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<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 8687: OSPF Routing with Cross-Address Family Traffic Engineering Tunnels</title>
<meta content="Anton Smirnov" name="author">
<meta content="Alvaro Retana" name="author">
<meta content="Michael Barnes" name="author">
<meta content="
       When using Traffic Engineering (TE) in a dual-stack IPv4/IPv6
      network, the Multiprotocol Label Switching (MPLS) TE Label Switched
      Path (LSP) infrastructure may be duplicated, even if the destination
      IPv4 and IPv6 addresses belong to the same remote router.


      In order to
      achieve an integrated MPLS TE LSP infrastructure, OSPF routes must be
      computed over MPLS TE tunnels created using information propagated in
      another OSPF instance. This issue is solved by advertising cross-address
      family (X-AF) OSPF TE information. 
       This document describes an update to RFC 5786 that allows for the easy
      identification of a router's local X-AF IP addresses. 
    " name="description">
<meta content="xml2rfc 2.35.0" name="generator">
<meta content="OSPF" name="keyword">
<meta content="IPv4" name="keyword">
<meta content="IPv6" name="keyword">
<meta content="TE" name="keyword">
<meta content="MPLS" name="keyword">
<meta content="8687" name="rfc.number">
<link href="rfc8687.xml" type="application/rfc+xml" rel="alternate">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
  this can be consolidated so that style settings occur only in one place, but
  for now the contents of this file consists first of the initial CSS work as
  provided to the RFC Formatter (xml2rfc) work, followed by itemized and
  commented changes found necssary during the development of the v3
  formatters.

*/

/* fonts */
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@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
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  width: extend-to-zoom;
}
@-ms-viewport {
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  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
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  font-size: 14px;
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  scroll-behavior: smooth;
}
.ears {
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}

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/* definition lists */
dl {
}
dl > dt {
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/* 
dl.nohang > dt {
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*/
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/* links */
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a[href] {
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/* XXX probably not this:
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/* The prepared/rendered info at the very bottom of the page */
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}

/* table of contents */
#toc  {
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}
nav.toc ul {
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}
nav.toc li {
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}
/* references */
.references dt {
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}
.references dd {
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}

.refInstance {
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.references .ascii {
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}

/* index */
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}
.index ul ul {
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}
.index li {
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/* make the index two-column on all but the smallest screens */
@media (min-width: 600px) {
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/* authors */
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address.vcard .nameRole {
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address.vcard .type {
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hr.addr {
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/* temporary notes */
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/* alternative layout for smaller screens */
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}

/* alternative layout for wide screens */
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/* pagination */
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/* This is commented out here, as the string-set: doesn't
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@page {
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/* Changes introduced to fix issues found during implementation */
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section {
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table td.text-right,
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/* Make the alternative author contact informatio look less like just another
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/* With it being possible to set tables with alignment
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address div.right {
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/* Provide table alignment support.  We can't use the alignX classes above
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table.center {
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 margin-right: auto;
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table.left {
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 margin-right: auto;
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/* Give the table caption label the same styling as the figcaption */
caption a[href] {
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/* Tweak the bcp14 keyword presentation */
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 h4 {
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/* Float artwork pilcrow to the right */
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/* Make pilcrows on dd visible */
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/* Make the placement of figcaption match that of a table's caption
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/* In print, the pilcrow won't show on hover, so prevent it from taking up space,
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}
/* Styling for the external metadata */
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<table class="ears">
<thead><tr>
<td class="left">RFC 8687</td>
<td class="center">OSPF Routing with Cross-AF TE Tunnels</td>
<td class="right">November 2019</td>
</tr></thead>
<tfoot><tr>
<td class="left">Smirnov, et al.</td>
<td class="center">Standards Track</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Internet Engineering Task Force (IETF)</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc8687" class="eref">8687</a></dd>
<dt class="label-updates">Updates:</dt>
<dd class="updates">
<a href="https://www.rfc-editor.org/rfc/rfc5786" class="eref">5786</a> </dd>
<dt class="label-category">Category:</dt>
<dd class="category">Standards Track</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2019-11" class="published">November 2019</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Authors:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">A. Smirnov</div>
<div class="org">Cisco Systems, Inc.</div>
</div>
<div class="author">
      <div class="author-name">A. Retana</div>
<div class="org">Futurewei Technologies, Inc.</div>
</div>
<div class="author">
      <div class="author-name">M. Barnes</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8687</h1>
<h1 id="title">OSPF Routing with Cross-Address Family Traffic Engineering Tunnels</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">When using Traffic Engineering (TE) in a dual-stack IPv4/IPv6
      network, the Multiprotocol Label Switching (MPLS) TE Label Switched
      Path (LSP) infrastructure may be duplicated, even if the destination
      IPv4 and IPv6 addresses belong to the same remote router.


