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.
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Katz & Ward Standards Track [Page 1]RFC 5881 BFD for IPv4 and IPv6 (Single Hop) June 20101. 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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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