SPRING Working Group Y. Liu Internet Draft China Mobile Intended status: Standards Track C. Lin Expires: October 30, 2024 New H3C Technologies Y. Qiu New H3C Technologies April 29, 2024 Measurement Method for Bandwidth of SRv6 Forwarding Path draft-liu-spring-srv6-bandwidth-measurement-00 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), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." 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Expires October, 2024 [Page 1] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Abstract This document proposes a method for measuring the actual bandwidth of SRv6 forwarding paths. Carrying the bandwidth information from bottleneck nodes along the packet path in the IPv6 extension header of data packets or active measurement packets, the head node and controller can obtain the actual minimum available bandwidth of the forwarding path in real-time. Table of Contents 1. Introduction ................................................ 3 2. Terminology ................................................. 3 3. Bandwidth Measurement Operation ............................. 4 3.1. The Processing Flow of Head Node ....................... 4 3.2. The Processing Flow of intermediate Node ............... 5 3.3. The Processing Flow of Egress Node ..................... 5 4. Definition of Minimum Available Bandwidth Option ............ 6 5. Definition of Minimum Available Bandwidth TLV ............... 7 6. Usecases of Bandwidth Measurement ........................... 7 7. IANA Considerations ......................................... 9 7.1. Destination Options and Hop-by-Hop Options Registry .... 9 7.2. Segment Routing Header TLVs Registry ................... 9 7.3. STAMP TLV Types Registry ............................... 9 8. Security Considerations ..................................... 9 9. References ................................................. 10 9.1. Normative References .................................. 10 9.2. Informative References ................................ 10 10. Acknowledgments ........................................... 10 Authors' Addresses ............................................ 11 Liu, et al. Expires October, 2024 [Page 2] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 1. Introduction Segment routing (SR) [RFC8402] is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node. The ingress node steers packets into a specific path according to the Segment Routing Policy (SR Policy) as defined in [RFC9256]. An SR Policy may have multiple candidate paths that are provisioned on the head node. Only the active candidate path MUST be used for forwarding traffic that is being steered onto that policy except for certain scenarios such as fast reroute where a backup candidate path may be used. A candidate path can be represented as a segment list or a set of segment lists. If a set of segment lists is associated with the active path of the policy, then the steering is per flow and weighted-ECMP (W-ECMP) based according to the relative weight of each valid segment list. Due to the different services carried by each node on the segment list path, and the differences in device forwarding capabilities, certain nodes on the forwarding path may experience traffic congestion when the network traffic is high. The actual maximum forwarding traffic of this path will become smaller than expected. Once this situation occurs, if the head node does not adjust the forwarding path in a timely manner and continues to forward to the SR policy path according to the initial preset bandwidth, it will inevitably cause packet loss beyond the bandwidth. To solve this problem, this document proposes a method for measuring the actual bandwidth of SRv6 forwarding paths. Carrying the bandwidth information from bottleneck nodes along the packet path in the IPv6 extension header of data packets or active performance measurement packets, the head node and controller can obtain the actual minimum available bandwidth of the forwarding path in real- time. When the actual available bandwidth or remaining bandwidth of the forwarding path does not meet the forwarding quality requirements, the controller or head node can quickly perceive and select a new path for the service traffic. 2. Terminology The definitions of the basic terms are identical to those found in Segment Routing Policy Architecture [RFC9256] and Simple Two-Way Active Measurement Protocol [RFC8762]. Liu, et al. Expires October, 2024 [Page 3] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 3. Bandwidth Measurement Operation Add Minimum Available Bandwidth Option for IPv6 extension headers to carry the minimum bandwidth information of the SRv6 forwarding path. The format of Minimum Available Bandwidth Option is detailed in Section 4. This minimum bandwidth information is carried over IPv6 extension header in a compare-and-replace manner across network devices along the path. When the egress node receives the message carrying bandwidth information, it parses the bandwidth field to obtain the actual minimum available bandwidth of the path. If it is an active measurement message of RTT, the egress node can reflect the head node of the minimum available bandwidth in the reflection packet of active performance measurement. Otherwise, the measurement results can also be reported to the controller. 