      In order to
      achieve an integrated MPLS TE LSP infrastructure, OSPF routes must be
      computed over MPLS TE tunnels created using information propagated in
      another OSPF instance. This issue is solved by advertising cross-address
      family (X-AF) OSPF TE information.<a href="#section-abstract-1" class="pilcrow">¶</a></p>
<p id="section-abstract-2">This document describes an update to RFC 5786 that allows for the easy
      identification of a router's local X-AF IP addresses.<a href="#section-abstract-2" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
<section id="section-boilerplate.1">
        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This is an Internet Standards Track document.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc8687">https://www.rfc-editor.org/info/rfc8687</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="copyright">
<section id="section-boilerplate.2">
        <h2 id="name-copyright-notice">
<a href="#name-copyright-notice" class="section-name selfRef">Copyright Notice</a>
        </h2>
<p id="section-boilerplate.2-1">
            Copyright (c) 2019 IETF Trust and the persons identified as the
            document authors. All rights reserved.<a href="#section-boilerplate.2-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<span><a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a></span>) in effect on the date of
            publication of this document. Please review these documents
            carefully, as they describe your rights and restrictions with
            respect to this document. Code Components extracted from this
            document must include Simplified BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Simplified BSD License.<a href="#section-boilerplate.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a><a href="#section-toc.1-1.1.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1"><a href="#section-2" class="xref">2</a>.  <a href="#name-requirements-language" class="xref">Requirements Language</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="xref">3</a>.  <a href="#name-operation" class="xref">Operation</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-backward-compatibility" class="xref">Backward Compatibility</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.4.2.1">
                <p id="section-toc.1-1.4.2.1.1"><a href="#section-4.1" class="xref">4.1</a>.  <a href="#name-automatically-switched-opti" class="xref">Automatically Switched Optical Networks</a><a href="#section-toc.1-1.4.2.1.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="xref">7</a>.  <a href="#name-references" class="xref">References</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.7.2.1">
                <p id="section-toc.1-1.7.2.1.1"><a href="#section-7.1" class="xref">7.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.7.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.7.2.2">
                <p id="section-toc.1-1.7.2.2.1"><a href="#section-7.2" class="xref">7.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.7.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-acknowledgements" class="xref">Acknowledgements</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-appendix.b" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">TE extensions to <span><a href="#RFC3630" class="xref">OSPFv2</a> [<a href="#RFC3630" class="xref">RFC3630</a>]</span> 
      and <span><a href="#RFC5329" class="xref">OSPFv3</a> [<a href="#RFC5329" class="xref">RFC5329</a>]</span> have been
      described to support intra-area
      TE in IPv4 and IPv6 networks, respectively. In both cases, the TE
      database provides a tight coupling between the routed protocol and
      advertised TE signaling information. In other words, any use of the TE
      database is limited to IPv4 for <span><a href="#RFC2328" class="xref"> OSPFv2</a> [<a href="#RFC2328" class="xref">RFC2328</a>]</span>
      and IPv6 for <span><a href="#RFC5340" class="xref">OSPFv3 </a> [<a href="#RFC5340" class="xref">RFC5340</a>]</span>.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">In a dual-stack network, it may be desirable to set up common MPLS TE
