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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" submissionType="IETF" category="std"
consensus="true" docName="draft-ietf-lsr-ospf-bfd-strict-mode-10" number="9355"
ipr="trust200902" updates="2328"> updates="2328" obsoletes="" xml:lang="en" tocInclude="true" tocDepth="3" symRefs="true" sortRefs="true" version="3">

  <!-- xml2rfc v2v3 conversion 3.15.0 -->
  <front>

    <title abbrev="OSPF BFD Strict-Mode">OSPF BFD Bidirectional Forwarding
    Detection (BFD) Strict-Mode</title>
    <seriesInfo name="RFC" value="9355"/>
    <author fullname="Ketan Talaulikar" initials="K." role="editor" surname="Talaulikar">
      <organization>Cisco Systems, Inc.</organization>
      <address>
        <postal>
          <street/>

          <city/>

          <code/>
          <country>India</country>
        </postal>
        <email>ketant.ietf@gmail.com</email>
      </address>
    </author>
    <author fullname="Peter Psenak" initials="P." surname="Psenak">
      <organization>Cisco Systems, Inc.</organization>
      <address>
        <postal>
          <street>Apollo
          <extaddr>Apollo Business Center</street> Center</extaddr>
          <street>Mlynske nivy 43</street>
          <city>Bratislava</city>
          <code>821 09</code>
          <country>Slovakia</country>
        </postal>
        <email>ppsenak@cisco.com</email>
      </address>
    </author>
    <author fullname="Albert Fu" initials="A." surname="Fu">
      <organization>Bloomberg</organization>
      <address>
        <postal>
          <street/>

          <street/>

          <city/>

          <code/>

          <country>USA</country>
          <country>United States of America</country>
        </postal>
        <email>afu14@bloomberg.net</email>
      </address>
    </author>

<author fullname="Rajesh M" initials="M." surname="Rajesh">
      <organization>Juniper Networks</organization>
      <address>
        <postal>
          <street/>

          <street/>

          <city/>

          <code/>
          <country>India</country>
        </postal>
        <email>mrajesh@juniper.net</email>
      </address>
    </author>
    <date year=""/>

    <area>Routing</area>

    <workgroup>Link State Routing</workgroup> year="2023" month="February"/>
    <area>rtg</area>
    <workgroup>lsr</workgroup>
    <keyword>IGP</keyword>
    <keyword>OSPF</keyword>

    <abstract>
      <t>This document specifies the extensions to OSPF that enable an OSPF
      router to signal the requirement for a Bidirectional Forwarding
      Detection (BFD) session prior to adjacency formation. Link-Local
      Signaling (LLS) is used to advertise the requirement for strict-mode BFD
      session establishment for an OSPF adjacency. If both OSPF neighbors
      advertise BFD strict-mode, adjacency formation will be blocked until a
      BFD session has been successfully established.</t>
      <t>This document updates RFC2328 RFC 2328 by augmenting the OSPF neighbor state
      machine with a check for BFD session up before progression from Init to
      Two-Way
      2-Way state when operating in OSPF BFD strict-mode.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="INTRO" title="Introduction"> numbered="true" toc="default">
      <name>Introduction</name>
      <t>Bidirectional Forwarding Detection (BFD) <xref target="RFC5880"/> target="RFC5880" format="default"/>
      enables routers to monitor data-plane data plane connectivity and to detect faults
      in the bidirectional path between them.
BFD is leveraged by routing
      protocols like OSPFv2 <xref target="RFC2328"/> target="RFC2328" format="default"/> and OSPFv3 <xref
      target="RFC5340"/> target="RFC5340" format="default"/> to detect connectivity failures for established
      adjacencies faster than the OSPF hello Hello dead timer detection and to trigger
      rerouting of traffic around the failure. The use of BFD for monitoring
      routing protocol adjacencies is described in <xref
      target="RFC5882"/>.</t> target="RFC5882" format="default"/>.</t>

