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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 8665: OSPF Extensions for Segment Routing</title>
<meta content="Peter Psenak" name="author">
<meta content="Stefano Previdi" name="author">
<meta content="Clarence Filsfils" name="author">
<meta content="Hannes Gredler" name="author">
<meta content="Rob Shakir" name="author">
<meta content="Wim Henderickx" name="author">
<meta content="Jeff Tantsura" name="author">
<meta content='
       Segment Routing (SR) allows a flexible definition of end-to-end
      paths within IGP topologies by encoding paths as sequences of
      topological subpaths called "segments". These segments are advertised
      by the link-state routing protocols (IS-IS and OSPF). 
       This document describes the OSPFv2 extensions required for Segment Routing. 
    ' name="description">
<meta content="xml2rfc 2.35.0" name="generator">
<meta content="MPLS" name="keyword">
<meta content="SID" name="keyword">
<meta content="IGP" name="keyword">
<meta content="OSPF" name="keyword">
<meta content="Label advertisement" name="keyword">
<meta content="Segment Routing" name="keyword">
<meta content="8665" name="rfc.number">
<link href="rfc8665.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 */
@import url('https://fonts.googleapis.com/css?family=Noto+Sans'); /* Sans-serif */
@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
  zoom: 1.0;
  width: extend-to-zoom;
}
@-ms-viewport {
  width: extend-to-zoom;
  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
  background-color: #fff;
  font-size: 14px;
  font-family: 'Noto Sans', Arial, Helvetica, sans-serif;
  line-height: 1.6;
  scroll-behavior: smooth;
}
.ears {
  display: none;
}

/* headings */
#title, h1, h2, h3, h4, h5, h6 {
  margin: 1em 0 0.5em;
  font-weight: bold;
  line-height: 1.3;
}
#title {
  clear: both;
  border-bottom: 1px solid #ddd;
  margin: 0 0 0.5em 0;
  padding: 1em 0 0.5em;
}
.author {
  padding-bottom: 4px;
}
h1 {
  font-size: 26px;
  margin: 1em 0;
}
h2 {
  font-size: 22px;
  margin-top: -20px;  /* provide offset for in-page anchors */
  padding-top: 33px;
}
h3 {
  font-size: 18px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h4 {
  font-size: 16px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h5, h6 {
  font-size: 14px;
}
#n-copyright-notice {
  border-bottom: 1px solid #ddd;
  padding-bottom: 1em;
  margin-bottom: 1em;
}
/* general structure */
p {
  padding: 0;
  margin: 0 0 1em 0;
  text-align: left;
}
div, span {
  position: relative;
}
div {
  margin: 0;
}
.alignRight.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignRight.art-text pre {
  padding: 0;
}
.alignRight {
  margin: 1em 0;
}
.alignRight > *:first-child {
  border: none;
  margin: 0;
  float: right;
  clear: both;
}
.alignRight > *:nth-child(2) {
  clear: both;
  display: block;
  border: none;
}
svg {
  display: block;
}
.alignCenter.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignCenter.art-text pre {
  padding: 0;
}
.alignCenter {
  margin: 1em 0;
}
.alignCenter > *:first-child {
  border: none;
  /* this isn't optimal, but it's an existence proof.  PrinceXML doesn't
     support flexbox yet.
  */
  display: table;
  margin: 0 auto;
}

/* lists */
ol, ul {
  padding: 0;
  margin: 0 0 1em 2em;
}
ol ol, ul ul, ol ul, ul ol {
  margin-left: 1em;
}
li {
  margin: 0 0 0.25em 0;
}
.ulCompact li {
  margin: 0;
}
ul.empty, .ulEmpty {
  list-style-type: none;
}
ul.empty li, .ulEmpty li {
  margin-top: 0.5em;
}
ul.compact, .ulCompact,
ol.compact, .olCompact {
  line-height: 100%;
  margin: 0 0 0 2em;
}

/* definition lists */
dl {
}
dl > dt {
  float: left;
  margin-right: 1em;
}
/* 
dl.nohang > dt {
  float: none;
}
*/
dl > dd {
  margin-bottom: .8em;
  min-height: 1.3em;
}
dl.compact > dd, .dlCompact > dd {
  margin-bottom: 0em;
}
dl > dd > dl {
  margin-top: 0.5em;
  margin-bottom: 0em;
}

/* links */
a {
  text-decoration: none;
}
a[href] {
  color: #22e; /* Arlen: WCAG 2019 */
}
a[href]:hover {
  background-color: #f2f2f2;
}
figcaption a[href],
a[href].selfRef {
  color: #222;
}
/* XXX probably not this:
a.selfRef:hover {
  background-color: transparent;
  cursor: default;
} */

/* Figures */
tt, code, pre, code {
  background-color: #f9f9f9;
  font-family: 'Roboto Mono', monospace;
}
pre {
  border: 1px solid #eee;
  margin: 0;
  padding: 1em;
}
img {
  max-width: 100%;
}
figure {
  margin: 0;
}
figure blockquote {
  margin: 0.8em 0.4em 0.4em;
}
figcaption {
  font-style: italic;
  margin: 0 0 1em 0;
}
@media screen {
  pre {
    overflow-x: auto;
    max-width: 100%;
    max-width: calc(100% - 22px);
  }
}

/* aside, blockquote */
aside, blockquote {
  margin-left: 0;
  padding: 1.2em 2em;
}
blockquote {
  background-color: #f9f9f9;
  color: #111; /* Arlen: WCAG 2019 */
  border: 1px solid #ddd;
  border-radius: 3px;
  margin: 1em 0;
}
cite {
  display: block;
  text-align: right;
  font-style: italic;
}

/* tables */
table {
  width: 100%;
  margin: 0 0 1em;
  border-collapse: collapse;
  border: 1px solid #eee;
}
th, td {
  text-align: left;
  vertical-align: top;
  padding: 0.5em 0.75em;
}
th {
  text-align: left;
  background-color: #e9e9e9;
}
tr:nth-child(2n+1) > td {
  background-color: #f5f5f5;
}
table caption {
  font-style: italic;
  margin: 0;
  padding: 0;
  text-align: left;
}
table p {
  /* XXX to avoid bottom margin on table row signifiers. If paragraphs should
     be allowed within tables more generally, it would be far better to select on a class. */
  margin: 0;
}

/* pilcrow */
a.pilcrow {
  color: #666; /* Arlen: AHDJ 2019 */
  text-decoration: none;
  visibility: hidden;
  user-select: none;
  -ms-user-select: none;
  -o-user-select:none;
  -moz-user-select: none;
  -khtml-user-select: none;
  -webkit-user-select: none;
  -webkit-touch-callout: none;
}
@media screen {
  aside:hover > a.pilcrow,
  p:hover > a.pilcrow,
  blockquote:hover > a.pilcrow,
  div:hover > a.pilcrow,
  li:hover > a.pilcrow,
  pre:hover > a.pilcrow {
    visibility: visible;
  }
  a.pilcrow:hover {
    background-color: transparent;
  }
}

/* misc */
hr {
  border: 0;
  border-top: 1px solid #eee;
}
.bcp14 {
  font-variant: small-caps;
}

.role {
  font-variant: all-small-caps;
}

/* info block */
#identifiers {
  margin: 0;
  font-size: 0.9em;
}
#identifiers dt {
  width: 3em;
  clear: left;
}
#identifiers dd {
  float: left;
  margin-bottom: 0;
}
#identifiers .authors .author {
  display: inline-block;
  margin-right: 1.5em;
}
#identifiers .authors .org {
  font-style: italic;
}

/* The prepared/rendered info at the very bottom of the page */
.docInfo {
  color: #666; /* Arlen: WCAG 2019 */
  font-size: 0.9em;
  font-style: italic;
  margin-top: 2em;
}
.docInfo .prepared {
  float: left;
}
.docInfo .prepared {
  float: right;
}

/* table of contents */
#toc  {
  padding: 0.75em 0 2em 0;
  margin-bottom: 1em;
}
nav.toc ul {
  margin: 0 0.5em 0 0;
  padding: 0;
  list-style: none;
}
nav.toc li {
  line-height: 1.3em;
  margin: 0.75em 0;
  padding-left: 1.2em;
  text-indent: -1.2em;
}
/* references */
.references dt {
  text-align: right;
  font-weight: bold;
  min-width: 7em;
}
.references dd {
  margin-left: 8em;
  overflow: auto;
}

.refInstance {
  margin-bottom: 1.25em;
}

.references .ascii {
  margin-bottom: 0.25em;
}

/* index */
.index ul {
  margin: 0 0 0 1em;
  padding: 0;
  list-style: none;
}
.index ul ul {
  margin: 0;
}
.index li {
  margin: 0;
  text-indent: -2em;
  padding-left: 2em;
  padding-bottom: 5px;
}
.indexIndex {
  margin: 0.5em 0 1em;
}
.index a {
  font-weight: 700;
}
/* make the index two-column on all but the smallest screens */
@media (min-width: 600px) {
  .index ul {
    -moz-column-count: 2;
    -moz-column-gap: 20px;
  }
  .index ul ul {
    -moz-column-count: 1;
    -moz-column-gap: 0;
  }
}

/* authors */
address.vcard {
  font-style: normal;
  margin: 1em 0;
}

address.vcard .nameRole {
  font-weight: 700;
  margin-left: 0;
}
address.vcard .label {
  font-family: "Noto Sans",Arial,Helvetica,sans-serif;
  margin: 0.5em 0;
}
address.vcard .type {
  display: none;
}
.alternative-contact {
  margin: 1.5em 0 1em;
}
hr.addr {
  border-top: 1px dashed;
  margin: 0;
  color: #ddd;
  max-width: calc(100% - 16px);
}

/* temporary notes */
.rfcEditorRemove::before {
  position: absolute;
  top: 0.2em;
  right: 0.2em;
  padding: 0.2em;
  content: "The RFC Editor will remove this note";
  color: #9e2a00; /* Arlen: WCAG 2019 */
  background-color: #ffd; /* Arlen: WCAG 2019 */
}
.rfcEditorRemove {
  position: relative;
  padding-top: 1.8em;
  background-color: #ffd; /* Arlen: WCAG 2019 */
  border-radius: 3px;
}
.cref {
  background-color: #ffd; /* Arlen: WCAG 2019 */
  padding: 2px 4px;
}
.crefSource {
  font-style: italic;
}
/* alternative layout for smaller screens */
@media screen and (max-width: 1023px) {
  body {
    padding-top: 2em;
  }
  #title {
    padding: 1em 0;
  }
  h1 {
    font-size: 24px;
  }
  h2 {
    font-size: 20px;
    margin-top: -18px;  /* provide offset for in-page anchors */
    padding-top: 38px;
  }
  #identifiers dd {
    max-width: 60%;
  }
  #toc {
    position: fixed;
    z-index: 2;
    top: 0;
    right: 0;
    padding: 0;
    margin: 0;
    background-color: inherit;
    border-bottom: 1px solid #ccc;
  }
  #toc h2 {
    margin: -1px 0 0 0;
    padding: 4px 0 4px 6px;
    padding-right: 1em;
    min-width: 190px;
    font-size: 1.1em;
    text-align: right;
    background-color: #444;
    color: white;
    cursor: pointer;
  }
  #toc h2::before { /* css hamburger */
    float: right;
    position: relative;
    width: 1em;
    height: 1px;
    left: -164px;
    margin: 6px 0 0 0;
    background: white none repeat scroll 0 0;
    box-shadow: 0 4px 0 0 white, 0 8px 0 0 white;
    content: "";
  }
  #toc nav {
    display: none;
    padding: 0.5em 1em 1em;
    overflow: auto;
    height: calc(100vh - 48px);
    border-left: 1px solid #ddd;
  }
}

/* alternative layout for wide screens */
@media screen and (min-width: 1024px) {
  body {
    max-width: 724px;
    margin: 42px auto;
    padding-left: 1.5em;
    padding-right: 29em;
  }
  #toc {
    position: fixed;
    top: 42px;
    right: 42px;
    width: 25%;
    margin: 0;
    padding: 0 1em;
    z-index: 1;
  }
  #toc h2 {
    border-top: none;
    border-bottom: 1px solid #ddd;
    font-size: 1em;
    font-weight: normal;
    margin: 0;
    padding: 0.25em 1em 1em 0;
  }
  #toc nav {
    display: block;
    height: calc(90vh - 84px);
    bottom: 0;
    padding: 0.5em 0 0;
    overflow: auto;
  }
  img { /* future proofing */
    max-width: 100%;
    height: auto;
  }
}

/* pagination */
@media print {
  body {

    width: 100%;
  }
  p {
    orphans: 3;
    widows: 3;
  }
  #n-copyright-notice {
    border-bottom: none;
  }
  #toc, #n-introduction {
    page-break-before: always;
  }
  #toc {
    border-top: none;
    padding-top: 0;
  }
  figure, pre {
    page-break-inside: avoid;
  }
  figure {
    overflow: scroll;
  }
  h1, h2, h3, h4, h5, h6 {
    page-break-after: avoid;
  }
  h2+*, h3+*, h4+*, h5+*, h6+* {
    page-break-before: avoid;
  }
  pre {
    white-space: pre-wrap;
    word-wrap: break-word;
    font-size: 10pt;
  }
  table {
    border: 1px solid #ddd;
  }
  td {
    border-top: 1px solid #ddd;
  }
}

/* This is commented out here, as the string-set: doesn't
   pass W3C validation currently */
/*
.ears thead .left {
  string-set: ears-top-left content();
}

.ears thead .center {
  string-set: ears-top-center content();
}

.ears thead .right {
  string-set: ears-top-right content();
}

.ears tfoot .left {
  string-set: ears-bottom-left content();
}

.ears tfoot .center {
  string-set: ears-bottom-center content();
}

.ears tfoot .right {
  string-set: ears-bottom-right content();
}
*/

@page :first {
  padding-top: 0;
  @top-left {
    content: normal;
    border: none;
  }
  @top-center {
    content: normal;
    border: none;
  }
  @top-right {
    content: normal;
    border: none;
  }
}

@page {
  size: A4;
  margin-bottom: 45mm;
  padding-top: 20px;
  /* The follwing is commented out here, but set appropriately by in code, as
     the content depends on the document */
  /*
  @top-left {
    content: 'Internet-Draft';
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-left {
    content: string(ears-top-left);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-center {
    content: string(ears-top-center);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-right {
    content: string(ears-top-right);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @bottom-left {
    content: string(ears-bottom-left);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-center {
    content: string(ears-bottom-center);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-right {
      content: '[Page ' counter(page) ']';
      vertical-align: top;
      border-top: solid 1px #ccc;
  }
  */

}

/* Changes introduced to fix issues found during implementation */
/* Make sure links are clickable even if overlapped by following H* */
a {
  z-index: 2;
}
/* Separate body from document info even without intervening H1 */
section {
  clear: both;
}


/* Top align author divs, to avoid names without organization dropping level with org names */
.author {
  vertical-align: top;
}

/* Leave room in document info to show Internet-Draft on one line */
#identifiers dt {
  width: 8em;
}

