Network Working Group R. Bush
Internet-Draft Internet Initiative Japan
Updates: 4271 (if approved) K. Patel
Intended status: Standards Track Arrcus, Inc.
Expires: May 23, 2018 D. Ward
Cisco Systems
November 19, 2017
Extended Message support for BGP
draft-ietf-idr-bgp-extended-messages-24
Abstract
The BGP specification mandates a maximum BGP message size of 4096
octets. As BGP is extended to support newer AFI/SAFIs and other
features, there is a need to extend the maximum message size beyond
4096 octets. This document updates the BGP specification RFC4271 by
providing an extension to BGP to extend its current maximum message
size from 4096 octets to 65535 octets for all except the OPEN
message.
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 https://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 May 23, 2018.
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Copyright Notice
Copyright (c) 2017 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
(https://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. BGP Extended Message . . . . . . . . . . . . . . . . . . . . 2
3. Extended message Capability for BGP . . . . . . . . . . . . . 3
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 4
6. Changes to RFC4271 . . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . 4
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The BGP specification [RFC4271] mandates a maximum BGP message size
of 4096 octets. As BGP is extended to support newer AFI/SAFIs and
newer capabilities (e.g., [I-D.ietf-sidr-bgpsec-protocol]), there is
a need to extend the maximum message size beyond 4096 octets. This
draft provides an extension to BGP to extend its current message size
limit from 4096 octets to 65535 octetsfor all except the OPEN
message.
2. BGP Extended Message
A BGP message over 4096 octets in length is a BGP Extended Message.
BGP Extended Messages have maximum message size of 65535 octets. The
smallest message that may be sent consists of a BGP header without a
data portion (19 octets).
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3. Extended message Capability for BGP
To advertise the BGP Extended Message Capability to a peer, a BGP
speaker uses BGP Capabilities Advertisement [RFC5492]. By
advertising the BGP Extended Message Capability to a peer, a BGP
speaker conveys that it is able to send, receive, and properly handle
BGP Extended Messages.
A peer which does not advertise this capability MUST NOT send BGP
Extended Messages, and BGP Extended Messages MUST NOT be sent to it.
The BGP Extended Message Capability is a new BGP Capability [RFC5492]
defined with Capability code 6 and Capability length 0.
4. Operation
A BGP speaker that is willing to send and receive BGP Extended
Messages with a peer SHOULD advertise the BGP Extended Message
Capability to the peer using BGP Capabilities Advertisement
[RFC5492]. A BGP speaker MAY send Extended Messages to its peer only
if it has received the Extended Message Capability from that peer.
The Extended Message Capability only applies to all messages except
for the OPEN message. This exception is reduce compexity of
providing backward compatibility
An implementation that advertises support for BGP Extended Messages
MUST be capable of receiving a message with a length up to and
including 65535 octets.
Applications generating information which might be encapsulated
within BGP messages MUST limit the size of their payload to take the
maximum message size into account.
A BGP announcement will, in the normal case, propagate throughout the
BGP speaking Internet; and there will undoubtedly be BGP speakers
which do not have the Extended Message capability. Therefore putting
an attribute which can not be decomposed to 4096 octets or less in an
Extended Message is a likely path to routing failure.
It is RECOMMENDED that BGP protocol developers and implementers are
conservative in their application and use of Extended Messages.
Future protocol specifications will need to describe how to handle
peers which can only accomodate 4096 octet messages.
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5. Error Handling
A BGP speaker that has the ability to use Extended Messages but has
not advertised the BGP Extended Messages capability, presumably due
to configuration, SHOULD NOT accept an Extended Message. A speaker
MAY implement a more liberal policy and accept Extended Messages,
even from a peer to which it has not advertised the capability, in
the interest of preserving the BGP session if at all possible.
A BGP speaker that does not advertise the BGP Extended Messages
capability might also genuinely not support Extended Messages. Such
a speaker would be expected to follow the error handling procedures
of [RFC4271] if it receives an Extended Message. Similarly, any
speaker that treats an improper Extended Message as a fatal error,
MUST treat it similarly.
The inconsistency between the local and remote BGP speakers MUST be
flagged to the network operator through standard operational
interfaces. The information should include the NLRI and as much
relevant information as reasonably possible.
6. Changes to RFC4271
[RFC4271] states "The value of the Length field MUST always be at
least 19 and no greater than 4096." This document changes the latter
number to 65535 for all except the OPEN message.
[RFC4271] Sec 6.1, specifies raising an error if the length of a
message is over 4096 octets. For all messages except the OPEN
message, if the receiver has advertised the capability to receive
Extended Messages, this document raises that limit to 65535.
7. IANA Considerations
The IANA has made an early allocation for this new BGP BGP Extended
Message Capability referring to this document.
Registry: BGP Capability Code
Value Description Document
----- ----------------------------------- -------------
6 BGP-Extended Message [this draft]
8. Security Considerations
This extension to BGP does not change BGP's underlying security
issues; see [RFC4272].
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Section 5 allowed a receiver to accept an Extended Message even
though they had not advertised the capability. This slippery slope
will surely lead to sloppy implementations sending Extended Messages
when the receiver is not prepared to deal with them, e.g. to peer
groups. At best, this will result in errors; at worst, buffer
overflows.
Due to increased (over [RFC4272]) memory requirements for buffering,
there may be increased exposure to resource exhaustion, intentional
or unintentional.
9. Acknowledgments
The authors thank Alvaro Retana, Enke Chen, Susan Hares, John
Scudder, John Levine, and Job Snijders for their input; and Oliver
Borchert and Kyehwan Lee for their implementations and testing.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<http://www.rfc-editor.org/info/rfc4272>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <http://www.rfc-editor.org/info/rfc5492>.
10.2. Informative References
[I-D.ietf-sidr-bgpsec-protocol]
Lepinski, M., "BGPSEC Protocol Specification", draft-ietf-
sidr-bgpsec-protocol-07 (work in progress), February 2013.
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Authors' Addresses
Randy Bush
Internet Initiative Japan
5147 Crystal Springs
Bainbridge Island, Washington 98110
United States of America
Email: randy@psg.com
Keyur Patel
Arrcus, Inc.
Email: keyur@arrcus.com
Dave Ward
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: dward@cisco.com
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