rfc9687v2.txt		rfc9687.txt
	Internet Engineering Task Force (IETF) J. Snijders		Internet Engineering Task Force (IETF) J. Snijders
	Request for Comments: 9687 Fastly		Request for Comments: 9687 Fastly
	Updates: 4271 B. Cartwright-Cox		Updates: 4271 B. Cartwright-Cox
	Category: Standards Track Port 179		Category: Standards Track Port 179
	ISSN: 2070-1721 Y. Qu		ISSN: 2070-1721 Y. Qu
	Futurewei		Futurewei
	October 2024		November 2024
	Border Gateway Protocol 4 (BGP-4) Send Hold Timer		Border Gateway Protocol 4 (BGP-4) Send Hold Timer
	Abstract		Abstract
	This document defines the SendHoldTimer, along with the		This document defines the SendHoldTimer, along with the
	SendHoldTimer_Expires event, for the Border Gateway Protocol (BGP)		SendHoldTimer_Expires event, for the Border Gateway Protocol (BGP)
	Finite State Machine (FSM). Implementation of the SendHoldTimer		Finite State Machine (FSM). Implementation of the SendHoldTimer
	helps overcome situations where a BGP connection is not terminated		helps overcome situations where a BGP connection is not terminated
	after the local system detects that the remote system is not		after the local system detects that the remote system is not
	skipping to change at line 119 ¶		skipping to change at line 119 ¶
	In implementations lacking the concept of a SendHoldTimer, a		In implementations lacking the concept of a SendHoldTimer, a
	malfunctioning or overwhelmed remote speaker may cause data on the		malfunctioning or overwhelmed remote speaker may cause data on the
	BGP socket in the local system to accumulate ad infinitum. This		BGP socket in the local system to accumulate ad infinitum. This
	could result in forwarding failure and traffic loss, as the		could result in forwarding failure and traffic loss, as the
	overwhelmed speaker continues to utilize stale routes.		overwhelmed speaker continues to utilize stale routes.
	An example fault state: as BGP runs over TCP [RFC9293], it is		An example fault state: as BGP runs over TCP [RFC9293], it is
	possible for a BGP speaker in the Established state to encounter a		possible for a BGP speaker in the Established state to encounter a
	BGP speaker that is advertising a TCP Receive Window (RCV.WND) of		BGP speaker that is advertising a TCP Receive Window (RCV.WND) of
	size zero. This 0 window prevents the local system from sending		size zero. The size zero of this window prevents the local system
	KEEPALIVE, UPDATE, or any other critical BGP messages across the		from sending KEEPALIVE, UPDATE, or any other critical BGP messages
	network socket to the remote speaker.		across the network socket to the remote speaker.
	Generally BGP implementations have no visibility into lower-layer		Generally BGP implementations have no visibility into lower-layer
	subsystems such as TCP or the speaker's current Receive Window size,		subsystems such as TCP or the speaker's current Receive Window size,
	and there is no existing BGP mechanism for such a blocked connection		and there is no existing BGP mechanism for such a blocked connection
	to be recognized. Hence BGP implementations are not able to handle		to be recognized. Hence BGP implementations are not able to handle
	this situation in a consistent fashion.		this situation in a consistent fashion.
	The primary issue that arises when a BGP speaker is unable to send a		The primary issue that arises when a BGP speaker is unable to send a
	BGP message to a remote speaker is that the affected speaker may end		BGP message to a remote speaker is that the affected speaker may end
	up operating with outdated routing information. Failure of the BGP		up operating with outdated routing information. Failure of the BGP
End of changes. 2 change blocks.
	4 lines changed or deleted		4 lines changed or added
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