<?xml version="1.0"encoding="US-ASCII"?>encoding="UTF-8"?> <!DOCTYPE rfcSYSTEM "rfc2629.dtd"> <?rfc toc="yes"?> <?rfc tocompact="yes"?> <?rfc tocdepth="3"?> <?rfc tocindent="yes"?> <?rfc symrefs="yes"?> <?rfc sortrefs="yes"?> <?rfc comments="yes"?> <?rfc inline="yes"?> <?rfc compact="yes"?> <?rfc subcompact="no"?>[ <!ENTITY nbsp " "> <!ENTITY zwsp "​"> <!ENTITY nbhy "‑"> <!ENTITY wj "⁠"> ]> <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">OSPFBFDBidirectional 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 BusinessCenter</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> <dateyear=""/> <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 updatesRFC2328RFC 2328 by augmenting the OSPF neighbor state machine with a check for BFD session up before progression from Init toTwo-Way2-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) <xreftarget="RFC5880"/>target="RFC5880" format="default"/> enables routers to monitordata-planedata plane connectivity and to detect faults in the bidirectional path between them. BFD is leveraged by routing protocols like OSPFv2 <xreftarget="RFC2328"/>target="RFC2328" format="default"/> and OSPFv3 <xreftarget="RFC5340"/>target="RFC5340" format="default"/> to detect connectivity failures for established adjacencies faster than the OSPFhelloHello dead timer detection and to trigger rerouting of traffic around the failure. The use of BFD for monitoring routing protocol adjacencies is described in <xreftarget="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 orpoor qualitypoor-quality link may result in intermittent packet drops. In such scenarios,inimplementations prior to the extensions specified in thisdocument, an OSPF adjacencydocument may still get an OSPF adjacency established over such alink butlink; however, given the more aggressive monitoring intervals supported by BFD, a BFD session may not get established and/or mayflap over it.flap. The trafficthat getsforwarded over such a link would experience packetdropsdrops, and the failure of the BFD session establishmentwouldwill not enable fast routing convergence. OSPF adjacency flaps may occur over such linksaswhen 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 beneficialtonot 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 routersbothsupport 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".ItStrict-mode introducesthesignaling support in OSPF to achieve the blocking of adjacency formation until BFD session establishment occurs, as described insection 4.1 of<xreftarget="RFC5882"/>.</t>target="RFC5882" sectionFormat="of" section="4.1"/>.</t> <t>This document specifies the OSPF protocol extensions using Link-Local Signaling (LLS) <xreftarget="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 <xreftarget="BBIT"/>).target="BBIT" format="default"/>). It also introduces an extensionforto OSPFv3Link-Local Signalling (LLS)LLS of the interface IPv4 address (refer to <xreftarget="IFADDRTLV"/>)target="IFADDRTLV" format="default"/>) to be used for the BFD session setup when OSPFv3 is used for an IPv4address-familyAddress Family (AF) instance.</t> <t>This document updates <xreftarget="RFC2328"/>target="RFC2328" format="default"/> by augmenting the OSPF neighbor state machine with a check for BFD session up before progression from Init toTwo-Way2-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 <xreftarget="RFC5883"/>target="RFC5883" format="default"/> procedures.</t> <t>A similar functionality for IS-IS is specified in <xreftarget="RFC6213"/>.</t>target="RFC6213" format="default"/>.</t> <sectiontitle="Requirements Language"> <t>Thenumbered="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 inBCP 14BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shownhere.</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 andFlags field.Flags. This bit is defined for the LLS block that is included in Hello and Database Description (DD)packets andpackets. The B-bit indicates that BFD is enabled on the link and that the router requests OSPF BFD strict-mode. <xreftarget="IANA"/>target="IANA" format="default"/> describes the position of the B-bit.</t> <t>A routerMUST<bcp14>MUST</bcp14> include the LLS block with the B-bit set in the LLS Type 1 Extended Options and FlagsTLVin its Hello and DD packets when OSPF BFD strict-mode is enabled on the link.</t> </section> <section anchor="IFADDRTLV"title="Localnumbered="true" toc="default"> <name>Local Interface IPv4 AddressTLV">TLV</name> <t>The Local Interface IPv4 Address TLV is an LLS TLV defined for OSPFv3 IPv4 AF instance <xreftarget="RFC5838"/>target="RFC5838" format="default"/> protocol operation as described in <xreftarget="OSPFV3AF"/>.</t>target="OSPFV3AF" format="default"/>.</t> <t>It has the followingformat:<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 IPv4Address: TheAddress:</dt> <dd>The primary IPv4 address of the localinterface.</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 <xreftarget="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 sessionfirstwith 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 <xreftarget="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 BFDstrict-mode)</t> <t><list style="hanging"> <t>Instrict-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 associatedinterface.</t> </list></t> <t>Initinterface.</dd> <dt>Init (with OSPF BFDstrict-mode)</t> <t><list style="hanging"> <t>Instrict-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 isrequested,requested if it's not already completed (e.g., in the event of transition from2-way2-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 theHello packetLLS Type 1 Extended Options andFlags.</t> </list></t> <t>WheneverFlags 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 byOSPF andOSPF; subsequent BFD session establishment is similarly requested by OSPF upon transitioning into Init state. This may result inthe deletion and creation of theBFD sessionrespectivelydeletion and creation, respectively, when OSPF is the only client interested in the BFD session with the neighbor address.