<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-ietf-ospf-segment-routing-extensions-27"
     ipr="trust200902">
  <front>
    <title abbrev="OSPF Extensions for Segment Routing">OSPF Extensions for
    Segment Routing</title>

    <author fullname="Peter Psenak" initials="P." role="editor"
            surname="Psenak">
      <organization>Cisco Systems, Inc.</organization>

      <address>
        <postal>
          <street>Apollo Business Center</street>

          <street>Mlynske nivy 43</street>

          <city>Bratislava</city>

          <code>821 09</code>

          <country>Slovakia</country>
        </postal>

        <email>ppsenak@cisco.com</email>
      </address>
    </author>

    <author fullname="Stefano Previdi" initials="S." role="editor"
            surname="Previdi">
      <organization>Cisco Systems, Inc.</organization>

      <address>
        <postal>
          <street>Via Del Serafico, 200</street>

          <city>Rome</city>

          <code>00142</code>

          <country>Italy</country>
        </postal>

        <email>stefano@previdi.net</email>
      </address>
    </author>

    <author fullname="Clarence Filsfils" initials="C." surname="Filsfils">
      <organization>Cisco Systems, Inc.</organization>

      <address>
        <postal>
          <street/>

          <city>Brussels</city>

          <region/>

          <code/>

          <country>Belgium</country>
        </postal>

        <email>cfilsfil@cisco.com</email>
      </address>
    </author>

    <author fullname="Hannes Gredler" initials="H." surname="Gredler">
      <organization>RtBrick Inc.</organization>   
      <address>
      <postal>
          <street/>

          <city/>

          <region/>

          <code/>

          <country></country>
        </postal>
        
        <email>hannes@rtbrick.com</email>
      </address>
    </author>
    
    <author fullname="Rob Shakir" initials="R." surname="Shakir">
      <organization>Google, Inc.</organization>

      <address>
        <postal>
          <street>1600 Amphitheatre Parkway</street>

          <city>Mountain View</city>

          <code>94043</code>
          
          <region>CA</region>
          
          <country>US</country>
        </postal>

        <email>robjs@google.com</email>
      </address>
    </author>

    <author fullname="Wim Henderickx" initials="W." surname="Henderickx">
      <organization>Nokia</organization>

      <address>
        <postal>
          <street>Copernicuslaan 50</street>

          <city>Antwerp</city>

          <code>2018</code>

          <country>BE</country>
        </postal>

        <email>wim.henderickx@nokia.com</email>
      </address>
    </author>
    
    <author fullname="Jeff Tantsura" initials="J." surname="Tantsura">
      <organization>Apstra, Inc.</organization>

      <address>
        <postal>
          <street/>

          <city/>

          <region/>

          <code/>

          <country></country>
        </postal>

        <email>jefftant.ietf@gmail.com</email>
      </address>
    </author>
    

    <date/>

    <area>Routing</area>

    <workgroup>Open Shortest Path First IGP</workgroup>

    <keyword>MPLS</keyword>

    <keyword>SID</keyword>

    <keyword>IGP</keyword>

    <keyword>OSPF</keyword>

    <keyword>Label advertisement</keyword>

    <keyword>Segment Routing</keyword>

    <abstract>
      <t>Segment Routing (SR) allows a flexible definition of end-to-end
      paths within IGP topologies by encoding paths as sequences of
      topological sub-paths, called "segments". These segments are advertised
      by the link-state routing protocols (IS-IS and OSPF).</t>

      <t>This draft describes the OSPFv2 extensions required for Segment Routing.</t>
    </abstract>

    <note title="Requirements Language">
      <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
      "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
      document are to be interpreted as described in <xref
      target="RFC2119"></xref>.</t>
    </note>
  </front>

  <middle>
    <section title="Introduction">
      <t>Segment Routing (SR) allows a flexible definition of end-to-end
      paths within IGP topologies by encoding paths as sequences of
      topological sub-paths, 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 
      does not require any additional signalling (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 signalling. However, SR can 
      interoperate in the presence of LSPs established with RSVP or LDP.</t>
      
      <t>There are additional segment types, e.g., Binding SID defined in <xref
      target="I-D.ietf-spring-segment-routing"/>.</t>

      <t>This draft describes the OSPF extensions required for Segment Routing.</t>

      <t>Segment Routing architecture is described in <xref
      target="I-D.ietf-spring-segment-routing"/>.</t>

      <t>Segment Routing use cases are described in <xref target="RFC7855"/>.</t>
    </section>

    <section title="Segment Routing Identifiers">
      <t>Segment Routing defines various types of Segment Identifiers (SIDs):
      Prefix-SID, Adjacency-SID, LAN Adjacency SID, and Binding SID.</t>

      <t>Extended Prefix/Link Opaque LSAs defined in <xref target="RFC7684"/> are used for 
      advertisements of the various SID types.</t>

