rfc9747v1.txt		rfc9747.txt
	skipping to change at line 190 ¶		skipping to change at line 190 ¶
	BFD Echo packets sent from device A, the one-hop-away BFD peer device		BFD Echo packets sent from device A, the one-hop-away BFD peer device
	B immediately loops them back by normal IP forwarding. This allows		B immediately loops them back by normal IP forwarding. This allows
	device A to rapidly detect a connectivity loss to device B. Note		device A to rapidly detect a connectivity loss to device B. Note
	that device B would not intercept any received Unaffiliated BFD Echo		that device B would not intercept any received Unaffiliated BFD Echo
	packet or parse any BFD protocol field within the Unaffiliated BFD		packet or parse any BFD protocol field within the Unaffiliated BFD
	Echo packet.		Echo packet.
	An Unaffiliated BFD Echo session is not actually a BFD session		An Unaffiliated BFD Echo session is not actually a BFD session
	because there is no coordination of BFD protocol state between the		because there is no coordination of BFD protocol state between the
	two link ends: the remote end does not support BFD and so cannot		two link ends: the remote end does not support BFD and so cannot
	engage in a BFD session. The local end as an initiator may regard		engage in a BFD session. From the standpoint of the local end (as an
	the Unaffiliated BFD Echo session as a BFD session from its own		initiator), the Unaffiliated BFD Echo session may be regarded as a
	standpoint.		BFD session.
	For the Unaffiliated Echo procedure, an Unaffiliated BFD Echo session		For the Unaffiliated Echo procedure, an Unaffiliated BFD Echo session
	is established on device A. The session MUST adhere to the BFD state		is established on device A. The session MUST adhere to the BFD state
	machine specified in Section 6.2 of [RFC5880], with the exception		machine specified in Section 6.2 of [RFC5880], with the exception
	that the received state is not derived from BFD Control packets		that the received state is not derived from BFD Control packets
	originating from the remote system, but rather from packets that are		originating from the remote system, but rather from packets that are
	generated by the local system and looped back from the remote system.		generated by the local system and looped back from the remote system.
	Consequently, the AdminDown state is not utilized in Unaffiliated BFD		Consequently, the AdminDown state is not utilized in Unaffiliated BFD
	Echo.		Echo.
	BFD Control packets are transmitted and received as Unaffiliated BFD		BFD Control packets are transmitted and received as Unaffiliated BFD
	Echo packets, using UDP destination port 3785, as defined in		Echo packets, using UDP destination port 3785, as defined in
	[RFC5881]. The standard procedures for BFD Asynchronous sessions are		[RFC5881]. The standard procedures for BFD Asynchronous sessions are
	applied to the looped BFD Control packets, including packet		applied to the looped BFD Control packets, including packet
	validation and authentication, in accordance with [RFC5880].		validation and authentication, in accordance with [RFC5880].
	Once an Unaffiliated BFD Echo session is created on device A, it		Once an Unaffiliated BFD Echo session is created on device A, it
	starts sending Unaffiliated BFD Echo packets. Unaffiliated BFD Echo		starts sending Unaffiliated BFD Echo packets. Unaffiliated BFD Echo
	packets with zeroed "Your Discriminator" field are demultiplexed to		packets with zeroed "Your Discriminator" field are demultiplexed to
	the proper session based on the source IP address or UDP source port,		the proper session based on the source IP address or UDP source port.
	once the remote system loops back the local discriminator, all		After the remote system loops back the local discriminator, all
	further received packets are demultiplexed based on the "Your		further received packets are demultiplexed based on the "Your
	Discriminator" field only, which is conformed to the procedure		Discriminator" field only, which conforms to the procedure specified
	specified in Section 6.3 of [RFC5880]. An Unaffiliated BFD Echo		in Section 6.3 of [RFC5880]. An Unaffiliated BFD Echo packet follows
	packet follows the same encapsulation rules as for a BFD Echo packet		the same encapsulation rules as for a BFD Echo packet as specified in
	as specified in Section 4 of [RFC5881]. All Unaffiliated BFD Echo		Section 4 of [RFC5881]. All Unaffiliated BFD Echo packets for the
	packets for the session MUST be sent with a TTL or Hop Limit value of		session MUST be sent with a TTL or Hop Limit value of 255. Received
	255. Received packets MUST have a TTL or Hop Limit value of 254		packets MUST have a TTL or Hop Limit value of 254 (similar to
	(similar to Appendix A of [RFC5082] to verify against a configured		Appendix A of [RFC5082] to verify against a configured number of
	number of hops); otherwise, the received packets MUST be dropped.		hops); otherwise, the received packets MUST be dropped.
	In the context of an Unaffiliated BFD Echo packet, the "Desired Min		In the context of an Unaffiliated BFD Echo packet, the "Desired Min
	TX Interval" and "Required Min RX Interval" fields, as defined in		TX Interval" and "Required Min RX Interval" fields, as defined in
	[RFC5880], MUST be populated with a specific value to prevent the		[RFC5880], MUST be populated with a specific value to prevent the
	potential exposure of uninitialized memory. It is RECOMMENDED that		potential exposure of uninitialized memory. It is RECOMMENDED that
	these fields be set to a value of 1 second (1,000,000 microseconds).		these fields be set to a value of 1 second (1,000,000 microseconds).