3.1. The Processing Flow of Head Node The head node needs to add SRv6 encapsulation to the data packets forwarded through the SR policy path or the active performance measurement packets of the SR policy path. After enabling the bandwidth measurement function, the head node needs to add an IPv6 extension header with the Minimum Available Bandwidth Option when encapsulating SRv6 header. Initially, the head node fills in the minimum available bandwidth field as the minimum available bandwidth of the path on the head node. The Minimum Available Bandwidth Option can be encapsulated in the Hop-by-Hop Options header (HBH), in the Destination Options header (DoH), or in the SRH TLV. The specific encapsulation position is determined based on measurement requirements. If the minimum available bandwidth of all IPv6 nodes passing through needs to be measured, the head node should encapsulate the Minimum Available Bandwidth Option in HBH. If only the minimum bandwidth of each segment node on the SRv6 path needs to be measured, it is recommended to encapsulate the Minimum Available Bandwidth Option in DOH or in SRH TLV. Liu, et al. Expires October, 2024 [Page 4] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 3.2. The Processing Flow of intermediate Node After receiving the packet, the intermediate node parses the bandwidth value carried in IPv6 extension header and compares it with the actual bandwidth supported locally. If the local available bandwidth is smaller than the bandwidth value carried in the option, replace the bandwidth value in the option with the local available bandwidth. If the local available bandwidth is greater than or equal to the bandwidth value carried in the packet, the bandwidth value in the packet will not be modified. Afterwards, send the message to the next node according to the updated IPv6 packet. 3.3. The Processing Flow of Egress Node After the egress node receives the packet, before removing the SRv6 encapsulation, it needs to first parses the bandwidth value carried in the IPv6 extension header and compare it with the actual bandwidth supported locally. If the local available bandwidth is smaller than the bandwidth carried in the message, the local available bandwidth is used as the minimum available bandwidth for the SRv6 forwarding path. Otherwise, the minimum available bandwidth of the SRv6 forwarding path is the value obtained from the packet. After obtaining the minimum available bandwidth of the path, the egress node also needs to reflect the measurement results. There are following reflect methods: 1) The measurement results are reported to the controller through Netconf or gRPC. 2) If it is an active measurement message of RTT, the egress node needs to send reflection packets to the head node. So, extend the active measurement response message and carry the actual bandwidth obtained in the reflection packet. For example, when measuring the performance of SRv6 paths through STAMP testing, extend the STAMP TLV (see Section 5) and bring back the bandwidth of the forward path in the TLV. 3) Customize an IP packet that carries the measured bandwidth information and sends it to the head node. The encapsulation format of the reflection packet is outside the scope of this document. Liu, et al. Expires October, 2024 [Page 5] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 4. Definition of Minimum Available Bandwidth Option Minimum Available Bandwidth Option in the Hop-by-Hop Options Header and Destination Options Header is defined to carry the actual minimum available bandwidth of the SRv6 forwarding path. The encapsulation format in DOH and HBH is as follows. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Opt Data Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Minimum available bandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Minimum Available Bandwidth Option where: - Option Type: 8-bit identifier of the type. The encoding format references Section 4.2 of [RFC8200]. The value is to be assigned by IANA. - Opt Data Len: The length of the Option Data Fields of this option in bytes. - Minimum available bandwidth: 4-octet unsigned integer. The field is used to carry the minimum bandwidth value. The Minimum Available Bandwidth Option also can be encapsulated in the SRH TLV. The encapsulation format in SRH TLV is as follows. 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 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Minimum available bandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Minimum Available Bandwidth TLV Where: - Type: TBA - Length: 4 - Minimum available bandwidth: 4-octet unsigned integer. The field is used to carry the minimum bandwidth value. - Reserved: 16 bits. MUST be 0 on transmission. Liu, et al. Expires October, 2024 [Page 6] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 5. Definition of Minimum Available Bandwidth TLV Minimum Available Bandwidth TLV is defined to carry the actual minimum available bandwidth of the SR forwarding path in the STAMP reflection packet. The encapsulation format is as follows. