draft-ietf-idr-bgp-extended-messages-33.txt   draft-ietf-idr-bgp-extended-messages-34.txt 
Network Working Group R. Bush Network Working Group R. Bush
Internet-Draft IIJ & Arrcus Internet-Draft IIJ & Arrcus
Updates: 4271 (if approved) K. Patel Updates: 4271 (if approved) K. Patel
Intended status: Standards Track Arrcus, Inc. Intended status: Standards Track Arrcus, Inc.
Expires: January 3, 2020 D. Ward Expires: January 31, 2020 D. Ward
Cisco Systems Cisco Systems
July 2, 2019 July 30, 2019
Extended Message support for BGP Extended Message support for BGP
draft-ietf-idr-bgp-extended-messages-33 draft-ietf-idr-bgp-extended-messages-34
Abstract Abstract
The BGP specification mandates a maximum BGP message size of 4,096 The BGP specification mandates a maximum BGP message size of 4,096
octets. As BGP is extended to support newer AFI/SAFIs and other octets. As BGP is extended to support newer AFI/SAFIs and other
features, there is a need to extend the maximum message size beyond features, there is a need to extend the maximum message size beyond
4,096 octets. This document updates the BGP specification RFC4271 by 4,096 octets. This document updates the BGP specification RFC4271 by
extending the maximum message size from 4,096 octets to 65,535 octets extending the maximum message size from 4,096 octets to 65,535 octets
for all except the OPEN and KEEPALIVE messages. for all except the OPEN and KEEPALIVE messages.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2020. This Internet-Draft will expire on January 31, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2. BGP Extended Message . . . . . . . . . . . . . . . . . . . . 2 2. BGP Extended Message . . . . . . . . . . . . . . . . . . . . 2
3. Extended Message Capability for BGP . . . . . . . . . . . . . 3 3. Extended Message Capability for BGP . . . . . . . . . . . . . 3
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 4 5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 4
6. Changes to RFC4271 . . . . . . . . . . . . . . . . . . . . . 5 6. Changes to RFC4271 . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5 8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6 10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 6 10.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
The BGP specification [RFC4271] mandates a maximum BGP message size The BGP specification [RFC4271] mandates a maximum BGP message size
of 4,096 octets. As BGP is extended to support newer AFI/SAFIs and of 4,096 octets. As BGP is extended to support newer AFI/SAFIs and
newer capabilities (e.g., BGPsec [RFC8205] and BGP-LS [RFC7752]), newer capabilities (e.g., BGPsec [RFC8205] and BGP-LS [RFC7752]),
there is a need to extend the maximum message size beyond 4,096 there is a need to extend the maximum message size beyond 4,096
octets. This draft provides an extension to BGP to extend its octets. This draft provides an extension to BGP to extend its
message size limit from 4,096 octets to 65,535 octets for all except message size limit from 4,096 octets to 65,535 octets for all except
the OPEN and KEEPALIVE messages. the OPEN and KEEPALIVE messages.
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4. Operation 4. Operation
The Extended Message Capability applies to all messages except for The Extended Message Capability applies to all messages except for
the OPEN and KEEPALIVE messages. The former exception is to reduce the OPEN and KEEPALIVE messages. The former exception is to reduce
the complexity of providing backward compatibility. the complexity of providing backward compatibility.
A BGP speaker that is capable of sending and receiving BGP Extended A BGP speaker that is capable of sending and receiving BGP Extended
Messages SHOULD advertise the BGP Extended Message Capability to its Messages SHOULD advertise the BGP Extended Message Capability to its
peers using BGP Capabilities Advertisement [RFC5492]. A BGP speaker peers using BGP Capabilities Advertisement [RFC5492]. A BGP speaker
MAY send Extended Messages to a peer only if the Extended Message MAY send Extended Messages to a peer if the Extended Message
Capability was advertised by both peers. Capability was received from that peer.
An implementation that advertises the BGP Extended Message capability An implementation that advertises the BGP Extended Message capability
MUST be capable of receiving a message with a Length up to and MUST be capable of receiving a message with a Length up to and
including 65,535 octets. including 65,535 octets.
Applications generating information which might be encapsulated Applications generating information which might be encapsulated
within BGP messages MUST limit the size of their payload to take the within BGP messages MUST limit the size of their payload to take the
maximum message size into account. 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 greater than 4,096 octets is received If a BGP message with a Length greater than 4,096 octets is received
by a BGP listener who has not advertised the Extended Message by a BGP listener who has not advertised the Extended Message
Capability, the listener MUST treat this as a malformed message, and Capability, the listener will generate a NOTIFICATION with the Error
MUST generate a NOTIFICATION with the Error Subcode set to Bad Subcode set to Bad Message Length ([RFC4271] Sec 6.1).
Message Length (see [RFC4271] Sec 6.1).
A BGP UPDATE will (policy, best path, etc., allowing) typically A BGP UPDATE will (policy, best path, etc., allowing) typically
propagate throughout the BGP speaking Internet; and hence to BGP propagate throughout the BGP speaking Internet; and hence to BGP
speakers which may not support Extended Messages. Therefore, an speakers which may not support Extended Messages. Therefore, an
announcement in an Extended Message where the size of the attribute announcement in an Extended Message where the size of the attribute
set plus the NLRI is larger than 4,096 octets may cause lack of set plus the NLRI is larger than 4,096 octets may cause lack of
reachability. reachability.
