from PE2.  PE2 can demultiplex the BFD session
   based on the received 'Your Discriminator' field.

   When the link between PE1 and CE fails, PE1 sends a BFD control
   packet with the state set to AdminDown to PE2 through the BFD
   session.  If the packet is lost, PE2 also can detect the fault by the
   session detection time expiration.  PE2 becomes DF immediately, then
   the BUM packets can be forwarded to CE.

4.  Security Considerations

   This document does not introduce any new security considerations
   other than already discussed in [RFC7432] and [RFC5884].

5.  IANA Considerations

   There is no IANA consideration.

6.  Normative References

   [I-D.ietf-bess-evpn-df-election-framework]
              Rabadan, J., satyamoh@cisco.com, s., Sajassi, A., Drake,
              J., Nagaraj, K., and S. Sathappan, "Framework for EVPN
              Designated Forwarder Election Extensibility", draft-ietf-
              bess-evpn-df-election-framework-09 (work in progress),
              January 2019.

   [I-D.jain-bess-evpn-lsp-ping]
              Jain, P., Salam, S., Sajassi, A., Boutros, S., and G.
              Mirsky, "LSP-Ping Mechanisms for EVPN and PBB-EVPN",
              draft-jain-bess-evpn-lsp-ping-08 (work in progress),
              December 2018.

   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
              "Bidirectional Forwarding Detection (BFD) for MPLS Label
              Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
              June 2010, <https://www.rfc-editor.org/info/rfc5884>.

   [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>.

Authors' Addresses







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   Zheng(Sandy) Zhang
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: zzhang_ietf@hotmail.com


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

   Email: wang.yubao2@zte.com.cn


   Greg Mirsky
   ZTE Corporation

   Email: gregimirsky@gmail.com





























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