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<rfc category="std" docName="draft-ama-mpls-fm-rdi-00.txt" ipr="trust200902">
  <front>
    <title abbrev="MPLS FM OAM RDI">Reverse Defect Indicator for MPLS FM
    OAM</title>

    <author fullname="Ashesh Mishra" initials="A" surname="Mishra">
      <organization>O3b Networks</organization>

      <address>
        <postal>
          <street/>

          <city/>

          <region/>

          <code/>

          <country>USA</country>
        </postal>

        <phone/>

        <email>mishra.ashesh@outlook.com</email>
      </address>
    </author>

    <author fullname="Mahesh Jethanandani" initials="M" surname="Jethanandani">
      <organization/>

      <address>
        <postal>
          <street/>

          <city/>

          <region/>

          <code/>

          <country>USA</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>mjethanandani@gmail.com</email>

        <uri/>
      </address>
    </author>

    <author fullname="Ankur Saxena" initials="A" surname="Saxena">
      <organization>Ciena Corporation</organization>

      <address>
        <postal>
          <street>3939 North 1st Street</street>

          <city>San Jose</city>

          <region>CA</region>

          <code>95134</code>

          <country>USA</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>ankurpsaxena@gmail.com</email>

        <uri/>
      </address>
    </author>

    <date day="21" month="November" year="2017"/>

    <area>Network</area>

    <workgroup>Routing Working Group</workgroup>

    <keyword>Internet-Draft</keyword>

    <abstract>
      <t>This document describes extensions to the MPLS Fault Management
      Operations, Administration, and Management (MPLS FM OAM) in <xref
      target="RFC6427">RFC 6427</xref> to support Remote Defect Indication
      (RDI) functionality. Specifically, it describes a mechanism for
      propagating MPLS FM OAM messages to the upstream Label Edge Router (LER)
      in <xref target="RFC5921">MPLS-TP</xref> bi-directional (associated and
      co-routed) Label Switched Paths (LSPs).</t>
    </abstract>
  </front>

  <middle>
    <section title="Introduction">
      <t>The MPLS Fault Management Operations, Administration, and Management
      (MPLS FM OAM) in <xref target="RFC6427">RFC 6427</xref> describes a
      method to identify faults in MPLS transport networks, and a protocol to
      notify the upstream Label Edge Router (LER). However, in the case of
      <xref target="RFC5921">MPLS-TP</xref> bi-directional Label Switched
      Paths (LSPs), the fault must be coordinated on both, the upstream LER
      and the downstream LER (which is the upstream LER for the reverse
      path).</t>

      <t>In typical scenario, the Bidirectional Forwarding Detection (BFD)
      protocol, as described in <xref target="RFC5880">RFC 5880</xref>,
      detects the fault signaled by MPLS FM OAM on the upstream LER and
      propagates the fault on the reverse LSP to the other MPLS-TP LSP LER.
      This allows the two MPLS-TP LERs to coordinate failover to backup
      LSPs.</t>

      <t>This document proposes a mechanism to achieve MPLS FM OAM fault
      propagation on the MPLS-TP reverse LSP using a Reverse Defect Indicator
      (RDI) MPLS FM OAM message. This allows fast fault coordination between
      the bidirectional LSP end-points when the use of BFD is not
      feasible.</t>
    </section>

    <section title="Reverse Defect Indicator (RDI)">
      <t>The functionality proposed for MPLS FM OAM RDI is achieved by adding
      a RDI-flag in the MPLS Fault OAM message .</t>

      <t><figure title="Figure 1: RDI-Flag in MPLS FM OAM Flags">
          <artwork><![CDATA[            +-+-+-+-+-+---+-+-+
            |Reserved |RDI|L|R|
            +-+-+-+-+-+---+-+-+]]></artwork>
        </figure></t>

      <t>where:</t>

      <t>L-Flag and R-Flag are as defined in <xref target="RFC6427">RFC
      6427</xref>.</t>

      <t>RDI-Flag: Reverse Defect Indication Flag. The RDI-Flag is clear in
      the common MPLS FM OAM messages as defined in <xref target="RFC6427">RFC
      6427</xref>. The RDI-Flag is set to indicate that the message is MPLS FM
      OAM RDI.</t>
    </section>

    <section title="Theory of Operations">
      <section title="RDI Operation in Associated Bidirectional LSPs">
        <t><figure
            title="Figure 2: RDI Operation in Associated Bidirectional LSP">
            <artwork><![CDATA[                              ------------------>
                                  Forward LSP
                                            
                          +-------+         +-------+
                     +--> | LSR-1 | --X---> | LSR-2 | --+
                     |    +-------+  Fault  +-------+ AIS/LKR     
                     |                                  |
         +-------+ --+                                  +--> +-------+ 
         | LER-A |                 +-------+                 | LER-B |
         +-------+ <------RDI----- | LSR-3 | <------RDI----- +-------+
                                   +-------+

                                  Reverse LSP
                              <------------------]]></artwork>
          </figure></t>

        <t>Figure 1 depicts an associated bidirectional LSP with:</t>

        <t>Forward LSP (LER-A, LSR-1, LSR-2, LER-B)</t>

        <t>Reverse LSP (LER-B, LSR-3, LER-A)</t>

        <t>Scenario 1, Fault on LER-A: LSR-1 will detect a fault on the server
        sub-layer and generate AIS/LKR message on the upstream link for
        Forward LSP (towards LSR-2). LSR-2 will process the message and
        forward it, unaltered, upstream to LER-B. LER-B will process the
        message, set the RDI-Flag and forward it on the associated Reverse
        LSP. Because the RDI-Flag is set, LSR-3 does not need to process the
        message as the fault is not on the Reverse LSP and forwards it,
        unaltered, towards LER-A. LER-A, if it receives the message (the fault
        may only be on the forward LSP on LER-A) processes the message and
        discard it (RDI-Flag set received on Reverse LSP indicates the fault
        is on the Forward LSP, and vice-versa). When the fault clears, LSR-1
        will issue new set of AIS/LKR messages to clear the previous fault
        condition. This message is also propagated using the previous RDI
        logic to coordinate fault clear on the Reverse LSP.</t>

        <t>Scenario 2, Link fault or LSR fault on Forward LSP: Same logic as
        fault on LER-A.</t>
      </section>

      <section title="RDI Operation in Co-routed Bidirectional LSPs">
        <t>RDI is not a required mechanism in co-routed bidirectional LSPs as
        MPLS LSx on either direction of the fault will generate MPLS FM OAM
        messages and the fault is propagated to both LERs.</t>
      </section>
    </section>

    <section title="IANA Requirements">
      <t>None.</t>
    </section>

    <section title="Security Consideration">
      <t>No additional security impact because of addition of RDI-Flag in MPLS
      FM OAM messages.</t>
    </section>

    <section title="Acknowledgements">
      <t/>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include='reference.RFC.6427'?>

      <?rfc include='reference.RFC.5921'?>
    </references>

    <references title="Informative References">
      <?rfc include='reference.RFC.5880'?>
    </references>
  </back>
</rfc>