A BGP speaker with a mixture of peers some of which have advertised A BGP speaker with a mixture of peers some of which have advertised
the BGP Extended Message capability and some which have not, may the BGP Extended Message capability and some which have not, may
receive an UPDATE from one of its capable peers that produces an receive an UPDATE from one of its capable peers that produces an
ongoing announcement that is larger than 4,096 octets. When ongoing announcement that is larger than 4,096 octets. When
propagating that UPDATE onward to a neighbor which has not advertised propagating that UPDATE onward to a neighbor which has not advertised
the BGP Extended Message capability, the sender SHOULD try to reduce the BGP Extended Message capability, the sender SHOULD try to reduce
the outgoing message size by removing attributes eligible under the the outgoing message size by removing attributes eligible under the
"attribute discard" approach of [RFC7606]. If the message is still "attribute discard" approach of [RFC7606]. If the message is still
too big, then it must NOT be sent to the neighbor ([RFC4271], too big, then it must not be sent to the neighbor ([RFC4271],
Section 9.2). Additionally, if the NLRI was previously advertised to Section 9.2). Additionally, if the NLRI was previously advertised to
that peer, it must be withdrawn from service ([RFC4271], that peer, it must be withdrawn from service ([RFC4271],
Section 9.1.3). Section 9.1.3).
In an iBGP mesh, if BGP Extended Messages are to be advertized, all If an Autonomous System (AS) has multiple internal BGP speakers and
peers MUST advertize the BGP Extended Message capability. This is also has multiple external BGP neighbors, to present a consistent
not only for consistent internal routing, but also to give a external view care must be taken to ensure a consistent view within
consistent view to eBGP peers. the AS. In the context of BGP Extended Messages, a consistent view
can only be guaranteed if all the iBGP speakers advertise the BGP
Extended Message capability. If that is not the case, then the
operator should consider whether the BGP Extended Message capability
should be advertised to external peers or not.
During the incremental deployment of BGP Extended Messages and During the incremental deployment of BGP Extended Messages and
[RFC7606] in an iBGP mesh, or with eBGP peers, the operator should [RFC7606] in an iBGP mesh, or with eBGP peers, the operator should
monitor any routes dropped and any discarded attributes. monitor any routes dropped and any discarded attributes.
5. Error Handling 5. Error Handling
A BGP speaker that has the ability to use Extended Messages but has A BGP speaker that has the ability to use Extended Messages but has
not advertised the BGP Extended Messages capability, presumably due not advertised the BGP Extended Messages capability, presumably due
to configuration, MUST NOT accept an Extended Message. A speaker to configuration, MUST NOT accept an Extended Message. A speaker
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8. Security Considerations 8. Security Considerations
This extension to BGP does not change BGP's underlying security This extension to BGP does not change BGP's underlying security
issues; [RFC4272]. issues; [RFC4272].
Due to increased memory requirements for buffering, there may be Due to increased memory requirements for buffering, there may be
increased exposure to resource exhaustion, intentional or increased exposure to resource exhaustion, intentional or
unintentional. unintentional.
As this draft requires support for [RFC7606] UPDATE error handling, If a remote speaker is able to craft a large BGP Extended Message to
it inherits the security considerations of [RFC7606]. 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 Section 4, and in doing so cause an attack
by discarding attributes its peer may be expecting. The attributes
eligible under the "attribute discard" must have no effect on route
selection or installation [RFC7606].
If a remote attacker is able to craft a large BGP Extended Message to 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 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 Messages, peers which support BGP Extended Messages may act to reduce
the outgoing message, see Section 4, and in doing so cause a the outgoing message, see Section 4, and in doing so allow a
downgrade attack. downgrade attack. This would only affect the attacker's message,
where 'downgrade' has questionable meaning.
If a remote attacker is able to craft a large BGP Extended Message to 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 send on a path where one or more peers do not support BGP Extended
Messages, peers which support BGP Extended Messages may incur Messages, peers which support BGP Extended Messages may incur
resource load (processing, message resizing, etc.) reformatting the resource load (processing, message resizing, etc.) reformatting the
large messages. Worse, [RFC7606] "treat-as-withdraw" may large messages.
consistently withdraw announcements causing inconsistent routing.
9. Acknowledgments 9. Acknowledgments
The authors thank Alvaro Retana for an amazing review, Enke Chen, The authors thank Alvaro Retana for an amazing review, Enke Chen,
Susan Hares, John Scudder, John Levine, and Job Snijders for their Susan Hares, John Scudder, John Levine, and Job Snijders for their
input; and Oliver Borchert and Kyehwan Lee for their implementations input; and Oliver Borchert and Kyehwan Lee for their implementations
and testing. and testing.
10. References 10. References
10.1. Normative 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 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>. <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 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <http://www.rfc-editor.org/info/rfc5492>. 2009, <http://www.rfc-editor.org/info/rfc5492>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages", Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015, RFC 7606, DOI 10.17487/RFC7606, August 2015,
<http://www.rfc-editor.org/info/rfc7606>. <http://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. Informative References 10.2. Informative References
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<http://www.rfc-editor.org/info/rfc4272>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752, Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016, DOI 10.17487/RFC7752, March 2016,
<http://www.rfc-editor.org/info/rfc7752>. <http://www.rfc-editor.org/info/rfc7752>.
[RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol [RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
Specification", RFC 8205, DOI 10.17487/RFC8205, September Specification", RFC 8205, DOI 10.17487/RFC8205, September
2017, <https://www.rfc-editor.org/info/rfc8205>. 2017, <https://www.rfc-editor.org/info/rfc8205>.
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