      <section anchor="SIDLABEL" title="SID/Label Sub-TLV">
        <t>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 following
        format:<figure>
            <artwork> 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)                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

where:
</artwork>
          </figure><list style="hanging">
            <t>Type: 1</t>

            <t>Length: Variable, 3 or 4 octet</t>

            <t>SID/Label: If length is set to 3, then the 20 rightmost bits
            represent a label. If length is set to 4, then the value represents
            a 32-bit SID.</t>
            
            <t>The receiving router MUST ignore the SID/Label Sub-TLV if the length 
            is other then 3 or 4.</t>


          </list></t>
      </section>
    </section>

    <section anchor="SRCAP" title="Segment Routing Capabilities">
      <t>Segment Routing requires some additional router capabilities to be advertised 
      to other routers in the area.</t>

      <t>These SR capabilities are advertised in the Router Information Opaque LSA
      (defined in <xref target="RFC7770"/>). The TLVs defined below are applicable to 
       both OSPFv2 and OSPFv3; see also 
       <xref target="I-D.ietf-ospf-ospfv3-segment-routing-extensions"/></t>
      
      <section anchor="SRALGO" title="SR-Algorithm TLV">
        <t>The SR-Algorithm TLV is a top-level TLV of the Router Information Opaque LSA 
        (defined in <xref target="RFC7770"/>).</t>
        
        <t>The SR-Algorithm TLV is optional. It SHOULD only be advertised once
        in the Router Information Opaque LSA. If the SR-Algorithm TLV is not advertised 
        by the node, such node is considered as not being segment routing capable.</t>
        
        <t> 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 
        following format: <figure>
            <artwork>
 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 |               |
+-                                                             -+
|                                                               |
+                                                               +

where:</artwork>
          </figure><list style="hanging">
            <t>Type: 8</t>

            <t>Variable, in octets, dependent on number of algorithms advertised.</t>

            <t> Algorithm: Single octet identifying the algorithm. The following 
            values are defined by this document:<list style="hanging">
                            
                <t>0: 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
                MUST be included.</t>
                
                <t>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 MUST NOT alter the 
                SPF paths computed by Algorithm 1.</t>
 
              </list></t>
          </list></t>
          
        <t>When multiple SR-Algorithm TLVs are received from a given router, the receiver
        MUST use the first occurrence of the TLV in the Router Information LSA. If 
        the SR-Algorithm TLV appears in multiple Router Information LSAs that have 
        different flooding scopes, the SR-Algorithm TLV in the Router Information LSA 
        with the area-scoped flooding scope MUST be used. If the SR-Algorithm TLV appears 
        in multiple Router Information LSAs that have the same flooding scope, the 
        SR-Algorithm TLV in the Router Information (RI) LSA with the numerically smallest 
        Instance ID MUST be used and subsequent instances of the SR-Algorithm TLV 
        MUST be ignored.</t>  

        <t>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 REQUIRED.</t>
      </section>
      
      <section anchor="SIDRANGE" title="SID/Label Range TLV">
      
        <t>Prefix SIDs MAY be advertised in a form of an index as described in 
        <xref target="PREFIXSID"/>. Such 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.</t>
        
        <t>The SID/Label Range TLV is a top-level TLV of the Router Information 
        Opaque LSA (defined in <xref target="RFC7770"/>).</t>

        <t>The SID/Label Range TLV MAY appear multiple times and has the following
        format:<figure>
            <artwork>
 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)                    |
+-                                                             -+
|                                                               |
+                                                               +

where:</artwork>
          </figure><list style="hanging">
            <t>Type: 9</t>

            <t>Length: Variable, in octets, dependent on Sub-TLVs.</t>

            <t>Range Size: 3-octet SID/label range size (i.e., the number of SIDs or labels 
               in the range including the first SID/label). It MUST be greater than 0.</t>
               
            <t>Reserved: SHOULD be set to 0 on transmission and MUST be ignored on reception.</t>   
          </list></t>

        <t>Initially, the only supported Sub-TLV is the SID/Label Sub-TLV as defined 
        in <xref target="SIDLABEL"/>. The SID/Label Sub-TLV MUST 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. </t>
        
        <t>Only a single SID/Label Sub-TLV MAY be advertised in SID/Label Range TLV. If more 
        then one SID/Label Sub-TLVs are present, the SID/Label Range TLV MUST be ignored.</t>
        
        <t>Multiple occurrences of the SID/Label Range TLV MAY be
        advertised, in order to advertise multiple ranges. In such case:<list
            style="symbols">

            <t>The originating router MUST encode each range into a different SID/Label 
            Range TLV. </t>

