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<!ENTITY RFC6987 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6987.xml">
<!ENTITY RFC7770 SYSTEM "https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7770.xml">
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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" submissionType="IETF"
     consensus="true" docName="draft-ietf-ospf-ospfv2-hbit-12" number="8770" category="std" updates="6987" ipr="trust200902"> ipr="trust200902" obsoletes="" xml:lang="en" sortRefs="true" symRefs="true" tocInclude="true" version="3">
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   <front>
    <title>Host Router Support for OSPFv2</title>
    <seriesInfo name="RFC" value="8770"/>
    <author fullname="Keyur Patel" initials="K." surname="Patel">
      <organization>Arrcus</organization>
	<address><email>keyur@arrcus.com</email>
      <address>
        <email>keyur@arrcus.com</email>
      </address>
    </author>
    <author fullname="Padma Pillay-Esnault" initials="P." surname="Pillay-Esnault">
      <organization>PPE Consulting</organization>
	<address><email>padma.ietf@gmail.com</email>
      <address>
        <email>padma.ietf@gmail.com</email>
      </address>
    </author>
    <author fullname="Manish Bhardwaj" initials="M." surname="Bhardwaj">
      <organization>Cisco Systems</organization>
	<address><postal><street>170
      <address>
        <postal>
          <street>170 W. Tasman Drive</street>
	<street>San Jose,  CA 95134</street>
	<street>USA</street>
          <city>San Jose</city>
          <region>CA</region>
          <code>95134</code>
          <country>United States of America</country>
        </postal>
        <email>manbhard@cisco.com</email>
      </address>
    </author>
    <author fullname="Serpil Bayraktar" initials="S." surname="Bayraktar">
      <organization>Cisco Systems</organization>
	<address><postal><street>170
      <address>
        <postal>
          <street>170 W. Tasman Drive</street>
	<street>San Jose,  CA 95134</street>
	<street>USA</street>
          <city>San Jose</city>
          <region>CA</region>
          <code>95134</code>
          <country>United States of America</country>
        </postal>
        <email>serpil@cisco.com</email>
      </address>
    </author>
    <date day="18" month="December" year="2019"/>
	<workgroup>OSPF</workgroup>
	<abstract><t> month="April" year="2020"/>

<keyword>non-transit</keyword>

    <abstract>
      <t>
   The Open Shortest Path First Version 2 (OSPFv2) protocol does not
   have a mechanism for a node to repel transit traffic if it is on the
   shortest path.  This document defines a bit (Host-bit) that called the Host-bit (H-bit). This bit enables a
   router to advertise that it is a non-transit router.  It  This document also
   describes the changes needed to support the H-bit in the domain.  In
   addition, this document updates RFC 6987 to advertise type-2 Type 2 External
   and Not-So-Stubby-Area Not-So-Stubby Area (NSSA) Link State Advertisements (LSAs)
   (RFC 3101) with a high cost in order to repel traffic effectively.</t>
    </abstract>
  </front>
  <middle>
    <section title="Introduction" anchor="sect-1"><t> anchor="sect-1" numbered="true" toc="default">
      <name>Introduction</name>
      <t>
   The OSPFv2 protocol specifies a Shortest Path First (SPF) algorithm
   that identifies transit vertices based on their adjacencies.
   Therefore, OSPFv2 does not have a mechanism to prevent traffic
   transiting a participating node if it is a transit vertex in the only
   existing or shortest path to the destination.  The use of metrics to
   make the node undesirable can help to repel traffic only if an
   alternative better route exists.</t>
      <t>
   A mechanism to move traffic away from the shortest path is
   particularly useful for a number of use cases:</t>

	<t><list style="numbers"><t>To gracefully isolate
      <ol spacing="normal" type="1">
        <li>Graceful isolation of a router router, to avoid blackhole scenarios when
       there is a reload and possible long reconvergence times.</t>

	<t>Closet Switches times.</li>
        <li>Closet switches that are usually not usually used for transit traffic but need
       to participate in the topology.</t>

