draft-wang-lsr-flex-algo-link-loss-01.txt		draft-wang-lsr-flex-algo-link-loss-02.txt
	Network Working Group Y. Wang		Network Working Group Y. Wang
	Internet-Draft G. Xu		Internet-Draft G. Xu
	Intended status: Standards Track X. Geng		Intended status: Standards Track X. Geng
	Expires: 23 August 2024 J. Dong		Expires: 23 August 2024 J. Dong
	Huawei		Huawei
	20 February 2024		20 February 2024
	IGP Flexible Algorithm with Link Loss		IGP Flexible Algorithm with Link Loss
	draft-wang-lsr-flex-algo-link-loss-01		draft-wang-lsr-flex-algo-link-loss-02
	Abstract		Abstract
	IGP Flexible Algorithms allow IGPs to compute constraint-based paths.		IGP Flexible Algorithms allow IGPs to compute constraint-based paths.
	Since link packet loss rate plays an important role in network		Since link packet loss rate plays an important role in network
	evaluation, links with high packet loss rate should be bypassed		evaluation, links with high packet loss rate should be bypassed
	during forwarding. This draft proposes a path computation method		during forwarding. This draft proposes a path computation method
	based on a maximum link loss constraint to prune unsatisfied links in		based on a maximum link loss constraint to prune unsatisfied links in
	Flexible Algorithms.		Flexible Algorithms.
	skipping to change at page 2, line 22 ¶		skipping to change at page 2, line 22 ¶
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	and restrictions with respect to this document. Code Components		and restrictions with respect to this document. Code Components
	extracted from this document must include Revised BSD License text as		extracted from this document must include Revised BSD License text as
	described in Section 4.e of the Trust Legal Provisions and are		described in Section 4.e of the Trust Legal Provisions and are
	provided without warranty as described in the Revised BSD License.		provided without warranty as described in the Revised BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Exclude Maximum Link Loss Sub-TLV . . . . . . . . . . . . . . 4		2. Exclude Maximum Link Loss Sub-TLV . . . . . . . . . . . . . . 3
	2.1. IS-IS Exclude Maximum Link Loss Sub-TLV . . . . . . . . . 4		2.1. IS-IS Exclude Maximum Link Loss Sub-TLV . . . . . . . . . 4
	2.2. OSPF Exclude Maximum Link Loss Sub-TLV . . . . . . . . . 5		2.2. OSPF Exclude Maximum Link Loss Sub-TLV . . . . . . . . . 5
	3. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 6		3. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 5
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		4. Operational Considerations . . . . . . . . . . . . . . . . . 6
	4.1. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
			5.1. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition
	Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6		Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6
	4.2. OSPF Sub-Sub-TLVs for Flexible Algorithm Definition		5.2. OSPF Sub-Sub-TLVs for Flexible Algorithm Definition
	Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6		Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6
	5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6		6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
	5.1. Normative References . . . . . . . . . . . . . . . . . . 6		6.1. Normative References . . . . . . . . . . . . . . . . . . 6
	5.2. Informative References . . . . . . . . . . . . . . . . . 7		6.2. Informative References . . . . . . . . . . . . . . . . . 7
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Introduction		1. Introduction
	Link packet loss rate (link loss) is a measure of the percentage of		Link packet loss rate (link loss) is a measure of the percentage of
	data packets that are lost during transmission over a network. It is		data packets that are lost during transmission over a network. It is
	an important performance metric that directly impacts the quality of		an important performance metric that directly impacts the quality of
	service, network congestion, security, and overall network		service, network congestion, security, and overall network
	efficiency. Ensuring a low packet loss rate is essential for		efficiency. Ensuring a low packet loss rate is essential for
	maintaining efficient and secure network operations. Consequently,		maintaining efficient and secure network operations. Consequently,
	skipping to change at page 3, line 10 ¶		skipping to change at page 3, line 4 ¶
	efficiency. Ensuring a low packet loss rate is essential for		efficiency. Ensuring a low packet loss rate is essential for
	maintaining efficient and secure network operations. Consequently,		maintaining efficient and secure network operations. Consequently,
	It is necessary to avoid passing through links with a high packet		It is necessary to avoid passing through links with a high packet
	loss rate during forwarding.		loss rate during forwarding.