/* Don't waste quite as much whitespace between label and value in doc info */
#identifiers dd {
  margin-left: 1em;
}

/* Give floating toc a background color (needed when it's a div inside section */
#toc {
  background-color: white;
}

/* Make the collapsed ToC header render white on gray also when it's a link */
@media screen and (max-width: 1023px) {
  #toc h2 a,
  #toc h2 a:link,
  #toc h2 a:focus,
  #toc h2 a:hover,
  #toc a.toplink,
  #toc a.toplink:hover {
    color: white;
    background-color: #444;
    text-decoration: none;
  }
}

/* Give the bottom of the ToC some whitespace */
@media screen and (min-width: 1024px) {
  #toc {
    padding: 0 0 1em 1em;
  }
}

/* Style section numbers with more space between number and title */
.section-number {
  padding-right: 0.5em;
}

/* prevent monospace from becoming overly large */
tt, code, pre, code {
  font-size: 95%;
}

/* Fix the height/width aspect for ascii art*/
pre.sourcecode,
.art-text pre {
  line-height: 1.12;
}


/* Add styling for a link in the ToC that points to the top of the document */
a.toplink {
  float: right;
  margin-right: 0.5em;
}

/* Fix the dl styling to match the RFC 7992 attributes */
dl > dt,
dl.dlParallel > dt {
  float: left;
  margin-right: 1em;
}
dl.dlNewline > dt {
  float: none;
}

/* Provide styling for table cell text alignment */
table td.text-left,
table th.text-left {
  text-align: left;
}
table td.text-center,
table th.text-center {
  text-align: center;
}
table td.text-right,
table th.text-right {
  text-align: right;
}

/* Make the alternative author contact informatio look less like just another
   author, and group it closer with the primary author contact information */
.alternative-contact {
  margin: 0.5em 0 0.25em 0;
}
address .non-ascii {
  margin: 0 0 0 2em;
}

/* With it being possible to set tables with alignment
  left, center, and right, { width: 100%; } does not make sense */
table {
  width: auto;
}

/* Avoid reference text that sits in a block with very wide left margin,
   because of a long floating dt label.*/
.references dd {
  overflow: visible;
}

/* Control caption placement */
caption {
  caption-side: bottom;
}

/* Limit the width of the author address vcard, so names in right-to-left
   script don't end up on the other side of the page. */

address.vcard {
  max-width: 30em;
  margin-right: auto;
}

/* For address alignment dependent on LTR or RTL scripts */
address div.left {
  text-align: left;
}
address div.right {
  text-align: right;
}

/* Provide table alignment support.  We can't use the alignX classes above
   since they do unwanted things with caption and other styling. */
table.right {
 margin-left: auto;
 margin-right: 0;
}
table.center {
 margin-left: auto;
 margin-right: auto;
}
table.left {
 margin-left: 0;
 margin-right: auto;
}

/* Give the table caption label the same styling as the figcaption */
caption a[href] {
  color: #222;
}

@media print {
  .toplink {
    display: none;
  }

  /* avoid overwriting the top border line with the ToC header */
  #toc {
    padding-top: 1px;
  }

  /* Avoid page breaks inside dl and author address entries */
  .vcard {
    page-break-inside: avoid;
  }

