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.
	skipping to change at page 1, line 46 ¶		skipping to change at page 1, line 46 ¶
	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
	skipping to change at page 2, line 33 ¶		skipping to change at page 2, line 33 ¶
	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
	skipping to change at page 3, line 7 ¶		skipping to change at page 3, line 7 ¶
	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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