<t>When BFD monitoring is enabled for OSPF adjacencies by the network
      operator, the BFD session is bootstrapped based on the neighbor address
      information discovered by the exchange of OSPF Hello packets. Faults in
      the bidirectional forwarding detected via BFD then result in the OSPF
      adjacency being brought down. A degraded or poor quality poor-quality link may result
      in intermittent packet drops.  In such scenarios, in implementations prior to the extensions specified in this document, an OSPF adjacency document may still get an OSPF adjacency established over such a link but link; however, given the more aggressive monitoring intervals supported by BFD, a BFD session may not get established and/or may flap over it. flap.  The traffic that gets forwarded over such a link would
      experience packet drops drops, and the failure of the BFD session establishment would
      will not enable fast routing convergence.  OSPF adjacency flaps may
      occur over such links as when OSPF brings up the adjacency only for it to be
      brought down again by BFD.</t>
      <t>To avoid the routing churn associated with these scenarios, it would
      be beneficial to not to allow OSPF to establish an adjacency until a BFD
      session is successfully established and has stabilized.
      However, this
      would preclude the OSPF operation in an environment where not all OSPF
      routers both support BFD and have it enabled on the link. A solution is
      to block OSPF adjacency establishment until a BFD session is established
      as long as both neighbors advertise such a requirement. Such a mode of
      OSPF BFD usage is referred to as "strict-mode". It   Strict-mode introduces the
      signaling support in OSPF to achieve the blocking of adjacency formation
      until BFD session establishment occurs, as described in section 4.1 of <xref
      target="RFC5882"/>.</t> target="RFC5882" sectionFormat="of" section="4.1"/>.</t>
      <t>This document specifies the OSPF protocol extensions using Link-Local
      Signaling (LLS) <xref target="RFC5613"/> target="RFC5613" format="default"/> for a router
      to indicate to its neighbor the willingness to require BFD strict-mode for OSPF
      adjacency establishment (refer to <xref target="BBIT"/>). target="BBIT"
      format="default"/>).  It also introduces an extension for to
      OSPFv3 Link-Local Signalling (LLS) LLS of the interface IPv4 address (refer
      to <xref target="IFADDRTLV"/>) target="IFADDRTLV" format="default"/>) to be used for the BFD
      session setup when OSPFv3 is used for an IPv4 address-family Address Family (AF)
      instance.</t>
      <t>This document updates <xref target="RFC2328"/> target="RFC2328" format="default"/> by augmenting the OSPF
      neighbor state machine with a check for BFD session up before
      progression from Init to Two-Way 2-Way state when operating in OSPF BFD
      strict-mode.</t>
      <t>The extensions and procedures for OSPF BFD strict-mode also apply for
      adjacency over virtual links using BFD multi-hop <xref
      target="RFC5883"/> target="RFC5883" format="default"/> procedures.</t>
      <t>A similar functionality for IS-IS is specified in <xref
      target="RFC6213"/>.</t> target="RFC6213" format="default"/>.</t>
      <section title="Requirements Language">
        <t>The numbered="true" toc="default">
        <name>Requirements Language</name>
        <t>
    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
        "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
    NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and
        "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as
    described in BCP
        14 BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
    when, and only when, they appear in all capitals, as shown here.</t> here.
        </t>
      </section>
    </section>
    <section anchor="BBIT" title="LLS B-bit Flag"> numbered="true" toc="default">
      <name>LLS B-Bit Flag</name>
      <t>This document defines the B-bit in the LLS Type 1 Extended Options
      and Flags field. Flags. This bit is defined for the LLS block that is included
      in Hello and Database Description (DD) packets and packets. The B-bit indicates that
      BFD is enabled on the link and that the router requests OSPF BFD
      strict-mode. <xref
      target="IANA"/> target="IANA" format="default"/> describes the
      position of the B-bit.</t> <t>A router MUST <bcp14>MUST</bcp14> include the
      LLS block with the B-bit set in the LLS Type 1 Extended Options and
      Flags TLV in its Hello and DD packets when OSPF BFD strict-mode is
      enabled on the link.</t>
    </section>
    <section anchor="IFADDRTLV" title="Local numbered="true" toc="default">
      <name>Local Interface IPv4 Address TLV"> TLV</name>
      <t>The Local Interface IPv4 Address TLV is an LLS TLV defined for OSPFv3
      IPv4 AF instance <xref target="RFC5838"/> target="RFC5838" format="default"/> protocol operation as
      described in <xref target="OSPFV3AF"/>.</t> target="OSPFV3AF" format="default"/>.</t>