	<t>Overloaded topology.</li>
        <li>Overloaded routers that could use such a capability to temporarily
       repel traffic until they stabilize.</t>

	<t>BGP Route reflectors stabilize.</li>
        <li>BGP route reflectors, known as virtual Route Reflectors (vRRs), Reflectors,
       that are not in the forwarding path but are in central locations
       such as data centers.  Such Route Reflectors typically route reflectors are typically used
       for route distribution and are not capable of forwarding transit
       traffic.  However, they need to learn the OSPF topology to
       perform SPF computation for optimal routes and reachability
       resolution for its their clients
       <xref target="I-D.ietf-idr-bgp-optimal-route-reflection"/>.</t>

	</list>
	</t> target="BGP-ORR" format="default"/>.</li>
      </ol>
      <t>
   This document describes the functionality provided by the Host-bit (H-bit) (H-bit);
   this functionality that prevents other OSPFv2 routers from using the host router by excluding
   it in path calculations for transit traffic in OSPFv2 routing
   domains.  If the H-bit is set set, then the calculation of the shortest-
   path
   shortest-path tree for an area, as described in section 16.1 of <xref target="RFC2328"/>, target="RFC2328" sectionFormat="of" section="16.1"/>, is
   modified by including a check to verify that transit vertices DO NOT
   have the H-bit set (see <xref target="sect-4"/>). target="sect-4" format="default"/>).  Furthermore, in order to repel
   traffic effectively, this document updates <xref target="RFC6987"/> is updated target="RFC6987"
   format="default"/> so that type-2 Type&nbsp;2 External and
   NSSA LSAs Not-So-Stubby Area (NSSA)
   Link State Advertisements (LSAs) <xref target="RFC3101"/>
   are advertised with a high cost (see <xref target="sect-6"/>).  Open
   Shortest Path First Version 3 target="sect-6" format="default"/>).  OSPFv3 <xref target="RFC5340"/> defines an
   option bit for router-LSAs bit, known as the R-bit in <xref target="RFC5340"/> to support a R-bit, for router-LSAs; the H-bit supports similar functionality.</t>
    </section>
    <section title="Requirements Language" anchor="sect-2"><t>
   The anchor="sect-2" 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>
    </section>
    <section title="Host-bit Support" anchor="sect-3"><t> anchor="sect-3" numbered="true" toc="default">
      <name>Host-Bit Support</name>
      <t>
   This document defines a new router-LSA bit bit, known as the Host Bit Host-bit or
   the H-bit.  An OSPFv2 router advertising a router-LSA with the H-bit
   set indicates that it MUST NOT <bcp14>MUST NOT</bcp14> be used as a transit router (see
   <xref target="sect-4"/>) target="sect-4" format="default"/>) by other OSPFv2 routers in the
   area supporting that support the H-bit functionality.</t>
      <t>
   If the H-bit is not set set, then backwards backward compatibility is achieved achieved, as
   the behavior will be the same as in <xref target="RFC2328"/>.</t> target="RFC2328" format="default"/>.</t>
      <figure title="OSPF Router-LSA" anchor="ure-ospf-router-lsa"><artwork><![CDATA[ anchor="ure-ospf-router-lsa">
        <name>OSPF Router-LSA</name>
        <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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |            LS age             |     Options   |       1       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Link State ID                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     Advertising Router                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     LS sequence number                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         LS checksum           |             length            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |H|0|0|N|W|V|E|B|        0      |            # links            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Link ID                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Link Data                             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Type      |     # TOS     |            metric             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              ...                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      TOS      |        0      |          TOS metric           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Link ID                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         Link Data                             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              ...                              |
]]></artwork>                              |]]></artwork>
      </figure>
	<t><list style="hanging" hangIndent="-1"><t hangText="Bit

        <t>Bit H is the high-order bit of the OSPF flags flags, as shown below.">
	<vspace blankLines="0"/>
	</t>