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |STAMP TLV Flags| Type=TBA | Length=4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Minimum available bandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: STAMP Minimum Available Bandwidth TLV where: - STAMP TLV Flags: The STAMP TLV Flags follow the procedures described in [RFC8972] and this document. - Type: Type (value TBA) for the Minimum Available Bandwidth TLV. - Length: A 2-octet field equal to the length of the bandwidth field. - Minimum available bandwidth: 4-octet unsigned integer. The field is used to carry the minimum bandwidth value. If the STAMP session reflector supports bandwidth measurement function, after obtaining the minimum available bandwidth of the SR path, the Minimum Available Bandwidth TLV must be encapsulated in the reflection packet and the U Flag [RFC8972] MUST be set to 1. Otherwise, this TLV MUST not be carried in the reflection packet. 6. Usecases of Bandwidth Measurement Taking the SRv6 policy multipath scenario shown in Figure 4 as an example, for the traffic from node A to node E, the controller issues two candidate paths CP1 and CP2 to head node A. Liu, et al. Expires October, 2024 [Page 7] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 +-----+ +-----+ | | | | | G +--------+ +--+ H | | | | | | | +--+--+ +--+--+ | +-----+ | | | +--------+ B +--------------------+ | | +--------+ | | | +-----+ | | | +--+--+ +-----+ +--+--+ | +--+--+ | | | | | +--+ | | | A +-----+ C +-----+ D +-----+ E | | | | | | | | | +--+--+ +--+--+ +-----+ +--+--+ Ingress| | +-----+ | Egress Node | +--------+ | | Node +--------------------+ F +--------+ | | +-----+ Figure 4: SRv6 Network SR Policy POL1 Candidate Path CP1 Preference 200 Segment List 11 , Weight 1, 100M Segment List 12 , Weight 1, 100M Candidate Path CP2 Preference 100 Segment List 21 , Weight 1, 100M Segment List 22 , Weight 1, 100M The preset bandwidth for the segment list paths of CP1 and CP2 is 100Mbps. CP1 is the active candidate path, and CP2 is the backup. Normally, CP1 can forward 200Mbps traffic. If the active candidate path has traffic congestion and no longer meets forwarding requirements (The bandwidth must be greater than 150Mbps), it is necessary to promptly sense and switch to the backup candidate path. For this requirement, the available bandwidth measurement function can be enabled on the SRv6 policy. Because the traffic from node G to node H also passes through nodes B and D. If the traffic from node G to node H is relatively high, the link between node B and node D will be traffic congestion. For example, there is traffic congestion on node D. The actual available bandwidth of node D drops to below 50Mbps, that is, the available Liu, et al. Expires October, 2024 [Page 8] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 bandwidth of the active candidate path becomes less than 150Mbps, and the service traffic can be switched to CP2. 7. IANA Considerations 7.1. Destination Options and Hop-by-Hop Options Registry IANA has allocated a value for the Minimum Available Bandwidth Option Type from the IETF Review TLV range in the "Destination Options and Hop-by-Hop Options" registry [RFC8200] as follows. +=======+===================================+===============+ | Value | Description | Reference | +=======+===================================+===============+ | TBA | Minimum Available Bandwidth Option| This document | +-------+-----------------------------------+---------------+ 7.2. Segment Routing Header TLVs Registry IANA has allocated a value for the Minimum Available Bandwidth TLV Type from the IETF Review TLV range in the "Segment Routing Header TLVs" registry [RFC8754] as follows. +=======+==================================+================+ | Value | Description | Reference | +=======+==================================+================+ | TBA | Minimum Available Bandwidth TLV | This document | +-------+----------------------------------+----------------+ 7.3. STAMP TLV Types Registry IANA has allocated a value for the Minimum Available Bandwidth TLV Type from the IETF Review TLV range in the "STAMP TLV Types" registry [RFC8972] as follows. +=======+==================================+================+ | Value | Description | Reference | +=======+==================================+================+ | TBA | Minimum Available Bandwidth TLV | This document | +-------+----------------------------------+----------------+ 8. Security Considerations This document does not introduce any security considerations. The security considerations specified in [RFC8762] and [RFC8972] also apply to the extensions defined in this document. Liu, et al. Expires October, 2024 [Page 9] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8754] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, . [RFC8762] Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple Two-Way Active Measurement Protocol", RFC 8762, DOI 10.17487/RFC8762, March 2020, . [RFC8972] Mirsky, G., Min, X., Nydell, H., Foote, R., Masputra, A., and E. Ruffini, "Simple Two-Way Active Measurement Protocol Optional Extensions", RFC 8972, DOI 10.17487/RFC8972, January 2021, . [RFC9256] Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, July 2022, . 9.2. Informative References TBD 10. Acknowledgments The authors would like to thank the following for their valuable contributions of this document: TBD Liu, et al. Expires October, 2024 [Page 10] Internet-Draft SRv6 Path Bandwidth Measurement April 2024 Authors' Addresses Yisong Liu China Mobile Beijing China Email: liuyisong@chinamobile.com Changwang Lin New H3C Technologies Beijing China Email: linchangwang.04414@h3c.com Yuanxiang Qiu New H3C Technologies Beijing China Email: qiuyuanxiang@h3c.com Liu, et al. Expires October, 2024 [Page 11]