            <t>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 MUST ensure the order is the same after a graceful restart 
            (using checkpointing, non-volatile storage, or any other mechanism) in order 
            to assure the SID/label range and SID index correspondence is preserved 
            across graceful restarts.</t>
            
            <t> The receiving router MUST adhere to the order in which the ranges are 
            advertised when calculating a SID/label from a SID index.</t>
            
            <t>The originating router MUST NOT advertise overlapping ranges.</t>
            
            <t>When a router receives multiple overlapping ranges, it MUST conform
               to the procedures defined in <xref target="I-D.ietf-spring-segment-routing-mpls"/>.</t>
          </list></t>
          
      
        <t>The following example illustrates the advertisement of multiple ranges:<figure
            suppress-title="true">
            <artwork>
   The originating router advertises the following ranges:
   
      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
      
   The receiving routers concatenate the ranges and build the Segment 
   Routing Global Block (SRGB) as follows:
   
   SRGB = [100, 199]
          [1000, 1099]
          [500, 599]

   The indexes span multiple ranges:

      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
      ...
</artwork>
          </figure></t>

        <t>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 REQUIRED.</t>
      </section>
       
      <section anchor="SRLB" title="SR Local Block TLV">
                
        <t>The SR Local Block TLV (SRLB TLV) contains the range of labels the	
		node has reserved for local SIDs. SIDs from the SRLB MAY 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 
		<xref target="I-D.ietf-spring-segment-routing-mpls"/>.
		The SRLB TLV is used to advertise the SRLB.</t>
		
		<t>The SRLB TLV is a top-level TLV of the Router Information 
        Opaque LSA (defined in <xref target="RFC7770"/>).</t>

        <t>The SRLB TLV MAY appear multiple times in the Router Information
         Opaque LSA and has the following format:<figure>
            <artwork>
 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)                    |
+-                                                             -+
|                                                               |
+                                                               +

where:</artwork>
          </figure>
          <list style="hanging">
            <t>Type: 14</t>

            <t>Length: Variable, in octets, dependent on Sub-TLVs.</t>

            <t>Range Size: 3-octet SID/label range size (i.e., the number of SIDs or labels 
               in the range including the first SID/label). It MUST be greater than 0.</t>
               
            <t>Reserved: SHOULD be set to 0 on transmission and MUST be ignored on reception.</t>   
          </list></t>

        <t>Initially, the only supported Sub-TLV is the SID/Label Sub-TLV as defined 
        in <xref target="SIDLABEL"/>. The SID/Label Sub-TLV MUST 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.</t>
        
        <t>Only a single SID/Label Sub-TLV MAY be advertised in the SRLB TLV. If more 
        then one SID/Label Sub-TLVs are present, the SRLB TLV MUST be ignored.</t>
        
        <t>The originating router MUST NOT advertise overlapping ranges.</t>
        
        <t>Each time a SID from the SRLB is allocated, it SHOULD 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.</t>
		 		
		<t>Within the context of OSPF, the reporting of local SIDs is done through 
		OSPF Sub-TLVs such as the Adjacency-SID (<xref target="ADJSID"/>). However, 
		the reporting of allocated local SIDs can also be done through other means 
		and protocols which are outside the scope of this document.</t>
		
		<t>A router advertising the SRLB TLV MAY also have other label ranges, outside 
		of the SRLB, used for its local allocation purposes which are 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.</t>	
		 
        <t>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 REQUIRED.</t>
     </section>
     
      <section anchor="SRMS-Pref" title="SRMS Preference TLV">
     
      <t>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 <xref target="I-D.ietf-spring-segment-routing-ldp-interop"/>. 
      SRMS preference is defined in 
      <xref target="I-D.ietf-spring-segment-routing-ldp-interop"/>.</t>
      
      <t>The SRMS Preference TLV is a top-level TLV of the 
      Router Information Opaque LSA (defined in <xref target="RFC7770"/>).</t>

        <t>The SRMS Preference TLV MAY only be advertised
         once in the Router Information Opaque LSA and has the following format:<figure>
            <artwork>
 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                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

where:</artwork>
          </figure>
          <list style="hanging">
            <t>Type: 15</t>

            <t>Length: 4 octets</t>

            <t>Preference: 1 octet. SRMS preference value from 0 to 255.</t>
            
            <t>Reserved: SHOULD be set to 0 on transmission and MUST be ignored on reception.</t>
          </list></t>
          
    <t>When multiple SRMS Preference TLVs are received from a given router, the receiver
    MUST use the first occurrence of the TLV in the Router Information LSA. If the
    SRMS Preference TLV appears in multiple Router Information LSAs that have different 
    flooding scopes, the SRMS Preference TLV in the Router Information LSA with the 
    narrowest flooding scope MUST be used. If the SRMS Preference TLV appears in 
    multiple Router Information LSAs that have the same flooding scope, the SRMS 
    Preference TLV in the Router Information LSA with the numerically smallest Instance ID
    MUST be used and subsequent instances of the SRMS Preference TLV MUST be ignored.</t>
	
