One document matched: draft-tantsura-isis-segment-routing-msd-01.xml

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<rfc category="std" docName="draft-tantsura-isis-segment-routing-msd-01"
	ipr="trust200902">  

  <front>
    <title abbrev="">Signaling  MSD (Maximum SID Depth) using IS-IS</title>

    <author fullname="Jeff Tantsura" initials="J.T." surname="Tantsura">
      <organization>Individual</organization>
      <address>
	<email>jefftant.ietf@gmail.com</email>
      </address>
    </author>

    <author fullname="Uma Chunduri" initials="U.C." surname="Chunduri">
      <organization>Ericsson</organization>
      <address>
      <email>uma.chunduri@ericsson.com</email>
      </address>
    </author>

    <date day="8" month="July" year="2016" />

    <area>Routing</area>

    <workgroup>IS-IS Working Group</workgroup>

    <keyword>Internet-Draft</keyword>

    <keyword>BGP-LS</keyword>
    
    <keyword>SID</keyword>
   
    <keyword>MSD </keyword>

    <keyword>IS-IS</keyword>

    <abstract>
	    <t>This document proposes a way to expose Maximum SID Depth (MSD) supported by a node at node and/or link level
	    by an ISIS Router. In a Segment Routing (SR) enabled network a centralized controller that programs SR tunnels
	    at the head-end node needs to know the MSD information at
	    node level and/or link level to push the label stack of an
	    appropriate depth. </t>
    </abstract>
  </front>

  

<middle>
	  <section title="Introduction">
			 
 		  <t>When Segment Routing tunnels are computed by a centralized
                  controller, it is crucial that the controller knows
		  the MSD "Maximum SID Depth" of the node or link SR tunnel exits over, so it doesn't
                  download a path with SID (label stack) of a depth more than the node
                  or link used is capable of imposing. This document describes how
                  to use IS-IS to expose the MSD of the node or link to a
		  centralized controller.</t>

	           <t>PCEP SR extensions <xref target="I-D.ietf-pce-segment-routing"/> has defined MSD, 
		      to signal  in SR PCE Capability TLV, METRIC Object. However, If PCEP is not supported 
		      by a node (head-end of the SR tunnel) and controller does not participate in IGP routing 
		      it has no way to learn the MSD of the node or link configured. BGP-LS <xref target="RFC7752"/> defines a  
		      way to expose topology and associated different attributes, capabilities of the nodes in that topology to a centralized
		      controller and MSD has been defined in <xref target="I-D.tantsura-bgp-ls-segment-routing-msd"/>. For this information 
		      to be advertised by BGP for the all nodes and links of the network, where this is provisioned, IS-IS module should have this information in the LSDB.</t>

		  
	     <t><xref target="I-D.ietf-isis-mpls-elc"/> defines, RLSDC  which indicates how many labels a node can read to take a decision to insert an Entropy Label (EL) 
		     and is different than how many labels a node can push as defined by MSD in this draft.</t>

	     	     <section title="Conventions used in this document">
   <section title="Terminology">

    <t>BGP-LS: Distribution of Link-State and TE
	    Information using Border Gateway Protocol </t>

    <t>ISIS: Intermediate System to Intermediate System</t>
	    
    <t>MSD: Maximum SID Depth </t>

   <t> PCC:  Path Computation Client </t>

   <t> PCE:  Path Computation Element </t>

   <t> PCEP:  Path Computation Element Protocol </t>

   <t> SID:  Segment Identifier </t>

   <t> SR:  Segment routing </t>
   
         </section>    
</section>  

      <section 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">RFC 2119</xref>.</t>
      </section>
    </section>

    <section anchor="Abbreviations_Terminology" title="Terminology">
      <t>This memo makes use of the terms defined in <xref
      target="RFC4971"/>.</t>
    </section>

    <section anchor="NODE_LEVEL" title="Node MSD Advertisement ">
      <t>A new sub-TLV within the body of IS-IS Router Capability TLV  <xref target="RFC4971"/>, called
      Node MSD sub-TLV is defined to carry the provisioned SID depth 
      of the router originating the Router Capability TLV. Node MSD is the lowest MSD supported 
      by the node and can be provisioned in IS-IS instance.
      </t>
      <t>The Type (1 byte)  of this sub-TLV is TBD.</t>
      <t>    Length is 1 bytes, and </t>
      <t>    the Value field contains MSD of the router originating the Router Capability TLV. Node MSD 
	      is a number in the range of 0-254. 0 represents lack of the ability to push MSD 
	      of any depth; any other value represents that of the node. This value SHOULD 
	      represent the lowest value supported by node.</t>
      <t>This TLV is optional. The scope of the advertisement is specific to the deployment.
      </t>
    </section>

    <section anchor="LINK_LEVEL" title="LINK MSD Advertisement ">
      <t>A new sub-TLV  called Link MSD sub-TLV is defined to carry the provisioned SID depth 
      of the interface associated with the link. </t>
      <t>The Type (1 byte) of this TLV is TBD.</t>
      <t>    Length is 1 byte, and </t>
      <t>    the Value field contains Link MSD of the router originating the corresponding IS extended reachability 
	      TLV  <xref target="RFC5305"/> or MT IS TLV <xref target="RFC5120"/>. 
	      Link MSD is a number in the range of 0-254. 0 represents lack of the ability to push MSD 
	      of any depth; any other value represents that of the particular link MSD value. </t>

    </section>
    <section anchor="Acknowledgements" title="Acknowledgements">
	    <t>TBD </t>

      <!---->
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <t>This document includes a request to IANA to allocate sub-TLV type
	      codes for the new TLV proposed in  <xref target="NODE_LEVEL"> </xref> 
	       of this document from IS-IS Router Capability TLV Registry as defined by <xref target="RFC4971"/>.
	       Also for link MSD,  we request IANA to allocate new sub-TLV codes  as defined  in <xref target="LINK_LEVEL"> </xref> from 
	       IS extended reachability TLV (22) and MT IS TLV (222) registry.
      </t>

      <!---->
    </section>

    <section anchor="Security" title="Security Considerations">
     <t>This document describes a mechanism for advertising Segment Routing SID depth supported at node and link level 
	     information through IS-IS LSPs and does not introduce 
	     any new security issues.
     </t>

      <!---->
    </section>
  </middle>

  <back>
    <references title="Normative References">
      &RFC2119;

      <?rfc include="reference.RFC.4971"?>
      <?rfc include="reference.RFC.5305"?>

      <!---->
    </references>

    <references title="Informative References">
      <?rfc include="reference.I-D.ietf-pce-segment-routing"?>
      <?rfc include="reference.I-D.tantsura-bgp-ls-segment-routing-msd"?>
      <?rfc include="reference.I-D.ietf-isis-mpls-elc"?>
      <?rfc include="reference.RFC.7752"?>
      <?rfc include="reference.RFC.1195"?>
      <?rfc include="reference.RFC.5120"?>
      <!---->
    </references>
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