      LSPs to carry traffic destined to addresses from different address
      families on a router. The use of common LSPs eases potential scalability
      and management concerns by halving the number of LSPs in the
      network.  Besides, it allows operators to group traffic based on
   business characteristics, class of service, and/or applications;
   the operators are not constrained by the network protocol used.<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">For example, an LSP created based on MPLS TE information propagated
      by an OSPFv2 instance can be used to transport both IPv4 and IPv6
      traffic, as opposed to using both OSPFv2 and OSPFv3 to provision a
      separate LSP for each address family. Even if, in some cases, the address-family-specific traffic is to be separated, calculation from a common TE
      database may prove to be operationally beneficial.<a href="#section-1-3" class="pilcrow">¶</a></p>
<p id="section-1-4">During the SPF calculation on the TE tunnel
      head-end router, OSPF
      computes shortcut routes using TE tunnels. A commonly used algorithm for
      computing shortcuts is defined in <span>[<a href="#RFC3906" class="xref">RFC3906</a>]</span>. For that or
      any similar algorithm to work with a common MPLS TE infrastructure in a
      dual-stack network, a requirement is to reliably map the X-AF addresses
      to the corresponding tail-end router. This mapping is a challenge
      because the Link State Advertisements (LSAs) containing the routing
      information are carried in one
      OSPF instance, while the TE calculations may be done using a TE database
      from a different OSPF instance.<a href="#section-1-4" class="pilcrow">¶</a></p>
<p id="section-1-5">A simple solution to this problem is to rely on the Router ID to
      identify a node in the corresponding OSPFv2 and OSPFv3 Link State
      Databases (LSDBs). This solution would mandate both instances on the
      same router to be configured with the same Router ID. However, relying
      on the correctness of configuration puts additional burden and cost on
      the operation of the network. The network becomes even more difficult to
      manage if OSPFv2 and OSPFv3 topologies do not match exactly, for example,
      if area borders are chosen differently in the two protocols. Also, if
      the routing processes do fall out of sync (e.g., having different Router
      IDs for local administrative reasons), there is no defined way for other
      routers to discover such misalignment and to take corrective measures
      (such as to avoid routing traffic through affected TE tunnels or
      alerting the network administrators). The use of misaligned Router IDs
      may result in delivering the traffic to the wrong tail-end router, which
      could lead to suboptimal routing or even traffic loops.<a href="#section-1-5" class="pilcrow">¶</a></p>
<p id="section-1-6">This document describes an update to <span>[<a href="#RFC5786" class="xref">RFC5786</a>]</span> that
      allows for the easy identification of a router's local X-AF IP
      addresses. <span>[<a href="#RFC5786" class="xref">RFC5786</a>]</span> defined the Node IPv4 Local Address
      and Node IPv6 Local Address sub-TLVs of the Node Attribute TLV for a
      router to advertise additional local IPv4 and IPv6 addresses. However,
      <span>[<a href="#RFC5786" class="xref">RFC5786</a>]</span> did not describe the advertisement and usage of
      these sub-TLVs when the address family of the advertised local address
      differed from the address family of the OSPF traffic engineering
      protocol.<a href="#section-1-6" class="pilcrow">¶</a></p>
<p id="section-1-7">This document updates <span>[<a href="#RFC5786" class="xref">RFC5786</a>]</span> so that a router can
      also announce one or more local X-AF addresses using the corresponding
      Local Address sub-TLV. Routers using the <span><a href="#RFC5786" class="xref">Node