	The link loss is advertised by the Unidirectional Link Loss Sub-TLV		The link loss is advertised by the Unidirectional Link Loss Sub-TLV
	defined in [RFC8570] by IS-IS and [RFC7471] by OSPF, which describes		defined in [RFC8570] by IS-IS and [RFC7471] by OSPF, which describes
	the loss (as a packet percentage) between two directly connected IS-		the loss (as a packet percentage) between two directly connected IS-
	IS neighbors. This Sub-TLV is carried in the Application-Specific		IS neighbors. This Sub-TLV is carried in the Application-Specific
	Link Attributes Sub-TLV advertised by IS-IS [RFC9479] or OSPF		Link Attributes Sub-TLV advertised by IS-IS [RFC9479] or OSPF
	[RFC9492]. The link packet loss rate can be measured by methods such		[RFC9492]. The link packet loss rate can be measured by methods such
	as TWAMP [RFC5357] and STAMP [RFC8762], which is beyond the scope of		as TWAMP [RFC5357] and STAMP [RFC8762], which is beyond the scope of
	this draft.		this document.
	IGP Flexible Algorithms allow IGPs to compute constraint-based paths		IGP Flexible Algorithms allow IGPs to compute constraint-based paths
	[RFC9350]. Current path computation methods are based on calculating		[RFC9350]. Current path computation methods are based on calculating
	the minimum cost of the path from the source to the destination.		the minimum cost of the path from the source to the destination.
	Flex-Algorithm has already supported path computation with the IGP		Flex-Algorithm has already supported path computation with the IGP
	cost, the minimum link delay and the traffic-engineering metric.		cost, the minimum link delay and the traffic-engineering metric.
	[I-D.ietf-lsr-flex-algo-bw-con] defines a family of generic metrics		[I-D.ietf-lsr-flex-algo-bw-con] defines a family of generic metrics
	(e.g. bandwidth based metric type) and bandwidth related constraints		(e.g. bandwidth based metric type) and bandwidth related constraints
	to support path computation based on bandwidth. However, current		to support path computation based on bandwidth. However, current
	calculation types and metric types cannot support path computation		calculation types and metric types cannot support path computation
	based on link loss, since the cost of the path should be defined as		based on link loss, since the cost of the path should be defined as
	the maximum/minimum value among all passing links.		the maximum/minimum value among all passing links.
	To overcome the above issue, there are two solutions. First, new		To overcome the above issue, there are two solutions. First, new
	operators like maximum value operator can be defined, which works as		operators like maximum value operator can be defined, which works as
	a step function. When the link loss exceeds a threshold, the cost of		a step function. When the link loss exceeds a threshold, the cost of
	the link is set to the maximum. Second, new Flexible Algorithm		the link is set to the maximum. Second, new Flexible Algorithm
	Definition (FAD) constraints can be defined to exclude links that do		Definition (FAD) constraints can be defined to exclude links that do
	not meet the link loss requirements during path calculation. The		not meet the link loss requirements during path calculation. The
	second method is specifically demonstrated in this draft. The		second method is specifically demonstrated in this document. The
	general ideas are as below.		general ideas are as below.
	1. The link loss is used as a link constraint for path		1. The link loss is used as a link constraint for path
	computation. That is, the link whose loss rate is greater than		computation. That is, the link whose loss rate is greater than
	the specified value is excluded.		the specified value is excluded.
	2. Metric-type remains unchanged: igp, te, and delay.		2. Metric-type remains unchanged: igp, te, and delay.
	With a new FAD constraint Sub-TLV advertised by IGP, links with low		With a new FAD constraint Sub-TLV advertised by IGP, links with low
	packet loss rate will be selected for path computation. The new		packet loss rate will be selected for path computation. The new
	Exclude Maximum Link Loss Sub-TLVs are defined in Section 2. The		Exclude Maximum Link Loss Sub-TLVs are defined in Section 2. The
	Flex-Algorithm calculation method based on link loss is presented in		Flex-Algorithm calculation method based on link loss is presented in
	Section 3.		Section 3. Link packet loss rate is obtained from the existing
			Unidirectional Link Loss Sub-TLV defined in RFC9479 and RFC9492.