	</list>
	</t> below.</t>
      <figure title="OSPF anchor="ure-ospf-router-lsa-option-bits">
        <name>OSPF Router-LSA Option bits" anchor="ure-ospf-router-lsa-option-bits"><artwork><![CDATA[ Bits</name>
        <artwork name="" type="" align="left" alt=""><![CDATA[
                            0 1 2 3 4 5 6 7
                            +-+-+-+-+-+-+-+-+
                            |H|0|0|N|W|V|E|B|
                            +-+-+-+-+-+-+-+-+
]]></artwork>
                            +-+-+-+-+-+-+-+-+]]></artwork>
      </figure>
      <t>
   When the H-bit is set, the OSPFv2 router is a Host host (non-transit)
   router and is incapable of forwarding transit traffic.  In this mode,
   the other OSPFv2 routers in the area MUST NOT <bcp14>MUST NOT</bcp14> use the host router for
   transit traffic, traffic but may send traffic to its local destinations.</t>
      <t>
   An OSPFv2 router originating a router-LSA with the H-bit set MUST <bcp14>MUST</bcp14>
   advertise all its non-stub links with a link cost of MaxLinkMetric
   <xref target="RFC6987"/>.</t> target="RFC6987" format="default"/>.</t>
      <t>
   When the H-bit is set, an Area Border Router (ABR) MUST <bcp14>MUST</bcp14> advertise the
   same H-bit setting in its self-originated router-LSAs for all
   attached areas.  The consistency of the setting will prevent inter-
   area
   inter&nbhy;area traffic transiting through the router by suppressing
   advertisement
   advertisements of prefixes from other routers in the area in its
   summary LSAs.
   summary-LSAs.  Only IPv4 prefixes associated with its local
   interfaces MUST <bcp14>MUST</bcp14> be advertised in summary-LSAs to provide reachability
   to end hosts attached to a router with the H-bit set.</t>
      <t>
   When the H-bit is set set, the host router cannot act as an AS Boundary Autonomous System
   Border Router (ASBR).  Indeed, ASBR ASBRs are transit routers to prefixes that are
   typically imported through redistribution of prefixes from other
   routing protocols.  Therefore, non-local IPv4 prefixes, e.g., those
   imported from other routing protocols, SHOULD NOT <bcp14>SHOULD NOT</bcp14> be advertised in
   AS-external-LSAs if the H-bit is set.  Some use cases, such as an
   overloaded router or a router being gracefully isolated, may benefit
   from continued advertisement advertisements of non-local prefixes.  In these cases,
   the type 2-metric Type&nbsp;2 metric in AS-external-LSAs MUST <bcp14>MUST</bcp14> be set to
   LSInfinity <xref target="RFC2328"/> to
   repel traffic.(see Section 6 traffic (see <xref target="sect-6"/> of this document).</t>
    </section>
    <section title="SPF Modifications" anchor="sect-4"><t> anchor="sect-4" numbered="true" toc="default">
      <name>SPF Modifications</name>
      <t>
   The SPF calculation described in section 16.1 <xref target="RFC2328"/> will be target="RFC2328" sectionFormat="of"
   section="16.1"/> is
   modified to ensure that the routers originating router-LSAs with the
   H-bit set will not be used for transit traffic.  The  Step 2 (2) is
   modified to include a check on H-bit the H-bit, as shown below.  (Please note
   that all of the sub-procedures of Step 2 (2) remain unchanged and are not included in
   the excerpt below.)</t>

	<t><list style="empty" hangIndent="13">
	<t><list style="hanging" hangIndent="3"><t hangText="2) Call
      <ul empty="true" spacing="normal">
        <li>
          <dl newline="false" spacing="normal" indent="5">
            <dt>(2)</dt><dd>Call the vertex just added to the">
	<vspace blankLines="0"/> the
            tree vertex V. "vertex V".  Examine the LSA
            associated with vertex V.  This is
            a lookup in the Area A's Area&nbsp;A's link state
            database based on the Vertex ID. If
            this is a router-LSA, and the H-bit
            of the router-LSA is set, and
            vertex V is not the root, then the
            router should not be used for transit
            and step Step (3) should be executed
            immediately. If this is a router-LSA, router-LSA
            and bit V of the router-LSA (see
                   Section
            Appendix A.4.2) is set, set Area A's
            TransitCapability to TRUE. In any case,
            each link described by the LSA gives
            the cost to an adjacent vertex.  For
            each described link, link (say it joins
            vertex V to vertex W):
	</t>