</t> <t>An implementationMUST 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 viaits Hellothe LLSoptions.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 implementationSHOULD<bcp14>SHOULD</bcp14> start BFD session establishment only in 2-Waystateor 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 packetsMUST 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 initsthe LLS Type 1 Extended Options and Flags advertised in subsequent HelloLLS 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 toAdmin reasonAdminDown State (described in <xreftarget="RFC5882"/> and hencetarget="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 or2-way2-Way withnon-DRrouters that are not designated routers on a multi-access interface) with a neighbor that also supports OSPF BFD strict-mode, then an implementationSHOULD 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 implementationMAY<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="OSPFv3numbered="true" toc="default"> <name>OSPFv3 IPv4Address-Family Specifics"> <t>MultipleAFsupportSpecifics</name> <t>Support for multiple AFs in OSPFv3 <xreftarget="RFC5838"/>target="RFC5838" format="default"/> requires the use of an IPv6 link-local address as the source address for Hellopacketspackets, even when forming adjacencies for IPv4 AF instances. In most deployments of OSPFv3 IPv4AF,AFs, it is required that BFD is used to monitor and verify IPv4 data plane connectivity between the routers on thelink and,link; hence, the BFD session issetupset 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 firsthello).Hello). The use of the Local Interface IPv4 Address TLV (as defined in <xreftarget="IFADDRTLV"/>)target="IFADDRTLV" format="default"/>) in the LLS blockofadvertised in OSPFv3 Hello packets for IPv4 AF instances makes this possible. Implementations that support OSPF BFD strict-mode for OSPFv3 IPv4 AF instancesMUST<bcp14>MUST</bcp14> include the Local Interface IPv4 Address TLV in the LLS blockofadvertised in their Hello packets whenever the B-bit is also set in the LLS Type 1 Extended Options andFlags field.Flags. A receiverMUST<bcp14>MUST</bcp14> ignore the B-bit (i.e., not operate instrict modestrict-mode for BFD) when the Local Interface IPv4 Address TLV is not present in OSPFv3 Hello messages for OSPFv3 IPv4 AFOSPFv3instances.</t> </section> <section anchor="GR"title="Gracefulnumbered="true" toc="default"> <name>Graceful RestartConsiderations">Considerations</name> <t>An implementation needs to handle scenarios where both graceful restart (GR) and the OSPF BFD strict-mode are deployed together. TheGRgraceful restart aspects related to process restart scenarios discussed insection 3.3 of<xreftarget="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 sessionestablishment,establishment in OSPF BFD strict-mode, the resultant delay in adjacency formation may affect or break the GR-based recovery. In such cases, it isRECOMMENDED<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 &numbered="true" toc="default"> <name>Operations and ManagementConsiderations">Considerations</name> <t>An implementationSHOULD<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 mayflapflap, resulting in OSPF adjacency flaps.This in turnIn 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 adjacencybringupfollowing BFD session establishment) and/or dampening (a delay in bringing up the OSPF adjacencybringupfollowing 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><xreftarget="I-D.ietf-ospf-yang"/>target="RFC9129" format="default"/> specifies the base OSPF YANGmodel.module. The required configuration and operational elements for this feature are expected to beintroduceintroduced as augmentation to this base OSPF YANGmodel.</t>module.</t> </section> <section anchor="BACKW"title="Backward Compatibility">numbered="true" toc="default"> <name>Backward Compatibility</name> <t>An implementationMUST<bcp14>MUST</bcp14> support OSPF adjacency formation and operations with a neighbor router that does not advertise the OSPF BFD strict-modecapability -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. ImplementationsMAY<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. ImplementationsMAY<bcp14>MAY</bcp14> provide a local configuration option to enable BFD without the OSPF BFDstrict-modestrict-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 blockofadvertised in Hello packets from its neighbors and continue to establish BFDsessions, 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 blockofadvertised 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 orimplementationsimplementation 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-bitishas been assigned the bit position0x00000010</t> <t>o In0x00000010.</li> <li>In the "Link Local Signaling TLV Identifiers (LLS Types)" registry, the Type 21ishas been assigned to the Local Interface IPv4 AddressTLV</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"/>" <xreftarget="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 OSPFhelloHello message could prevent an OSPF adjacency from forming or lead to the failureto detectof detecting bidirectional forwarding failures. If authentication is being used in the OSPF routing domain <xreftarget="RFC5709"/><xref target="RFC7474"/>,target="RFC5709" format="default"/> <xref target="RFC7474" format="default"/>, then the Cryptographic Authentication TLV <xreftarget="RFC5613"/> MUSTtarget="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 fromAcee 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 MozhiPerumal, Russ Housley, and Wes Hardaker.</t>Perumal"/>, <contact fullname="Russ Housley"/>, and <contact fullname="Wes Hardaker"/>.</t> <t>The authors would like to acknowledgeDylan<contact fullname="Dylan vanOudheusdenOudheusden"/> for highlighting the problems in using OSPF BFD strict-mode for BFDsessionsessions for OSPFv3 IPv4 AFinstance with OSPFv3instances andBaalajee S<contact fullname="Baalajee S"/> for his suggestions on the approach to address it.</t> <t>The authors would like to thankJohn 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>