draft-ietf-idr-bgp-extended-messages-31.txt   draft-ietf-idr-bgp-extended-messages-32.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 1, 2020 D. Ward Expires: January 3, 2020 D. Ward
Cisco Systems Cisco Systems
June 30, 2019 July 2, 2019
Extended Message support for BGP Extended Message support for BGP
draft-ietf-idr-bgp-extended-messages-31 draft-ietf-idr-bgp-extended-messages-32
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 1, 2020. This Internet-Draft will expire on January 3, 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 . . . . . . . . . . . . . . . . . 7 10.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 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
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2. BGP Extended Message 2. BGP Extended Message
A BGP message over 4,096 octets in length is a 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. BGP Extended Messages have a maximum message size of 65,535 octets.
The smallest message that may be sent consists of a BGP KEEPALIVE The smallest message that may be sent consists of a BGP KEEPALIVE
which consists of 19 octets. which consists of 19 octets.
3. Extended Message Capability for BGP 3. Extended Message Capability for BGP
The BGP Extended Message Capability is a new BGP Capability [RFC5492]
defined with Capability code 6 and Capability length 0.
To advertise the BGP Extended Message Capability to a peer, a BGP To advertise the BGP Extended Message Capability to a peer, a BGP
speaker uses BGP Capabilities Advertisement [RFC5492]. By speaker uses BGP Capabilities Advertisement [RFC5492]. By
advertising the BGP Extended Message Capability to a peer, a BGP advertising the BGP Extended Message Capability to a peer, a BGP
speaker conveys that it is able to send, receive, and properly speaker conveys that it is able to send, receive, and properly
handle, see Section 4, BGP Extended Messages. handle, see Section 4, BGP Extended Messages.
The BGP Extended Message Capability is a new BGP Capability [RFC5492]
defined with Capability code 6 and Capability length 0.
A peer which does not advertise this capability MUST NOT send BGP A peer which does not advertise this capability MUST NOT send BGP
Extended Messages, and BGP Extended Messages MUST NOT be sent to it. Extended Messages, and BGP Extended Messages MUST NOT be sent to it.
Peers that wish to use the BGP Extended Message capability must Peers that wish to use the BGP Extended Message capability MUST
support Error Handling for BGP UPDATE Messages per [RFC7606]. support Error Handling for BGP UPDATE Messages per [RFC7606].
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 a backward compatibility the complexity of providing a 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 its peer only if both peers have MAY send Extended Messages to a peer only if the Extended Message
negotiated the Extended Message Capability with each other. Capability was advertised by both peers.
An implementation that advertises support for BGP Extended Messages 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.
If a BGP message with a Length lgreater than 4,096 octets is received If a BGP message with a Length lgreater 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 MUST treat this as a malformed message, and
MUST generate a NOTIFICATION with the Error Subcode set to Bad MUST generate a NOTIFICATION with the Error Subcode set to Bad
Message Length (see [RFC4271] Sec 6.1). Message Length (see [RFC4271] Sec 6.1).
A BGP announcement will (policy, best path, etc., allowing) propagate A BGP announcement will (policy, best path, etc., allowing) propagate
throughout the BGP speaking Internet; and hence to BGP speakers which throughout the BGP speaking Internet; and hence to BGP speakers which
may not have the Extended Message capability. Therefore, an may not have the Extended Message capability. 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 can not be decomposed to 4,096 octets or less may set plus the NLRI can not be decomposed to 4,096 octets or less may
cause lack of reachability. cause lack of reachability.
A speaker capable of BGP Extended Messages having a mixture of peers A BGP UPDATE will typically propagate throughout the BGP speaking
some of which have not exchanged the BGP Extended Message capability, Internet; and hence to BGP speakers which may not support Extended
may receive an announcement from one of its capable peers that would Messages. Therefore, a route announcement in an Extended Message
(due to the new AS on the path, new added attributes, etc.) produce where the size of the attribute set plus the NLRI is larger than
an ongoing announcement that would be over 4,096 octets. When 4,096 octets or less may cause lack of reachability.
propagating that update onward to a neighbor with which it has not
negotiated the BGP Extended Message capability, the sender SHOULD try
to reduce the outgoing message size by downgrading BGPsec to BGP4,
decomposing a multi-NLRI update producing multiple updates with fewer
NLRI per update, removing attributes eligible under the attribute
discard approach of [RFC7606], etc. If the resulting message would
still be over the 4,096 octet limit, the sender SHOULD treat-as-
withdraw per [RFC7606].