	</list>
	</t>

	</list>
	</t> W):</dd>
          </dl>
        </li>
      </ul>
    </section>
    <section title="Auto Discovery anchor="sect-5" numbered="true" toc="default">
      <name>Autodiscovery and Backward Compatibility" anchor="sect-5"><t> Compatibility</name>
      <t>
   To reduce the possibility of any routing loops due to partial
   deployment, this document defines an OSPF Router Information (RI) LSA
   capability bit <xref target="RFC7770"/> capability.  The target="RFC7770" format="default"/>.  See
   <xref target="sect-7"/> (<xref target="tab-2"/>).
      </t>

   <t>The RI LSA MUST <bcp14>MUST</bcp14> be area-scoped.  Bit:</t>

	<t><list style="empty" hangIndent="7">
	<t><list style="hanging" hangIndent="-1"><t hangText="Bit">
	Capabilities
	<vspace blankLines="0"/>
	<list style="empty"><t>          7         Host Router Support capability</t>

	</list>
	</t>

	</list>
	</t>

	</list>
	</t>

	<t><list hangIndent="7" style="hanging"><t>
          Table 1: OSPF Router Information LSA Capabilities</t>

	</list>
	</t> area-scoped.</t>
      <t>
   Auto Discovery
   Autodiscovery via announcement of the OSPF Host Router Support Capability capability
   (<xref target="sect-7"/>)
   ensures that the H-bit functionality and its associated SPF changes
   MUST
   <bcp14>MUST</bcp14> only take effect if all the routers in a given OSPF area support
   this functionality.</t>
      <t>
   In normal operation, it is possible that the RI LSA will fail to
   reach all routers in an area in a timely manner.  For example, if a
   new router without H-bit support joins an area that previously had
   only H-bit capable H-bit-capable routers with the H-bit set set, then it may take some time
   for the RI LSA to propagate to all routers.  While it is propagating, the
   routers in the area will gradually detect the presence of a router
   that does not supporting support the capability and will revert back to the normal SPF
   calculation.  During the propagation time, the area as a whole is
   unsure of the status of the new router, and that router; this type of situation can cause temporary
   transient loops.</t>
      <t>
   The following recommendations will mitigate transient routing loops:</t>

	<t><list style="symbols"><t>Implementations
      <ul spacing="normal">
        <li>Implementations are RECOMMENDED <bcp14>RECOMMENDED</bcp14> to provide a configuration
      parameter to manually override enforcement of the H-bit
      functionality in partial deployments where the topology guarantees
      that OSPFv2 routers not supporting the H-bit do not compute routes
      resulting in routing loops.</t>

	<t>All loops.</li>
        <li>All routers with the H-bit set MUST <bcp14>MUST</bcp14> advertise all of the router's
      non-stub links with a metric equal to MaxLinkMetric <xref target="RFC6987"/> target="RFC6987" format="default"/> in
      its LSAs in order to avoid prevent OSPFv2 (unless last resort) routers (unless a last-resort path)
      that do not
      supporting support the H-bit from attempting to use it the non-stub links for transit
      traffic.</t>

	<t>All
      traffic.</li>
        <li>All routers supporting the H-Bit MUST H-bit <bcp14>MUST</bcp14> check the RI LSAs of all
      nodes in the area to verify that all nodes support the H-Bit H-bit
      before actively using the H-Bit H-bit feature.  If any router does not
      advertise the OSPF Host Router Support capability (<xref target="sect-7"/>), then the SPF
      Modifications (<xref target="sect-4"/>) MUST NOT
      modifications described in <xref target="sect-4" format="default"/> <bcp14>MUST NOT</bcp14> be used in the area.</t>