      <t>It has the following format:<figure>
          <artwork><![CDATA[ format:</t>
      <artwork name="" type="" align="left" alt=""><![CDATA[
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Type             |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 Local Interface IPv4 Address                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

where:
]]></artwork>
        </figure><list style="hanging">
          <t>Type: 21</t>

          <t>Length: 4 octets</t>

          <t>Local
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
      <t>where:</t>
<dl newline="false" spacing="normal">
	<dt>Type:</dt>
        <dd>21</dd>
        <dt>Length:</dt>
        <dd>4 octets</dd>
        <dt>Local Interface IPv4 Address: The Address:</dt>
        <dd>The primary IPv4 address of the local interface.</t>
        </list></t> interface.</dd>
      </dl>
    </section>
    <section anchor="PROCEDURES" title="Procedures"> numbered="true" toc="default">
      <name>Procedures</name>
      <t>A router supporting OSPF BFD strict-mode advertises this capability
      through its Hello packets as described in <xref target="BBIT"/>. target="BBIT" format="default"/>. When a
      router supporting OSPF BFD strict-mode discovers a new neighbor router
      that also supports OSPF BFD strict-mode, it will establish a BFD session
      first with that neighbor first before bringing up the OSPF adjacency as
      described further in this section.</t>
      <t>This document updates the OSPF neighbor state machine as described in
      <xref target="RFC2328"/>. target="RFC2328" format="default"/>. Specifically, the operations related to the
      Init state are modified as described below when OSPF BFD strict-mode is used:</t>

      <t>Init
      <dl newline="true" spacing="normal">
        <dt>Init (without OSPF BFD strict-mode)</t>

      <t><list style="hanging">
          <t>In strict-mode):</dt>
        <dd>In this state, a Hello packet has recently been received from the
          neighbor. However, bidirectional communication has not yet been
          established with the neighbor (i.e., the router itself did not
          appear in the neighbor's Hello packet). All neighbors in this state
          (or higher) are listed in the Hello packets sent from the associated
          interface.</t>
        </list></t>

      <t>Init
          interface.</dd>
      <dt>Init (with OSPF BFD strict-mode)</t>

      <t><list style="hanging">
          <t>In strict-mode):</dt>
        <dd>In this state, a Hello packet has recently been received from the
        neighbor. However, bidirectional communication has not yet been
        established with the neighbor (i.e., the router itself did not appear
        in the neighbor's Hello packet). BFD session establishment with the
        neighbor is requested, requested if it's not already completed (e.g., in the
        event of transition from 2-way 2-Way state).  Neighbors in
      Init state or higher will be listed in Hello packets associated
      with the interface if they either have a corresponding BFD session
      established or have not advertised OSPF BFD strict-mode in the Hello
          packet LLS
      Type 1 Extended Options and Flags.</t>
        </list></t>

