IS-IS BFD-Enabled TLV
RFC 6213

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Internet Engineering Task Force (IETF)                          C. Hopps
Request for Comments: 6213                                   L. Ginsberg
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                               April 2011

                         IS-IS BFD-Enabled TLV

Abstract

   This document describes a type-length-value (TLV) for use in the IS-
   IS routing protocol that allows for the proper use of the
   Bidirectional Forwarding Detection (BFD) protocol.  There exist
   certain scenarios in which IS-IS will not react appropriately to a
   BFD-detected forwarding plane failure without use of either this TLV
   or some other method.

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 5741.

   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/rfc6213.

Copyright Notice

   Copyright (c) 2011 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
   (http://trustee.ietf.org/license-info) 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.

Hopps & Ginsberg             Standards Track                    [Page 1]
RFC 6213                  IS-IS BFD-Enabled TLV               April 2011

Table of Contents

   1. Introduction ....................................................2
      1.1. Requirements Language ......................................2
   2. The Problem .....................................................2
   3. The Solution ....................................................3
      3.1. State Definitions ..........................................3
      3.2. Adjacency Establishment and Maintenance ....................4
      3.3. Advertisement of Topology-Specific IS Neighbors ............4
   4. Transition ......................................................4
   5. Graceful Restart ................................................5
   6. The BFD-Enabled TLV .............................................5
   7. Security Considerations .........................................6
   8. IANA Considerations .............................................6
   9. Acknowledgements ................................................6
   10. Normative References ...........................................7

1.  Introduction

   The Bidirectional Forwarding Detection (BFD) protocol [RFC5880] is a
   protocol that allows for detection of a forwarding plane failure
   between two routers.  A router can use [RFC5880] to validate that a
   peer router's forwarding ability is functioning.

   One specific application of BFD as described in [RFC5882] is to
   verify the forwarding ability of an IS-IS [RFC1195] router's
   adjacencies; however, the method described in [RFC5882] does not
   allow for certain failure scenarios.  We will define a TLV that will
   allow for proper response to the detection of all forwarding failures
   where the use of BFD is employed with IS-IS.

1.1.  Requirements Language

   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 RFC 2119 [RFC2119].

2.  The Problem

   We observe that, in order to allow for mixed use (i.e., some routers
   running BFD and some not), [RFC5882] does not require a BFD session
   be established prior to the establishment of an IS-IS adjacency.
   Thus, if a router A has neighbors B and C, and B does not support
   BFD, A would still form adjacencies with B and C, and it would only
   establish a BFD session with C.

Hopps & Ginsberg             Standards Track                    [Page 2]
RFC 6213                  IS-IS BFD-Enabled TLV               April 2011

   The problem with this solution is that it assumes that the
   transmission and receipt of IS-IS Hellos (IIHs) shares fate with
   forwarded data packets.  This is not a fair assumption to make given
   that the primary use of BFD is to protect IPv4 (and IPv6) forwarding,
   and IS-IS does not utilize IPv4 or IPv6 for sending or receiving its