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Versions: 00 01 draft-ietf-bfd-large-packets

Network Working Group                                            J. Haas
Internet-Draft                                    Juniper Networks, Inc.
Intended status: Standards Track                                   A. Fu
Expires: April 19, 2019                                        Bloomberg
                                                        October 16, 2018

                   BFD Encapsulated in Large Packets


   The Bidirectional Forwarding Detection (BFD) protocol is commonly
   used to verify connectivity between two systems.  BFD packets are
   typically very small.  It is desirable in some circumstances to know
   that not only is the path between two systems reachable, but also
   that it is capable of carrying a payload of a particular size.  This
   document discusses thoughts on how to implement such a mechanism
   using BFD in Asynchronous mode.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   be interpreted as described in [RFC2119] only when they appear in all
   upper case.  They may also appear in lower or mixed case as English
   words, without normative meaning.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 19, 2019.

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Copyright Notice

   Copyright (c) 2018 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  BFD Encapsulated in Large Packets . . . . . . . . . . . . . .   3
   3.  Implementation and Deployment Considerations  . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Bidirectional Forwarding Detection (BFD) [RFC5880] protocol is
   commonly used to verify connectivity between two systems.  However,
   some applications may require that the Path MTU [RFC1191] between
   those two systems meets a certain minimum criteria.  When the Path
   MTU decreases below the minimum threshold, those applications may
   wish to consider the path unusable.

   BFD may be encapsulated in a number of transport protocols.  An
   example of this is single-hop BFD [RFC5881].  In that case, the link
   MTU configuration is typically enough to guarantee communication
   between the two systems for that size MTU.  BFD Echo mode
   (Section 6.4 of [RFC5880]) is sufficient to permit verification of
   the Path MTU of such directly connected systems.  Previous proposals
   ([I-D.haas-xiao-bfd-echo-path-mtu]) have been made for testing Path
   MTU for such directly connected systems.  However, in the case of
   multi-hop BFD [RFC5883], this guarantee does not hold.

   The encapsulation of BFD in multi-hop sessions is a simple UDP
   packet.  The BFD elements of procedure (Section 6.8.6 of [RFC5880])

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   covers validating the BFD payload.  However, the specification is
   silent on the length of the encapsulation that is carrying the BFD
   PDU.  While it is most common that the transport protocol payload
   (i.e.  UDP) length is the exact size of the BFD PDU, this is not
   required by the elements of procedure.  This leads to the possibility
   that the transport protocol length may be larger than the contained

2.  BFD Encapsulated in Large Packets

   Support for BFD between two systems is typically configured, even if
   the actual session may be dynamically created by a client protocol.
   A new BFD variable is defined in this document:

       The BFD transport protocol payload size is increased to this
       value.  The contents of this additional payload MUST be zero.
       The minimum size of this variable MUST NOT be smaller than
       permitted by the element of BFD procedure; 24 or 26 - see
       Section 6.8.6 of [RFC5880].

   The Don't Fragment bit (Section 2.3 of [RFC0791]) of the IP payload,
   when using IPv4 encapsulation, MUST be set.

3.  Implementation and Deployment Considerations

   While this document proposes no change to the BFD protocol,
   implementations may not permit arbitrarily padded transport PDUs to
   carry BFD packets.  While Section 6 of [RFC5880] warns against
   excessive pedantry, implementations may not work with this mechanism
   without additional support.  Additional changes to the base BFD
   protocol may be required to permit negotiation of this functionality
   and the padding value.

   It is also worthy of note that even if an implementation can function
   with larger transport PDUs, that additional packet size may have
   impact on BFD scaling.

   This mechanism also can be applied to other forms of BFD, including
   S-BFD [RFC7880].

4.  Security Considerations

   This document does not change the underlying security considerations
   of the BFD protocol or its encapsulations.

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5.  IANA Considerations

   This document introduces no additional considerations to IANA.

6.  References

6.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981, <https://www.rfc-

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010, <https://www.rfc-

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
              June 2010, <https://www.rfc-editor.org/info/rfc5883>.

   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
              Pallagatti, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,

6.2.  Informative References

              Haas, J. and M. Xiao, "Application of the BFD Echo
              function for Path MTU Verification or Detection", draft-
              haas-xiao-bfd-echo-path-mtu-01 (work in progress), July

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              DOI 10.17487/RFC1191, November 1990, <https://www.rfc-

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Authors' Addresses

   Jeffrey Haas
   Juniper Networks, Inc.
   1133 Innovation Way
   Sunnyvale, CA  94089

   Email: jhaas@juniper.net

   Albert Fu

   Email: afu14@bloomberg.net

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