      Attribute TLV</a> [<a href="#RFC5786" class="xref">RFC5786</a>]</span> can include non-TE-enabled interface addresses in
      their OSPF TE advertisements and also use the same sub-TLVs to carry
      X-AF information, facilitating the mapping described above.<a href="#section-1-7" class="pilcrow">¶</a></p>
<p id="section-1-8">The method specified in this document can also be used to compute the
      X-AF mapping of the egress Label Switching Router (LSR) for sub-LSPs of
      a Point-to-Multipoint LSP <span>[<a href="#RFC4461" class="xref">RFC4461</a>]</span>. Considerations of
      using Point-to-Multipoint MPLS TE for X-AF traffic forwarding is outside
      the scope of this document.<a href="#section-1-8" class="pilcrow">¶</a></p>
</section>
<section id="section-2">
      <h2 id="name-requirements-language">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-requirements-language" class="section-name selfRef">Requirements Language</a>
      </h2>
<p id="section-2-1">
    The key words "<span class="bcp14">MUST</span>", "<span class="bcp14">MUST NOT</span>",
    "<span class="bcp14">REQUIRED</span>", "<span class="bcp14">SHALL</span>", "<span class="bcp14">SHALL NOT</span>", "<span class="bcp14">SHOULD</span>", "<span class="bcp14">SHOULD NOT</span>",
    "<span class="bcp14">RECOMMENDED</span>", "<span class="bcp14">NOT RECOMMENDED</span>",
    "<span class="bcp14">MAY</span>", and "<span class="bcp14">OPTIONAL</span>" in this document are
    to be interpreted as described in BCP 14 <span>[<a href="#RFC2119" class="xref">RFC2119</a>]</span>
        <span>[<a href="#RFC8174" class="xref">RFC8174</a>]</span> when, and only when, they appear in all capitals,
    as shown here.<a href="#section-2-1" class="pilcrow">¶</a></p>
</section>
<section id="section-3">
      <h2 id="name-operation">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-operation" class="section-name selfRef">Operation</a>
      </h2>
<p id="section-3-1">To implement the X-AF routing technique described in this document,
      OSPFv2 will advertise the Node IPv6 Local Address sub-TLV and OSPFv3
      will advertise the Node IPv4 Local Address sub-TLV, possibly in addition
      to advertising other IP addresses as documented by <span>[<a href="#RFC5786" class="xref">RFC5786</a>]</span>.<a href="#section-3-1" class="pilcrow">¶</a></p>
<p id="section-3-2">Multiple instances of OSPFv3 are needed if it is used for both IPv4
      and IPv6 <span>[<a href="#RFC5838" class="xref">RFC5838</a>]</span>. The operation in this section is
      described with OSPFv2 as the protocol used for IPv4; that is the most
      common case. The case of OSPFv3 being used for IPv4 follows the same
      procedure as what is indicated for OSPFv2 below.<a href="#section-3-2" class="pilcrow">¶</a></p>
<p id="section-3-3">On a node that implements X-AF routing, each OSPF instance
      advertises, using the Node Local Address sub-TLV, all X-AF IPv6 (for
      OSPFv2 instance) or IPv4 (for OSPFv3) addresses local to the router that
      can be used by the Constrained Shortest Path First (CSPF) to calculate MPLS TE LSPs:<a href="#section-3-3" class="pilcrow">¶</a></p>
<ul>
<li id="section-3-4.1">The OSPF instance <span class="bcp14">MUST</span> advertise the IP address listed in the Router
          Address TLV <span>[<a href="#RFC3630" class="xref">RFC3630</a>]</span> <span>[<a href="#RFC5329" class="xref">RFC5329</a>]</span> of
          the X-AF instance maintaining the TE database.<a href="#section-3-4.1" class="pilcrow">¶</a>
</li>
        <li id="section-3-4.2">The OSPF instance <span class="bcp14">SHOULD</span> include additional local addresses
          advertised by the X-AF OSPF instance in its Node Local Address
          sub-TLVs.<a href="#section-3-4.2" class="pilcrow">¶</a>
</li>
        <li id="section-3-4.3">An implementation <span class="bcp14">MAY</span> advertise other local X-AF addresses.<a href="#section-3-4.3" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-3-5">When TE information is advertised in an OSPF instance, both natively