	2. Exclude Maximum Link Loss Sub-TLV		2. Exclude Maximum Link Loss Sub-TLV
	A new Exclude Maximum Link Loss Sub-TLV is defined as a sub-TLV of		A new Exclude Maximum Link Loss Sub-TLV is defined as a sub-TLV of
	the FAD TLV. To guarantee loop free forwarding, all routers that		the FAD TLV. To guarantee loop free forwarding, all routers that
	participate in a Flex-Algorithm MUST agree on the FAD. Selected		participate in a Flex-Algorithm MUST agree on the FAD. Selected
	nodes within the IGP domain MUST advertise FADs as described in		nodes within the IGP domain MUST advertise FADs as described in
	Sections 5, 6, and 7 of [RFC9350].		Sections 5, 6, and 7 of [RFC9350].
	The Exclude Maximum Link Loss Sub-TLV is proposed to specify the		The Exclude Maximum Link Loss Sub-TLV is proposed to specify the
	skipping to change at page 4, line 25 ¶		skipping to change at page 4, line 17 ¶
	TLV, all links with packet loss rate larger than the defined maximum		TLV, all links with packet loss rate larger than the defined maximum
	link loss value will be excluded from the Flex-Algorithm topology.		link loss value will be excluded from the Flex-Algorithm topology.
	2.1. IS-IS Exclude Maximum Link Loss Sub-TLV		2.1. IS-IS Exclude Maximum Link Loss Sub-TLV
	IS-IS Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a		IS-IS Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a
	sub-TLV of the IS-IS FAD sub-TLV. It has the following format:		sub-TLV of the IS-IS FAD sub-TLV. It has the following format:
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length |		| Type | Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Max Link Loss |		| Max Link Loss |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Type: 252(TBA)		Type: 252(TBA)
	Length: 3 octets		Length: 3 octets
	Max Link Loss: This 24-bit field carries link packet loss as a		Max Link Loss: This 24-bit field carries link packet loss as a
	percentage of the total traffic sent over a configurable interval.		percentage of the total traffic sent over a configurable interval.
	The basic unit is 0.000003%, where (2^24 - 2) is 50.331642%. This		The basic unit is 0.000003%, where (2^24 - 2) is 50.331642%. This
	value is the highest packet-loss percentage that can be expressed.		value is the highest packet-loss percentage that can be expressed.
	Therefore, measured values that are larger than the field maximum		Therefore, measured values that are larger than the field maximum
	skipping to change at page 5, line 25 ¶		skipping to change at page 5, line 12 ¶
	FAD contains the FAEML sub-TLV, then it MUST NOT be excluded from the		FAD contains the FAEML sub-TLV, then it MUST NOT be excluded from the
	Flex-Algorithm topology.		Flex-Algorithm topology.
	2.2. OSPF Exclude Maximum Link Loss Sub-TLV		2.2. OSPF Exclude Maximum Link Loss Sub-TLV
	OSPF Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a		OSPF Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a
	sub-TLV of the OSPF FAD sub-TLV. It has the following format:		sub-TLV of the OSPF FAD sub-TLV. It has the following format:
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length |		| Type | Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Max Link Loss |		| Max Link Loss |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Type: 252(TBA)		Type: 252(TBA)
	Length: 3 octets		Length: 3 octets
	Max Link Loss: This 24-bit field carries link packet loss as a		Max Link Loss: This 24-bit field carries link packet loss as a
	percentage of the total traffic sent over a configurable interval.		percentage of the total traffic sent over a configurable interval.
	The basic unit is 0.000003%, where (2^24 - 2) is 50.331642%. This		The basic unit is 0.000003%, where (2^24 - 2) is 50.331642%. This
	value is the highest packet-loss percentage that can be expressed.		value is the highest packet-loss percentage that can be expressed.
