Host Router Support for OSPFv2
RFC 8770

Document Type RFC - Proposed Standard (April 2020; No errata)
Updates RFC 6987
Authors Keyur Patel  , Padma Pillay-Esnault  , Manish Bhardwaj  , Serpil Bayraktar 
Last updated 2020-04-09
Replaces draft-keyupate-ospf-ospfv2-hbit
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Internet Engineering Task Force (IETF)                          K. Patel
Request for Comments: 8770                                        Arrcus
Updates: 6987                                          P. Pillay-Esnault
Category: Standards Track                                 PPE Consulting
ISSN: 2070-1721                                              M. Bhardwaj
                                                            S. Bayraktar
                                                           Cisco Systems
                                                              April 2020

                     Host Router Support for OSPFv2


   The Open Shortest Path First Version 2 (OSPFv2) protocol does not
   have a mechanism for a node to repel transit traffic if it is on the
   shortest path.  This document defines a bit called the Host-bit
   (H-bit).  This bit enables a router to advertise that it is a non-
   transit router.  This document also describes the changes needed to
   support the H-bit in the domain.  In addition, this document updates
   RFC 6987 to advertise Type 2 External and Not-So-Stubby Area (NSSA)
   Link State Advertisements (LSAs) (RFC 3101) with a high cost in order
   to repel traffic effectively.

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

Copyright Notice

   Copyright (c) 2020 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with 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.

Table of Contents

   1.  Introduction
   2.  Requirements Language
   3.  Host-Bit Support
   4.  SPF Modifications
   5.  Autodiscovery and Backward Compatibility
   6.  OSPF AS-External-LSAs / NSSA-LSAs with Type 2 Metrics
   7.  IANA Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Authors' Addresses

1.  Introduction

   The OSPFv2 protocol specifies a Shortest Path First (SPF) algorithm
   that identifies transit vertices based on their adjacencies.
   Therefore, OSPFv2 does not have a mechanism to prevent traffic
   transiting a participating node if it is a transit vertex in the only
   existing or shortest path to the destination.  The use of metrics to
   make the node undesirable can help to repel traffic only if an
   alternative better route exists.

   A mechanism to move traffic away from the shortest path is
   particularly useful for a number of use cases:

   1.  Graceful isolation of a router, to avoid blackhole scenarios when
       there is a reload and possible long reconvergence times.

   2.  Closet switches that are not usually used for transit traffic but
       need to participate in the topology.

   3.  Overloaded routers that could use such a capability to
       temporarily repel traffic until they stabilize.

   4.  BGP route reflectors, known as virtual Route Reflectors, that are
       not in the forwarding path but are in central locations such as
       data centers.  Such route reflectors are typically used for route
       distribution and are not capable of forwarding transit traffic.
       However, they need to learn the OSPF topology to perform SPF
       computation for optimal routes and reachability resolution for
       their clients [BGP-ORR].

   This document describes the functionality provided by the Host-bit
   (H-bit); this functionality prevents other OSPFv2 routers from using
   the host router by excluding it in path calculations for transit
   traffic in OSPFv2 routing domains.  If the H-bit is set, then the
   calculation of the shortest-path tree for an area, as described in
   Section 16.1 of [RFC2328], is modified by including a check to verify
   that transit vertices DO NOT have the H-bit set (see Section 4).
   Furthermore, in order to repel traffic effectively, this document
   updates [RFC6987] so that Type 2 External and Not-So-Stubby Area
   (NSSA) Link State Advertisements (LSAs) [RFC3101] are advertised with
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