}
/* Avoid wrapping of URLs in references */
@media screen {
  .references a {
    white-space: nowrap;
  }
}
/* Tweak the bcp14 keyword presentation */
.bcp14 {
  font-variant: small-caps;
  font-weight: bold;
  font-size: 0.9em;
}
/* Tweak the invisible space above H* in order not to overlay links in text above */
 h2 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 31px;
 }
 h3 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
 h4 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
/* Float artwork pilcrow to the right */
@media screen {
  .artwork a.pilcrow {
    display: block;
    line-height: 0.7;
    margin-top: 0.15em;
  }
}
/* Make pilcrows on dd visible */
@media screen {
  dd:hover > a.pilcrow {
    visibility: visible;
  }
}
/* Make the placement of figcaption match that of a table's caption
   by removing the figure's added bottom margin */
.alignLeft.art-text,
.alignCenter.art-text,
.alignRight.art-text {
   margin-bottom: 0;
}
.alignLeft,
.alignCenter,
.alignRight {
  margin: 1em 0 0 0;
}
/* In print, the pilcrow won't show on hover, so prevent it from taking up space,
   possibly even requiring a new line */
@media print {
  a.pilcrow {
    display: none;
  }
}
/* Styling for the external metadata */
div#external-metadata {
  background-color: #eee;
  padding: 0.5em;
  margin-bottom: 0.5em;
  display: none;
}
div#internal-metadata {
  padding: 0.5em;                       /* to match the external-metadata padding */
}
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  <link href="urn:issn:2070-1721" rel="alternate">
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<table class="ears">
<thead><tr>
<td class="left">RFC 8665</td>
<td class="center">OSPF Extensions for Segment Routing</td>
<td class="right">December 2019</td>
</tr></thead>
<tfoot><tr>
<td class="left">Psenak, 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/rfc8665" class="eref">8665</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="2019-12" class="published">December 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">P. Psenak, <span class="editor">Ed.</span>
</div>
<div class="org">Cisco Systems, Inc.</div>
</div>
<div class="author">
      <div class="author-name">S. Previdi, <span class="editor">Ed.</span>
</div>
<div class="org">Cisco Systems, Inc.</div>
</div>
<div class="author">
      <div class="author-name">C. Filsfils</div>
<div class="org">Cisco Systems, Inc.</div>
</div>
<div class="author">
      <div class="author-name">H. Gredler</div>
<div class="org">RtBrick Inc.</div>
</div>
<div class="author">
      <div class="author-name">R. Shakir</div>
<div class="org">Google, Inc.</div>
</div>
<div class="author">
      <div class="author-name">W. Henderickx</div>
<div class="org">Nokia</div>
</div>
<div class="author">
      <div class="author-name">J. Tantsura</div>
<div class="org">Apstra, Inc.</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8665</h1>
<h1 id="title">OSPF Extensions for Segment Routing</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">Segment Routing (SR) allows a flexible definition of end-to-end
      paths within IGP topologies by encoding paths as sequences of
      topological subpaths called "segments". These segments are advertised
      by the link-state routing protocols (IS-IS and OSPF).<a href="#section-abstract-1" class="pilcrow">¶</a></p>
<p id="section-abstract-2">This document describes the OSPFv2 extensions required for Segment Routing.<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/rfc8665">https://www.rfc-editor.org/info/rfc8665</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
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            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>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.1.2.1">
                <p id="section-toc.1-1.1.2.1.1"><a href="#section-1.1" class="xref">1.1</a>.  <a href="#name-requirements-language" class="xref">Requirements Language</a><a href="#section-toc.1-1.1.2.1.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</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-segment-routing-identifiers" class="xref">Segment Routing Identifiers</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.2.2.1">
                <p id="section-toc.1-1.2.2.1.1"><a href="#section-2.1" class="xref">2.1</a>.  <a href="#name-sid-label-sub-tlv" class="xref">SID/Label Sub-TLV</a><a href="#section-toc.1-1.2.2.1.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</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-segment-routing-capabilitie" class="xref">Segment Routing Capabilities</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.3.2.1">
                <p id="section-toc.1-1.3.2.1.1"><a href="#section-3.1" class="xref">3.1</a>.  <a href="#name-sr-algorithm-tlv" class="xref">SR-Algorithm TLV</a><a href="#section-toc.1-1.3.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.3.2.2">
                <p id="section-toc.1-1.3.2.2.1"><a href="#section-3.2" class="xref">3.2</a>.  <a href="#name-sid-label-range-tlv" class="xref">SID/Label Range TLV</a><a href="#section-toc.1-1.3.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.3.2.3">
                <p id="section-toc.1-1.3.2.3.1"><a href="#section-3.3" class="xref">3.3</a>.  <a href="#name-sr-local-block-tlv" class="xref">SR Local Block TLV</a><a href="#section-toc.1-1.3.2.3.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.3.2.4">
                <p id="section-toc.1-1.3.2.4.1"><a href="#section-3.4" class="xref">3.4</a>.  <a href="#name-srms-preference-tlv" class="xref">SRMS Preference TLV</a><a href="#section-toc.1-1.3.2.4.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</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-ospf-extended-prefix-range-" class="xref">OSPF Extended Prefix Range TLV</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
</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-prefix-sid-sub-tlv" class="xref">Prefix-SID Sub-TLV</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-adjacency-segment-identifie" class="xref">Adjacency Segment Identifier (Adj-SID)</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.6.2.1">
                <p id="section-toc.1-1.6.2.1.1"><a href="#section-6.1" class="xref">6.1</a>.  <a href="#name-adj-sid-sub-tlv" class="xref">Adj-SID Sub-TLV</a><a href="#section-toc.1-1.6.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.6.2.2">
                <p id="section-toc.1-1.6.2.2.1"><a href="#section-6.2" class="xref">6.2</a>.  <a href="#name-lan-adj-sid-sub-tlv" class="xref">LAN Adj-SID Sub-TLV</a><a href="#section-toc.1-1.6.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</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-elements-of-procedure" class="xref">Elements of Procedure</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-intra-area-segment-routing-" class="xref">Intra-area Segment Routing in OSPFv2</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-inter-area-segment-routing-" class="xref">Inter-area Segment Routing in OSPFv2</a><a href="#section-toc.1-1.7.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.7.2.3">
                <p id="section-toc.1-1.7.2.3.1"><a href="#section-7.3" class="xref">7.3</a>.  <a href="#name-segment-routing-for-externa" class="xref">Segment Routing for External Prefixes</a><a href="#section-toc.1-1.7.2.3.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.7.2.4">
                <p id="section-toc.1-1.7.2.4.1"><a href="#section-7.4" class="xref">7.4</a>.  <a href="#name-advertisement-of-adj-sid" class="xref">Advertisement of Adj-SID</a><a href="#section-toc.1-1.7.2.4.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.7.2.4.2.1">
                    <p id="section-toc.1-1.7.2.4.2.1.1"><a href="#section-7.4.1" class="xref">7.4.1</a>.  <a href="#name-advertisement-of-adj-sid-on" class="xref">Advertisement of Adj-SID on Point-to-Point Links</a><a href="#section-toc.1-1.7.2.4.2.1.1" class="pilcrow">¶</a></p>
</li>
                  <li class="toc ulEmpty" id="section-toc.1-1.7.2.4.2.2">
                    <p id="section-toc.1-1.7.2.4.2.2.1"><a href="#section-7.4.2" class="xref">7.4.2</a>.  <a href="#name-adjacency-sid-on-broadcast-" class="xref">Adjacency SID on Broadcast or NBMA Interfaces</a><a href="#section-toc.1-1.7.2.4.2.2.1" class="pilcrow">¶</a></p>
</li>
                </ul>
</li>
            </ul>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-8" class="xref">8</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.8.2.1">
                <p id="section-toc.1-1.8.2.1.1"><a href="#section-8.1" class="xref">8.1</a>.  <a href="#name-ospf-router-information-ri-" class="xref">OSPF Router Information (RI) TLVs Registry</a><a href="#section-toc.1-1.8.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.8.2.2">
                <p id="section-toc.1-1.8.2.2.1"><a href="#section-8.2" class="xref">8.2</a>.  <a href="#name-ospfv2-extended-prefix-opaq" class="xref">OSPFv2 Extended Prefix Opaque LSA TLVs Registry</a><a href="#section-toc.1-1.8.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.8.2.3">
                <p id="section-toc.1-1.8.2.3.1"><a href="#section-8.3" class="xref">8.3</a>.  <a href="#name-ospfv2-extended-prefix-tlv-" class="xref">OSPFv2 Extended Prefix TLV Sub-TLVs Registry</a><a href="#section-toc.1-1.8.2.3.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.8.2.4">
                <p id="section-toc.1-1.8.2.4.1"><a href="#section-8.4" class="xref">8.4</a>.  <a href="#name-ospfv2-extended-link-tlv-su" class="xref">OSPFv2 Extended Link TLV Sub-TLVs Registry</a><a href="#section-toc.1-1.8.2.4.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.8.2.5">
                <p id="section-toc.1-1.8.2.5.1"><a href="#section-8.5" class="xref">8.5</a>.  <a href="#name-igp-algorithm-types-registr" class="xref">IGP Algorithm Types Registry</a><a href="#section-toc.1-1.8.2.5.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-9" class="xref">9</a>.  <a href="#name-tlv-sub-tlv-error-handling" class="xref">TLV/Sub-TLV Error Handling</a><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#section-10" class="xref">10</a>. <a href="#name-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.10.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.11">
            <p id="section-toc.1-1.11.1"><a href="#section-11" class="xref">11</a>. <a href="#name-references" class="xref">References</a><a href="#section-toc.1-1.11.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.11.2.1">
                <p id="section-toc.1-1.11.2.1.1"><a href="#section-11.1" class="xref">11.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.11.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="toc ulEmpty" id="section-toc.1-1.11.2.2">
                <p id="section-toc.1-1.11.2.2.1"><a href="#section-11.2" class="xref">11.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.11.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.12">
            <p id="section-toc.1-1.12.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-acknowledgements" class="xref">Acknowledgements</a><a href="#section-toc.1-1.12.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.13">
            <p id="section-toc.1-1.13.1"><a href="#section-appendix.b" class="xref"></a><a href="#name-contributors" class="xref">Contributors</a><a href="#section-toc.1-1.13.1" class="pilcrow">¶</a></p>
</li>
          <li class="toc ulEmpty" id="section-toc.1-1.14">
            <p id="section-toc.1-1.14.1"><a href="#section-appendix.c" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a><a href="#section-toc.1-1.14.1" 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">Segment Routing (SR) allows a flexible definition of end-to-end
      paths within IGP topologies by encoding paths as sequences of
      topological subpaths called "segments". These segments are advertised
      by the link-state routing protocols (IS-IS and OSPF). Prefix segments
      represent an ECMP-aware shortest path to a prefix (or a node), as per
      the state of the IGP topology. Adjacency segments represent a hop over a
      specific adjacency between two nodes in the IGP. A prefix segment is typically 
      a multi-hop path while an adjacency segment, in most cases, is a one-hop path. SR's 
      control plane can be applied to both IPv6 and MPLS data planes, and it
      does not require any additional signaling (other than IGP extensions).
      The IPv6 data plane is out of the scope of this specification; it is not applicable 
      to OSPFv2, which only supports the IPv4 address family. When used in MPLS
      networks, SR paths do not require any LDP or RSVP-TE signaling. However, SR can 
      interoperate in the presence of LSPs established with RSVP or LDP.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">There are additional segment types, e.g., Binding Segment Identifier (SID) defined in <span>[<a href="#RFC8402" class="xref">RFC8402</a>]</span>.<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">This document describes the OSPF extensions required for Segment Routing.<a href="#section-1-3" class="pilcrow">¶</a></p>
<p id="section-1-4">Segment Routing architecture is described in <span>[<a href="#RFC8402" class="xref">RFC8402</a>]</span>.<a href="#section-1-4" class="pilcrow">¶</a></p>
<p id="section-1-5">Segment Routing use cases are described in <span>[<a href="#RFC7855" class="xref">RFC7855</a>]</span>.<a href="#section-1-5" class="pilcrow">¶</a></p>
<section id="section-1.1">
        <h3 id="name-requirements-language">
<a href="#section-1.1" class="section-number selfRef">1.1. </a><a href="#name-requirements-language" class="section-name selfRef">Requirements Language</a>
        </h3>
<p id="section-1.1-1">
    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-1.1-1" class="pilcrow">¶</a></p>
</section>
</section>
<section id="section-2">
      <h2 id="name-segment-routing-identifiers">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-segment-routing-identifiers" class="section-name selfRef">Segment Routing Identifiers</a>
      </h2>
<p id="section-2-1">Segment Routing defines various types of Segment Identifiers (SIDs):
      Prefix-SID, Adjacency SID, LAN Adjacency SID, and Binding SID.<a href="#section-2-1" class="pilcrow">¶</a></p>
<p id="section-2-2">Extended Prefix/Link Opaque Link State Advertisements (LSAs) defined in <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span> are used for 
      advertisements of the various SID types.<a href="#section-2-2" class="pilcrow">¶</a></p>
<div id="SIDLABEL">
<section id="section-2.1">
        <h3 id="name-sid-label-sub-tlv">
<a href="#section-2.1" class="section-number selfRef">2.1. </a><a href="#name-sid-label-sub-tlv" class="section-name selfRef">SID/Label Sub-TLV</a>
        </h3>
<p id="section-2.1-1">The SID/Label Sub-TLV appears in multiple TLVs or sub-TLVs defined
        later in this document. It is used to advertise the SID or label
        associated with a prefix or adjacency. The SID/Label Sub-TLV has the following
        format:<a href="#section-2.1-1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-2.1-2">
<pre> 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         SID/Label (variable)                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</pre><a href="#section-2.1-2" class="pilcrow">¶</a>
</div>
<p id="section-2.1-3">where:<a href="#section-2.1-3" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-2.1-4.1">
            <dl class="dlParallel" id="section-2.1-4.1.1">
              <dt id="section-2.1-4.1.1.1">Type:</dt>
              <dd id="section-2.1-4.1.1.2">1<a href="#section-2.1-4.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-2.1-4.1.1.3">Length:</dt>
              <dd id="section-2.1-4.1.1.4">3 or 4 octets<a href="#section-2.1-4.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-2.1-4.1.1.5">SID/Label:</dt>
              <dd id="section-2.1-4.1.1.6">
                <p id="section-2.1-4.1.1.6.1">If the length is set to 3, then the 20 rightmost bits
            represent a label. If the length is set to 4, then the value represents
            a 32-bit SID.<a href="#section-2.1-4.1.1.6.1" class="pilcrow">¶</a></p>
</dd>
</dl>
</li>
        </ul>
</section>
</div>
</section>
<div id="SRCAP">
<section id="section-3">
      <h2 id="name-segment-routing-capabilitie">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-segment-routing-capabilitie" class="section-name selfRef">Segment Routing Capabilities</a>
      </h2>
<p id="section-3-1">Segment Routing requires some additional router capabilities to be advertised 
      to other routers in the area.<a href="#section-3-1" class="pilcrow">¶</a></p>
<p id="section-3-2">These SR capabilities are advertised in the Router Information Opaque LSA
      (defined in <span>[<a href="#RFC7770" class="xref">RFC7770</a>]</span>). The TLVs defined below are applicable to 
       both OSPFv2 and OSPFv3; see also 
       <span>[<a href="#RFC8666" class="xref">RFC8666</a>]</span>.<a href="#section-3-2" class="pilcrow">¶</a></p>
<div id="SRALGO">
<section id="section-3.1">
        <h3 id="name-sr-algorithm-tlv">
<a href="#section-3.1" class="section-number selfRef">3.1. </a><a href="#name-sr-algorithm-tlv" class="section-name selfRef">SR-Algorithm TLV</a>
        </h3>
<p id="section-3.1-1">The SR-Algorithm TLV is a top-level TLV of the Router Information Opaque LSA 
        (defined in <span>[<a href="#RFC7770" class="xref">RFC7770</a>]</span>).<a href="#section-3.1-1" class="pilcrow">¶</a></p>
<p id="section-3.1-2">The SR-Algorithm TLV is optional. It <span class="bcp14">SHOULD</span> only be advertised once
        in the Router Information Opaque LSA. If the SR-Algorithm TLV is not advertised 
        by the node, such a node is considered as not being Segment Routing capable.<a href="#section-3.1-2" class="pilcrow">¶</a></p>
<p id="section-3.1-3"> An SR Router can use various algorithms when calculating reachability
        to OSPF routers or prefixes in an OSPF area. Examples of these algorithms are 
        metric-based Shortest Path First (SPF), various flavors of Constrained SPF, etc.
        The SR-Algorithm TLV allows a router to advertise the algorithms currently used 
        by the router to other routers in an OSPF area. The SR-Algorithm TLV has 
        the following format:<a href="#section-3.1-3" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.1-4">
<pre>
 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Algorithm 1 | Algorithm...  |   Algorithm n |               |
+-                                                             -+
|                                                               |
+                                                               +
</pre><a href="#section-3.1-4" class="pilcrow">¶</a>
</div>
<p id="section-3.1-5">where:<a href="#section-3.1-5" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-3.1-6.1">
            <dl class="dlParallel" id="section-3.1-6.1.1">
              <dt id="section-3.1-6.1.1.1">Type:</dt>
              <dd id="section-3.1-6.1.1.2">8<a href="#section-3.1-6.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-3.1-6.1.1.3">Length:</dt>
              <dd id="section-3.1-6.1.1.4">Variable, in octets, depending on the number of algorithms advertised<a href="#section-3.1-6.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-3.1-6.1.1.5">Algorithm:</dt>
              <dd id="section-3.1-6.1.1.6">
                <p id="section-3.1-6.1.1.6.1">Single octet identifying the algorithm. The following 
            values are defined by this document:<a href="#section-3.1-6.1.1.6.1" class="pilcrow">¶</a></p>
<dl class="dlParallel" id="section-3.1-6.1.1.6.2">
                  <dt id="section-3.1-6.1.1.6.2.1">0:</dt>