      (i.e., as per RFC <span>[<a href="#RFC3630" class="xref">RFC3630</a>]</span> or <span>[<a href="#RFC5329" class="xref">RFC5329</a>]</span>)
      and as X-AF Node Attribute TLV, it is left to local configuration to
      determine which TE database is used to compute routes for the OSPF
      instance.<a href="#section-3-5" class="pilcrow">¶</a></p>
<p id="section-3-6">On Area Border Routers (ABRs), each advertised X-AF IP address <span class="bcp14">MUST</span> be
      advertised into, at most, one area. If OSPFv2 and OSPFv3 ABRs coincide
      (i.e., the areas for all OSPFv2 and OSPFv3 interfaces
      are the same), then the X-AF addresses <span class="bcp14">MUST</span> be advertised into the same
      area in both instances. This allows other ABRs connected to the same set
      of areas to know with which area to associate computed MPLS TE
      tunnels.<a href="#section-3-6" class="pilcrow">¶</a></p>
<p id="section-3-7">During the X-AF routing calculation, X-AF IP addresses are used to
      map locally created LSPs to tail-end routers in the
      LSDB. The mapping algorithm can be described as:<a href="#section-3-7" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-3-8.1">Walk the list of all MPLS TE tunnels for which the computing
          router is a head end. For each MPLS TE tunnel T:<a href="#section-3-8.1" class="pilcrow">¶</a>
</li>
        <li class="ulEmpty" id="section-3-8.2">
          <ol start="1" type="1" class="normal" id="section-3-8.2.1">
            <li id="section-3-8.2.1.1">If T's destination address is from the same address family as the
          OSPF instance associated with the LSDB, then the extensions defined
          in this document do not apply.<a href="#section-3-8.2.1.1" class="pilcrow">¶</a>
</li>
            <li id="section-3-8.2.1.2">Otherwise, it is a X-AF MPLS TE tunnel. Note the tunnel's destination
          IP address.<a href="#section-3-8.2.1.2" class="pilcrow">¶</a>
</li>
            <li id="section-3-8.2.1.3">Walk the X-AF IP addresses in the LSDBs of all connected areas.
          If a matching IP address is found, advertised by router R in area A,
          then mark the tunnel T as belonging to area A and terminating on
          tail-end router R. Assign the intra-area SPF cost to reach router R
          within area A as the IGP cost of tunnel T.<a href="#section-3-8.2.1.3" class="pilcrow">¶</a>
</li>
          </ol>
</li>
      </ul>
<p id="section-3-9">After completing this calculation, each TE tunnel is associated with
      an area and tail-end router in terms of the routing LSDB of the
      computing OSPF instance and has a cost.<a href="#section-3-9" class="pilcrow">¶</a></p>
<p id="section-3-10">The algorithm described above is to be used only if the Node Local
      Address sub-TLV includes X-AF information.<a href="#section-3-10" class="pilcrow">¶</a></p>
<p id="section-3-11">Note that, for clarity of description, the mapping algorithm is
     specified as a single calculation.  Implementations may choose to support equivalent mapping
     functionality without implementing the algorithm as described.<a href="#section-3-11" class="pilcrow">¶</a></p>
<p id="section-3-12">As an example, consider a router in a dual-stack network 
      using OSPFv2 and OSPFv3 for IPv4 and IPv6 routing, respectively. Suppose the OSPFv2
      instance is used to propagate MPLS TE information and the router is
      configured to accept TE LSPs terminating at local addresses 198.51.100.1
      and 198.51.100.2. The router advertises in OSPFv2 the IPv4 address
      198.51.100.1 in the Router Address TLV, the additional local IPv4
      address 198.51.100.2 in the Node IPv4 Local Address sub-TLV, and other
      TE TLVs as required by <span>[<a href="#RFC3630" class="xref">RFC3630</a>]</span>. If the
      OSPFv3 instance in the network is enabled for X-AF TE routing (that is,
      to use MPLS TE LSPs computed by OSPFv2 for IPv6 routing), then the
      OSPFv3 instance of the router will advertise the Node IPv4 Local Address
      sub-TLV listing the local IPv4 addresses 198.51.100.1 and 198.51.100.2.
