Network Working Group Y. Wang Internet-Draft G. Xu Intended status: Standards Track X. Geng Expires: 26 December 2024 J. Dong Huawei P. Psenak Cisco Systems 24 June 2024 IGP Flexible Algorithm with Link Loss draft-wang-lsr-flex-algo-link-loss-03 Abstract IGP Flexible Algorithms allow IGPs to compute constraint-based paths. Since link packet loss rate plays an important role in network evaluation, links with high packet loss rate should be bypassed during forwarding. This draft proposes a path computation method based on a maximum link loss constraint to prune unsatisfied links in Flexible Algorithms. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 26 December 2024. Wang, et al. Expires 26 December 2024 [Page 1] Internet-Draft IGP Flex-Algorithm with Link Loss June 2024 Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Exclude Maximum Link Loss Sub-TLV . . . . . . . . . . . . . . 3 2.1. IS-IS Exclude Maximum Link Loss Sub-TLV . . . . . . . . . 4 2.2. OSPF Exclude Maximum Link Loss Sub-TLV . . . . . . . . . 5 3. Calculation of Flexible Algorithm Paths . . . . . . . . . . . 5 4. Operational Considerations . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5.1. IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. OSPF Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1. Normative References . . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction 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 an important performance metric that directly impacts the quality of service, network congestion, security, and overall network efficiency. Ensuring a low packet loss rate is essential for maintaining efficient and secure network operations. Consequently, It is necessary to avoid passing through links with a high packet loss rate during forwarding. The link loss is advertised by the Unidirectional Link Loss Sub-TLV defined in [RFC8570] by IS-IS and [RFC7471] by OSPF, which describes the loss (as a packet percentage) between two directly connected IS- IS neighbors. This Sub-TLV is carried in the Application-Specific Link Attributes Sub-TLV advertised by IS-IS [RFC9479] or OSPF Wang, et al. Expires 26 December 2024 [Page 2] Internet-Draft IGP Flex-Algorithm with Link Loss June 2024 [RFC9492]. The link packet loss rate can be measured by methods such as TWAMP [RFC5357] and STAMP [RFC8762], which is beyond the scope of this document. The link-loss measurement should be consistent in the IGP routing domain. IGP Flexible Algorithms allow IGPs to compute constraint-based paths [RFC9350]. Current path computation methods are based on calculating the minimum cost of the path from the source to the destination. Flex-Algorithm has already supported path computation with the IGP cost, the minimum link delay and the traffic-engineering metric. [I-D.ietf-lsr-flex-algo-bw-con] defines a family of generic metrics (e.g. bandwidth based metric type) and bandwidth related constraints to support path computation based on bandwidth. However, current calculation types and metric types cannot support path computation based on link loss, since the cost of the path should be defined as the maximum/minimum value among all passing links. To overcome the above issue, there are two solutions. First, new operators like maximum value operator can be defined, which works as a step function. When the link loss exceeds a threshold, the cost of the link is set to the maximum. Second, new Flexible Algorithm Definition (FAD) constraints can be defined to exclude links that do not meet the link loss requirements during path calculation. The second method is specifically demonstrated in this document. The general ideas are as below. 1. The link loss is used as a link constraint for path computation. That is, the link whose loss rate is greater than the specified value is excluded. 2. Metric-type remains unchanged: igp, te, and delay. With a new FAD constraint Sub-TLV advertised by IGP, links with low packet loss rate will be selected for path computation. The new Exclude Maximum Link Loss Sub-TLVs are defined in Section 2. The Flex-Algorithm calculation method based on link loss is presented in 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 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 participate in a Flex-Algorithm MUST agree on the FAD. Selected nodes within the IGP domain MUST advertise FADs as described in Sections 5, 6, and 7 of [RFC9350]. Wang, et al. Expires 26 December 2024 [Page 3] Internet-Draft IGP Flex-Algorithm with Link Loss June 2024 The Exclude Maximum Link Loss Sub-TLV is proposed to specify the upper limit of the link loss. When this Sub-TLV is carried in a FAD TLV, all links with packet loss rate larger than the defined maximum link loss value will be excluded from the Flex-Algorithm topology. 2.1. IS-IS Exclude Maximum Link Loss Sub-TLV 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: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Max Link Loss | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 252(TBA) Length: 3 octets Max Link Loss: This 24-bit field carries link packet loss as a percentage of the total traffic sent over a configurable interval. 