                  <dd style="margin-left: 3.0em" id="section-3.1-6.1.1.6.2.2">Shortest Path First (SPF) algorithm based on link
              metric. This is the standard shortest path algorithm as computed
              by the OSPF protocol.  Consistent with the deployed practice for
              link-state protocols, Algorithm 0 permits any node to overwrite
              the SPF path with a different path based on its local policy. If
              the SR-Algorithm TLV is advertised, Algorithm 0
              <span class="bcp14">MUST</span> be included.<a href="#section-3.1-6.1.1.6.2.2" class="pilcrow">¶</a>
</dd>
<dt id="section-3.1-6.1.1.6.2.3">1:</dt>
                  <dd style="margin-left: 3.0em" id="section-3.1-6.1.1.6.2.4">Strict Shortest Path First (SPF) algorithm based on link metric. 
                The algorithm is identical to Algorithm 0, but Algorithm 1 requires  that 
                all nodes along the path will honor the SPF routing decision. Local policy
                at the node claiming support for Algorithm 1 <span class="bcp14">MUST NOT</span> alter the 
                SPF paths computed by Algorithm 1.<a href="#section-3.1-6.1.1.6.2.4" class="pilcrow">¶</a>
</dd>
</dl>
</dd>
</dl>
</li>
        </ul>
<p id="section-3.1-7">When multiple SR-Algorithm TLVs are received from a given router,
        the receiver <span class="bcp14">MUST</span> use the first occurrence of the TLV in the Router
        Information Opaque LSA. If the SR-Algorithm TLV appears in multiple Router
        Information Opaque LSAs that have different flooding scopes, the SR-Algorithm
        TLV in the Router Information Opaque LSA with the area-scoped flooding scope
        <span class="bcp14">MUST</span> be used. If the SR-Algorithm TLV appears in multiple Router
        Information Opaque LSAs that have the same flooding scope, the SR-Algorithm
        TLV in the Router Information (RI) Opaque LSA with the numerically smallest
        Instance ID <span class="bcp14">MUST</span> be used and subsequent instances of the SR-Algorithm
        TLV <span class="bcp14">MUST</span> be ignored.<a href="#section-3.1-7" class="pilcrow">¶</a></p>
<p id="section-3.1-8">The RI LSA can be advertised at any of the defined opaque flooding 
        scopes (link, area, or Autonomous System (AS)). For the purpose of 
        SR-Algorithm TLV advertisement, area-scoped flooding is <span class="bcp14">REQUIRED</span>.<a href="#section-3.1-8" class="pilcrow">¶</a></p>
</section>
</div>
<div id="SIDRANGE">
<section id="section-3.2">
        <h3 id="name-sid-label-range-tlv">
<a href="#section-3.2" class="section-number selfRef">3.2. </a><a href="#name-sid-label-range-tlv" class="section-name selfRef">SID/Label Range TLV</a>
        </h3>
<p id="section-3.2-1">Prefix-SIDs <span class="bcp14">MAY</span> be advertised in the form of an index as described in 
        <a href="#PREFIXSID" class="xref">Section 5</a>. Such an index defines the offset in the SID/Label space 
        advertised by the router. The SID/Label Range TLV is used to advertise such SID/Label
        space.<a href="#section-3.2-1" class="pilcrow">¶</a></p>
<p id="section-3.2-2">The SID/Label Range TLV is a top-level TLV of the Router Information 
        Opaque LSA (defined in <span>[<a href="#RFC7770" class="xref">RFC7770</a>]</span>).<a href="#section-3.2-2" class="pilcrow">¶</a></p>
<p id="section-3.2-3">The SID/Label Range TLV <span class="bcp14">MAY</span> appear multiple times and has the following
        format:<a href="#section-3.2-3" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.2-4">
<pre>
 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Range Size                 |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Sub-TLVs (variable)                    |
+-                                                             -+
|                                                               |
+                                                               +</pre><a href="#section-3.2-4" class="pilcrow">¶</a>
</div>
<p id="section-3.2-5">where:<a href="#section-3.2-5" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-3.2-6.1">
            <dl class="dlParallel" id="section-3.2-6.1.1">
              <dt id="section-3.2-6.1.1.1">Type:</dt>
              <dd id="section-3.2-6.1.1.2">9<a href="#section-3.2-6.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-3.2-6.1.1.3">Length:</dt>
              <dd id="section-3.2-6.1.1.4">Variable, in octets, depending on the sub-TLVs<a href="#section-3.2-6.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-3.2-6.1.1.5">Range Size:</dt>
              <dd id="section-3.2-6.1.1.6">3-octet SID/label range size (i.e., the number of SIDs or labels 
               in the range including the first SID/label). It <span class="bcp14">MUST</span> be greater than 0.<a href="#section-3.2-6.1.1.6" class="pilcrow">¶</a>
</dd>
<dt id="section-3.2-6.1.1.7">Reserved:</dt>
              <dd id="section-3.2-6.1.1.8">
                <span class="bcp14">SHOULD</span> be set to 0 on transmission and <span class="bcp14">MUST</span> be ignored on reception<a href="#section-3.2-6.1.1.8" class="pilcrow">¶</a>
</dd>
</dl>
</li>
        </ul>
<p id="section-3.2-7">Initially, the only supported sub-TLV is the SID/Label Sub-TLV as defined 
        in <a href="#SIDLABEL" class="xref">Section 2.1</a>. The SID/Label Sub-TLV <span class="bcp14">MUST</span> be included 
        in the SID/Label Range TLV. The SID/Label advertised in the SID/Label Sub-TLV 
        represents the first SID/Label in the advertised range.<a href="#section-3.2-7" class="pilcrow">¶</a></p>
<p id="section-3.2-8">Only a single SID/Label Sub-TLV <span class="bcp14">MAY</span> be advertised in the SID/Label Range TLV. If more 
        than one SID/Label Sub-TLV is present, the SID/Label Range TLV <span class="bcp14">MUST</span> be ignored.<a href="#section-3.2-8" class="pilcrow">¶</a></p>
<p id="section-3.2-9">Multiple occurrences of the SID/Label Range TLV <span class="bcp14">MAY</span> be
        advertised in order to advertise multiple ranges. In such a case:<a href="#section-3.2-9" class="pilcrow">¶</a></p>
<ul>
<li id="section-3.2-10.1">The originating router <span class="bcp14">MUST</span> encode each range into a different SID/Label 
            Range TLV.<a href="#section-3.2-10.1" class="pilcrow">¶</a>
</li>
          <li id="section-3.2-10.2">The originating router decides the order in which the set of SID/Label 
            Range TLVs are advertised inside the Router Information Opaque LSA. The 
            originating router <span class="bcp14">MUST</span> ensure the order is the same after a graceful restart 
            (using checkpointing, nonvolatile storage, or any other mechanism) in order 
            to ensure the SID/Label range and SID index correspondence is preserved 
            across graceful restarts.<a href="#section-3.2-10.2" class="pilcrow">¶</a>
</li>
          <li id="section-3.2-10.3"> The receiving router <span class="bcp14">MUST</span> adhere to the order in which the ranges are 
            advertised when calculating a SID/Label from a SID index.<a href="#section-3.2-10.3" class="pilcrow">¶</a>
</li>
          <li id="section-3.2-10.4">The originating router <span class="bcp14">MUST NOT</span> advertise overlapping ranges.<a href="#section-3.2-10.4" class="pilcrow">¶</a>
</li>
          <li id="section-3.2-10.5">When a router receives multiple overlapping ranges, it <span class="bcp14">MUST</span> conform
               to the procedures defined in <span>[<a href="#RFC8660" class="xref">RFC8660</a>]</span>.<a href="#section-3.2-10.5" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-3.2-11">The following example illustrates the advertisement of multiple ranges.<a href="#section-3.2-11" class="pilcrow">¶</a></p>
<p id="section-3.2-12">The originating router advertises the following ranges:<a href="#section-3.2-12" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.2-13">
<pre>
      Range 1: Range Size: 100   SID/Label Sub-TLV: 100
      Range 1: Range Size: 100   SID/Label Sub-TLV: 1000
      Range 1: Range Size: 100   SID/Label Sub-TLV: 500</pre><a href="#section-3.2-13" class="pilcrow">¶</a>
</div>
<p id="section-3.2-14">The receiving routers concatenate the ranges and build the Segment 
   Routing Global Block (SRGB) as follows:<a href="#section-3.2-14" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.2-15">
<pre> 
   SRGB = [100, 199]
          [1000, 1099]
          [500, 599]</pre><a href="#section-3.2-15" class="pilcrow">¶</a>
</div>
<p id="section-3.2-16">The indexes span multiple ranges:<a href="#section-3.2-16" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.2-17">
<pre> 
      index 0 means label 100
      ...
      index 99 means label 199
      index 100 means label 1000
      index 199 means label 1099
      ...
      index 200 means label 500
      ...</pre><a href="#section-3.2-17" class="pilcrow">¶</a>
</div>
<p id="section-3.2-18">The RI LSA can be advertised at any of the defined flooding scopes
        (link, area, or autonomous system (AS)). For the purpose of  
        SID/Label Range TLV advertisement, area-scoped flooding is <span class="bcp14">REQUIRED</span>.<a href="#section-3.2-18" class="pilcrow">¶</a></p>
</section>
</div>
<div id="SRLB">
<section id="section-3.3">
        <h3 id="name-sr-local-block-tlv">
<a href="#section-3.3" class="section-number selfRef">3.3. </a><a href="#name-sr-local-block-tlv" class="section-name selfRef">SR Local Block TLV</a>
        </h3>
<p id="section-3.3-1">The SR Local Block TLV (SRLB TLV) contains the range of labels the 
 node has reserved for Local SIDs. SIDs from the SRLB <span class="bcp14">MAY</span> be used for 
 Adjacency SIDs but also by components other than the OSPF protocol.  
 As an example, an application or a controller can instruct the router 
 to allocate a specific Local SID. Some controllers or applications can 
 use the control plane to discover the available set of Local SIDs on 
 a particular router. In such cases, the SRLB is advertised in the control plane.
 The requirement to advertise the SRLB is further described in 
 <span>[<a href="#RFC8660" class="xref">RFC8660</a>]</span>.
 The SRLB TLV is used to advertise the SRLB.<a href="#section-3.3-1" class="pilcrow">¶</a></p>
<p id="section-3.3-2">The SRLB TLV is a top-level TLV of the Router Information 
        Opaque LSA (defined in <span>[<a href="#RFC7770" class="xref">RFC7770</a>]</span>).<a href="#section-3.3-2" class="pilcrow">¶</a></p>
<p id="section-3.3-3">The SRLB TLV <span class="bcp14">MAY</span> appear multiple times in the Router Information
         Opaque LSA and has the following format:<a href="#section-3.3-3" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.3-4">
<pre>
 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Range Size                 |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Sub-TLVs (variable)                    |
+-                                                             -+
|                                                               |
+                                                               +</pre><a href="#section-3.3-4" class="pilcrow">¶</a>
</div>
<p id="section-3.3-5">where:<a href="#section-3.3-5" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-3.3-6.1">
            <dl class="dlParallel" id="section-3.3-6.1.1">
              <dt id="section-3.3-6.1.1.1">Type:</dt>
              <dd id="section-3.3-6.1.1.2">14<a href="#section-3.3-6.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-3.3-6.1.1.3">Length:</dt>
              <dd id="section-3.3-6.1.1.4">Variable, in octets, depending on the sub-TLVs<a href="#section-3.3-6.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-3.3-6.1.1.5">Range Size:</dt>
              <dd id="section-3.3-6.1.1.6">3-octet SID/Label range size (i.e., the number of SIDs or labels 
               in the range including the first SID/Label). It <span class="bcp14">MUST</span> be greater than 0.<a href="#section-3.3-6.1.1.6" class="pilcrow">¶</a>
</dd>
<dt id="section-3.3-6.1.1.7">Reserved:</dt>
              <dd id="section-3.3-6.1.1.8">
                <span class="bcp14">SHOULD</span> be set to 0 on transmission and <span class="bcp14">MUST</span> be ignored on reception<a href="#section-3.3-6.1.1.8" class="pilcrow">¶</a>
</dd>
</dl>
</li>
        </ul>
<p id="section-3.3-7">Initially, the only supported sub-TLV is the SID/Label Sub-TLV as defined 
        in <a href="#SIDLABEL" class="xref">Section 2.1</a>. The SID/Label Sub-TLV <span class="bcp14">MUST</span> be included 
        in the SRLB TLV. The SID/Label advertised in the SID/Label Sub-TLV represents
        the first SID/Label in the advertised range.<a href="#section-3.3-7" class="pilcrow">¶</a></p>
<p id="section-3.3-8">Only a single SID/Label Sub-TLV <span class="bcp14">MAY</span> be advertised in the SRLB TLV. If more 
        than one SID/Label Sub-TLV is present, the SRLB TLV <span class="bcp14">MUST</span> be ignored.<a href="#section-3.3-8" class="pilcrow">¶</a></p>
<p id="section-3.3-9">The originating router <span class="bcp14">MUST NOT</span> advertise overlapping ranges.<a href="#section-3.3-9" class="pilcrow">¶</a></p>
<p id="section-3.3-10">Each time a SID from the SRLB is allocated, it <span class="bcp14">SHOULD</span> also be reported to all
 components (e.g., controller or applications) in order for these components to 
 have an up-to-date view of the current SRLB allocation. This is required to avoid
 collisions between allocation instructions.<a href="#section-3.3-10" class="pilcrow">¶</a></p>
<p id="section-3.3-11">Within the context of OSPF, the reporting of Local SIDs is done through 
 OSPF sub-TLVs, such as the Adjacency SID (<a href="#ADJSID" class="xref">Section 6</a>). However, 
 the reporting of allocated Local SIDs can also be done through other means 
 and protocols, which are outside the scope of this document.<a href="#section-3.3-11" class="pilcrow">¶</a></p>
<p id="section-3.3-12">A router advertising the SRLB TLV <span class="bcp14">MAY</span> also have other label ranges, outside 
 of the SRLB, used for its local allocation purposes and not advertised in
 the SRLB TLV. For example, it is possible that an Adjacency SID is allocated using 
 a local label that is not part of the SRLB.<a href="#section-3.3-12" class="pilcrow">¶</a></p>
<p id="section-3.3-13">The RI LSA can be advertised at any of the defined flooding scopes
        (link, area, or autonomous system (AS)). For the purpose of  
         SRLB TLV advertisement, area-scoped flooding is <span class="bcp14">REQUIRED</span>.<a href="#section-3.3-13" class="pilcrow">¶</a></p>
</section>
</div>
<div id="SRMS-Pref">
<section id="section-3.4">
        <h3 id="name-srms-preference-tlv">
<a href="#section-3.4" class="section-number selfRef">3.4. </a><a href="#name-srms-preference-tlv" class="section-name selfRef">SRMS Preference TLV</a>
        </h3>
<p id="section-3.4-1">The Segment Routing Mapping Server Preference TLV (SRMS Preference TLV) is used to 
      advertise a preference associated with the node that acts as an SR Mapping Server.
      The role of an SRMS is described in <span>[<a href="#RFC8661" class="xref">RFC8661</a>]</span>. 
      SRMS preference is defined in 
      <span>[<a href="#RFC8661" class="xref">RFC8661</a>]</span>.<a href="#section-3.4-1" class="pilcrow">¶</a></p>
<p id="section-3.4-2">The SRMS Preference TLV is a top-level TLV of the 
      Router Information Opaque LSA (defined in <span>[<a href="#RFC7770" class="xref">RFC7770</a>]</span>).<a href="#section-3.4-2" class="pilcrow">¶</a></p>
<p id="section-3.4-3">The SRMS Preference TLV <span class="bcp14">MAY</span> only be advertised
         once in the Router Information Opaque LSA and has the following format:<a href="#section-3.4-3" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-3.4-4">
<pre>
 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Preference    |                 Reserved                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</pre><a href="#section-3.4-4" class="pilcrow">¶</a>
</div>
<p id="section-3.4-5">where:<a href="#section-3.4-5" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-3.4-6.1">
            <dl class="dlParallel" id="section-3.4-6.1.1">
              <dt id="section-3.4-6.1.1.1">Type:</dt>
              <dd id="section-3.4-6.1.1.2">15<a href="#section-3.4-6.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-3.4-6.1.1.3">Length:</dt>
              <dd id="section-3.4-6.1.1.4">4 octets<a href="#section-3.4-6.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-3.4-6.1.1.5">Preference:</dt>
              <dd id="section-3.4-6.1.1.6">1 octet, with an SRMS preference value from 0 to 255<a href="#section-3.4-6.1.1.6" class="pilcrow">¶</a>
</dd>
<dt id="section-3.4-6.1.1.7">Reserved:</dt>
              <dd id="section-3.4-6.1.1.8">
                <span class="bcp14">SHOULD</span> be set to 0 on transmission and <span class="bcp14">MUST</span> be ignored on reception<a href="#section-3.4-6.1.1.8" class="pilcrow">¶</a>
</dd>
</dl>
</li>
        </ul>
<p id="section-3.4-7">When multiple SRMS Preference TLVs are received from a given router, the receiver
    <span class="bcp14">MUST</span> use the first occurrence of the TLV in the Router
    Information Opaque LSA. If the
    SRMS Preference TLV appears in multiple Router Information Opaque LSAs that have different 
    flooding scopes, the SRMS Preference TLV in the Router Information Opaque LSA with the 
    narrowest flooding scope <span class="bcp14">MUST</span> be used. If the SRMS Preference TLV appears in 
    multiple Router Information Opaque LSAs that have the same flooding scope, the SRMS 
    Preference TLV in the Router Information Opaque LSA with the numerically smallest Instance ID
    <span class="bcp14">MUST</span> be used and subsequent instances of the SRMS Preference TLV <span class="bcp14">MUST</span> be ignored.<a href="#section-3.4-7" class="pilcrow">¶</a></p>
<p id="section-3.4-8">The RI LSA can be advertised at any of the defined flooding scopes (link, area, 
 or autonomous system (AS)). For the purpose of the SRMS 
 Preference TLV advertisement, AS-scoped flooding <span class="bcp14">SHOULD</span> be used. This is because SRMS 
 servers can be located in a different area than consumers of the SRMS advertisements. 
 If the SRMS advertisements from the SRMS server are only used inside the SRMS server's 
 area, area-scoped flooding <span class="bcp14">MAY</span> be used.<a href="#section-3.4-8" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="PFXRANGE">
<section id="section-4">
      <h2 id="name-ospf-extended-prefix-range-">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-ospf-extended-prefix-range-" class="section-name selfRef">OSPF Extended Prefix Range TLV</a>
      </h2>
<p id="section-4-1">In some cases, it is useful to advertise attributes for a range of
      prefixes.  The SR Mapping Server, which is described in <span>[<a href="#RFC8661" class="xref">RFC8661</a>]</span>, is an example where we need a
      single advertisement to advertise SIDs for multiple prefixes from a
      contiguous address range.<a href="#section-4-1" class="pilcrow">¶</a></p>
<p id="section-4-2">The OSPF Extended Prefix Range TLV, which is a top-level TLV of the
      Extended Prefix LSA described in <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span> is defined for this purpose.<a href="#section-4-2" class="pilcrow">¶</a></p>
<p id="section-4-3">Multiple OSPF Extended Prefix Range TLVs <span class="bcp14">MAY</span> be
      advertised in each OSPF Extended Prefix Opaque LSA, but all prefix
      ranges included in a single OSPF Extended Prefix Opaque LSA
      <span class="bcp14">MUST</span> have the same flooding scope. The OSPF Extended