	<t>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 SHOULD be used. This is because SRMS 
	servers can be located in a different area then 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 MAY be used.</t>
      
     </section>
      
     </section>
     
    <section anchor="PFXRANGE" title="OSPF Extended Prefix Range TLV">
      <t>In some cases it is useful to advertise attributes for a range of prefixes. 
	  The Segment Routing Mapping Server, which is described in 
	  <xref target="I-D.ietf-spring-segment-routing-ldp-interop"/>, is an example 
	  where we need a single advertisement to advertise SIDs for multiple prefixes from a 
	  contiguous address range.</t>
      
      <t>The OSPF Extended Prefix Range TLV, which is a top level TLV of the Extended 
      Prefix LSA described in <xref target="RFC7684"/> is defined for this purpose.</t>
        
      <t>Multiple OSPF Extended Prefix Range TLVs MAY be advertised in each OSPF 
      Extended Prefix Opaque LSA, but all prefix ranges included in a single OSPF Extended
      Prefix Opaque LSA MUST have the same flooding scope. The OSPF Extended Prefix Range
      TLV has the following format: <figure>
            <artwork>
 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)                      |
+-                                                             -+
|                                                               |

where: </artwork>
          </figure><list style="hanging">
            <t>Type: 2</t>

            <t>Length: Variable, in octets, dependent on Sub-TLVs.</t>

            <t>Prefix length: Length of prefix in bits.</t>

            <t>AF: 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.</t>
            
            <t>Range size: Represents the number of prefixes that are covered by the
            advertisement. The Range Size MUST NOT 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).</t>
			
			<t>Flags: Single octet field. The following flags are defined: <figure
                align="center">
                <artwork>
                      
  0  1  2  3  4  5  6  7 
+--+--+--+--+--+--+--+--+
|IA|  |  |  |  |  |  |  |
+--+--+--+--+--+--+--+--+

where:</artwork>
              </figure><list style="hanging">
                <t>IA-Flag: Inter-Area flag. If set, advertisement is of inter-area type. 
                An ABR that is advertising the OSPF Extended Prefix Range TLV between areas 
                MUST set this bit. </t>
                
                <t>This bit is used to prevent redundant flooding of Prefix Range TLVs 
                between areas as follows:
                 <list style="hanging">
                
                <t> An ABR only propagates an inter-area Prefix Range advertisement from 
                the backbone area to connected non-backbone 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:
                <list style="hanging">
                
                    <t> An ABR always prefers intra-area Prefix Range advertisements over 
                    inter-area advertisements.</t> 
                
                    <t> An ABR does not consider inter-area Prefix Range advertisements coming 
                    from non-backbone areas.</t> 
                
                    </list></t>
                </list></t>   
              </list></t>
              
            <t>Reserved: SHOULD be set to 0 on transmission and MUST be ignored on reception.</t>  

            <t>Address Prefix: 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.</t>
          </list></t>
    </section>

    <section anchor="PREFIXSID" title="Prefix SID Sub-TLV">
      <t>The Prefix SID Sub-TLV is a Sub-TLV of the OSPF Extended Prefix TLV described 
      in <xref target="RFC7684"/> and the OSPF Extended Prefix Range
      TLV described in <xref target="PFXRANGE"/>. It MAY appear more than once in the 
      parent TLV and has the following format: <figure>
          <artwork>
 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)                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

where:</artwork>
          </figure><list style="hanging">
            <t>Type: 2</t>

            <t>Length: 7 or 8 octets, dependent on the V-flag</t>

            <t>Flags: Single octet field. The following flags are defined: <figure
                align="center">
                <artwork>
                      
  0  1  2  3  4  5  6  7 
+--+--+--+--+--+--+--+--+
|  |NP|M |E |V |L |  |  |
+--+--+--+--+--+--+--+--+

where:</artwork>
              </figure><list style="hanging">

                <t>NP-Flag: No-PHP flag. If set, then the penultimate hop MUST
                NOT pop the Prefix-SID before delivering packets to the
                node that advertised the Prefix-SID.</t>
                
                <t>M-Flag: Mapping Server Flag.  If set, the SID was advertised
                by a Segment Routing Mapping Server as described in 
                <xref target="I-D.ietf-spring-segment-routing-ldp-interop"/>.</t>
                
                <t>E-Flag: Explicit-Null Flag. If set, any upstream neighbor 
                of the Prefix-SID originator MUST replace the Prefix-SID with 
                the Explicit-NULL label (0 for IPv4) before forwarding the packet.</t>
                
                <t>V-Flag: Value/Index Flag. If set, then the Prefix-SID 
                carries an absolute value. If not set, then the Prefix-SID carries 
                an index.</t>
                
