Network Working Group
Internet Engineering Task Force (IETF) R. Bush
Internet-Draft
Request for Comments: 8654 Arrcus & IIJ
Updates: 4271 (if approved) K. Patel
Intended status:
Category: Standards Track Arrcus, Inc.
Expires: February 17, 2020
ISSN: 2070-1721 D. Ward
Cisco Systems
August 16,
October 2019
Extended Message support Support for BGP
draft-ietf-idr-bgp-extended-messages-36
Abstract
The BGP specification (RFC 4271) mandates a maximum BGP message size
of 4,096 octets. As BGP is extended to support newer AFI/SAFIs new Address Family
Identifiers (AFIs), Subsequent AFIs (SAFIs), and other features,
there is a need to extend the maximum message size beyond 4,096
octets. This document updates the BGP specification RFC4271 by extending the
maximum message size from 4,096 octets to 65,535 octets for all
messages except the for OPEN and KEEPALIVE messages.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on February 17, 2020.
https://www.rfc-editor.org/info/rfc8654.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language
2. BGP Extended Message . . . . . . . . . . . . . . . . . . . . 2
3. BGP Extended Message Capability for BGP . . . . . . . . . . . . . 3
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 4
6. Changes to RFC4271 . . . . . . . . . . . . . . . . . . . . . 5 RFC 4271
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1.
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2.
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The BGP specification [RFC4271] mandates a maximum BGP message size
of 4,096 octets. As BGP is extended to support newer AFI/SAFIs new AFIs, SAFIs, and
newer
other capabilities (e.g., BGPsec [RFC8205] and BGP-LS BGP - Link State (BGP-
LS) [RFC7752]), there is a need to extend the maximum message size
beyond 4,096 octets. This draft document provides an extension to BGP to
extend its the message size limit from 4,096 octets to 65,535 octets for
all messages except
the for OPEN and KEEPALIVE messages.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. BGP Extended Message
A BGP message over 4,096 octets in length is a BGP Extended Message.
BGP Extended Messages have a maximum message size of 65,535 octets.
The smallest message that may be sent consists of is a BGP KEEPALIVE KEEPALIVE, which
consists of 19 octets.
3. BGP Extended Message Capability for BGP
The BGP Extended Message Capability is a new BGP Capability capability [RFC5492]
defined with Capability code Code 6 and Capability length Length 0.
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 receive and properly handle, see
Section 4, handle BGP
Extended Messages. Messages (see Section 4).
Peers that wish to use the BGP Extended Message capability Capability MUST
support Error Handling error handling for BGP UPDATE Messages messages per [RFC7606].
4. Operation
The BGP Extended Message Capability applies to all messages except
for
the OPEN and KEEPALIVE messages. The former exception is to These exceptions reduce the
complexity of providing backward compatibility.
A BGP speaker that is capable of receiving BGP Extended Messages
SHOULD advertise the BGP Extended Message Capability to its peers
using BGP Capabilities Advertisement [RFC5492]. A BGP speaker MAY
send BGP Extended Messages to a peer only if the BGP Extended Message
Capability was received from that peer.
An implementation that advertises the BGP Extended Message capability Capability
MUST be capable of receiving a message with a Length length up to and
including 65,535 octets.
Applications generating information which that might be encapsulated within
BGP messages MUST limit the size of their payload to take the maximum
message size into account.
During the years of incremental deployment, speakers that are capable
of Extended Messages should not simply pack as many NLRI in a message
as they can, or otherwise unnecessarily generate UPDATES above the
4,096 octet pre- Extended Message limit, so as not to require
downstream routers to decompose for peers that do not support
Extended Messages. See Section 8.
If a BGP message with a Length length greater than 4,096 octets is received
by a BGP listener who has not advertised the BGP Extended Message
Capability, the listener will generate a NOTIFICATION with the Error
Subcode set to Bad Message Length ([RFC4271] Sec ([RFC4271], Section 6.1).
A BGP UPDATE will (policy, (if allowed by policy, best path, etc., allowing) etc.) typically
propagate throughout the BGP speaking Internet; BGP-speaking Internet and hence to BGP
speakers which that may not support BGP Extended Messages. Therefore, an
announcement in an a BGP Extended Message where the size of the
attribute set plus the NLRI is larger than 4,096 octets may cause
lack of reachability.
A BGP speaker that has advertised the BGP Extended Message capability Capability
to its peers, peers may receive an UPDATE from one of its peers that
produces an ongoing announcement that is larger than 4,096 octets.
When propagating that UPDATE onward to a neighbor which that has not
advertised the BGP Extended Message capability, Capability, the speaker SHOULD
try to reduce the outgoing message size by removing attributes
eligible under the "attribute discard" approach of [RFC7606]. If the
message is still too big, then it must not be sent to the neighbor
([RFC4271], Section 9.2). Additionally, if the NLRI was previously
advertised to that peer, it must be withdrawn from service
([RFC4271], Section 9.1.3).