      Other routers in the OSPFv3 network will use this information to
      reliably identify this router as the egress LSR for MPLS TE LSPs
      terminating at either 198.51.100.1 or 198.51.100.2.<a href="#section-3-12" class="pilcrow">¶</a></p>
</section>
<section id="section-4">
      <h2 id="name-backward-compatibility">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-backward-compatibility" class="section-name selfRef">Backward Compatibility</a>
      </h2>
<p id="section-4-1">Only routers that serve as endpoints for one or more TE tunnels <span class="bcp14">MUST</span>
      be upgraded to support the procedures described herein:<a href="#section-4-1" class="pilcrow">¶</a></p>
<ul>
<li id="section-4-2.1">Tunnel tail-end routers advertise the Node IPv4 Local Address
          sub-TLV and/or the Node IPv6 Local Address sub-TLV.<a href="#section-4-2.1" class="pilcrow">¶</a>
</li>
        <li id="section-4-2.2">Tunnel head-end routers perform the X-AF routing calculation.<a href="#section-4-2.2" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-4-3"> Both the endpoints <span class="bcp14">MUST</span> be upgraded before the tail end starts
      advertising the X-AF information. Other routers in the network do not
      need to support X-AF procedures.<a href="#section-4-3" class="pilcrow">¶</a></p>
<section id="section-4.1">
        <h3 id="name-automatically-switched-opti">
<a href="#section-4.1" class="section-number selfRef">4.1. </a><a href="#name-automatically-switched-opti" class="section-name selfRef">Automatically Switched Optical Networks</a>
        </h3>
<p id="section-4.1-1"><span>[<a href="#RFC6827" class="xref">RFC6827</a>]</span> updates 
        <span>[<a href="#RFC5786" class="xref">RFC5786</a>]</span> by
        defining extensions to be used in an Automatically Switched Optical
        Network (ASON). The Local TE Router ID sub-TLV is required for
        determining ASON reachability. The implication is that if the Local TE
        Router ID sub-TLV is present in the Node Attribute TLV, then the
        procedures in <span>[<a href="#RFC6827" class="xref">RFC6827</a>]</span> apply, regardless of whether
        any X-AF information is advertised.<a href="#section-4.1-1" class="pilcrow">¶</a></p>
</section>
</section>
<section id="section-5">
      <h2 id="name-security-considerations">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-5-1">This document describes the use of the Local Address sub-TLVs to
      provide X-AF information. The advertisement of these sub-TLVs, in any
      OSPF instance, is not precluded by <span>[<a href="#RFC5786" class="xref">RFC5786</a>]</span>. As such, no
      new security threats are introduced beyond the considerations in <span><a href="#RFC2328" class="xref">OSPFv2</a> [<a href="#RFC2328" class="xref">RFC2328</a>]</span>, <span><a href="#RFC5340" class="xref">OSPFv3</a> [<a href="#RFC5340" class="xref">RFC5340</a>]</span>,
      and <span>[<a href="#RFC5786" class="xref">RFC5786</a>]</span>.<a href="#section-5-1" class="pilcrow">¶</a></p>
<p id="section-5-2">The X-AF information is not used for SPF computation or normal
      routing, so the mechanism specified here has no effect on IP routing.
      However, generating incorrect information or tampering with the
      sub-TLVs may have an effect on traffic engineering computations.
