Bidirectional Forwarding Detection (BFD)
RFC 5880

Internet Engineering Task Force (IETF)                           D. Katz
Request for Comments: 5880                                       D. Ward
Category: Standards Track                               Juniper Networks
ISSN: 2070-1721                                                June 2010

                Bidirectional Forwarding Detection (BFD)

Abstract

   This document describes a protocol intended to detect faults in the
   bidirectional path between two forwarding engines, including
   interfaces, data link(s), and to the extent possible the forwarding
   engines themselves, with potentially very low latency.  It operates
   independently of media, data protocols, and routing protocols.

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/rfc5880.

Copyright Notice

   Copyright (c) 2010 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.

Katz & Ward                  Standards Track                    [Page 1]
RFC 5880           Bidirectional Forwarding Detection          June 2010

Table of Contents

   1. Introduction ....................................................3
      1.1. Conventions Used in This Document ..........................4
   2. Design ..........................................................4
   3. Protocol Overview ...............................................5
      3.1. Addressing and Session Establishment .......................5
      3.2. Operating Modes ............................................5
   4. BFD Control Packet Format .......................................7
      4.1. Generic BFD Control Packet Format ..........................7
      4.2. Simple Password Authentication Section Format .............11
      4.3. Keyed MD5 and Meticulous Keyed MD5 Authentication
           Section Format ............................................11
      4.4. Keyed SHA1 and Meticulous Keyed SHA1
           Authentication Section Format .............................13
   5. BFD Echo Packet Format .........................................14
   6. Elements of Procedure ..........................................14
      6.1. Overview ..................................................14
      6.2. BFD State Machine .........................................16
      6.3. Demultiplexing and the Discriminator Fields ...............17
      6.4. The Echo Function and Asymmetry ...........................18
      6.5. The Poll Sequence .........................................19
      6.6. Demand Mode ...............................................19
      6.7. Authentication ............................................21
           6.7.1. Enabling and Disabling Authentication ..............21
           6.7.2. Simple Password Authentication .....................22
           6.7.3. Keyed MD5 and Meticulous Keyed MD5 Authentication ..23
           6.7.4. Keyed SHA1 and Meticulous Keyed SHA1
                  Authentication .....................................25
      6.8. Functional Specifics ......................................27
           6.8.1. State Variables ....................................27
           6.8.2. Timer Negotiation ..................................30
           6.8.3. Timer Manipulation .................................31
           6.8.4. Calculating the Detection Time .....................32
           6.8.5. Detecting Failures with the Echo Function ..........33
           6.8.6. Reception of BFD Control Packets ...................33
           6.8.7. Transmitting BFD Control Packets ...................36
           6.8.8. Reception of BFD Echo Packets ......................39
           6.8.9. Transmission of BFD Echo Packets ...................39
           6.8.10. Min Rx Interval Change ............................40