draft-ietf-idr-bgp-extended-messages-32.txt   draft-ietf-idr-bgp-extended-messages-33.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 3, 2020 D. Ward
Cisco Systems Cisco Systems
July 2, 2019 July 2, 2019
Extended Message support for BGP Extended Message support for BGP
draft-ietf-idr-bgp-extended-messages-32 draft-ietf-idr-bgp-extended-messages-33
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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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 . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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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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 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 only if the Extended Message
Capability was advertised by both peers. Capability was advertised by both peers.
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.
If a BGP message with a Length lgreater 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 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 UPDATE will (policy, best path, etc., allowing) typically
throughout the BGP speaking Internet; and hence to BGP speakers which propagate throughout the BGP speaking Internet; and hence to BGP
may not have the Extended Message capability. 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 can not be decomposed to 4,096 octets or less may set plus the NLRI is larger than 4,096 octets may cause lack of
cause lack of reachability. reachability.
A BGP UPDATE will typically propagate throughout the BGP speaking
Internet; and hence to BGP speakers which may not support Extended
Messages. Therefore, a route announcement in an Extended Message
where the size of the attribute set plus the NLRI is larger than
4,096 octets or less may cause lack of 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 SHOULD 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 In an iBGP mesh, if BGP Extended Messages are to be advertized, all
peers MUST advertize the BGP Extended Message Capability and peers MUST advertize the BGP Extended Message capability. This is
[RFC7606]. This is not only for consistent internal routing, but not only for consistent internal routing, but also to give a
also to give a consistent view to eBGP peers. 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" and any discarded monitor any routes dropped and any discarded attributes.
attributes.
It is RECOMMENDED that BGP protocol developers and implementers are
conservative in their application and use of Extended Messages.
Future protocol specifications MUST describe how to handle peers
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, MUST NOT accept an Extended Message. A speaker to configuration, MUST NOT accept an Extended Message. A speaker
MUST 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 follow the error an improper Extended Message as a fatal error, MUST follow the error
handling procedures of [RFC4271]. handling procedures of [RFC4271].
It is RECOMMENDED that BGP protocol developers and implementers are
conservative in their application and use of Extended Messages.
Future protocol specifications MUST describe how to handle peers
which can only accommodate 4,096 octet messages.
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
 End of changes. 11 change blocks. 
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