Common Interval Support in Bidirectional Forwarding Detection
RFC 7419

Document Type RFC - Informational (December 2014; No errata)
Updates RFC 5880
Last updated 2015-10-14
Stream IETF
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Stream WG state Submitted to IESG for Publication Jan 2015
Document shepherd Jeffrey Haas
Shepherd write-up Show (last changed 2014-07-28)
IESG IESG state RFC 7419 (Informational)
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Responsible AD Adrian Farrel
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IANA IANA review state Version Changed - Review Needed
IANA action state No IC
Internet Engineering Task Force (IETF)                          N. Akiya
Request for Comments: 7419                               M. Binderberger
Updates: 5880                                              Cisco Systems
Category: Informational                                        G. Mirsky
ISSN: 2070-1721                                                 Ericsson
                                                           December 2014

     Common Interval Support in Bidirectional Forwarding Detection

Abstract

   Bidirectional Forwarding Detection (BFD) requires that messages be
   transmitted at regular intervals and provides a way to negotiate the
   interval used by BFD peers.  Some BFD implementations may be
   restricted to only support several interval values.  When such BFD
   implementations speak to each other, there is a possibility of two
   sides not being able to find a common value for the interval to run
   BFD sessions.

   This document updates RFC 5880 by defining a small set of interval
   values for BFD that we call "Common Intervals" and recommends
   implementations to support the defined intervals.  This solves the
   problem of finding an interval value that both BFD speakers can
   support while allowing a simplified implementation as seen for
   hardware-based BFD.  It does not restrict an implementation from
   supporting more intervals in addition to the Common Intervals.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc7419.

Akiya, et al.                 Informational                     [Page 1]
RFC 7419             Common Interval Support in BFD        December 2014

Copyright Notice

   Copyright (c) 2014 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
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   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
   2.  The Problem with Few Supported Intervals  . . . . . . . . . .   3
   3.  Well-Defined, Common Intervals  . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Why Some Values Are in the Common Interval Set . . .   6
   Appendix B.  Timer Adjustment with Non-identical Interval Sets  .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The Bidirectional Forwarding Detection (BFD) standard [RFC5880]
   describes how to calculate the transmission interval and the
   detection time.  However, it does not make any statement about how to
   solve a situation where one BFD speaker cannot support the calculated
   value.  In practice, this may not have been a problem as long as
   software-implemented timers were used and as long as the granularity
   of such timers was small compared to the interval values being
   supported, i.e. as long as the error in the timer interval was small
   compared to 25 percent jitter.

   In the meantime, requests exist for very fast interval values, down
   to 3.3 msec for the MPLS Transport Profile (MPLS-TP).  At the same
   time, the requested scale for the number of BFD sessions is
   increasing.  Both requirements have driven vendors to use Network
   Processors (NP), Field Programmable Gate Arrays (FPGAs), or other
   hardware-based solutions to offload the periodic packet transmission
   and the timeout detection in the receive direction.  A potential
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