Internet DRAFT - draft-haas-bfd-large-packets
draft-haas-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
draft-haas-bfd-large-packets-01
Abstract
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
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
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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
BFD PDU.
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:
bfd.PaddedPduSize
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-
editor.org/info/rfc791>.
[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-
editor.org/info/rfc2119>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[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-
editor.org/info/rfc5881>.
[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,
<https://www.rfc-editor.org/info/rfc7880>.
6.2. Informative References
[I-D.haas-xiao-bfd-echo-path-mtu]
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
2011.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990, <https://www.rfc-
editor.org/info/rfc1191>.
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Authors' Addresses
Jeffrey Haas
Juniper Networks, Inc.
1133 Innovation Way
Sunnyvale, CA 94089
US
Email: jhaas@juniper.net
Albert Fu
Bloomberg
Email: afu14@bloomberg.net
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