In an iBGP mesh, all peers SHOULD support the BGP Extended Message A BGP speaker with a mixture of peers some of which have advertised
Capability and [RFC7606]. Only then is it consistent to deploy with the BGP Extended Message capability and some which have not, may
eBGP peers. receive an UPDATE from one of its capable peers that produces an
ongoing announcement that is larger than 4,096 octets. When
propagating that UPDATE onward to a neighbor which has not advertised
the BGP Extended Message capability, the sender 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 SHOULD be withdrawn from service ([RFC4271],
Section 9.1.3).
In an iBGP mesh, if BGP Extended Messages are to be advertized, all
peers MUST advertize the BGP Extended Message Capability and
[RFC7606]. This is not only for consistent internal routing, but
also to give a consistent view to eBGP peers.
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 as "treat-as-withdraw". monitor any routes dropped as "treat-as-withdraw" and any discarded
attributes.
It is RECOMMENDED that BGP protocol developers and implementers are It is RECOMMENDED that BGP protocol developers and implementers are
conservative in their application and use of Extended Messages. conservative in their application and use of Extended Messages.
Future protocol specifications will need to describe how to handle Future protocol specifications MUST describe how to handle peers
peers which can only accommodate 4,096 octet messages. which can only accommodate 4,096 octet messages.
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, SHOULD NOT accept an Extended Message. A speaker to configuration, MUST NOT accept an Extended Message. A speaker
SHOULD NOT implement a more liberal policy accepting BGP Extended MUST NOT implement a more liberal policy accepting BGP Extended
Messages. Messages.
A BGP speaker that does not advertise the BGP Extended Messages A BGP speaker that does not advertise the BGP Extended Messages
capability might also genuinely not support Extended Messages. Such capability might also genuinely not support Extended Messages. Such
a speaker will follow the error handling procedures of [RFC4271] if a speaker will follow the error handling procedures of [RFC4271] if
it receives an Extended Message. Similarly, any speaker that treats it receives an Extended Message. Similarly, any speaker that treats
an improper Extended Message as a fatal error, MUST treat it an improper Extended Message as a fatal error, MUST follow the error
similarly. handling procedures of [RFC4271].
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 6. Changes to RFC4271
[RFC4271] states "The value of the Length field MUST always be at [RFC4271] states "The value of the Length field MUST always be at
least 19 and no greater than 4,096." This document changes the least 19 and no greater than 4,096." This document changes the
latter number to 65,535 for all except the OPEN and KEEPALIVE latter number to 65,535 for all except the OPEN and KEEPALIVE
messages. messages.
[RFC4271] Sec 6.1, specifies raising an error if the length of a [RFC4271] Sec 6.1, specifies raising an error if the length of a
message is over 4,096 octets. For all messages except the OPEN message is over 4,096 octets. For all messages except the OPEN
message, if the receiver has advertised the BGP Extended Messages message, if the receiver has advertised the BGP Extended Messages
Capability, this document raises that limit to 65,535. Capability, this document raises that limit to 65,535.
7. IANA Considerations 7. IANA Considerations
The IANA has made an early allocation for this new BGP Extended The IANA has made an early allocation for this new BGP Extended
Message Capability referring to this document. Message Capability referring to this document.
Registry: BGP Capability Code Registry: Capability Codes
Value Description Document Value Description Document
----- ----------------------------------- ------------- ----- ----------------------------------- -------------
6 BGP-Extended Message [this draft] 6 BGP Extended Message [this draft]
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; see [RFC4272]. issues; [RFC4272].
Section 5 allows a receiver to accept an Extended Message even though
it had not advertised the capability. This slippery slope could 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 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, As this draft requires support for [RFC7606] UPDATE error handling,
it inherits the security considerations of [RFC7606]. BGP peers may it inherits the security considerations of [RFC7606].
avoid such issues by using Authenticated Encryption with additional
Data (AEAD) ciphers [RFC5116] and discard messages that do not
verify.
If a remote attacker is able to craft a large BGP Extended Message to If a remote attacker 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 produce a the outgoing message, see Section 4, and in doing so cause a
downgrade attack, e.g. convert BGPsec to BGP4. downgrade attack.
If a remote attacker is able to craft a large BGP Extended Message to If a remote attacker 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. Worse, [RFC7606] "treat-as-withdraw" may
consistently withdraw announcements causing inconsistent routing. consistently withdraw announcements causing inconsistent routing.
BGP routes are filtered by policies set by the operators.
Implementations may provide policies to filter routes that would
cause the "treat-as-withdraw" from being passed by an extended
message speaker.
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
[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", [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006, RFC 4272, DOI 10.17487/RFC4272, January 2006,
<http://www.rfc-editor.org/info/rfc4272>. <http://www.rfc-editor.org/info/rfc4272>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<http://www.rfc-editor.org/info/rfc5116>.
[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>.
10.2. Informative References 10.2. Informative References
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