                <t>L-Flag: 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.</t> 
                
                <t>Other bits: Reserved. These MUST be zero when sent and are ignored when
                received.</t>
              </list></t>
              
            <t>Reserved: SHOULD be set to 0 on transmission and MUST be ignored on reception.</t>  

            <t>MT-ID: Multi-Topology ID (as defined in <xref
            target="RFC4915"/>).</t>

            <t>Algorithm: Single octet identifying the algorithm the Prefix-SID
            is associated with as defined in <xref target="SRALGO"/>.</t>
            
            <t>A router receiving a Prefix-SID from a remote node and with an  algorithm 
            value that such remote node has not advertised in the SR-Algorithm Sub-TLV
            (<xref target="SRALGO"/>) MUST ignore the Prefix-SID Sub-TLV.</t>
        
            <t>SID/Index/Label: According to the V and L flags, it contains:
            <list style="hanging">
            
            <t>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</t>
             
            <t>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.</t>
            
            <t>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 MUST	
		 	   be ignored.</t>
            </list></t>
            
          </list></t>

        <t>If an OSPF router advertises multiple Prefix-SIDs for the same prefix,
        topology and algorithm, all of them MUST be ignored.</t>
        	     
        <t>When calculating the outgoing label for the prefix, the router MUST
        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 MUST be done
        regardless of whether the next-hop router contributes to the best path to the
        prefix.</t>

        <t>The NP-Flag (No-PHP) MUST be set and the E-flag MUST 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.</t>
        
        <t>The NP-Flag (No-PHP) MUST be set and the E-flag MUST be clear for Prefix-SIDs 
        allocated to redistributed prefixes, unless the redistributed prefix is directly
        attached to the ASBR.</t>
              
        <t>If the NP-Flag is not set, then any upstream neighbor of the Prefix-SID
        originator MUST pop the Prefix-SID. This is equivalent to the penultimate
        hop popping mechanism used in the MPLS dataplane. If the NP-flag is not set, 
        then the received E-flag is ignored.</t>
        
        <t>If the NP-flag is set then:<list style="hanging">
        
        <t> If the E-flag is not set, then any upstream neighbor of the Prefix-SID 
        originator MUST keep the Prefix-SID on top of the stack.  This is useful when
        the originator of the Prefix-SID need to stitch the incoming packet into a continuing
        MPLS LSP to the final destination. This could occur at an Area Border Router
        (prefix propagation from one area to another) or at an AS Boundary Router 
        (prefix propagation from one domain to another).</t>
         
         <t>If the E-flag is set, then any upstream neighbor of the Prefix-SID originator 
         MUST 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.</t>
         </list></t>
                  
        <t>When the M-Flag is set, the NP-flag and the E-flag MUST be ignored at reception.</t>
        
        <t>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 SHOULD be done in following cases:
        <list style="hanging">
        	<t>The Prefix is intra-area type and the downstream neighbor is the originator 
        	of the prefix.</t>
        	
        	<t>The Prefix is inter-area type and 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 section 2.1 of 
        	<xref target="RFC7684"/>.</t>
        	
        	<t> The Prefix is external type and 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 section 2.1 of 
        	<xref target="RFC7684"/>.</t>
        </list></t>
        

		<t>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.</t>
		
        <t>Example 1: If the following router addresses (loopback addresses)
        need to be mapped into the corresponding Prefix SID indexes: <figure
            suppress-title="true">
            <artwork>
          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
           </artwork>
          </figure></t>

        <t>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.</t>

        <t>Example 2: If the following prefixes need to be mapped into the
        corresponding Prefix-SID indexes: <figure suppress-title="true">
            <artwork>
          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
           </artwork>
          </figure></t>

        <t>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.</t>
      </section>

    <section anchor="ADJSID" title="Adjacency Segment Identifier (Adj-SID)">
      <t>An Adjacency Segment Identifier (Adj-SID) represents a router
      adjacency in Segment Routing.</t>

    
      <section anchor="ADJSIDSUBTLV" title="Adj-SID Sub-TLV">
        <t>Adj-SID is an optional Sub-TLV of the Extended Link TLV defined in 
        <xref target="RFC7684"/>. It MAY appear multiple times
        in the Extended Link TLV. 
        
