Advertising Per-Algorithm Label Blocks
draft-bowers-spring-adv-per-algorithm-label-blocks-01

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SPRING Working Group                                           C. Bowers
Internet-Draft                                                 P. Sarkar
Intended status: Standards Track                              H. Gredler
Expires: December 26, 2015                              Juniper Networks
                                                           June 24, 2015

                 Advertising Per-Algorithm Label Blocks
         draft-bowers-spring-adv-per-algorithm-label-blocks-01

Abstract

   Segment routing uses globally-known labels to accomplish destination-
   based forwarding along shortest paths computed using Dijkstra's
   algorithm with IGP metrics.  This draft discusses how to use segment
   routing to accomplish destination-based forwarding along paths
   computed using other algorithms and metrics.  In particular, the
   draft contrasts two different options for associating labels with
   different algorithms for computing forwarding next-hops.

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   This Internet-Draft will expire on December 26, 2015.

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   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Destination-based forwarding in segment routing using other
       algorithms  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Practical implications of using the per-algorithm node index
       option  . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Advantages of using the per-algorithm label block option  . .   5
   5.  ISIS extensions to encode per-algorithm label blocks  . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Management Considerations . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   10. Informative References  . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   [I-D.ietf-spring-segment-routing] describes the segment routing
   architecture.  In segment routing, LDP-like forwarding behavior along
   shortest paths is achieved using globally-known node labels.
   Globally-known node labels can be distributed in one of two ways.
   Each router can directly advertise a globally unique node label in
   the IGP.  Or each router can advertise a globally unique node index
   value as well as a locally assigned label block, allowing any router
   in the IGP area to determine the mapping of locally-assigned label to
   globally unique node index for any other router in the area.

   This draft focuses on the case where the combination of global node
   index and local label block is used to distribute locally-significant
   labels.  Figure 1 shows the formula used to determine the locally-
   significant label values corresponding to shortest path forwarding
   next-hops computed using Dijkstra's shortest path first algorithm
   with IGP metrics, which is the default mode of operation for segment
   routing.

         SPF_Label(X,D) = Label_Block(X) + Node_Index(D)

         X is the node for which the label has local significance
         D is the destination node

    Figure 1: Formula for determining locally-significant shortest path
                                  labels

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