      Prefix Range TLV has the following format:<a href="#section-4-3" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-4-4">
<pre>
 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length |     AF        |         Range Size            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Flags       |                Reserved                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Address Prefix (variable)                 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Sub-TLVs (variable)                      |
+-                                                             -+
|                                                               |
</pre><a href="#section-4-4" class="pilcrow">¶</a>
</div>
<p id="section-4-5">where:<a href="#section-4-5" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-4-6.1">
          <dl class="dlParallel" id="section-4-6.1.1">
            <dt id="section-4-6.1.1.1">Type:</dt>
            <dd id="section-4-6.1.1.2">2<a href="#section-4-6.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-4-6.1.1.3">Length:</dt>
            <dd id="section-4-6.1.1.4">Variable, in octets, depending on the sub-TLVs<a href="#section-4-6.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-4-6.1.1.5">Prefix Length:</dt>
            <dd id="section-4-6.1.1.6">Length of prefix in bits<a href="#section-4-6.1.1.6" class="pilcrow">¶</a>
</dd>
<dt id="section-4-6.1.1.7">AF:</dt>
            <dd id="section-4-6.1.1.8">Address family for the prefix.  Currently, the only supported
        value is 0 for IPv4 unicast. The inclusion of address family in this
        TLV allows for future extension.<a href="#section-4-6.1.1.8" class="pilcrow">¶</a>
</dd>
<dt id="section-4-6.1.1.9">Range Size:</dt>
            <dd id="section-4-6.1.1.10">Represents the number of prefixes that are covered by the
        advertisement. The Range Size <span class="bcp14">MUST NOT</span> exceed the
        number of prefixes that could be satisfied by the Prefix Length
        without including the IPv4 multicast address range (224.0.0.0/3).<a href="#section-4-6.1.1.10" class="pilcrow">¶</a>
</dd>
<dt id="section-4-6.1.1.11">Flags:</dt>
            <dd id="section-4-6.1.1.12">
              <p id="section-4-6.1.1.12.1">Single-octet field. The following flags are defined:<a href="#section-4-6.1.1.12.1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-4-6.1.1.12.2">
<pre>
     0  1  2  3  4  5  6  7 
   +--+--+--+--+--+--+--+--+
   |IA|  |  |  |  |  |  |  |
   +--+--+--+--+--+--+--+--+</pre><a href="#section-4-6.1.1.12.2" class="pilcrow">¶</a>
</div>
<p id="section-4-6.1.1.12.3">where:<a href="#section-4-6.1.1.12.3" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-4-6.1.1.12.4.1">
                  <dl class="dlParallel" id="section-4-6.1.1.12.4.1.1">
                    <dt id="section-4-6.1.1.12.4.1.1.1">IA-Flag:</dt>
                    <dd id="section-4-6.1.1.12.4.1.1.2">
                      <p id="section-4-6.1.1.12.4.1.1.2.1">Inter-Area Flag. If set, advertisement is of
                  inter-area type.  An Area Border Router (ABR) that is
                  advertising the OSPF Extended Prefix Range TLV between areas
                  <span class="bcp14">MUST</span> set this bit.<a href="#section-4-6.1.1.12.4.1.1.2.1" class="pilcrow">¶</a></p>
<p id="section-4-6.1.1.12.4.1.1.2.2">This bit is used to prevent redundant flooding of Prefix
   Range TLVs between areas as follows:<a href="#section-4-6.1.1.12.4.1.1.2.2" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-4-6.1.1.12.4.1.1.2.3.1">
                          <p id="section-4-6.1.1.12.4.1.1.2.3.1.1">
 An ABR only propagates an inter-area Prefix Range
 advertisement from the backbone area to connected
 nonbackbone areas if the advertisement is considered
 to be the best one. The following rules are used to
 select the best range from the set of advertisements
 for the same Prefix Range:<a href="#section-4-6.1.1.12.4.1.1.2.3.1.1" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-4-6.1.1.12.4.1.1.2.3.1.2.1">An ABR always prefers intra-area Prefix Range
   advertisements over inter-area advertisements.<a href="#section-4-6.1.1.12.4.1.1.2.3.1.2.1" class="pilcrow">¶</a>
</li>
                            <li class="ulEmpty" id="section-4-6.1.1.12.4.1.1.2.3.1.2.2">An ABR does not consider inter-area Prefix Range
   advertisements coming from nonbackbone areas.<a href="#section-4-6.1.1.12.4.1.1.2.3.1.2.2" class="pilcrow">¶</a>
</li>
                          </ul>
</li>
                      </ul>
</dd>
</dl>
</li>
              </ul>
</dd>
<dt id="section-4-6.1.1.13">Reserved:</dt>
            <dd id="section-4-6.1.1.14">
              <span class="bcp14">SHOULD</span> be set to 0 on transmission and
 <span class="bcp14">MUST</span> be ignored on reception<a href="#section-4-6.1.1.14" class="pilcrow">¶</a>
</dd>
<dt id="section-4-6.1.1.15">Address Prefix:</dt>
            <dd id="section-4-6.1.1.16">For the address family IPv4 unicast, the prefix itself is
 encoded as a 32-bit value. The default route is represented by
 a prefix of length 0. Prefix encoding for other address
 families is beyond the scope of this specification.<a href="#section-4-6.1.1.16" class="pilcrow">¶</a>
</dd>
</dl>
</li>
      </ul>
</section>
</div>
<div id="PREFIXSID">
<section id="section-5">
      <h2 id="name-prefix-sid-sub-tlv">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-prefix-sid-sub-tlv" class="section-name selfRef">Prefix-SID Sub-TLV</a>
      </h2>
<p id="section-5-1">The Prefix-SID Sub-TLV is a sub-TLV of the OSPF Extended Prefix TLV described 
      in <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span> and the OSPF Extended Prefix Range
      TLV described in <a href="#PFXRANGE" class="xref">Section 4</a>. It <span class="bcp14">MAY</span> appear more than once in the 
      parent TLV and has the following format:<a href="#section-5-1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-5-2">
<pre>
 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Flags    |   Reserved    |      MT-ID    |    Algorithm  | 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     SID/Index/Label (variable)                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</pre><a href="#section-5-2" class="pilcrow">¶</a>
</div>
<p id="section-5-3">where:<a href="#section-5-3" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-5-4.1">
          <dl class="dlParallel" id="section-5-4.1.1">
            <dt id="section-5-4.1.1.1">Type:</dt>
            <dd id="section-5-4.1.1.2">2<a href="#section-5-4.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.3">Length:</dt>
            <dd id="section-5-4.1.1.4">7 or 8 octets, depending on the V-Flag<a href="#section-5-4.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.5">Flags:</dt>
            <dd id="section-5-4.1.1.6">
              <p id="section-5-4.1.1.6.1">Single-octet field. The following flags are defined:<a href="#section-5-4.1.1.6.1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-5-4.1.1.6.2">
<pre>                      
     0  1  2  3  4  5  6  7 
   +--+--+--+--+--+--+--+--+
   |  |NP|M |E |V |L |  |  |
   +--+--+--+--+--+--+--+--+</pre><a href="#section-5-4.1.1.6.2" class="pilcrow">¶</a>
</div>
<p id="section-5-4.1.1.6.3">where:<a href="#section-5-4.1.1.6.3" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-5-4.1.1.6.4.1">
                  <dl class="dlParallel" id="section-5-4.1.1.6.4.1.1">
                    <dt id="section-5-4.1.1.6.4.1.1.1">NP-Flag:</dt>
                    <dd id="section-5-4.1.1.6.4.1.1.2">No-PHP (Penultimate Hop Popping) Flag. If set, then the
            penultimate hop <span class="bcp14">MUST NOT</span> pop the Prefix-SID before
            delivering packets to the node that advertised the
            Prefix-SID.<a href="#section-5-4.1.1.6.4.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.6.4.1.1.3">M-Flag:</dt>
                    <dd id="section-5-4.1.1.6.4.1.1.4">Mapping Server Flag.  If set, the SID was advertised
                by an SR Mapping Server as described in 
                <span>[<a href="#RFC8661" class="xref">RFC8661</a>]</span>.<a href="#section-5-4.1.1.6.4.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.6.4.1.1.5">E-Flag:</dt>
                    <dd id="section-5-4.1.1.6.4.1.1.6">Explicit Null Flag. If set, any upstream neighbor of the
            Prefix-SID originator <span class="bcp14">MUST</span> replace the Prefix-SID
            with the Explicit NULL label (0 for IPv4) before forwarding the
            packet.<a href="#section-5-4.1.1.6.4.1.1.6" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.6.4.1.1.7">V-Flag:</dt>
                    <dd id="section-5-4.1.1.6.4.1.1.8">Value/Index Flag. If set, then the Prefix-SID 
                carries an absolute value. If not set, then the Prefix-SID carries 
                an index.<a href="#section-5-4.1.1.6.4.1.1.8" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.6.4.1.1.9">L-Flag:</dt>
                    <dd id="section-5-4.1.1.6.4.1.1.10">Local/Global Flag. If set, then the value/index 
                carried by the Prefix-SID has local significance. If not set, then
                the value/index carried by this sub-TLV has global significance.<a href="#section-5-4.1.1.6.4.1.1.10" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.6.4.1.1.11">Other bits:</dt>
                    <dd id="section-5-4.1.1.6.4.1.1.12">Reserved. These <span class="bcp14">MUST</span> be zero when sent and are
            ignored when received.<a href="#section-5-4.1.1.6.4.1.1.12" class="pilcrow">¶</a>
</dd>
</dl>
</li>
              </ul>
</dd>
<dt id="section-5-4.1.1.7">Reserved:</dt>
            <dd id="section-5-4.1.1.8">
              <span class="bcp14">SHOULD</span> be set to 0 on transmission and
        <span class="bcp14">MUST</span> be ignored on reception<a href="#section-5-4.1.1.8" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.9">MT-ID:</dt>
            <dd id="section-5-4.1.1.10">Multi-Topology ID (as defined in <span>[<a href="#RFC4915" class="xref">RFC4915</a>]</span>)<a href="#section-5-4.1.1.10" class="pilcrow">¶</a>
</dd>
<dt id="section-5-4.1.1.11">Algorithm:</dt>
            <dd id="section-5-4.1.1.12">
              <p id="section-5-4.1.1.12.1">Single octet identifying the algorithm the Prefix-SID is
        associated with as defined in <a href="#SRALGO" class="xref">Section 3.1</a><a href="#section-5-4.1.1.12.1" class="pilcrow">¶</a></p>
<p id="section-5-4.1.1.12.2">A router receiving a Prefix-SID from a remote node and with an
        algorithm value that the remote node has not advertised in the
        SR-Algorithm TLV (<a href="#SRALGO" class="xref">Section 3.1</a>)
        <span class="bcp14">MUST</span> ignore the Prefix-SID Sub-TLV.<a href="#section-5-4.1.1.12.2" class="pilcrow">¶</a></p>
</dd>
<dt id="section-5-4.1.1.13">SID/Index/Label:</dt>
            <dd id="section-5-4.1.1.14">
              <p id="section-5-4.1.1.14.1">According to the V- and L-Flags, it contains:<a href="#section-5-4.1.1.14.1" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-5-4.1.1.14.2.1">V-Flag is set to 0 and L-Flag is set to 0: The SID/Index/Label
            field is a 4-octet index defining the offset in the SID/Label
            space advertised by this router.<a href="#section-5-4.1.1.14.2.1" class="pilcrow">¶</a>
</li>
                <li class="ulEmpty" id="section-5-4.1.1.14.2.2">V-Flag is set to 1 and L-Flag is set to 1: The SID/Index/Label
            field is a 3-octet local label where the 20 rightmost bits are
            used for encoding the label value.<a href="#section-5-4.1.1.14.2.2" class="pilcrow">¶</a>
</li>
                <li class="ulEmpty" id="section-5-4.1.1.14.2.3">All other combinations of V-Flag and L-Flag are invalid and
            any SID Advertisement received with an invalid setting for V- and L-Flags <span class="bcp14">MUST</span> be ignored.<a href="#section-5-4.1.1.14.2.3" class="pilcrow">¶</a>
</li>
              </ul>
</dd>
</dl>
</li>
      </ul>
<p id="section-5-5">If an OSPF router advertises multiple Prefix-SIDs for the same prefix,
        topology, and algorithm, all of them <span class="bcp14">MUST</span> be ignored.<a href="#section-5-5" class="pilcrow">¶</a></p>
<p id="section-5-6">When calculating the outgoing label for the prefix, the router <span class="bcp14">MUST</span>
        take into account, as described below, the E-, NP-, and M-Flags advertised by the next-hop router if
        that router advertised the SID for the prefix.  This <span class="bcp14">MUST</span> be done
        regardless of whether the next-hop router contributes to the best path to the
        prefix.<a href="#section-5-6" class="pilcrow">¶</a></p>
<p id="section-5-7">The NP-Flag (No-PHP) <span class="bcp14">MUST</span> be set and the E-Flag
      <span class="bcp14">MUST</span> be clear for Prefix-SIDs 
        allocated to inter-area prefixes that are originated by the ABR based on intra-area
        or inter-area reachability between areas unless the advertised prefix is directly
        attached to the ABR.<a href="#section-5-7" class="pilcrow">¶</a></p>
<p id="section-5-8">The NP-Flag (No-PHP) <span class="bcp14">MUST</span> be set and the E-Flag
      <span class="bcp14">MUST</span> be clear for Prefix-SIDs 
        allocated to redistributed prefixes, unless the redistributed prefix is directly
        attached to the Autonomous System Boundary Router (ASBR).<a href="#section-5-8" class="pilcrow">¶</a></p>
<p id="section-5-9">If the NP-Flag is not set, then:<a href="#section-5-9" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-5-10.1">Any upstream neighbor of the Prefix-SID originator <span class="bcp14">MUST</span> pop
the Prefix-SID. This is equivalent to the penultimate hop-popping mechanism
used in the MPLS data plane.<a href="#section-5-10.1" class="pilcrow">¶</a>
</li>
        <li class="ulEmpty" id="section-5-10.2">The received E-Flag is ignored.<a href="#section-5-10.2" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-5-11">If the NP-Flag is set and the E-Flag is not set, then:<a href="#section-5-11" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-5-12.1">Any upstream neighbor of the Prefix-SID originator <span class="bcp14">MUST</span>
keep the Prefix-SID on top of the stack. This is useful when the originator of
the Prefix-SID needs to stitch the incoming packet into a continuing MPLS LSP
to the final destination. This could occur at an ABR (prefix propagation from
one area to another) or at an  ASBR (prefix propagation from one
domain to another).<a href="#section-5-12.1" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-5-13">If both the NP-Flag and E-Flag are set, then:<a href="#section-5-13" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-5-14.1">Any upstream neighbor of the Prefix-SID originator <span class="bcp14">MUST</span>
replace the Prefix-SID with an Explicit NULL label. This is useful, e.g., when
the originator of the Prefix-SID is the final destination for the related
prefix and the originator wishes to receive the packet with the original EXP
bits.<a href="#section-5-14.1" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-5-15">When the M-Flag is set, the NP-Flag and the E-Flag <span class="bcp14">MUST</span> be ignored on reception.<a href="#section-5-15" class="pilcrow">¶</a></p>
<p id="section-5-16">As the Mapping Server does not specify the originator of a prefix advertisement,
        it is not possible to determine PHP behavior solely based on the Mapping Server 
        Advertisement. However, PHP behavior <span class="bcp14">SHOULD</span> be done in the following cases:<a href="#section-5-16" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-5-17.1">The Prefix is intra-area type and the downstream neighbor is the originator 
         of the prefix.<a href="#section-5-17.1" class="pilcrow">¶</a>
</li>
        <li class="ulEmpty" id="section-5-17.2">The Prefix is inter-area type and the downstream neighbor is an
 ABR, which is advertising prefix reachability and is also generating
 the Extended Prefix TLV with the A-Flag set for this prefix as
 described in <span><a href="https://www.rfc-editor.org/rfc/rfc7684#section-2.1" class="relref">Section 2.1</a> of [<a href="#RFC7684" class="xref">RFC7684</a>]</span>.<a href="#section-5-17.2" class="pilcrow">¶</a>
</li>
        <li class="ulEmpty" id="section-5-17.3"> The Prefix is external type and the downstream neighbor is an ASBR,
        which is advertising prefix reachability and is also generating the
        Extended Prefix TLV with the A-Flag set for this prefix as described
        in <span><a href="https://www.rfc-editor.org/rfc/rfc7684#section-2.1" class="relref">Section 2.1</a> of [<a href="#RFC7684" class="xref">RFC7684</a>]</span>.<a href="#section-5-17.3" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-5-18">When a Prefix-SID is advertised in an Extended Prefix Range TLV, then
      the value advertised in the Prefix-SID Sub-TLV is interpreted as a
      starting SID/Label value.<a href="#section-5-18" class="pilcrow">¶</a></p>
<p id="section-5-19">Example 1: If the following router addresses (loopback addresses)
        need to be mapped into the corresponding Prefix-SID indexes:<a href="#section-5-19" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-5-20">
<pre>
          Router-A: 192.0.2.1/32, Prefix-SID: Index 1
          Router-B: 192.0.2.2/32, Prefix-SID: Index 2
          Router-C: 192.0.2.3/32, Prefix-SID: Index 3
          Router-D: 192.0.2.4/32, Prefix-SID: Index 4</pre><a href="#section-5-20" class="pilcrow">¶</a>
</div>
<p id="section-5-21">then the Prefix field in the Extended Prefix Range TLV would be set to
        192.0.2.1, Prefix Length would be set to 32, Range Size would be set to 4, and
        the Index value in the Prefix-SID Sub-TLV would be set to 1.<a href="#section-5-21" class="pilcrow">¶</a></p>
<p id="section-5-22">Example 2: If the following prefixes need to be mapped into the
        corresponding Prefix-SID indexes:<a href="#section-5-22" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-5-23">
<pre>
           192.0.2.0/30, Prefix-SID: Index 51
           192.0.2.4/30, Prefix-SID: Index 52
           192.0.2.8/30, Prefix-SID: Index 53
          192.0.2.12/30, Prefix-SID: Index 54
          192.0.2.16/30, Prefix-SID: Index 55
          192.0.2.20/30, Prefix-SID: Index 56
          192.0.2.24/30, Prefix-SID: Index 57</pre><a href="#section-5-23" class="pilcrow">¶</a>
</div>
<p id="section-5-24">then the Prefix field in the Extended Prefix Range TLV would be set to
        192.0.2.0, Prefix Length would be set to 30, Range Size would be 7, and 
        the Index value in the Prefix-SID Sub-TLV would be set to 51.<a href="#section-5-24" class="pilcrow">¶</a></p>
</section>
</div>
<div id="ADJSID">
<section id="section-6">
      <h2 id="name-adjacency-segment-identifie">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-adjacency-segment-identifie" class="section-name selfRef">Adjacency Segment Identifier (Adj-SID)</a>
      </h2>
<p id="section-6-1">An Adjacency Segment Identifier (Adj-SID) represents a router
      adjacency in Segment Routing.<a href="#section-6-1" class="pilcrow">¶</a></p>
<div id="ADJSIDSUBTLV">
<section id="section-6.1">
        <h3 id="name-adj-sid-sub-tlv">
<a href="#section-6.1" class="section-number selfRef">6.1. </a><a href="#name-adj-sid-sub-tlv" class="section-name selfRef">Adj-SID Sub-TLV</a>
        </h3>
<p id="section-6.1-1">Adj-SID is an optional sub-TLV of the Extended Link TLV defined in 
        <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span>. It <span class="bcp14">MAY</span> appear multiple times
        in the Extended Link TLV. 
        
