draft-ietf-idr-bgp-extended-messages-34.txt   draft-ietf-idr-bgp-extended-messages-35.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 31, 2020 D. Ward Expires: February 1, 2020 D. Ward
Cisco Systems Cisco Systems
July 30, 2019 July 31, 2019
Extended Message support for BGP Extended Message support for BGP
draft-ietf-idr-bgp-extended-messages-34 draft-ietf-idr-bgp-extended-messages-35
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 31, 2020. This Internet-Draft will expire on February 1, 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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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] The BGP Extended Message Capability is a new BGP Capability [RFC5492]
defined with Capability code 6 and Capability length 0. 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 receive and properly handle, see
handle, see Section 4, BGP Extended Messages. Section 4, 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.
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 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 receiving BGP Extended Messages
Messages SHOULD advertise the BGP Extended Message Capability to its SHOULD advertise the BGP Extended Message Capability to its peers
peers using BGP Capabilities Advertisement [RFC5492]. A BGP speaker using BGP Capabilities Advertisement [RFC5492]. A BGP speaker MAY
MAY send Extended Messages to a peer if the Extended Message send Extended Messages to a peer only if the Extended Message
Capability was received from that peer. 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.
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Capability, the listener will generate a NOTIFICATION with the Error Capability, the listener will generate a NOTIFICATION with the Error
Subcode set to Bad Message Length ([RFC4271] Sec 6.1). Subcode set to Bad Message Length ([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 that has advertised the BGP Extended Message capability
the BGP Extended Message capability and some which have not, may to its peers, may receive an UPDATE from one of its peers that
receive an UPDATE from one of its capable peers that produces an produces an ongoing announcement that is larger than 4,096 octets.
ongoing announcement that is larger than 4,096 octets. When When propagating that UPDATE onward to a neighbor which has not
propagating that UPDATE onward to a neighbor which has not advertised advertised the BGP Extended Message capability, the speaker SHOULD
the BGP Extended Message capability, the sender SHOULD try to reduce try to reduce the outgoing message size by removing attributes
the outgoing message size by removing attributes eligible under the eligible under the "attribute discard" approach of [RFC7606]. If the
"attribute discard" approach of [RFC7606]. If the message is still message is still too big, then it must not be sent to the neighbor
too big, then it must not be sent to the neighbor ([RFC4271], ([RFC4271], Section 9.2). Additionally, if the NLRI was previously
Section 9.2). Additionally, if the NLRI was previously advertised to advertised to that peer, it must be withdrawn from service
that peer, it must be withdrawn from service ([RFC4271], ([RFC4271], Section 9.1.3).
Section 9.1.3).
If an Autonomous System (AS) has multiple internal BGP speakers and If an Autonomous System (AS) has multiple internal BGP speakers and
also has multiple external BGP neighbors, to present a consistent also has multiple external BGP neighbors, to present a consistent
external view care must be taken to ensure a consistent view within external view care must be taken to ensure a consistent view within
the AS. In the context of BGP Extended Messages, a consistent view the AS. In the context of BGP Extended Messages, a consistent view
can only be guaranteed if all the iBGP speakers advertise the BGP can only be guaranteed if all the iBGP speakers advertise the BGP
Extended Message capability. If that is not the case, then the Extended Message capability. If that is not the case, then the
operator should consider whether the BGP Extended Message capability operator should consider whether the BGP Extended Message capability
should be advertised to external peers or not. should be advertised to external peers or not.
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