	However, upon receipt, these values MUST be ignored and MUST NOT be		However, upon receipt, these values MUST be ignored and MUST NOT be
	used in the calculation of the Detection Time.		used in the calculation of the Detection Time.
	The "Required Min Echo RX Interval" field, as defined in [RFC5880],		The "Required Min Echo RX Interval" field, as defined in [RFC5880],
	skipping to change at line 252 ¶		skipping to change at line 252 ¶
	by default on hosts. The method for provisioning device B to loop		by default on hosts. The method for provisioning device B to loop
	back Unaffiliated BFD Echo packets is outside the scope of this		back Unaffiliated BFD Echo packets is outside the scope of this
	document.		document.
	Similar to what's specified in [RFC5880], the Unaffiliated BFD Echo		Similar to what's specified in [RFC5880], the Unaffiliated BFD Echo
	session begins with the periodic, slow transmission of Unaffiliated		session begins with the periodic, slow transmission of Unaffiliated
	BFD Echo packets. The slow transmission rate should be no greater		BFD Echo packets. The slow transmission rate should be no greater
	than one packet per second, until the session on device A is Up.		than one packet per second, until the session on device A is Up.
	After the session is Up, the provisioned transmission interval is		After the session is Up, the provisioned transmission interval is
	used. When the Unaffiliated BFD Echo session on device A goes Down,		used. When the Unaffiliated BFD Echo session on device A goes Down,
	the slow transmission rate is resumed. The "Detect Mult" defined in		the slow transmission rate is resumed. The "Detect Mult" field
	[RFC5880] MUST be set to a value provisioned on device A. When the		defined in [RFC5880] MUST be set to a value provisioned on device A.
	bfd.SessionState is Up and a "Detect Mult" number of Unaffiliated BFD		When the bfd.SessionState is Up and a "Detect Mult" number of
	Echo packets have not arrived at device A as they should, the device		Unaffiliated BFD Echo packets have not arrived at device A as they
	A "MUST set bfd.SessionState to Down and bfd.LocalDiag to 2 (Echo		should, the device A "MUST set bfd.SessionState to Down and
	Function Failed)", as specified in Section 6.8.5 of [RFC5880].		bfd.LocalDiag to 2 (Echo Function Failed)", as specified in
			Section 6.8.5 of [RFC5880].
	In summary, the Unaffiliated BFD Echo packet reuses the format of the		In summary, the Unaffiliated BFD Echo packet reuses the format of the
	BFD Control packet defined in [RFC5880], and the fields within the		BFD Control packet defined in [RFC5880], and the fields within the
	Unaffiliated BFD Echo packet are populated as follows:		Unaffiliated BFD Echo packet are populated as follows:
	* My Discriminator: MUST be set to the provisioned local		* My Discriminator: MUST be set to the provisioned local
	discriminator.		discriminator.
	* Your Discriminator: MUST initially be set to 0, and then MUST be		* Your Discriminator: MUST initially be set to 0, and then MUST be
	set to the value of "My Discriminator" looped back from the remote		set to the value of "My Discriminator" looped back from the remote
	skipping to change at line 418 ¶		skipping to change at line 419 ¶
	The 1st and 2nd paragraphs of Section 6.8.9 of [RFC5880] are updated		The 1st and 2nd paragraphs of Section 6.8.9 of [RFC5880] are updated
	as below:		as below:
	OLD TEXT		OLD TEXT
	| BFD Echo packets MUST NOT be transmitted when bfd.SessionState is		| BFD Echo packets MUST NOT be transmitted when bfd.SessionState is
	| not Up. BFD Echo packets MUST NOT be transmitted unless the last		| not Up. BFD Echo packets MUST NOT be transmitted unless the last
	| BFD Control packet received from the remote system contains a		| BFD Control packet received from the remote system contains a
	| nonzero value in Required Min Echo RX Interval.		| nonzero value in Required Min Echo RX Interval.
			|
			| BFD Echo packets MAY be transmitted when bfd.SessionState is Up.
			| The interval between transmitted BFD Echo packets MUST NOT be less
			| than the value advertised by the remote system in Required Min
			| Echo RX Interval, except as follows: [...]
	NEW TEXT		NEW TEXT
	| When a system is using the Echo function with either Asynchronous		| When a system is using the Echo function with either Asynchronous
	| or Demand mode, BFD Echo packets MUST NOT be transmitted when		| or Demand mode, BFD Echo packets MUST NOT be transmitted when
	| bfd.SessionState is not Up, and BFD Echo packets MUST NOT be		| bfd.SessionState is not Up, and BFD Echo packets MUST NOT be
	| transmitted unless the last BFD Control packet received from the		| transmitted unless the last BFD Control packet received from the
	| remote system contains a nonzero value in Required Min Echo RX		| remote system contains a nonzero value in Required Min Echo RX
	| Interval.		| Interval.
			|
	OLD TEXT
	| BFD Echo packets MAY be transmitted when bfd.SessionState is Up.
	| The interval between transmitted BFD Echo packets MUST NOT be less
	| than the value advertised by the remote system in Required Min
	| Echo RX Interval...