      Specifically, TE traffic may be delivered to the wrong tail-end router,
      which could lead to suboptimal routing, traffic loops, or exposing
      the traffic to attacker inspection or modification. These threats are
      already present in other TE-related specifications, and their
      considerations apply here as well, including <span>[<a href="#RFC3630" class="xref">RFC3630</a>]</span>
      and <span>[<a href="#RFC5329" class="xref">RFC5329</a>]</span>.<a href="#section-5-2" class="pilcrow">¶</a></p>
</section>
<section id="section-6">
      <h2 id="name-iana-considerations">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-6-1">This document has no IANA actions.<a href="#section-6-1" class="pilcrow">¶</a></p>
</section>
<section id="section-7">
      <h2 id="name-references">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-7.1">
        <h3 id="name-normative-references">
<a href="#section-7.1" class="section-number selfRef">7.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="RFC2119">[RFC2119]</dt>
        <dd>
<span class="refAuthor">Bradner, S.</span>, <span class="refTitle">"Key words for use in RFCs to Indicate Requirement Levels"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 2119</span>, <span class="seriesInfo">DOI 10.17487/RFC2119</span>, <time datetime="1997-03">March 1997</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>&gt;</span>. </dd>
<dt id="RFC3630">[RFC3630]</dt>
        <dd>
<span class="refAuthor">Katz, D.</span><span class="refAuthor">, Kompella, K.</span><span class="refAuthor">, and D. Yeung</span>, <span class="refTitle">"Traffic Engineering (TE) Extensions to OSPF Version 2"</span>, <span class="seriesInfo">RFC 3630</span>, <span class="seriesInfo">DOI 10.17487/RFC3630</span>, <time datetime="2003-09">September 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3630">https://www.rfc-editor.org/info/rfc3630</a>&gt;</span>. </dd>
<dt id="RFC5329">[RFC5329]</dt>
        <dd>
<span class="refAuthor">Ishiguro, K.</span><span class="refAuthor">, Manral, V.</span><span class="refAuthor">, Davey, A.</span><span class="refAuthor">, and A. Lindem, Ed.</span>, <span class="refTitle">"Traffic Engineering Extensions to OSPF Version 3"</span>, <span class="seriesInfo">RFC 5329</span>, <span class="seriesInfo">DOI 10.17487/RFC5329</span>, <time datetime="2008-09">September 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5329">https://www.rfc-editor.org/info/rfc5329</a>&gt;</span>. </dd>
<dt id="RFC5786">[RFC5786]</dt>
        <dd>
<span class="refAuthor">Aggarwal, R.</span><span class="refAuthor"> and K. Kompella</span>, <span class="refTitle">"Advertising a Router's Local Addresses in OSPF Traffic Engineering (TE) Extensions"</span>, <span class="seriesInfo">RFC 5786</span>, <span class="seriesInfo">DOI 10.17487/RFC5786</span>, <time datetime="2010-03">March 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5786">https://www.rfc-editor.org/info/rfc5786</a>&gt;</span>. </dd>
<dt id="RFC8174">[RFC8174]</dt>
      <dd>
<span class="refAuthor">Leiba, B.</span>, <span class="refTitle">"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 8174</span>, <span class="seriesInfo">DOI 10.17487/RFC8174</span>, <time datetime="2017-05">May 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>&gt;</span>. </dd>
</dl>
</section>
<section id="section-7.2">
        <h3 id="name-informative-references">
<a href="#section-7.2" class="section-number selfRef">7.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="RFC2328">[RFC2328]</dt>
        <dd>
<span class="refAuthor">Moy, J.</span>, <span class="refTitle">"OSPF Version 2"</span>, <span class="seriesInfo">STD 54</span>, <span class="seriesInfo">RFC 2328</span>, <span class="seriesInfo">DOI 10.17487/RFC2328</span>, <time datetime="1998-04">April 1998</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2328">https://www.rfc-editor.org/info/rfc2328</a>&gt;</span>. </dd>
<dt id="RFC3906">[RFC3906]</dt>
        <dd>
<span class="refAuthor">Shen, N.</span><span class="refAuthor"> and H. Smit</span>, <span class="refTitle">"Calculating Interior Gateway Protocol (IGP) Routes Over Traffic Engineering Tunnels"</span>, <span class="seriesInfo">RFC 3906</span>, <span class="seriesInfo">DOI 10.17487/RFC3906</span>, <time datetime="2004-10">October 2004</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3906">https://www.rfc-editor.org/info/rfc3906</a>&gt;</span>. </dd>