	Therefore, measured values that are larger than the field maximum		Therefore, measured values that are larger than the field maximum
	skipping to change at page 6, line 22 ¶		skipping to change at page 6, line 10 ¶
	A new rule is added to the rules used to prune links from the		A new rule is added to the rules used to prune links from the
	topology during the Flex-Algorithm computation in Section 13 of		topology during the Flex-Algorithm computation in Section 13 of
	[RFC9350].		[RFC9350].
	1. Check if any exclude FAEML rule is part of the Flex-Algorithm		1. Check if any exclude FAEML rule is part of the Flex-Algorithm
	definition. If such exclude rule exists and the link has link		definition. If such exclude rule exists and the link has link
	loss advertised, check if the link satisfies the FAEML rule. If		loss advertised, check if the link satisfies the FAEML rule. If
	not, the link MUST be pruned from the computation.		not, the link MUST be pruned from the computation.
	4. IANA Considerations		4. Operational Considerations
	4.1. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV		In some scenarios, the link packet loss rate may fluctuate around the
			threshold value. Consequently, the link status can be frequently
			changed between available and unavailable, which could lead to
			frequent flex-algo calculation. To solve this problem, a suppression
			mechanism can be developed. When the packet loss rate is detected on
			a frequent change, a timer can be set to delay the update process.
			5. IANA Considerations
			5.1. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
	Type: 252(TBA)		Type: 252(TBA)
	Description: IS-IS Exclude Maximum Link Loss Sub-TLV		Description: IS-IS Exclude Maximum Link Loss Sub-TLV
	Reference: This document Section 2.1		Reference: This document Section 2.1
	4.2. OSPF Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV		5.2. OSPF Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
	Type: 252(TBA)		Type: 252(TBA)
	Description: OSPF Exclude Maximum Link Loss Sub-TLV		Description: OSPF Exclude Maximum Link Loss Sub-TLV
	Reference: This document Section 2.2		Reference: This document Section 2.2
	5. References		6. References
	5.1. Normative References		6.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic		[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
	Engineering", RFC 5305, DOI 10.17487/RFC5305, October		Engineering", RFC 5305, DOI 10.17487/RFC5305, October
	2008, <https://www.rfc-editor.org/info/rfc5305>.		2008, <https://www.rfc-editor.org/info/rfc5305>.
	skipping to change at page 7, line 34 ¶		skipping to change at page 7, line 34 ¶
	[RFC9479] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and		[RFC9479] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
	J. Drake, "IS-IS Application-Specific Link Attributes",		J. Drake, "IS-IS Application-Specific Link Attributes",
	RFC 9479, DOI 10.17487/RFC9479, October 2023,		RFC 9479, DOI 10.17487/RFC9479, October 2023,
	<https://www.rfc-editor.org/info/rfc9479>.		<https://www.rfc-editor.org/info/rfc9479>.
	[RFC9492] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,		[RFC9492] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
	J., and J. Drake, "OSPF Application-Specific Link		J., and J. Drake, "OSPF Application-Specific Link
	Attributes", RFC 9492, DOI 10.17487/RFC9492, October 2023,		Attributes", RFC 9492, DOI 10.17487/RFC9492, October 2023,
	<https://www.rfc-editor.org/info/rfc9492>.		<https://www.rfc-editor.org/info/rfc9492>.
	5.2. Informative References		6.2. Informative References
	[I-D.ietf-lsr-flex-algo-bw-con]		[I-D.ietf-lsr-flex-algo-bw-con]
	Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak,		Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak,
	P., and T. Li, "Flexible Algorithms: Bandwidth, Delay,		P., and T. Li, "Flexible Algorithms: Bandwidth, Delay,
	Metrics and Constraints", Work in Progress, Internet-		Metrics and Constraints", Work in Progress, Internet-
	Draft, draft-ietf-lsr-flex-algo-bw-con-07, 26 September		Draft, draft-ietf-lsr-flex-algo-bw-con-07, 26 September
	2023, <https://datatracker.ietf.org/doc/html/draft-ietf-		2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
	lsr-flex-algo-bw-con-07>.		lsr-flex-algo-bw-con-07>.
	[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.		[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
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