        The Adj-SID Sub-TLV has the following format:<a href="#section-6.1-1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-6.1-2">
<pre> 
 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Flags     |    Reserved   |   MT-ID       |  Weight       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                   SID/Label/Index (variable)                  |
+---------------------------------------------------------------+</pre><a href="#section-6.1-2" class="pilcrow">¶</a>
</div>
<p id="section-6.1-3">where:<a href="#section-6.1-3" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-6.1-4.1">
            <dl class="dlParallel" id="section-6.1-4.1.1">
              <dt id="section-6.1-4.1.1.1">Type:</dt>
              <dd id="section-6.1-4.1.1.2">2<a href="#section-6.1-4.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.3">Length:</dt>
              <dd id="section-6.1-4.1.1.4">7 or 8 octets, depending on the V-Flag<a href="#section-6.1-4.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.5">Flags:</dt>
              <dd id="section-6.1-4.1.1.6">
                <p id="section-6.1-4.1.1.6.1">Single-octet field containing the following flags:<a href="#section-6.1-4.1.1.6.1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-6.1-4.1.1.6.2">
<pre>    
    0 1 2 3 4 5 6 7 
   +-+-+-+-+-+-+-+-+
   |B|V|L|G|P|     |
   +-+-+-+-+-+-+-+-+</pre><a href="#section-6.1-4.1.1.6.2" class="pilcrow">¶</a>
</div>
<p id="section-6.1-4.1.1.6.3">where:<a href="#section-6.1-4.1.1.6.3" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-6.1-4.1.1.6.4.1">
                    <dl class="dlParallel" id="section-6.1-4.1.1.6.4.1.1">
                      <dt id="section-6.1-4.1.1.6.4.1.1.1">B-Flag:</dt>
                      <dd id="section-6.1-4.1.1.6.4.1.1.2">Backup Flag. If set, the Adj-SID refers to an
                adjacency that is eligible for protection (e.g., using IP Fast
 Reroute or MPLS-FRR (MPLS-Fast Reroute)
                as described in <span><a href="https://www.rfc-editor.org/rfc/rfc8402#section-2.1" class="relref">Section 2.1</a> of [<a href="#RFC8402" class="xref">RFC8402</a>]</span>.<a href="#section-6.1-4.1.1.6.4.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.6.4.1.1.3">V-Flag:</dt>
                      <dd id="section-6.1-4.1.1.6.4.1.1.4">Value/Index Flag. If set, then the Adj-SID 
                carries an absolute value. If not set, then the Adj-SID carries 
                an index.<a href="#section-6.1-4.1.1.6.4.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.6.4.1.1.5">L-Flag:</dt>
                      <dd id="section-6.1-4.1.1.6.4.1.1.6">Local/Global Flag. If set, then the value/index 
                carried by the Adj-SID has local significance. If not set, then
                the value/index carried by this sub-TLV has global significance.<a href="#section-6.1-4.1.1.6.4.1.1.6" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.6.4.1.1.7">G-Flag:</dt>
                      <dd id="section-6.1-4.1.1.6.4.1.1.8">Group Flag. When set, the G-Flag indicates that the 
                Adj-SID refers to a group of adjacencies (and therefore <span class="bcp14">MAY</span> be assigned
                to other adjacencies as well).<a href="#section-6.1-4.1.1.6.4.1.1.8" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.6.4.1.1.9">P-Flag:</dt>
                      <dd id="section-6.1-4.1.1.6.4.1.1.10">Persistent Flag. When set, the P-Flag indicates that 
     the Adj-SID is persistently allocated, i.e., the Adj-SID value 
     remains consistent across router restart and/or interface flap.<a href="#section-6.1-4.1.1.6.4.1.1.10" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.6.4.1.1.11">Other bits:</dt>
                      <dd id="section-6.1-4.1.1.6.4.1.1.12">Reserved. These <span class="bcp14">MUST</span> be zero when sent and are ignored when
                received.<a href="#section-6.1-4.1.1.6.4.1.1.12" class="pilcrow">¶</a>
</dd>
</dl>
</li>
                </ul>
</dd>
<dt id="section-6.1-4.1.1.7">Reserved:</dt>
              <dd id="section-6.1-4.1.1.8">
                <span class="bcp14">SHOULD</span> be set to 0 on transmission and <span class="bcp14">MUST</span> be ignored on reception<a href="#section-6.1-4.1.1.8" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.9">MT-ID:</dt>
              <dd id="section-6.1-4.1.1.10">Multi-Topology ID (as defined in <span>[<a href="#RFC4915" class="xref">RFC4915</a>]</span><a href="#section-6.1-4.1.1.10" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.11">Weight:</dt>
              <dd id="section-6.1-4.1.1.12"> Weight used for load-balancing purposes. The use of the
            weight is defined in <span>[<a href="#RFC8402" class="xref">RFC8402</a>]</span>.<a href="#section-6.1-4.1.1.12" class="pilcrow">¶</a>
</dd>
<dt id="section-6.1-4.1.1.13">SID/Index/Label:</dt>
              <dd id="section-6.1-4.1.1.14">As described in <a href="#PREFIXSID" class="xref">Section 5</a><a href="#section-6.1-4.1.1.14" class="pilcrow">¶</a>
</dd>
</dl>
</li>
        </ul>
<p id="section-6.1-5">An SR-capable router <span class="bcp14">MAY</span> allocate an Adj-SID for each of its
        adjacencies and set the B-Flag when the adjacency is eligible for protection by 
        an FRR mechanism (IP or MPLS) as described in
 <span><a href="https://www.rfc-editor.org/rfc/rfc8402#section-3.5" class="relref">Section 3.5</a> of [<a href="#RFC8402" class="xref">RFC8402</a>]</span>.<a href="#section-6.1-5" class="pilcrow">¶</a></p>
<p id="section-6.1-6">An SR-capable router <span class="bcp14">MAY</span> allocate more than one Adj-SID to an adjacency.<a href="#section-6.1-6" class="pilcrow">¶</a></p>
<p id="section-6.1-7">An SR-capable router <span class="bcp14">MAY</span> allocate the same Adj-SID to different adjacencies.<a href="#section-6.1-7" class="pilcrow">¶</a></p>
<p id="section-6.1-8">When the P-Flag is not set, the Adj-SID <span class="bcp14">MAY</span> be persistent. When 
     the P-Flag is set, the Adj-SID <span class="bcp14">MUST</span> be persistent.<a href="#section-6.1-8" class="pilcrow">¶</a></p>
</section>
</div>
<div id="LANADJSIDSUBTLV">
<section id="section-6.2">
        <h3 id="name-lan-adj-sid-sub-tlv">
<a href="#section-6.2" class="section-number selfRef">6.2. </a><a href="#name-lan-adj-sid-sub-tlv" class="section-name selfRef">LAN Adj-SID Sub-TLV</a>
        </h3>
<p id="section-6.2-1">The LAN Adjacency SID is an optional sub-TLV of the Extended Link TLV defined in 
        <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span>. It <span class="bcp14">MAY</span> appear multiple
        times in the Extended Link TLV. It is used to advertise a SID/Label for an adjacency 
        to a non-DR (Designated Router) router on a broadcast, Non-Broadcast Multi-Access (NBMA), or hybrid <span>[<a href="#RFC6845" class="xref">RFC6845</a>]</span> network.<a href="#section-6.2-1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-6.2-2">
<pre>
 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Flags     |    Reserved   |     MT-ID     |    Weight     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Neighbor ID                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    SID/Label/Index (variable)                 |
+---------------------------------------------------------------+</pre><a href="#section-6.2-2" class="pilcrow">¶</a>
</div>
<p id="section-6.2-3">where:<a href="#section-6.2-3" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-6.2-4.1">
            <dl class="dlParallel" id="section-6.2-4.1.1">
              <dt id="section-6.2-4.1.1.1">Type:</dt>
              <dd id="section-6.2-4.1.1.2">3<a href="#section-6.2-4.1.1.2" class="pilcrow">¶</a>
</dd>
<dt id="section-6.2-4.1.1.3">Length:</dt>
              <dd id="section-6.2-4.1.1.4">11 or 12 octets, depending on the V-Flag<a href="#section-6.2-4.1.1.4" class="pilcrow">¶</a>
</dd>
<dt id="section-6.2-4.1.1.5">Flags:</dt>
              <dd id="section-6.2-4.1.1.6">Same as in <a href="#ADJSIDSUBTLV" class="xref">Section 6.1</a><a href="#section-6.2-4.1.1.6" class="pilcrow">¶</a>
</dd>
<dt id="section-6.2-4.1.1.7">Reserved:</dt>
              <dd id="section-6.2-4.1.1.8">
                <span class="bcp14">SHOULD</span> be set to 0 on transmission and <span class="bcp14">MUST</span> be ignored on reception<a href="#section-6.2-4.1.1.8" class="pilcrow">¶</a>
</dd>
<dt id="section-6.2-4.1.1.9">MT-ID:</dt>
              <dd id="section-6.2-4.1.1.10">Multi-Topology ID (as defined in <span>[<a href="#RFC4915" class="xref">RFC4915</a>]</span>)<a href="#section-6.2-4.1.1.10" class="pilcrow">¶</a>
</dd>
<dt id="section-6.2-4.1.1.11">Weight:</dt>
              <dd id="section-6.2-4.1.1.12">Weight used for load-balancing purposes. The use of the
            weight is defined in <span>[<a href="#RFC8402" class="xref">RFC8402</a>]</span>.<a href="#section-6.2-4.1.1.12" class="pilcrow">¶</a>
</dd>
<dt id="section-6.2-4.1.1.13">Neighbor ID:</dt>
              <dd id="section-6.2-4.1.1.14">The Router ID of the neighbor for which the LAN Adjacency SID is 
            advertised<a href="#section-6.2-4.1.1.14" class="pilcrow">¶</a>
</dd>
<dt id="section-6.2-4.1.1.15">SID/Index/Label:</dt>
              <dd id="section-6.2-4.1.1.16">
                <p id="section-6.2-4.1.1.16.1">As described in <a href="#PREFIXSID" class="xref">Section 5</a><a href="#section-6.2-4.1.1.16.1" class="pilcrow">¶</a></p>
</dd>
</dl>
</li>
        </ul>
<p id="section-6.2-5">When the P-Flag is not set, the LAN Adjacency SID <span class="bcp14">MAY</span> be persistent.  When
the P-Flag is set, the LAN Adjacency SID <span class="bcp14">MUST</span> be persistent.<a href="#section-6.2-5" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<section id="section-7">
      <h2 id="name-elements-of-procedure">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-elements-of-procedure" class="section-name selfRef">Elements of Procedure</a>
      </h2>
<section id="section-7.1">
        <h3 id="name-intra-area-segment-routing-">
<a href="#section-7.1" class="section-number selfRef">7.1. </a><a href="#name-intra-area-segment-routing-" class="section-name selfRef">Intra-area Segment Routing in OSPFv2</a>
        </h3>
<p id="section-7.1-1">An OSPFv2 router that supports Segment Routing <span class="bcp14">MAY</span> advertise Prefix-
        SIDs for any prefix to which it is advertising reachability (e.g.,
        a loopback IP address as described in <a href="#PREFIXSID" class="xref">Section 5</a>).<a href="#section-7.1-1" class="pilcrow">¶</a></p>
<p id="section-7.1-2">A Prefix-SID can also be advertised by the SR Mapping Servers (as
        described in <span>[<a href="#RFC8661" class="xref">RFC8661</a>]</span>). A Mapping
        Server advertises Prefix-SIDs for remote prefixes that exist in the
        OSPFv2 routing domain. Multiple Mapping Servers can advertise Prefix-SIDs 
        for the same prefix; in which case, the same Prefix-SID <span class="bcp14">MUST</span> be advertised by
        all of them. The flooding scope of the OSPF Extended Prefix Opaque LSA
        that is generated by the SR Mapping Server could be either area scoped
        or AS scoped and is determined based on the configuration of the 
        SR Mapping Server.<a href="#section-7.1-2" class="pilcrow">¶</a></p>
<p id="section-7.1-3">An SR Mapping Server <span class="bcp14">MUST</span> use the OSPF Extended Prefix Range TLV when advertising SIDs
        for prefixes. Prefixes of different route types can be combined in a single OSPF 
        Extended Prefix Range TLV advertised by an SR Mapping Server. Because the OSPF 
        Extended Prefix Range TLV doesn't include a Route-Type field, as in the OSPF 
        Extended Prefix TLV, it is possible to include adjacent prefixes from different 
        route types in the OSPF Extended Prefix Range TLV.<a href="#section-7.1-3" class="pilcrow">¶</a></p>
<p id="section-7.1-4">Area-scoped OSPF Extended Prefix Range TLVs are propagated between areas. Similar 
        to propagation of prefixes between areas, an ABR only propagates the OSPF Extended 
        Prefix Range TLV that it considers to be the best from the set it received. The 
        rules used to pick the best OSPF Extended Prefix Range TLV are described in 
        <a href="#PFXRANGE" class="xref">Section 4</a>.<a href="#section-7.1-4" class="pilcrow">¶</a></p>
<p id="section-7.1-5">When propagating an OSPF Extended Prefix Range TLV between areas, ABRs <span class="bcp14">MUST</span> set the
        IA-Flag. This is used to prevent redundant flooding of the OSPF Extended 
        Prefix Range TLV between areas as described in <a href="#PFXRANGE" class="xref">Section 4</a>.<a href="#section-7.1-5" class="pilcrow">¶</a></p>
</section>
<section id="section-7.2">
        <h3 id="name-inter-area-segment-routing-">
<a href="#section-7.2" class="section-number selfRef">7.2. </a><a href="#name-inter-area-segment-routing-" class="section-name selfRef">Inter-area Segment Routing in OSPFv2</a>
        </h3>
<p id="section-7.2-1">In order to support SR in a multiarea environment, OSPFv2 <span class="bcp14">MUST</span>
        propagate Prefix-SID information between areas. The following
        procedure is used to propagate Prefix-SIDs between areas.<a href="#section-7.2-1" class="pilcrow">¶</a></p>
<p id="section-7.2-2">When an OSPF ABR advertises a Type-3 Summary LSA from an intra-area
        prefix to all its connected areas, it will also originate an OSPF Extended
        Prefix Opaque LSA as described in <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span>. 
        The flooding scope of the OSPF Extended Prefix Opaque LSA type will be set to
        area-local scope. The route type in the OSPF Extended Prefix TLV is set to
        inter-area. The Prefix-SID Sub-TLV will be included in this LSA and
        the Prefix-SID value will be set as follows:<a href="#section-7.2-2" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-7.2-3.1">The ABR will look at its best path to the prefix in the source
            area and find the advertising router associated with the best
            path to that prefix.<a href="#section-7.2-3.1" class="pilcrow">¶</a>
</li>
          <li class="ulEmpty" id="section-7.2-3.2">The ABR will then determine if this router advertised a
            Prefix-SID for the prefix and use it when advertising the
            Prefix-SID to other connected areas.<a href="#section-7.2-3.2" class="pilcrow">¶</a>
</li>
          <li class="ulEmpty" id="section-7.2-3.3">If no Prefix-SID was advertised for the prefix in the source
            area by the router that contributes to the best path to the
            prefix, the originating ABR will use the Prefix-SID advertised by any
            other router when propagating the Prefix-SID for the prefix to other areas.<a href="#section-7.2-3.3" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-7.2-4">When an OSPF ABR advertises Type-3 Summary LSAs from an inter-area
        route to all its connected areas, it will also originate an OSPF Extended
        Prefix Opaque LSA as described in <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span>. 