	</list>
	</t> area.</li>
      </ul>
    </section>
    <section title="OSPF AS-External-LSAs/NSSA LSAs anchor="sect-6" numbered="true" toc="default">
      <name>OSPF AS-External-LSAs / NSSA-LSAs with Type 2 Metrics" anchor="sect-6"><t> Metrics</name>
      <t>
   When calculating the path to a prefix in an OSPF AS-External-LSA AS-external-LSA or
   NSSA-LSA <xref target="RFC3101"/> target="RFC3101" format="default"/> with a Type-2 Type&nbsp;2 metric, the advertised Type-2 Type&nbsp;2 metric
   is taken as more significant than the OSPF intra-area or inter-area
   path.  Hence, advertising the links with MaxLinkMetric as specified
   in <xref target="RFC6987"/> target="RFC6987" format="default"/> does not discourage transit
   traffic when calculating AS
   external AS-external or NSSA routes with Type-2 Type&nbsp;2 metrics.</t>
      <t>
   Consequently, this document updates <xref target="RFC6987"/> is updated target="RFC6987" format="default"/> so that the Type-2 Type&nbsp;2 metric in any
   self-originated AS-External-LSAs AS-external-LSAs or NSSA-LSAs is advertised as
   LSInfinity-1 <xref target="RFC2328"/>. target="RFC2328" format="default"/>.
  If the H-bit is set, then the Type-2 Type&nbsp;2 metric
   MUST
   <bcp14>MUST</bcp14> be set to LSInfinity.</t>
    </section>
    <section title="IANA Considerations" anchor="sect-7"><t>
   This document requests the anchor="sect-7" numbered="true" toc="default">
      <name>IANA Considerations</name>
      <t>
   IANA to assign has registered the 0x80 following value to the Host-
   Bit (H-bit)in in the OSPFv2
   "OSPFv2 Router Properties Registry</t>

	<t><list style="empty" hangIndent="7">
	<t><list style="hanging" hangIndent="-1"><t hangText="Value">
	Description                   Reference
	<vspace blankLines="0"/>
	</t>

	<t hangText="0x80">
	Host (H-bit)                 This Document
	<vspace blankLines="0"/>
	</t>

	</list>
	</t>

	</list>
	</t> Registry".</t>

<table anchor="tab-1">
  <name>H-Bit</name>
  <thead>
    <tr>
      <th>Value</th>
      <th>Description</th>
      <th>Reference</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>0x80</td>
      <td>Host (H-bit)</td>
      <td>RFC 8770</td>
    </tr>
  </tbody>
</table>

      <t>
   This document requests the
   IANA to assign the Bit Number value of 7
   to has registered the Host Router Support Capability following in the OSPF "OSPF Router
   Informational Capability Bits Registry.</t>

	<t><list style="empty" hangIndent="7">
	<t><list style="hanging" hangIndent="3"><t hangText="Bit Number">
	Capability Name           Reference
	<vspace blankLines="1"/>
	7          OSPF Bits" registry.</t>

<table anchor="tab-2">
  <name>OSPF Host Router        This Document
	</t>

	</list>
	</t>

	</list>
	</t> Capability Bit</name>
  <thead>
    <tr>
      <th>Bit Number</th>
      <th>Capability Name</th>
      <th>Reference</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td align="center">7</td>
      <td>OSPF Host Router</td>
      <td>RFC 8770</td>
    </tr>
  </tbody>
</table>

    </section>
    <section title="Security Considerations" anchor="sect-8"><t> anchor="sect-8" numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>
   This document introduces the H-bit H-bit, which is a capability feature that
   restricts the use of a router for transit, while only its local
   destinations are reachable.  This is a subset of the operations of a
   normal router and therefore should not introduce new security
   considerations beyond those already known in OSPFv2 <xref target="RFC2328"/>. target="RFC2328" format="default"/>.  The
   feature introduces the advertising advertisement of a host router capability
   information to all OSPFv2 routers in an area.  This information can
   be leveraged for discovery and verification that all routers in the
   area support the capability before the feature is turned on.  In the
   event that a rogue or buggy router advertises incorrectly advertises its
   capability the
   capability, possible cases are:</t>