        The Adj-SID Sub-TLV has the following format: <figure>
            <artwork> 
 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)                  |
+---------------------------------------------------------------+

where:</artwork>
          </figure><list style="hanging">
            <t>Type: 2</t>

            <t>Length: 7 or 8 octets, dependent on the V flag.</t>

            <t>Flags: Single octet field containing the following flags:<figure align="center">
                <artwork>    
 0 1 2 3 4 5 6 7 
+-+-+-+-+-+-+-+-+
|B|V|L|G|P|     |
+-+-+-+-+-+-+-+-+

where:</artwork>
              </figure><list style="hanging">
                <t>B-Flag: Backup Flag. If set, the Adj-SID refers to an
                adjacency that is eligible for protection (e.g., using IPFRR or MPLS-FRR)
                as described in section 3.5 of <xref
                target="I-D.ietf-spring-segment-routing"/>.</t>
                
                <t>The V-Flag: Value/Index Flag. If set, then the Adj-SID 
                carries an absolute value. If not set, then the Adj-SID carries 
                an index.</t>
                
                <t>The L-Flag: 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.</t> 
         
                <t>The G-Flag: Group Flag. When set, the G-Flag indicates that the 
                Adj-SID refers to a group of adjacencies (and therefore MAY be assigned
                to other adjacencies as well).</t>
                
                <t>P-Flag. 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.</t>

                <t>Other bits: Reserved. These MUST be zero when sent and are ignored when
                received.</t>
              </list></t>
              
            <t>Reserved: SHOULD be set to 0 on transmission and MUST be ignored on reception.</t>  

            <t>MT-ID: Multi-Topology ID (as defined in <xref
            target="RFC4915"/>.</t>

            <t>Weight: Weight used for load-balancing purposes. The use of the
            weight is defined in <xref
            target="I-D.ietf-spring-segment-routing"/>.</t>

            <t>SID/Index/Label: as described in <xref target="PREFIXSID"/>.</t>
            
          </list></t>

        <t>An SR capable router MAY 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 section 3.5 of <xref
            target="I-D.ietf-spring-segment-routing"/>.</t>
            
        <t>An SR capable router MAY allocate more than one Adj-SID to an adjacency</t>
        
        <t>An SR capable router MAY allocate the same Adj-SID to different adjacencies</t>
        
        <t>When the P-flag is not set, the Adj-SID MAY be persistent. When	
	    the P-flag is set, the Adj-SID MUST be persistent.</t> 
	       
      </section>

      <section anchor="LANADJSIDSUBTLV" title="LAN Adj-SID Sub-TLV">
        <t>LAN Adj-SID is an optional Sub-TLV of the Extended Link TLV defined in 
        <xref target="RFC7684"/>. It MAY appear multiple
        times in the Extended-Link TLV. It is used to advertise a SID/Label for an adjacency 
        to a non-DR router on a broadcast, NBMA, or hybrid <xref target="RFC6845"/> network.
        <figure>
            <artwork>
 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)                 |
+---------------------------------------------------------------+

where:</artwork>
          </figure><list style="hanging">
            <t>Type: 3</t>

            <t>Length: 11 or 12 octets, dependent on V-flag.</t>

            <t>Flags: same as in <xref target="ADJSIDSUBTLV"/></t>
            
            <t>Reserved: SHOULD be set to 0 on transmission and MUST be ignored on reception.</t>

            <t>MT-ID: Multi-Topology ID (as defined in <xref
            target="RFC4915"/>.</t>

            <t>Weight: Weight used for load-balancing purposes. The use of the
            weight is defined in <xref target="I-D.ietf-spring-segment-routing"/>.</t>
            
            <t>Neighbor ID: The Router ID of the neighbor for which the LAN-Adj-SID is 
            advertised.</t>

            <t>SID/Index/Label: as described in <xref target="PREFIXSID"/>.</t>
            
            <t>When the P-flag is not set, the Adj-SID MAY be persistent. When	
	        the P-flag is set, the Adj-SID MUST be persistent.</t> 
            
          </list></t>
      </section>
    </section>

    <section title="Elements of Procedure">
      <section title="Intra-area Segment routing in OSPFv2 ">
        <t>An OSPFv2 router that supports segment routing MAY advertise Prefix-
        SIDs for any prefix to which it is advertising reachability (e.g.,
        a loopback IP address as described in <xref target="PREFIXSID"/>).</t>

        <t>A Prefix-SID can also be advertised by the SR Mapping Servers (as
        described in <xref
        target="I-D.ietf-spring-segment-routing-ldp-interop"/>). 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 MUST 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.</t>
        
        <t>An SR Mapping Server MUST 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.</t>
        
        <t>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 
        <xref target="PFXRANGE"/>.</t> 
        
        <t>When propagating an OSPF Extended Prefix Range TLV between areas, ABRs MUST set the
        IA-Flag, that is used to prevent redundant flooding of the OSPF Extended 
        Prefix Range TLV between areas as described in <xref target="PFXRANGE"/>.</t>
        
      </section>

      <section title="Inter-area Segment routing in OSPFv2">
        <t>In order to support SR in a multi-area environment, OSPFv2 MUST
        propagate Prefix-SID information between areas. The following
        procedure is used to propagate Prefix SIDs between areas.</t>