        The flooding scope of the OSPF Extended Prefix Opaque LSA type will be set to
        area-local scope. The route type in the OSPF Extended Prefix TLV is set to
        inter-area. The Prefix-SID Sub-TLV will be included in this LSA and
        the Prefix-SID will be set as follows:<a href="#section-7.2-4" class="pilcrow">¶</a></p>
<ul class="ulEmpty">
<li class="ulEmpty" id="section-7.2-5.1">The ABR will look at its best path to the prefix in the backbone
            area and find the advertising router associated with the best
            path to that prefix.<a href="#section-7.2-5.1" class="pilcrow">¶</a>
</li>
          <li class="ulEmpty" id="section-7.2-5.2">The ABR will then determine if such a router advertised a
          Prefix-SID for the prefix and use it when advertising the Prefix-SID
          to other connected areas.<a href="#section-7.2-5.2" class="pilcrow">¶</a>
</li>
          <li class="ulEmpty" id="section-7.2-5.3">If no Prefix-SID was advertised for the prefix in the backbone
            area by the ABR that contributes to the best path to the prefix,
            the originating ABR will use the Prefix-SID advertised by any
            other router when propagating the Prefix-SID for the prefix to other areas.<a href="#section-7.2-5.3" class="pilcrow">¶</a>
</li>
        </ul>
</section>
<section id="section-7.3">
        <h3 id="name-segment-routing-for-externa">
<a href="#section-7.3" class="section-number selfRef">7.3. </a><a href="#name-segment-routing-for-externa" class="section-name selfRef">Segment Routing for External Prefixes</a>
        </h3>
<p id="section-7.3-1">Type-5 LSAs are flooded domain wide. When an ASBR, which supports
        SR, generates Type-5 LSAs, it <span class="bcp14">SHOULD</span> also originate
        OSPF Extended Prefix Opaque LSAs as described in <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span>.  The flooding scope of the
        OSPF Extended Prefix Opaque LSA type is set to AS-wide scope.  The route
        type in the OSPF Extended Prefix TLV is set to external. The
        Prefix-SID Sub-TLV is included in this LSA and the Prefix-SID value
        will be set to the SID that has been reserved for that prefix.<a href="#section-7.3-1" class="pilcrow">¶</a></p>
<p id="section-7.3-2">When a Not-So-Stubby Area (NSSA) <span>[<a href="#RFC3101" class="xref">RFC3101</a>]</span> ABR translates Type-7 LSAs into Type-5 
        LSAs, it <span class="bcp14">SHOULD</span> also advertise the Prefix-SID for the prefix. The NSSA ABR determines
        its best path to the prefix advertised in the translated Type-7 LSA
        and finds the advertising router associated with that path. If the
        advertising router has advertised a Prefix-SID for the prefix, then
        the NSSA ABR uses it when advertising the Prefix-SID for the Type-5
        prefix. Otherwise, the Prefix-SID advertised by any other router will
        be used.<a href="#section-7.3-2" class="pilcrow">¶</a></p>
</section>
<section id="section-7.4">
        <h3 id="name-advertisement-of-adj-sid">
<a href="#section-7.4" class="section-number selfRef">7.4. </a><a href="#name-advertisement-of-adj-sid" class="section-name selfRef">Advertisement of Adj-SID</a>
        </h3>
<p id="section-7.4-1">The Adjacency Segment Routing Identifier (Adj-SID) is advertised
        using the Adj-SID Sub-TLV as described in <a href="#ADJSID" class="xref">Section 6</a>.<a href="#section-7.4-1" class="pilcrow">¶</a></p>
<section id="section-7.4.1">
          <h4 id="name-advertisement-of-adj-sid-on">
<a href="#section-7.4.1" class="section-number selfRef">7.4.1. </a><a href="#name-advertisement-of-adj-sid-on" class="section-name selfRef">Advertisement of Adj-SID on Point-to-Point Links</a>
          </h4>
<p id="section-7.4.1-1">An Adj-SID <span class="bcp14">MAY</span> be advertised for any adjacency on a point-to-point (P2P) link that is
          in neighbor state 2-Way or higher. If the adjacency on a P2P link
          transitions from the FULL state, then the Adj-SID for that adjacency
          <span class="bcp14">MAY</span> be removed from the area. If the adjacency transitions to a
          state lower than 2-Way, then the Adj-SID Advertisement <span class="bcp14">MUST</span> be withdrawn from the
          area.<a href="#section-7.4.1-1" class="pilcrow">¶</a></p>
</section>
<section id="section-7.4.2">
          <h4 id="name-adjacency-sid-on-broadcast-">
<a href="#section-7.4.2" class="section-number selfRef">7.4.2. </a><a href="#name-adjacency-sid-on-broadcast-" class="section-name selfRef">Adjacency SID on Broadcast or NBMA Interfaces</a>
          </h4>
<p id="section-7.4.2-1">Broadcast, NBMA, or hybrid <span>[<a href="#RFC6845" class="xref">RFC6845</a>]</span> networks in OSPF are 
          represented by a star topology where the Designated Router (DR) is the central
          point to which all other routers on the broadcast, NBMA, or hybrid network connect.
          As a result, routers on the broadcast, NBMA, or hybrid network advertise only 
          their adjacency to the DR. Routers that do not act as DR do not form or 
          advertise adjacencies with each other. They do, however, maintain 2-Way adjacency
          state with each other and are directly reachable.<a href="#section-7.4.2-1" class="pilcrow">¶</a></p>
<p id="section-7.4.2-2">When Segment Routing is used, each router on the broadcast, NBMA, or hybrid
           network <span class="bcp14">MAY</span> advertise the Adj-SID for its adjacency to the DR using
          the Adj-SID Sub-TLV as described in <a href="#ADJSIDSUBTLV" class="xref">Section 6.1</a>.<a href="#section-7.4.2-2" class="pilcrow">¶</a></p>
<p id="section-7.4.2-3">SR-capable routers <span class="bcp14">MAY</span> also advertise a LAN Adjacency SID for other neighbors
          (e.g., Backup Designated Router, DR-OTHER, etc.) on the broadcast, NBMA, or hybrid network using the 
          LAN Adj-SID Sub-TLV as described in <a href="#LANADJSIDSUBTLV" class="xref">Section 6.2</a>.<a href="#section-7.4.2-3" class="pilcrow">¶</a></p>
</section>
</section>
</section>
<div id="IANA">
<section id="section-8">
      <h2 id="name-iana-considerations">
<a href="#section-8" class="section-number selfRef">8. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-8-1">This specification updates several existing OSPF
      registries and creates a new IGP registry.<a href="#section-8-1" class="pilcrow">¶</a></p>
<div id="RITLVREG">
<section id="section-8.1">
        <h3 id="name-ospf-router-information-ri-">
<a href="#section-8.1" class="section-number selfRef">8.1. </a><a href="#name-ospf-router-information-ri-" class="section-name selfRef">OSPF Router Information (RI) TLVs Registry</a>
        </h3>
<p id="section-8.1-1">The following values have been allocated:<a href="#section-8.1-1" class="pilcrow">¶</a></p>
<span id="name-ospf-router-information-ri-t"></span><div id="IANA1">
<table class="left" id="table-1">
          <caption>
<a href="#table-1" class="selfRef">Table 1</a>:
<a href="#name-ospf-router-information-ri-t" class="selfRef">OSPF Router Information (RI) TLVs</a>
          </caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Value</th>
              <th class="text-left" rowspan="1" colspan="1">TLV Name</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">8</td>
              <td class="text-left" rowspan="1" colspan="1">SR-Algorithm TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">9</td>
              <td class="text-left" rowspan="1" colspan="1">SID/Label Range TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">14</td>
              <td class="text-left" rowspan="1" colspan="1">SR Local Block TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">15</td>
              <td class="text-left" rowspan="1" colspan="1">SRMS Preference TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
          </tbody>
        </table>
</div>
</section>
</div>
<div id="EPLTLVREG">
<section id="section-8.2">
        <h3 id="name-ospfv2-extended-prefix-opaq">
<a href="#section-8.2" class="section-number selfRef">8.2. </a><a href="#name-ospfv2-extended-prefix-opaq" class="section-name selfRef">OSPFv2 Extended Prefix Opaque LSA TLVs Registry</a>
        </h3>
<p id="section-8.2-1">The following values have been allocated:<a href="#section-8.2-1" class="pilcrow">¶</a></p>
<span id="name-ospfv2-extended-prefix-opaqu"></span><div id="IANA2">
<table class="left" id="table-2">
          <caption>
<a href="#table-2" class="selfRef">Table 2</a>:
<a href="#name-ospfv2-extended-prefix-opaqu" class="selfRef">OSPFv2 Extended Prefix Opaque LSA TLVs</a>
          </caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Value</th>
              <th class="text-left" rowspan="1" colspan="1">Description</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">2</td>
              <td class="text-left" rowspan="1" colspan="1">OSPF Extended Prefix Range TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
          </tbody>
        </table>
</div>
</section>
</div>
<div id="EPLSTLVREG">
<section id="section-8.3">
        <h3 id="name-ospfv2-extended-prefix-tlv-">
<a href="#section-8.3" class="section-number selfRef">8.3. </a><a href="#name-ospfv2-extended-prefix-tlv-" class="section-name selfRef">OSPFv2 Extended Prefix TLV Sub-TLVs Registry</a>
        </h3>
<p id="section-8.3-1">The following values have been allocated:<a href="#section-8.3-1" class="pilcrow">¶</a></p>
<span id="name-ospfv2-extended-prefix-tlv-s"></span><div id="IANA3">
<table class="left" id="table-3">
          <caption>
<a href="#table-3" class="selfRef">Table 3</a>:
<a href="#name-ospfv2-extended-prefix-tlv-s" class="selfRef">OSPFv2 Extended Prefix TLV Sub-TLVs</a>
          </caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Value</th>
              <th class="text-left" rowspan="1" colspan="1">Description</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">1</td>
              <td class="text-left" rowspan="1" colspan="1">SID/Label Sub-TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">2</td>
              <td class="text-left" rowspan="1" colspan="1">Prefix-SID Sub-TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
          </tbody>
        </table>
</div>
</section>
</div>
<div id="ELLSTLVREG">
<section id="section-8.4">
        <h3 id="name-ospfv2-extended-link-tlv-su">
<a href="#section-8.4" class="section-number selfRef">8.4. </a><a href="#name-ospfv2-extended-link-tlv-su" class="section-name selfRef">OSPFv2 Extended Link TLV Sub-TLVs Registry</a>
        </h3>
<p id="section-8.4-1">The following initial values have been allocated:<a href="#section-8.4-1" class="pilcrow">¶</a></p>
<span id="name-ospfv2-extended-link-tlv-sub"></span><div id="IANA4">
<table class="left" id="table-4">
          <caption>
<a href="#table-4" class="selfRef">Table 4</a>:
<a href="#name-ospfv2-extended-link-tlv-sub" class="selfRef">OSPFv2 Extended Link TLV Sub-TLVs</a>
          </caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Value</th>
              <th class="text-left" rowspan="1" colspan="1">Description</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">1</td>
              <td class="text-left" rowspan="1" colspan="1">SID/Label Sub-TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">2</td>
              <td class="text-left" rowspan="1" colspan="1">Adj-SID Sub-TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">3</td>
              <td class="text-left" rowspan="1" colspan="1">LAN Adj-SID/Label Sub-TLV</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
          </tbody>
        </table>
</div>
</section>
</div>
<div id="IGPALGOREG">
<section id="section-8.5">
        <h3 id="name-igp-algorithm-types-registr">
<a href="#section-8.5" class="section-number selfRef">8.5. </a><a href="#name-igp-algorithm-types-registr" class="section-name selfRef">IGP Algorithm Types Registry</a>
        </h3>
<p id="section-8.5-1">IANA has set up a subregistry called "IGP Algorithm Type" under the
       "Interior Gateway Protocol (IGP) Parameters" registry.
       The registration policy for this registry is "Standards Action" 
       (<span>[<a href="#RFC8126" class="xref">RFC8126</a>]</span> and <span>[<a href="#RFC7120" class="xref">RFC7120</a>]</span>).<a href="#section-8.5-1" class="pilcrow">¶</a></p>
<p id="section-8.5-2">Values in this registry come from the range 0-255.<a href="#section-8.5-2" class="pilcrow">¶</a></p>
<p id="section-8.5-3"> The initial values in the IGP Algorithm Type registry are
 as follows:<a href="#section-8.5-3" class="pilcrow">¶</a></p>
<span id="name-igp-algorithm-types"></span><div id="IANA5">
<table class="left" id="table-5">
          <caption>
<a href="#table-5" class="selfRef">Table 5</a>:
<a href="#name-igp-algorithm-types" class="selfRef">IGP Algorithm Types</a>
          </caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Value</th>
              <th class="text-left" rowspan="1" colspan="1">Description</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">0</td>
              <td class="text-left" rowspan="1" colspan="1">Shortest Path First (SPF) algorithm based on link metric. This is 
                the standard shortest path algorithm as computed by the IGP protocol.  
                Consistent with the deployed practice for link-state protocols,  Algorithm 0 
                permits any node to overwrite the SPF path with a different path based on
                its local policy.</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">1</td>
              <td class="text-left" rowspan="1" colspan="1">Strict Shortest Path First (SPF) algorithm based on link metric. 
                The algorithm is identical to Algorithm 0, but Algorithm 1 requires that 
                all nodes along the path will honor the SPF routing decision. Local policy
                at the node claiming support for Algorithm 1 <span class="bcp14">MUST NOT</span> alter the 
                SPF paths computed by Algorithm 1.</td>
              <td class="text-left" rowspan="1" colspan="1">This document</td>
            </tr>
          </tbody>
        </table>
</div>
</section>
</div>
</section>
</div>
<div id="Error-handling">
<section id="section-9">
      <h2 id="name-tlv-sub-tlv-error-handling">
<a href="#section-9" class="section-number selfRef">9. </a><a href="#name-tlv-sub-tlv-error-handling" class="section-name selfRef">TLV/Sub-TLV Error Handling</a>
      </h2>
<p id="section-9-1">For any new TLVs/sub-TLVs defined in this document, if the length is
invalid, the LSA in which it is advertised is considered malformed and <span class="bcp14">MUST</span> be
ignored. An error <span class="bcp14">SHOULD</span> be logged subject to rate limiting.<a href="#section-9-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Security">
<section id="section-10">
      <h2 id="name-security-considerations">
<a href="#section-10" class="section-number selfRef">10. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-10-1">With the OSPFv2 Segment Routing extensions defined herein,
