Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)
RFC 5881

Type RFC - Proposed Standard (June 2010; Errata)
Last updated 2013-03-02
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Internet Engineering Task Force (IETF)                           D. Katz
Request for Comments: 5881                                       D. Ward
Category: Standards Track                               Juniper Networks
ISSN: 2070-1721                                                June 2010

                Bidirectional Forwarding Detection (BFD)
                     for IPv4 and IPv6 (Single Hop)


   This document describes the use of the Bidirectional Forwarding
   Detection (BFD) protocol over IPv4 and IPv6 for single IP hops.

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

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
   ( 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 5881           BFD for IPv4 and IPv6 (Single Hop)          June 2010

1.  Introduction

   One very desirable application for Bidirectional Forwarding Detection
   (BFD) [BFD] is to track IPv4 and IPv6 connectivity between directly
   connected systems.  This could be used to supplement the detection
   mechanisms in routing protocols or to monitor router-host
   connectivity, among other applications.

   This document describes the particulars necessary to use BFD in this
   environment.  Interactions between BFD and other protocols and system
   functions are described in the BFD Generic Applications document

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [KEYWORDS].

2.  Applications and Limitations

   This application of BFD can be used by any pair of systems
   communicating via IPv4 and/or IPv6 across a single IP hop that is
   associated with an incoming interface.  This includes, but is not
   limited to, physical media, virtual circuits, and tunnels.

   Each BFD session between a pair of systems MUST traverse a separate
   network-layer path in both directions.  This is necessary for
   demultiplexing to work properly, and also because (by definition)
   multiple sessions would otherwise be protecting the same path.

   If BFD is to be used in conjunction with both IPv4 and IPv6 on a
   particular path, a separate BFD session MUST be established for each
   protocol (and thus encapsulated by that protocol) over that link.

   If the BFD Echo function is used, transmitted packets are immediately
   routed back towards the sender on the interface over which they were
   sent.  This may interact with other mechanisms that are used on the
   two systems that employ BFD.  In particular, ingress filtering
   [BCP38] is incompatible with the way Echo packets need to be sent.
   Implementations that support the Echo function MUST ensure that
   ingress filtering is not used on an interface that employs the Echo
   function or make an exception for ingress filtering Echo packets.

   An implementation of the Echo function also requires Application
   Programming Interfaces (APIs) that may not exist on all systems.  A
   system implementing the Echo function MUST be capable of sending

Katz & Ward                  Standards Track                    [Page 2]
RFC 5881           BFD for IPv4 and IPv6 (Single Hop)          June 2010

   packets to its own address, which will typically require bypassing
   the normal forwarding lookup.  This typically requires access to APIs
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