	NEW TEXT
	| When a system is using the Echo function with either Asynchronous		| When a system is using the Echo function with either Asynchronous
	| or Demand mode, BFD Echo packets MAY be transmitted when		| or Demand mode, BFD Echo packets MAY be transmitted when
	| bfd.SessionState is Up, and the interval between transmitted BFD		| bfd.SessionState is Up, and the interval between transmitted BFD
	| Echo packets MUST NOT be less than the value advertised by the		| Echo packets MUST NOT be less than the value advertised by the
	| remote system in Required Min Echo RX Interval...		| remote system in Required Min Echo RX Interval, except as follows:
			| [...]
	4. Operational Considerations		4. Operational Considerations
	All operational considerations from [RFC5880] apply. Since this		All operational considerations from [RFC5880] apply. Since this
	mechanism leverages existing BFD machinery, particularly periodic		mechanism leverages existing BFD machinery, particularly periodic
	pacing of traffic based on configuration, there's no real possibility		pacing of traffic based on configuration, there's no real possibility
	to create congestion. Moreover, creating congestion would be		to create congestion. Moreover, creating congestion would be
	counterproductive to check the bidirectional connectivity.		counterproductive to checking the bidirectional connectivity.
	Some devices that would benefit from the use of BFD may be unable to		Some devices that would benefit from the use of BFD may be unable to
	support the full BFD protocol. Examples of such devices include		support the full BFD protocol. Examples of such devices include
	servers running virtual machines, or Internet of Things (IoT)		servers running virtual machines, or Internet of Things (IoT)
	devices. By using Unaffiliated BFD Echo, these devices only need to		devices. By using Unaffiliated BFD Echo, these devices only need to
	support a basic loopback function.		support a basic loopback function.
	As specified in Section 2 of this document, some configuration is		As specified in Section 2 of this document, some configuration is
	needed to make the Unaffiliated BFD Echo work, although the		needed to make the Unaffiliated BFD Echo work, although the
	configuration won't go beyond the scope of [RFC5880]. At a BFD-		configuration won't go beyond the scope of [RFC5880]. At a BFD-
	enabled local system, the Unaffiliated BFD Echo session can coexist		enabled local system, the Unaffiliated BFD Echo session can coexist
	with another type of BFD session. In that scenario, the remote		with other types of BFD sessions. In that scenario, the remote
	system for the Unaffiliated BFD Echo session must be different from		system for the Unaffiliated BFD Echo session must be different from
	the remote system for the other type of BFD session, and the local		the remote system for any other type of BFD session, and the local
	system's discriminators for different BFD sessions must be different.		system's discriminators for different BFD sessions must be different.
	At the same time, it's not necessary for the local system to		At the same time, it's not necessary for the local system to
	differentiate the Unaffiliated BFD Echo session from the other type		differentiate the Unaffiliated BFD Echo session from the other types
	of BFD session.		of BFD sessions.
	5. Security Considerations		5. Security Considerations
	All security considerations from [RFC5880] and [RFC5881] apply.		All security considerations from [RFC5880] and [RFC5881] apply.
	Unaffiliated BFD Echo requires the remote device to loop Unaffiliated		Unaffiliated BFD Echo requires the remote device to loop Unaffiliated
	BFD Echo packets. In order to provide this service, the remote		BFD Echo packets. In order to provide this service, the remote
	device cannot make use of Unicast Strict Reverse Path Forwarding		device cannot make use of Unicast Strict Reverse Path Forwarding
	(RPF) [RFC3704], otherwise the Unaffiliated BFD Echo packets might		(RPF) [RFC3704], otherwise the Unaffiliated BFD Echo packets might
	not pass the RPF check at the remote device.		not pass the RPF check at the remote device.
	skipping to change at line 524 ¶		skipping to change at line 522 ¶
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	7.2. Informative References		7.2. Informative References
	[BBF-TR-146]		[BBF-TR-146]
	Broadband Forum, "TR-146: Subscriber Sessions", Broadband		Broadband Forum, "TR-146: Subscriber Sessions", Broadband
	Forum Technical Report, TR-146, Issue 1, May 2013,		Forum Technical Report, TR-146, Issue 1, May 2013,
	<https://www.broadband-forum.org/technical/download/TR-		<https://www.broadband-forum.org/pdfs/tr-146-1-0-0.pdf>.
	146.pdf>.
	[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed		[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
	Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March		Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
	2004, <https://www.rfc-editor.org/info/rfc3704>.		2004, <https://www.rfc-editor.org/info/rfc3704>.
	[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.		[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
	Pignataro, "The Generalized TTL Security Mechanism		Pignataro, "The Generalized TTL Security Mechanism
	(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,		(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
	<https://www.rfc-editor.org/info/rfc5082>.		<https://www.rfc-editor.org/info/rfc5082>.
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