      <t>Whenever Flags advertised in the Hello packet.</dd>
      </dl>
      <t>When the neighbor state transitions to Down state, the removal of
      the BFD session associated with that neighbor is requested by OSPF and OSPF;
      subsequent BFD session establishment is similarly requested by OSPF upon
      transitioning into Init state.
      This may result in the deletion and
      creation of the BFD session respectively deletion and creation, respectively, when OSPF is the only client
      interested in the BFD session with the neighbor address.</t>
      <t>An implementation MUST NOT <bcp14>MUST NOT</bcp14> wait for BFD session
      establishment in Init state unless OSPF BFD strict-mode is enabled by
      the operator on the interface and the specific neighbor indicates OSPF
      BFD strict-mode capability via its Hello the LLS options. Type 1 Extended Options and Flags advertised in the Hello packet.  When BFD is
      enabled, but OSPF BFD strict-mode has not been signaled by both
      neighbors, an implementation
      SHOULD <bcp14>SHOULD</bcp14> start BFD session
      establishment only in 2-Way state or greater state.  This makes it
      possible for an OSPF router to support BFD operation in both strict-mode
      and normal mode across different interfaces or even across different neighbors
      on the same multi-access interface.</t>
      <t>Once the OSPF state machine has moved beyond the Init state, any
      change in the B-bit advertised in subsequent Hello packets MUST NOT <bcp14>MUST NOT</bcp14>
      result in any trigger in either the OSPF adjacency or the BFD session
      management (i.e., the B-bit is considered only when in Init state).

Disabling BFD (or OSPF BFD strict-mode) on an OSPF interface would
      result in it not setting the B-bit in its the LLS Type 1 Extended Options and Flags advertised in subsequent Hello LLS options. packets.
      Disabling OSPF BFD strict-mode has no effect on BFD operations and would
      not result in the bringing down of any established BFD sessions.  Disabling BFD would result in the BFD session being brought down due to Admin
      reason AdminDown State (described in <xref target="RFC5882"/> and hence target="RFC5882" sectionFormat="of" section="3.2"/>); hence, it would not bring
down the OSPF adjacency.</t>
      <t>When BFD is enabled on an interface over which we already have an
      existing OSPF adjacency, it would result in the router setting the B-bit
      in its subsequent Hello packets and the initiation of BFD session
      establishment to the neighbor.

If the adjacency is already up (i.e., in
      its terminal state of Full or 2-way 2-Way with non-DR routers that are not designated routers on a
      multi-access interface) with a neighbor that also supports OSPF BFD
      strict-mode, then an implementation SHOULD NOT <bcp14>SHOULD NOT</bcp14> bring this adjacency down
      into the Init state to avoid disruption to routing operations and
      instead use the OSPF BFD strict-mode wait only after a transition to
      Init state. However, if the adjacency is not up, then an implementation
      MAY
      <bcp14>MAY</bcp14> bring such an adjacency down so it can use the OSPF BFD strict-mode
      for its adjacency establishment.</t>
      <section anchor="OSPFV3AF" title="OSPFv3 numbered="true" toc="default">
        <name>OSPFv3 IPv4 Address-Family Specifics">
        <t>Multiple AF support Specifics</name>
        <t>Support for multiple AFs in OSPFv3 <xref target="RFC5838"/> target="RFC5838"
        format="default"/> requires the use of an IPv6 link-local address as
        the source address for Hello
        packets packets, even when forming adjacencies
        for IPv4 AF instances.	In most deployments of OSPFv3 IPv4 AF, AFs, it is
        required that BFD is used to monitor and verify IPv4 data plane
        connectivity between the routers on the link and, link; hence, the BFD session
        is setup set up using IPv4 neighbor addresses.
	The IPv4 neighbor address on
        the interface is learned only later in the adjacency formation process
        when the neighbor's Link-LSA (Link State Advertisement) is received. This
        results in the setup of the BFD IPv4 session either after the
        adjacency is established or later in the adjacency formation
        sequence.</t>
        <t>To operate in OSPF BFD strict-mode, it is necessary for an OSPF
        router to learn its neighbor's IPv4 link address during the Init state
        of adjacency formation (ideally (ideally, when it receives the first hello). Hello). The
        use of the Local Interface IPv4 Address TLV (as defined in <xref
        target="IFADDRTLV"/>)
        target="IFADDRTLV" format="default"/>) in the LLS block of advertised in OSPFv3
        Hello packets for IPv4 AF instances makes this
        possible. Implementations that support OSPF BFD
   strict-mode for OSPFv3 IPv4 AF instances MUST <bcp14>MUST</bcp14> include the Local
   Interface IPv4 Address TLV in the LLS block of advertised in their Hello packets
   whenever the B-bit is also set in the LLS Type 1 Extended Options and Flags
        field. Flags. A receiver MUST
        <bcp14>MUST</bcp14> ignore the B-bit (i.e., not operate in strict
        mode strict-mode
        for BFD) when the Local Interface IPv4 Address TLV is not present in
        OSPFv3 Hello messages for OSPFv3 IPv4 AF OSPFv3 instances.</t>
      </section>
      <section anchor="GR" title="Graceful numbered="true" toc="default">
        <name>Graceful Restart Considerations"> Considerations</name>
        <t>An implementation needs to handle scenarios where both graceful
        restart (GR) and the OSPF BFD strict-mode are deployed together.  The
        GR graceful restart aspects related to process restart scenarios discussed in section 3.3 of <xref target="RFC5882"/> target="RFC5882" sectionFormat="of"
section="3.3"/> also apply with OSPF BFD strict-mode.  Additionally, in OSPF BFD
        strict-mode, since the
OSPF adjacency formation is delayed until the BFD session establishment, establishment in
OSPF BFD strict-mode, the resultant delay in adjacency formation may affect or
break the GR-based recovery. In such cases, it is
        RECOMMENDED <bcp14>RECOMMENDED</bcp14>
that the GR timers are set such that they provide sufficient time to allow for
normal BFD session establishment delays.</t>
      </section>
    </section>
    <section anchor="OPS" title="Operations &amp; numbered="true" toc="default">
      <name>Operations and Management Considerations"> Considerations</name>
      <t>An implementation SHOULD <bcp14>SHOULD</bcp14> report the BFD session status along with the
      OSPF Init adjacency state when OSPF BFD strict-mode is enabled and
      support logging operations on neighbor state transitions that include
      the BFD events. This allows an operator to detect scenarios where an
      OSPF adjacency may be stuck waiting for BFD session establishment.</t>
      <t>In network deployments with noisy or degraded links with intermittent
      packet loss, BFD sessions may flap flap, resulting in OSPF adjacency flaps.
      This in turn
      In turn, this may cause routing churn.  The use of OSPF BFD strict-mode
      along with mechanisms such as hold-down (a delay in bringing up the initial OSPF adjacency bringup following BFD
session establishment) and/or dampening (a delay in bringing up the OSPF adjacency bringup following failure detected by BFD) may help reduce the
frequency of adjacency flaps and therefore reduce the associated
routing churn.  The details of these mechanisms are
      outside the scope of this document.</t>