If an Autonomous System (AS) has multiple internal BGP speakers and
also has multiple external BGP neighbors, to present a consistent
external view care must be taken to
ensure a consistent view within the AS. AS in order to present a
consistent external view. In the context of BGP Extended Messages, a
consistent view can only be guaranteed if all the iBGP Internal BGP (iBGP)
speakers advertise the BGP Extended Message capability. Capability. If that is
not the case, then the operator should consider whether or not the
BGP Extended Message capability Capability should be advertised to external peers or not.
peers.
During the incremental deployment of BGP Extended Messages and use of
the "attribute discard" approach of [RFC7606] in an iBGP mesh, mesh or with eBGP
External BGP (eBGP) peers, the operator should monitor any routes
dropped and any discarded attributes.
5. Error Handling
A BGP speaker that has the ability to use BGP Extended Messages but
has not advertised the BGP Extended Messages capability, Message Capability, presumably
due to configuration, MUST NOT accept an a BGP Extended Message. A
speaker MUST NOT implement a more liberal policy accepting BGP
Extended Messages.
A BGP speaker that does not advertise the BGP Extended Messages
capability Message
Capability might also genuinely not support BGP Extended Messages.
Such a speaker will follow the error handling error-handling procedures of [RFC4271]
if it receives an a BGP Extended Message. Similarly, any speaker that
treats an improper BGP Extended Message as a fatal error, error MUST follow
the error
handling error-handling procedures of [RFC4271].
The UPDATE Message
Error Handling, handling for UPDATE messages, as specified in Section 6.3 of
[RFC4271], is unchanged. However, if a NOTIFICATION is to be sent to
a BGP speaker that has not advertised the BGP Extended Message
Capability, the size of the message MUST NOT exceed 4,096 octets.
It is RECOMMENDED that BGP protocol developers and implementers are
conservative in their application and use of BGP Extended Messages.
Future protocol specifications MUST describe how to handle peers
which that
can only accommodate 4,096 octet messages.
6. Changes to RFC4271 RFC 4271
[RFC4271] states "The value of the Length field MUST always be at
least 19 and no greater than 4,096." 4096." This document changes the latter
number to 65,535 for all messages except the for OPEN and KEEPALIVE
messages.
Section 6.1 of [RFC4271] Sec 6.1, specifies raising an error if the length of
a message is over 4,096 octets. For all messages except the for OPEN
message, and
KEEPALIVE messages, if the receiver has advertised the BGP Extended Messages
Message Capability, this document raises that limit to 65,535.
7. IANA Considerations
The
IANA has made an early the following allocation for this new BGP Extended
Message Capability referring to this document.
Registry: Capability Codes in the "Capability Codes"
registry:
+-------+----------------------+-----------+
| Value | Description Document
----- ----------------------------------- ------------- | Reference |
+=======+======================+===========+
| 6 | BGP Extended Message [this draft] | RFC 8654 |
+-------+----------------------+-----------+
Table 1: Addition to "Capability Codes"
Registry
8. Security Considerations
This extension to BGP does not change BGP's underlying security
issues;
issues [RFC4272].
Due to increased memory requirements for buffering, there may be
increased exposure to resource exhaustion, intentional or
unintentional.
If a remote speaker is able to craft a large BGP Extended Message to
send on a path where one or more peers do not support BGP Extended
Messages, peers which that support BGP Extended Messages may may:
* act to reduce the outgoing message, see message (see Section 4, and 4) and, in doing so
so, cause an attack by discarding attributes one or more of its peer
peers may be expecting. The attributes eligible under the
"attribute discard" approach must have no effect on route
selection or installation [RFC7606].
If a remote speaker is able to craft a large BGP Extended Message to
send on a path where one or more peers do not support BGP Extended
Messages, peers which support BGP Extended Messages may
* act to reduce the outgoing message, see message (see Section 4, and 4) and, in doing so
so, allow a downgrade attack. This would only affect the
attacker's message, where 'downgrade' has questionable meaning.
If a remote speaker is able to craft a large BGP Extended Message to
send on a path where one or more peers do not support BGP Extended
Messages, peers which support BGP Extended Messages may
* incur resource load (processing, message resizing, etc.) when
reformatting the large messages.
9.
10. References
10.1.
9.1. 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>.
<https://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>.
<https://www.rfc-editor.org/info/rfc4271>.
[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>. <https://www.rfc-editor.org/info/rfc5492>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<http://www.rfc-editor.org/info/rfc7606>.
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <http://www.rfc-editor.org/info/rfc8174>.
10.2. <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<http://www.rfc-editor.org/info/rfc4272>.
<https://www.rfc-editor.org/info/rfc4272>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<http://www.rfc-editor.org/info/rfc7752>.
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
Specification", RFC 8205, DOI 10.17487/RFC8205, September
2017, <https://www.rfc-editor.org/info/rfc8205>.
Acknowledgments
The authors thank Alvaro Retana for an amazing review, review; 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.
Authors' Addresses
Randy Bush
Arrcus & IIJ
5147 Crystal Springs
Bainbridge Island, Washington WA 98110
US
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
US
United States of America
Email: dward@cisco.com