<dt id="RFC4461">[RFC4461]</dt>
        <dd>
<span class="refAuthor">Yasukawa, S., Ed.</span>, <span class="refTitle">"Signaling Requirements for Point-to-Multipoint Traffic-Engineered MPLS Label Switched Paths (LSPs)"</span>, <span class="seriesInfo">RFC 4461</span>, <span class="seriesInfo">DOI 10.17487/RFC4461</span>, <time datetime="2006-04">April 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4461">https://www.rfc-editor.org/info/rfc4461</a>&gt;</span>. </dd>
<dt id="RFC5340">[RFC5340]</dt>
        <dd>
<span class="refAuthor">Coltun, R.</span><span class="refAuthor">, Ferguson, D.</span><span class="refAuthor">, Moy, J.</span><span class="refAuthor">, and A. Lindem</span>, <span class="refTitle">"OSPF for IPv6"</span>, <span class="seriesInfo">RFC 5340</span>, <span class="seriesInfo">DOI 10.17487/RFC5340</span>, <time datetime="2008-07">July 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5340">https://www.rfc-editor.org/info/rfc5340</a>&gt;</span>. </dd>
<dt id="RFC5838">[RFC5838]</dt>
        <dd>
<span class="refAuthor">Lindem, A., Ed.</span><span class="refAuthor">, Mirtorabi, S.</span><span class="refAuthor">, Roy, A.</span><span class="refAuthor">, Barnes, M.</span><span class="refAuthor">, and R. Aggarwal</span>, <span class="refTitle">"Support of Address Families in OSPFv3"</span>, <span class="seriesInfo">RFC 5838</span>, <span class="seriesInfo">DOI 10.17487/RFC5838</span>, <time datetime="2010-04">April 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5838">https://www.rfc-editor.org/info/rfc5838</a>&gt;</span>. </dd>
<dt id="RFC6827">[RFC6827]</dt>
      <dd>
<span class="refAuthor">Malis, A., Ed.</span><span class="refAuthor">, Lindem, A., Ed.</span><span class="refAuthor">, and D. Papadimitriou, Ed.</span>, <span class="refTitle">"Automatically Switched Optical Network (ASON) Routing for OSPFv2 Protocols"</span>, <span class="seriesInfo">RFC 6827</span>, <span class="seriesInfo">DOI 10.17487/RFC6827</span>, <time datetime="2013-01">January 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6827">https://www.rfc-editor.org/info/rfc6827</a>&gt;</span>. </dd>
</dl>
</section>
</section>
<div id="Acknowledgements">
<section id="section-appendix.a">
      <h2 id="name-acknowledgements">
<a href="#name-acknowledgements" class="section-name selfRef">Acknowledgements</a>
      </h2>
<p id="section-appendix.a-1">The authors would like to thank Peter Psenak and Eric Osborne for
      early discussions and Acee Lindem for discussing compatibility with ASON
      extensions. Also, Eric Vyncke, Ben Kaduk, and Roman Danyliw provided
      useful comments.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
<p id="section-appendix.a-2">We would also like to thank the authors of RFC 5786 for laying down
      the foundation for this work.<a href="#section-appendix.a-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="section-appendix.b">
      <h2 id="name-authors-addresses">
<a href="#name-authors-addresses" class="section-name selfRef">Authors' Addresses</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Anton Smirnov</span></div>
<div dir="auto" class="left"><span class="org">Cisco Systems, Inc.</span></div>
<div dir="auto" class="left"><span class="street-address">De Kleetlaan 6a</span></div>
<div dir="auto" class="left">
<span class="postal-code">1831</span> <span class="locality">Diegem</span>
</div>
<div dir="auto" class="left"><span class="country-name">Belgium</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:as@cisco.com" class="email">as@cisco.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Alvaro Retana</span></div>
<div dir="auto" class="left"><span class="org">Futurewei Technologies, Inc.</span></div>
<div dir="auto" class="left"><span class="street-address">2330 Central Expressway</span></div>
<div dir="auto" class="left">
<span class="locality">Santa Clara</span>, <span class="region">CA</span> <span class="postal-code">95050</span>
</div>
<div dir="auto" class="left"><span class="country-name">United States of America</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:alvaro.retana@futurewei.com" class="email">alvaro.retana@futurewei.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Michael Barnes</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:michael_barnes@usa.net" class="email">michael_barnes@usa.net</a>
</div>
</address>
</section>
</div>
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