      <t><xref target="I-D.ietf-ospf-yang"/> target="RFC9129" format="default"/> specifies the base OSPF YANG
      model.
      module. The required configuration and operational elements for this
      feature are expected to be introduce introduced as augmentation to this base OSPF
      YANG model.</t> module.</t>
    </section>
    <section anchor="BACKW" title="Backward Compatibility"> numbered="true" toc="default">
      <name>Backward Compatibility</name>
      <t>An implementation MUST <bcp14>MUST</bcp14> support OSPF adjacency formation and
      operations with a neighbor router that does not advertise the OSPF BFD
      strict-mode capability - capability: both when that neighbor router does not support
      BFD and when it does support BFD but does not signal the OSPF BFD
      strict-mode as described in this document. Implementations MAY <bcp14>MAY</bcp14> provide a
      local configuration option to force BFD operation only in OSPF BFD
      strict-mode (i.e, adjacency will not come up unless BFD session is
      established). In this case, an OSPF adjacency with a neighbor that does
      not support OSPF BFD strict-mode would not be established successfully.
      Implementations MAY <bcp14>MAY</bcp14> provide a local configuration option to enable BFD
      without the OSPF BFD strict-mode strict-mode, which results in the router not
      advertising the B-bit and BFD operation being performed in the same way
      as prior to this specification.</t>
      <t>The signaling specified in this document happens at a link-local
      level between routers on that link. A router that does not support this
      specification would ignore the B-bit in the LLS block of advertised in Hello packets
      from its neighbors and continue to establish BFD sessions, if enabled, sessions (if enabled)
      without delaying the OSPF adjacency formation. Since a router that does
      not support this specification would not have set the B-bit in the LLS
      block of advertised in its own Hello packets, its neighbor routers supporting this
      specification would not use OSPF BFD strict-mode with such OSPF routers.
      As a result, the behavior would be the same as without this
      specification. Therefore, there are no backward compatibility issues or
      implementations
      implementation considerations beyond what is specified herein.</t>
    </section>
    <section anchor="IANA" title="IANA Considerations"> numbered="true" toc="default">
      <name>IANA Considerations</name>
      <t>This specification makes the following updates under the "Open
      Shortest Path First (OSPF) Link Local Signaling (LLS) -
      Type/Length/Value Identifiers (TLV)" parameters.</t>