        <t>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 Extended
        Prefix Opaque LSA, as described in <xref target="RFC7684"/>. 
        The flooding scope of the 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: <list style="hanging">
            <t>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.</t>
            
            <t>The ABR will then determine if such router advertised a Prefix-SID	
			for the prefix and use it when advertising the Prefix-SID to other	
			connected areas.</t>

            <t>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.</t>
          </list></t>

        <t>When an OSPF ABR advertises Type-3 Summary LSAs from an inter-area
        route to all its connected areas, it will also originate an Extended
        Prefix Opaque LSA, as described in <xref target="RFC7684"/>. 
        The flooding scope of the Extended Prefix Opaque LSA type will be set to
        area-local scope. The route-type in 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: <list style="hanging">
            <t>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.</t>

            <t>The ABR will then determine if such router advertised a Prefix-SID
            for the prefix and use it when advertising the Prefix-SID to other
            connected areas.</t>

            <t>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.</t>
          </list></t>
      </section>

      <section title="Segment Routing for External Prefixes">
        <t>Type-5 LSAs are flooded domain wide. When an ASBR, which supports
        SR, generates Type-5 LSAs, it SHOULD also originate Extended Prefix
        Opaque LSAs, as described in <xref target="RFC7684"/>. 
        The flooding scope of the 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.</t>

        <t>When an NSSA <xref target="RFC3101"/> ABR translates Type-7 LSAs into Type-5 
        LSAs, it SHOULD 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.</t>
      </section>

      <section title="Advertisement of Adj-SID">
        <t>The Adjacency Segment Routing Identifier (Adj-SID) is advertised
        using the Adj-SID Sub-TLV as described in <xref target="ADJSID"/>.</t>

        <section title="Advertisement of Adj-SID on Point-to-Point Links">
          <t>An Adj-SID MAY be advertised for any adjacency on a 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
          MAY be removed from the area. If the adjacency transitions to a
          state lower then 2-Way, then the Adj-SID advertisement MUST be withdrawn from the
          area.</t>
        </section>

        <section title="Adjacency SID on Broadcast or NBMA Interfaces">
          <t>Broadcast, NBMA, or hybrid <xref target="RFC6845"/> 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.</t>

          <t>When Segment Routing is used, each router on the broadcast, NBMA, or hybrid
           network MAY advertise the Adj-SID for its adjacency to the DR using
          the Adj-SID Sub-TLV as described in <xref target="ADJSIDSUBTLV"/>.</t>

          <t>SR capable routers MAY also advertise a LAN-Adj-SID for other neighbors
          (e.g., BDR, DR-OTHER) on the broadcast, NBMA, or hybrid network using the 
          LAN-ADJ-SID Sub-TLV as described in <xref target="LANADJSIDSUBTLV"/>.</t>
        </section>
      </section>
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <t>This specification updates several existing OSPF registries.</t>

	  <section anchor="RITLVREG" title="OSPF Router Information (RI) TLVs Registry">
      
        <t>o 8 (IANA Preallocated) - SR-Algorithm TLV</t>

        <t>o 9 (IANA Preallocated) - SID/Label Range TLV</t>
                   
        <t>o 14 - SR Local Block TLV</t>
        
        <t>o 15 - SRMS Preference TLV</t>
        
        
	  </section>
      
      <section anchor="EPLTLVREG" title="OSPFv2 Extended Prefix Opaque LSA TLVs Registry">
  
	  <t>Following values are allocated:</t>
        
        <t>o 2 - OSPF Extended Prefix Range TLV</t>
      
      </section>
      
      <section anchor="EPLSTLVREG" title="OSPFv2 Extended Prefix TLV Sub-TLVs Registry">

      <t>Following values are allocated:</t>

        <t>o 1 - SID/Label Sub-TLV</t>

        <t>o 2 - Prefix SID Sub-TLV</t>

      </section>

      <section anchor="ELLSTLVREG" title="OSPFv2 Extended Link TLV Sub-TLVs Registry">

      <t>Following initial values are allocated:</t>

        <t>o 1 - SID/Label Sub-TLV</t>

        <t>o 2 - Adj-SID Sub-TLV</t>

        <t>o 3 - LAN Adj-SID/Label Sub-TLV</t>
      </section>
      
      <section anchor="IGPALGOREG" title="IGP Algorithm Type Registry">  
  
    <t>IANA is requested to set up a registry called "IGP Algorithm Type" under a new 
       category of "Interior Gateway Protocol (IGP) Parameters" IANA registries.
       The registration policy for this registry is "Standards Action" 
       (<xref target="RFC8126"/> and <xref target="RFC7120"/>).</t>

   <t>Values in this registry come from the range 0-255.</t>

   <t> The initial values in the IGP Algorithm Type registry are:<list style='hanging'>
   