      OSPFv2 will now program the MPLS data plane <span>[<a href="#RFC3031" class="xref">RFC3031</a>]</span> in addition to the IP
      data plane. Previously, LDP <span>[<a href="#RFC5036" class="xref">RFC5036</a>]</span> or another label distribution
      mechanism was required to advertise MPLS labels and program the MPLS data plane.<a href="#section-10-1" class="pilcrow">¶</a></p>
<p id="section-10-2">In general, the same types of attacks that can be carried out on the IP
      control plane can be carried out on the MPLS control plane resulting in traffic
      being misrouted in the respective data planes. However, the latter can be more
      difficult to detect and isolate.<a href="#section-10-2" class="pilcrow">¶</a></p>
<p id="section-10-3">Existing security extensions as described in <span>[<a href="#RFC2328" class="xref">RFC2328</a>]</span> and
       <span>[<a href="#RFC7684" class="xref">RFC7684</a>]</span> apply to these Segment Routing extensions. While 
       OSPF is under a single administrative domain, there can be deployments where 
       potential attackers have access to one or more networks in the OSPF routing domain. 
       In these deployments, stronger authentication mechanisms such as those specified 
       in <span>[<a href="#RFC7474" class="xref">RFC7474</a>]</span> <span class="bcp14">SHOULD</span> be used.<a href="#section-10-3" class="pilcrow">¶</a></p>
<p id="section-10-4">Implementations <span class="bcp14">MUST</span> assure that malformed TLVs and sub-TLVs defined in this document 
       are detected and do not provide a vulnerability for attackers to crash the OSPFv2 
       router or routing process. Reception of malformed TLVs or sub-TLVs <span class="bcp14">SHOULD</span> be counted 
       and/or logged for further analysis. Logging of malformed TLVs and sub-TLVs <span class="bcp14">SHOULD</span>
       be rate limited to prevent a Denial of Service (DoS) attack (distributed or otherwise) 
       from overloading the OSPF control plane.<a href="#section-10-4" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-11">
      <h2 id="name-references">
<a href="#section-11" class="section-number selfRef">11. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-11.1">
        <h3 id="name-normative-references">
<a href="#section-11.1" class="section-number selfRef">11.1. </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="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="RFC3101">[RFC3101]</dt>
        <dd>
<span class="refAuthor">Murphy, P.</span>, <span class="refTitle">"The OSPF Not-So-Stubby Area (NSSA) Option"</span>, <span class="seriesInfo">RFC 3101</span>, <span class="seriesInfo">DOI 10.17487/RFC3101</span>, <time datetime="2003-01">January 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3101">https://www.rfc-editor.org/info/rfc3101</a>&gt;</span>. </dd>
<dt id="RFC4915">[RFC4915]</dt>
        <dd>
<span class="refAuthor">Psenak, P.</span><span class="refAuthor">, Mirtorabi, S.</span><span class="refAuthor">, Roy, A.</span><span class="refAuthor">, Nguyen, L.</span><span class="refAuthor">, and P. Pillay-Esnault</span>, <span class="refTitle">"Multi-Topology (MT) Routing in OSPF"</span>, <span class="seriesInfo">RFC 4915</span>, <span class="seriesInfo">DOI 10.17487/RFC4915</span>, <time datetime="2007-06">June 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4915">https://www.rfc-editor.org/info/rfc4915</a>&gt;</span>. </dd>
<dt id="RFC6845">[RFC6845]</dt>
        <dd>
<span class="refAuthor">Sheth, N.</span><span class="refAuthor">, Wang, L.</span><span class="refAuthor">, and J. Zhang</span>, <span class="refTitle">"OSPF Hybrid Broadcast and Point-to-Multipoint Interface Type"</span>, <span class="seriesInfo">RFC 6845</span>, <span class="seriesInfo">DOI 10.17487/RFC6845</span>, <time datetime="2013-01">January 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6845">https://www.rfc-editor.org/info/rfc6845</a>&gt;</span>. </dd>
<dt id="RFC7120">[RFC7120]</dt>
        <dd>
<span class="refAuthor">Cotton, M.</span>, <span class="refTitle">"Early IANA Allocation of Standards Track Code Points"</span>, <span class="seriesInfo">BCP 100</span>, <span class="seriesInfo">RFC 7120</span>, <span class="seriesInfo">DOI 10.17487/RFC7120</span>, <time datetime="2014-01">January 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7120">https://www.rfc-editor.org/info/rfc7120</a>&gt;</span>. </dd>
<dt id="RFC7684">[RFC7684]</dt>
        <dd>
<span class="refAuthor">Psenak, P.</span><span class="refAuthor">, Gredler, H.</span><span class="refAuthor">, Shakir, R.</span><span class="refAuthor">, Henderickx, W.</span><span class="refAuthor">, Tantsura, J.</span><span class="refAuthor">, and A. Lindem</span>, <span class="refTitle">"OSPFv2 Prefix/Link Attribute Advertisement"</span>, <span class="seriesInfo">RFC 7684</span>, <span class="seriesInfo">DOI 10.17487/RFC7684</span>, <time datetime="2015-11">November 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7684">https://www.rfc-editor.org/info/rfc7684</a>&gt;</span>. </dd>
<dt id="RFC7770">[RFC7770]</dt>
        <dd>
<span class="refAuthor">Lindem, A., Ed.</span><span class="refAuthor">, Shen, N.</span><span class="refAuthor">, Vasseur, JP.</span><span class="refAuthor">, Aggarwal, R.</span><span class="refAuthor">, and S. Shaffer</span>, <span class="refTitle">"Extensions to OSPF for Advertising Optional Router Capabilities"</span>, <span class="seriesInfo">RFC 7770</span>, <span class="seriesInfo">DOI 10.17487/RFC7770</span>, <time datetime="2016-02">February 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7770">https://www.rfc-editor.org/info/rfc7770</a>&gt;</span>. </dd>
<dt id="RFC8126">[RFC8126]</dt>
        <dd>
<span class="refAuthor">Cotton, M.</span><span class="refAuthor">, Leiba, B.</span><span class="refAuthor">, and T. Narten</span>, <span class="refTitle">"Guidelines for Writing an IANA Considerations Section in RFCs"</span>, <span class="seriesInfo">BCP 26</span>, <span class="seriesInfo">RFC 8126</span>, <span class="seriesInfo">DOI 10.17487/RFC8126</span>, <time datetime="2017-06">June 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8126">https://www.rfc-editor.org/info/rfc8126</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>
<dt id="RFC8402">[RFC8402]</dt>
        <dd>
<span class="refAuthor">Filsfils, C., Ed.</span><span class="refAuthor">, Previdi, S., Ed.</span><span class="refAuthor">, Ginsberg, L.</span><span class="refAuthor">, Decraene, B.</span><span class="refAuthor">, Litkowski, S.</span><span class="refAuthor">, and R. Shakir</span>, <span class="refTitle">"Segment Routing Architecture"</span>, <span class="seriesInfo">RFC 8402</span>, <span class="seriesInfo">DOI 10.17487/RFC8402</span>, <time datetime="2018-07">July 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8402">https://www.rfc-editor.org/info/rfc8402</a>&gt;</span>. </dd>
<dt id="RFC8660">[RFC8660]</dt>
        <dd>
<span class="refAuthor">Bashandy, A., Ed.</span><span class="refAuthor">, Filsfils, C., Ed.</span><span class="refAuthor">, Previdi, S.</span><span class="refAuthor">, Decraene, B.</span><span class="refAuthor">, Litkowski, S.</span><span class="refAuthor">, and R. Shakir</span>, <span class="refTitle">"Segment Routing with MPLS Data Plane"</span>, <span class="seriesInfo">RFC 8660</span>, <span class="seriesInfo">DOI 10.17487/RFC8660</span>, <time datetime="2019-12">December 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8660">https://www.rfc-editor.org/info/rfc8660</a>&gt;</span>. </dd>
<dt id="RFC8661">[RFC8661]</dt>
      <dd>
<span class="refAuthor">Bashandy, A., Ed.</span><span class="refAuthor">, Filsfils, C., Ed.</span><span class="refAuthor">, Previdi, S.</span><span class="refAuthor">, Decraene, B.</span><span class="refAuthor">, and S. Litkowski</span>, <span class="refTitle">"Segment Routing Interworking with LDP"</span>, <span class="seriesInfo">RFC 8661</span>, <span class="seriesInfo">DOI 10.17487/RFC8661</span>, <time datetime="2019-12">December 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8661">https://www.rfc-editor.org/info/rfc8661</a>&gt;</span>. </dd>
</dl>
</section>
<section id="section-11.2">
        <h3 id="name-informative-references">
<a href="#section-11.2" class="section-number selfRef">11.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="RFC3031">[RFC3031]</dt>
        <dd>
<span class="refAuthor">Rosen, E.</span><span class="refAuthor">, Viswanathan, A.</span><span class="refAuthor">, and R. Callon</span>, <span class="refTitle">"Multiprotocol Label Switching Architecture"</span>, <span class="seriesInfo">RFC 3031</span>, <span class="seriesInfo">DOI 10.17487/RFC3031</span>, <time datetime="2001-01">January 2001</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3031">https://www.rfc-editor.org/info/rfc3031</a>&gt;</span>. </dd>
<dt id="RFC5036">[RFC5036]</dt>
        <dd>
<span class="refAuthor">Andersson, L., Ed.</span><span class="refAuthor">, Minei, I., Ed.</span><span class="refAuthor">, and B. Thomas, Ed.</span>, <span class="refTitle">"LDP Specification"</span>, <span class="seriesInfo">RFC 5036</span>, <span class="seriesInfo">DOI 10.17487/RFC5036</span>, <time datetime="2007-10">October 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5036">https://www.rfc-editor.org/info/rfc5036</a>&gt;</span>. </dd>
<dt id="RFC7474">[RFC7474]</dt>
        <dd>
<span class="refAuthor">Bhatia, M.</span><span class="refAuthor">, Hartman, S.</span><span class="refAuthor">, Zhang, D.</span><span class="refAuthor">, and A. Lindem, Ed.</span>, <span class="refTitle">"Security Extension for OSPFv2 When Using Manual Key Management"</span>, <span class="seriesInfo">RFC 7474</span>, <span class="seriesInfo">DOI 10.17487/RFC7474</span>, <time datetime="2015-04">April 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7474">https://www.rfc-editor.org/info/rfc7474</a>&gt;</span>. </dd>
<dt id="RFC7855">[RFC7855]</dt>
        <dd>
<span class="refAuthor">Previdi, S., Ed.</span><span class="refAuthor">, Filsfils, C., Ed.</span><span class="refAuthor">, Decraene, B.</span><span class="refAuthor">, Litkowski, S.</span><span class="refAuthor">, Horneffer, M.</span><span class="refAuthor">, and R. Shakir</span>, <span class="refTitle">"Source Packet Routing in Networking (SPRING) Problem Statement and Requirements"</span>, <span class="seriesInfo">RFC 7855</span>, <span class="seriesInfo">DOI 10.17487/RFC7855</span>, <time datetime="2016-05">May 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7855">https://www.rfc-editor.org/info/rfc7855</a>&gt;</span>. </dd>
<dt id="RFC8666">[RFC8666]</dt>
      <dd>
<span class="refAuthor">Psenak, P., Ed.</span><span class="refAuthor"> and S. Previdi, Ed.</span>, <span class="refTitle">"OSPFv3 Extensions for Segment Routing"</span>, <span class="seriesInfo">RFC 8666</span>, <span class="seriesInfo">DOI 10.17487/RFC8666</span>, <time datetime="2019-12">December 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8666">https://www.rfc-editor.org/info/rfc8666</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">We would like to thank Anton Smirnov for his contribution.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
<p id="section-appendix.a-2">Thanks to Acee Lindem for the detailed review of the document, corrections, 
       as well as discussion about details of the encoding.<a href="#section-appendix.a-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Contributors">
<section id="section-appendix.b">
      <h2 id="name-contributors">
<a href="#name-contributors" class="section-name selfRef">Contributors</a>
      </h2>
<p id="section-appendix.b-1">The following people gave a substantial contribution to the content
      of this document: Acee Lindem, Ahmed Bashandy, Martin Horneffer, Bruno Decraene,
      Stephane Litkowski, Igor Milojevic, and Saku Ytti.<a href="#section-appendix.b-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="section-appendix.c">
      <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">Peter Psenak (<span class="role">editor</span>)</span></div>
<div dir="auto" class="left"><span class="org">Cisco Systems, Inc.</span></div>
<div dir="auto" class="left"><span class="street-address">Apollo Business Center, Mlynske nivy 43</span></div>
<div dir="auto" class="left">
<span class="postal-code">821 09</span> <span class="locality">Bratislava</span>
</div>
<div dir="auto" class="left"><span class="country-name">Slovakia</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:ppsenak@cisco.com" class="email">ppsenak@cisco.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Stefano Previdi (<span class="role">editor</span>)</span></div>
<div dir="auto" class="left"><span class="org">Cisco Systems, Inc.</span></div>
<div dir="auto" class="left"><span class="street-address">Via Del Serafico, 200</span></div>
<div dir="auto" class="left">
<span class="postal-code">00142</span> <span class="locality">Rome</span> </div>
<div dir="auto" class="left"><span class="country-name">Italy</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:stefano@previdi.net" class="email">stefano@previdi.net</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Clarence Filsfils</span></div>
<div dir="auto" class="left"><span class="org">Cisco Systems, Inc.</span></div>
<div dir="auto" class="left"> <span class="locality">Brussels</span>
</div>
<div dir="auto" class="left"><span class="country-name">Belgium</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:cfilsfil@cisco.com" class="email">cfilsfil@cisco.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Hannes Gredler</span></div>
<div dir="auto" class="left"><span class="org">RtBrick Inc.</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:hannes@rtbrick.com" class="email">hannes@rtbrick.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Rob Shakir</span></div>
<div dir="auto" class="left"><span class="org">Google, Inc.</span></div>
<div dir="auto" class="left"><span class="street-address">1600 Amphitheatre Parkway</span></div>
<div dir="auto" class="left">
<span class="locality">Mountain View</span>, <span class="region">CA</span> <span class="postal-code">94043</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:robjs@google.com" class="email">robjs@google.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Wim Henderickx</span></div>
<div dir="auto" class="left"><span class="org">Nokia</span></div>
<div dir="auto" class="left"><span class="street-address">Copernicuslaan 50</span></div>
<div dir="auto" class="left">
<span class="postal-code">2018</span> <span class="locality">Antwerp</span>
</div>
<div dir="auto" class="left"><span class="country-name">Belgium</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:wim.henderickx@nokia.com" class="email">wim.henderickx@nokia.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Jeff Tantsura</span></div>
<div dir="auto" class="left"><span class="org">Apstra, Inc.</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:jefftant.ietf@gmail.com" class="email">jefftant.ietf@gmail.com</a>
</div>
</address>
</section>
</div>
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