      <t>IANA is requested to make permanent the following values that have
      been assigned via early allocation:</t>

      <t>o In
      <ul><li>In the "LLS Type 1 Extended Options and Flags" registry, the B-bit
      is
      has been assigned the bit position 0x00000010</t>

      <t>o In 0x00000010.</li>
      <li>In the "Link Local Signaling TLV Identifiers (LLS Types)" registry,
      the Type 21 is has been assigned to the Local Interface IPv4 Address TLV</t> TLV.</li>
      </ul>
    </section>
    <section anchor="Security" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>The security considerations for "OSPF Link-Local Signaling" "<xref target="RFC5613" format="title"/>" <xref
      target="RFC5613"/> target="RFC5613" format="default"/> also apply to the extension described in this
      document.

Inappropriate use of the B-bit in the LLS block of an OSPF
      hello Hello message could
prevent an OSPF adjacency from forming or lead to the failure to detect of detecting
bidirectional forwarding failures. If authentication is being used in the OSPF
routing domain <xref target="RFC5709"/><xref
      target="RFC7474"/>, target="RFC5709" format="default"/> <xref target="RFC7474"
format="default"/>, then the Cryptographic Authentication TLV <xref
      target="RFC5613"/> MUST
target="RFC5613" format="default"/> <bcp14>MUST</bcp14> also be used to
protect the contents of the LLS block.</t>
    </section>
  </middle>
  <back>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2328.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5340.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5882.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5613.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5838.xml"/>
      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5880.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5883.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6213.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7474.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5709.xml"/>

<!-- [I-D.ietf-ospf-yang] Published as RFC 9129 -->

        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9129.xml"/>
      </references>
    </references>
    <section anchor="Acknowledgements" title="Acknowledgements"> numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>The authors would like to acknowledge the review and inputs from Acee
      Lindem, Manish Gupta, Balaji Ganesh, Les Ginsberg, Robert Raszuk, Gyan
      Mishra, Muthu
      <contact fullname="Acee Lindem"/>, <contact fullname="Manish Gupta"/>,
      <contact fullname="Balaji Ganesh"/>, <contact fullname="Les Ginsberg"/>,
      <contact fullname="Robert Raszuk"/>, <contact fullname="Gyan Mishra"/>,
      <contact fullname="Muthu Arul Mozhi Perumal, Russ Housley, and Wes Hardaker.</t> Perumal"/>, <contact fullname="Russ
      Housley"/>, and <contact fullname="Wes Hardaker"/>.</t>
      <t>The authors would like to acknowledge Dylan <contact fullname="Dylan van Oudheusden
      Oudheusden"/> for highlighting the problems in using OSPF BFD
      strict-mode for BFD session sessions for OSPFv3 IPv4 AF instance with OSPFv3 instances and Baalajee S
      <contact fullname="Baalajee S"/> for his suggestions on the approach to
      address it.</t>
      <t>The authors would like to thank John Scudder <contact fullname="John Scudder"/>
      for his AD review and suggestions to improve the document.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2328.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5340.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5882.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5613.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5838.xml"?>
    </references>

    <references title="Informative References">
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5880.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5883.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6213.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7474.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.5709.xml"?>

      <?rfc include='reference.I-D.ietf-ospf-yang.xml'?>
    </references>
  </back>
</rfc>