An Algorithm for Computing IP/LDP Fast Reroute Using Maximally Redundant Trees (MRT-FRR)
RFC 7811

Document Type RFC - Proposed Standard (June 2016; No errata)
Last updated 2016-06-16
Replaces draft-enyedi-rtgwg-mrt-frr-algorithm
Stream IETF
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Stream WG state Submitted to IESG for Publication Jul 2015
Document shepherd Janos Farkas
Shepherd write-up Show (last changed 2015-12-10)
IESG IESG state RFC 7811 (Proposed Standard)
Consensus Boilerplate Yes
Telechat date
Responsible AD Alvaro Retana
Send notices to "Janos Farkas" <janos.farkas@ericsson.com>,aretana@cisco.com
IANA IANA review state Version Changed - Review Needed
IANA action state In Progress
Internet Engineering Task Force (IETF)                         G. Enyedi
Request for Comments: 7811                                    A. Csaszar
Category: Standards Track                                       Ericsson
ISSN: 2070-1721                                                 A. Atlas
                                                               C. Bowers
                                                        Juniper Networks
                                                              A. Gopalan
                                                   University of Arizona
                                                               June 2016

             An Algorithm for Computing IP/LDP Fast Reroute
               Using Maximally Redundant Trees (MRT-FRR)

Abstract

   This document supports the solution put forth in "An Architecture for
   IP/LDP Fast Reroute Using Maximally Redundant Trees (MRT-FRR)"
   (RFC 7812) by defining the associated MRT Lowpoint algorithm that is
   used in the Default MRT Profile to compute both the necessary
   Maximally Redundant Trees with their associated next hops and the
   alternates to select for MRT-FRR.

Status of This Memo

   This is an Internet Standards Track document.

   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.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7811.

Enyedi, et al.               Standards Track                    [Page 1]
RFC 7811                    MRT-FRR Algorithm                  June 2016

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   5
   3.  Terminology and Definitions . . . . . . . . . . . . . . . . .   5
   4.  Algorithm Key Concepts  . . . . . . . . . . . . . . . . . . .   6
     4.1.  Partial Ordering for Disjoint Paths . . . . . . . . . . .   7
     4.2.  Finding an Ear and the Correct Direction  . . . . . . . .   8
     4.3.  Lowpoint Values and Their Uses  . . . . . . . . . . . . .  11
     4.4.  Blocks in a Graph . . . . . . . . . . . . . . . . . . . .  14
     4.5.  Determining Localroot and Assigning Block-ID  . . . . . .  16
   5.  MRT Lowpoint Algorithm Specification  . . . . . . . . . . . .  18
     5.1.  Interface Ordering  . . . . . . . . . . . . . . . . . . .  18
     5.2.  MRT Island Identification . . . . . . . . . . . . . . . .  21
     5.3.  GADAG Root Selection  . . . . . . . . . . . . . . . . . .  21
     5.4.  Initialization  . . . . . . . . . . . . . . . . . . . . .  22
     5.5.  Constructing the GADAG Using Lowpoint Inheritance . . . .  23
     5.6.  Augmenting the GADAG by Directing All Links . . . . . . .  25
     5.7.  Compute MRT Next Hops . . . . . . . . . . . . . . . . . .  29
       5.7.1.  MRT Next Hops to All Nodes Ordered with Respect to
               the Computing Node  . . . . . . . . . . . . . . . . .  29
       5.7.2.  MRT Next Hops to All Nodes Not Ordered with Respect
               to the Computing Node . . . . . . . . . . . . . . . .  30
       5.7.3.  Computing Redundant Tree Next Hops in a 2-Connected
               Graph . . . . . . . . . . . . . . . . . . . . . . . .  31
       5.7.4.  Generalizing for a Graph That Isn't 2-Connected . . .  33
       5.7.5.  Complete Algorithm to Compute MRT Next Hops . . . . .  34
     5.8.  Identify MRT Alternates . . . . . . . . . . . . . . . . .  36
     5.9.  Named Proxy-Nodes . . . . . . . . . . . . . . . . . . . .  44
       5.9.1.  Determining Proxy-Node Attachment Routers . . . . . .  45
       5.9.2.  Computing If an Island Neighbor (IN) Is Loop-Free . .  45
       5.9.3.  Computing MRT Next Hops for Proxy-Nodes . . . . . . .  47
       5.9.4.  Computing MRT Alternates for Proxy-Nodes  . . . . . .  53
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