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. Therefore, measured values that are larger than the field maximum SHOULD be encoded as the maximum value. Figure 1: IS-IS FAEML Sub-TLV The FAEML sub-TLV MUST appear at most once in the FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the receiver. The maximum link loss advertised in FAEML Sub-TLV MUST be compared with the link loss advertised in Sub-Sub-TLV 36 [RFC8570] of ASLA Sub- TLV [RFC9479]. If L-Flag is set in the ASLA sub-TLV, the maximum link loss advertised in FAEML sub-TLV MUST be compared with the link loss advertised by the sub-TLV 36 of the TLV 22/222/23/223/141 [RFC5305] as defined in [RFC9479] Section 4.2. If the link loss is larger than the maximum link loss advertised in FAEML sub-TLV, the link MUST be excluded from the Flex-Algorithm topology. If a link does not have the link loss advertised but the FAD contains the FAEML sub-TLV, then it MUST NOT be excluded from the Flex-Algorithm topology. Wang, et al. Expires 26 December 2024 [Page 4] Internet-Draft IGP Flex-Algorithm with Link Loss June 2024 2.2. OSPF Exclude Maximum Link Loss Sub-TLV 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: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Max Link Loss | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: 252(TBA) Length: 3 octets Max Link Loss: This 24-bit field carries link packet loss as a percentage of the total traffic sent over a configurable interval. 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. Therefore, measured values that are larger than the field maximum SHOULD be encoded as the maximum value. Figure 2: OSPF FAEML Sub-TLV The FAEML sub-TLV MUST appear at most once in the FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the receiver. The maximum link loss advertised in FAEML Sub-TLV MUST be compared with the link loss advertised in Sub-Sub-TLV 30 [RFC7471] of ASLA Sub- TLV [RFC9492]. The ASLA Sub-TLV is advertised in Extended Link Opaque LSAs [RFC7684] for OSPFv2 and E-Router-LSAs [RFC8362] for OSPFv3. If the link loss is larger than the maximum link loss advertised in FAEML sub-TLV, the link MUST be excluded from the Flex-Algorithm topology. If a link does not have the link loss advertised but the FAD contains the FAEML sub-TLV, then it MUST NOT be excluded from the Flex-Algorithm topology. 3. Calculation of Flexible Algorithm Paths A new rule is added to the rules used to prune links from the topology during the Flex-Algorithm computation in Section 13 of [RFC9350]. Wang, et al. Expires 26 December 2024 [Page 5] Internet-Draft IGP Flex-Algorithm with Link Loss June 2024 1. Check if any exclude FAEML rule is part of the Flex-Algorithm definition. If such exclude rule exists and the link has link loss advertised, check if the link satisfies the FAEML rule. If not, the link MUST be pruned from the computation. 4. Operational Considerations In some scenarios, the link status can be frequently changed between available and unavailable since the link packet loss rate may fluctuate around the threshold value. Consequently, flex-algo calculation may be triggered frequently. There are a few mechanisms to solve this problem. 1. Delayed collection: IGP advertised loss could be calculated on an interval which is long enough, such as 10 minutes. 2. Averaging and normalization: IGP advertised loss should be some form of average (e.g. exponential weighted average) from the collected loss values and the advertised loss can be normalized to avoid advertising non-significant changes in loss. 3. Flapping suppression: When the IGP advertised loss 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) Description: IS-IS Exclude Maximum Link Loss Sub-TLV Reference: This document Section 2.1 5.2. OSPF Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV Type: 252(TBA) Description: OSPF Exclude Maximum Link Loss Sub-TLV Reference: This document Section 2.2 6. References 6.1. Normative References Wang, et al. Expires 26 December 2024 [Page 6] Internet-Draft IGP Flex-Algorithm with Link Loss June 2024 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008, . [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and F. Baker, "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 2018, . [RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K., and A. Gulko, "IGP Flexible Algorithm", RFC 9350, DOI 10.17487/RFC9350, February 2023, . [RFC9479] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and J. Drake, "IS-IS Application-Specific Link Attributes", RFC 9479, DOI 10.17487/RFC9479, October 2023, . [RFC9492] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura, J., and J. Drake, "OSPF Application-Specific Link Attributes", RFC 9492, DOI 10.17487/RFC9492, October 2023, . 6.2. Informative References [I-D.ietf-lsr-flex-algo-bw-con] Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak, P., and T. Li, "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints", Work in Progress, Internet- Draft, draft-ietf-lsr-flex-algo-bw-con-12, 19 May 2024, . Wang, et al. Expires 26 December 2024 [Page 7] Internet-Draft IGP Flex-Algorithm with Link Loss June 2024 [RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)", RFC 5357, DOI 10.17487/RFC5357, October 2008, . [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. Previdi, "OSPF Traffic Engineering (TE) Metric Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, . [RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March 2019, . [RFC8762] Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple Two-Way Active Measurement Protocol", RFC 8762, DOI 10.17487/RFC8762, March 2020, . Authors' Addresses Yifan Wang Huawei Huawei Bld., No. 156 Beiqing Rd. Beijing 100095 China Email: wangyifan82@huawei.com Guoqi Xu Huawei Email: xuguoqi@huawei.com Xuesong Geng Huawei Email: gengxuesong@huawei.com Jie Dong Huawei Email: jie.dong@huawei.com Peter Psenak Cisco Systems Wang, et al. Expires 26 December 2024 [Page 8] Internet-Draft IGP Flex-Algorithm with Link Loss June 2024 Email: ppsenak@cisco.com Wang, et al. Expires 26 December 2024 [Page 9]