	<t><list style="symbols"><t>The scenarios are as follows:</t>
      <ul spacing="normal">
        <li>The router does not have the capability but sends the H-Bit H-bit set in
      its LSAs: LSAs. In this case, there is a possibility of a routing loop.
      However loop is possible.
      However, this is mitigated by the fact that this router should be
      avoided anyway.  Moreover, the link metrics cost (MaxLinkMetric)
      of this router will mitigate this situation.  In any case, a
      router advertising the H-bit capability without its links link metrics cost
      equal to MaxLinkMetric may could be an indicator that this is a rogue
      router and should be avoided.</t>

	<t>The avoided.</li>
        <li>The router has the capability but sends the H-Bit H-bit clear in its
      LSAs:
      LSAs. In this case, the router merely prevents the support of other
      H-bit routers in the area and prevents all the routers to run from running the modified
      SPF.  The impact is  Any impacts are also mitigated in this scenario, as other H-Bit H-bit routers in the
      area also advertise the MaxLinkMetric cost cost, so they will still be
      avoided unless they are the last resort path.</t>

	<t>The last&nbhy;resort path.</li>
        <li>The rogue router is on the only transit path for some destinations
      and sends the H-Bit H-bit set (for no good/valid reason) in its LSAs LSAs, and
      effectively partition partitions the network.  This case is indistinguishable
      from the normal case where the an operator may consciously decide to
      set the H-bit to perform maintenance on a router that is on the
      only transit path.  The OSPF protocol will continue to function
      within the partitioned domains.</t>

	</list>
	</t> domains.</li>
      </ul>
    </section>
  </middle>
  <back>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2328.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6987.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7770.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
      </references>
      <references>
        <name>Informative References</name>

<!-- draft-ietf-idr-bgp-optimal-route-reflection (I-D Exists) -->
<!-- Repository file missing "editor" entry, so have to do "long way" -->
        <reference anchor="BGP-ORR"
target="https://tools.ietf.org/html/draft-ietf-idr-bgp-optimal-route-reflection-20">
          <front>
            <title>BGP Optimal Route Reflection (BGP-ORR)</title>
            <seriesInfo name="Work in Progress, Internet-Draft," value="draft-ietf-idr-bgp-optimal-route-reflection-20"/>
            <author initials="R" surname="Raszuk" fullname="Robert Raszuk" role="editor">
              <organization/>
            </author>
            <author initials="C" surname="Cassar" fullname="Christian Cassar">
              <organization/>
            </author>
            <author initials="E" surname="Aman" fullname="Erik Aman">
              <organization/>
            </author>
            <author initials="B" surname="Decraene" fullname="Bruno Decraene">
              <organization/>
            </author>
            <author initials="K" surname="Wang" fullname="Kevin Wang">
              <organization/>
            </author>
            <date month="January" day="8" year="2020"/>
          </front>
        </reference>

<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3101.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5340.xml"/>
      </references>
    </references>
    <section title="Acknowledgements" anchor="sect-9"><t> anchor="acknowledgements" numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>
   The authors would like to acknowledge Hasmit Grover <contact fullname="Hasmit Grover"/> for discovery of discovering
   the limitation in <xref target="RFC6987"/>, Acee Lindem, Abhay Roy, David Ward,
   Burjiz Pithawala, target="RFC6987" format="default"/>, and Michael Barnes <contact
   fullname="Acee Lindem"/>, <contact fullname="Abhay Roy"/>, <contact
   fullname="David Ward"/>, <contact fullname="Burjiz Pithawala"/>, and <contact fullname="Michael Barnes"/> for their comments.</t>
    </section>

	</middle>

	<back>
	<references title="Normative References">
	&RFC2119;
	&RFC2328;
	&RFC6987;
	&RFC7770;
	&RFC8174;
	</references>
	<references title="Informative References">
	&I-D.ietf-idr-bgp-optimal-route-reflection;
	&RFC3101;
	&RFC5340;
	</references>
  </back>
</rfc>