                <t>0: 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.</t>
                
                <t>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 MUST NOT alter the 
                SPF paths computed by Algorithm 1.</t>
                   
    </list></t>
   </section>  
    </section>
    
    <section anchor="Implementation" title="Implementation Status">
    
    <t>An implementation survey with seven questions related to the
   implementer's support of OSPFv2 Segment Routing was sent to
   the OSPF WG list and several known implementers. This section
   contains responses from three implementers who completed the survey.
   No external means were used to verify the accuracy of the information
   submitted by the respondents.  The respondents are considered experts
   on the products they reported on.  Additionally, responses were
   omitted from implementers who indicated that they have not
   implemented the function yet.</t>
   
   <t>This section will be removed before publication as an RFC.</t>
   
   <t>Responses from Nokia (former Alcatel-Lucent):</t>
   	
   		<t>Link to a web page describing the implementation:
   		https://infoproducts.alcatel-lucent.com/cgi-bin/dbaccessfilename.cgi/3HE10799AAAATQZZA01_V1_7450%20ESS%207750%20SR%20and%207950%20XRS%20Unicast%20Routing%20Protocols%20Guide%20R14.0.R1.pdf</t>
   		
   		<t>The implementation's level of maturity: Production.</t> 
		
		<t>Coverage: We have implemented all sections and have support for the latest draft.</t>
				 
		<t>Licensing: Part of the software package that needs to be purchased.</t>
		
		<t>Implementation experience: Great spec. We also performed inter-operability 
		testing with Cisco's OSPF Segment Routing implementation. </t>
		    
		<t>Contact information: wim.henderickx@nokia.com </t>
				
	<t> Responses from Cisco Systems: </t>
   	
   		<t> Link to a web page describing the implementation:</t>
   		<t> http://www.segment-routing.net/home/tutorial</t> 		
   		
   		
   		<t> The implementation's level of maturity: Production.</t> 
		
		<t> Coverage: All sections have been implemented according to the latest draft.</t> 
		 
		<t> Licensing: Part of a commercial software package.</t>
		
		<t> Implementation experience: Many aspects of the draft are result of the  
		actual implementation experience, as the draft evolved from its initial version 
		to the current one. Interoperability testing with Alcatel-Lucent 
		was performed, which confirmed the draft's ability to serve as a reference for the 
		implementors.</t>
		    
		<t> Contact information: ppsenak@cisco.com </t>	  
		
	<t> Responses from Juniper: </t>
   	
   		<t> The implementation's name and/or a link to a web page describing
        the implementation:</t>
   		<t> Feature name is OSPF SPRING</t> 		
   		
   		<t> The implementation's level of maturity: 
   		To be released in 16.2 (second half of 2016)</t> 
		
		<t> Coverage: All sections implemented except Sections 4, and 6.</t> 
		 
		<t> Licensing: JUNOS Licensing needed.</t>
		
		<t> Implementation experience: NA</t>
		    
		<t> Contact information: shraddha@juniper.net </t>	    
		
 </section>

    <section anchor="Security" title="Security Considerations">
      
      <t>With the OSPFv2 segment routing extensions defined herein,
      OSPFv2 will now program the MPLS data plane [RFC3031] in addition to the IP
      data plane. Previously, LDP [RFC5036] or another label distribution
      mechanism was required to advertise MPLS labels and program the MPLS data plane.</t> 
      
      <t>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.</t>
      
      <t>Existing security extensions as described in <xref target="RFC2328"></xref> and
       <xref target="RFC7684"></xref> 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 <xref target="RFC7474"></xref> SHOULD be used.</t>
       
       <t>Implementations MUST assure that malformed TLV and Sub-TLV 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 TLV or Sub-TLV SHOULD be counted 
       and/or logged for further analysis. Logging of malformed TLVs and Sub-TLVs SHOULD
       be rate-limited to prevent a Denial of Service (DoS) attack (distributed or otherwise) 
       from overloading the OSPF control plane.</t>
           
    </section>

    <section anchor="Contributors" title="Contributors">
      <t>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, Rob Shakir and Saku Ytti.</t>
    </section>

    <section anchor="Acknowledgements" title="Acknowledgements">
      <t>We would like to thank Anton Smirnov for his contribution.</t>
   
      <t>Thanks to Acee Lindem for the detail review of the draft, corrections, 
       as well as discussion about details of the encoding.</t>
    </section>
  </middle>

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

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7770.xml"?>

      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4915.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7684.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6845.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7120.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3101.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2328.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-spring-segment-routing.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-spring-segment-routing-ldp-interop.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-spring-segment-routing-mpls.xml"?>

      <?rfc ?>
    </references>

    <references title="Informative References">
              
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7855.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7474.xml"?>
      
      <?rfc include="http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-ospf-ospfv3-segment-routing-extensions.xml"?>
      
      </references>
  </back>
</rfc>
