SPRING Working Group G. Mirsky Internet-Draft Ericsson Intended status: Standards Track J. Tantsura Expires: 2 February 2024 NVDIA I. Varlashkin Google M. Chen Huawei J. Wenying CMCC 1 August 2023 Bidirectional Forwarding Detection (BFD) in Segment Routing Networks Using MPLS Dataplane draft-ietf-spring-bfd-08 Abstract Segment Routing (SR) architecture leverages the paradigm of source routing. It can be realized in the Multiprotocol Label Switching (MPLS) network without any change to the data plane. A segment is encoded as an MPLS label, and an ordered list of segments is encoded as a stack of labels. Bidirectional Forwarding Detection (BFD) is expected to monitor any existing path between systems. This document defines how to use Label Switched Path (LSP) Ping to bootstrap a BFD session, optional control of the selection of a segment list as the reverse direction of the BFD session, applicability of BFD Demand mode, and Seamless BFD in the SR-MPLS domain. Also, the document describes the use of the BFD Echo function with the BFD Control packet payload. 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 2 February 2024. Mirsky, et al. Expires 2 February 2024 [Page 1] Internet-Draft BFD in SPRING MPLS August 2023 Copyright Notice Copyright (c) 2023 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4 2. Bootstrapping BFD Session over Segment Routed Tunnel with MPLS Data Plane . . . . . . . . . . . . . . . . . . . . . . . 4 3. Use BFD Reverse Path TLV over Segment Routed MPLS Tunnel . . 5 4. Use Non-FEC Path TLV . . . . . . . . . . . . . . . . . . . . 5 5. BFD Reverse Path TLV over Segment Routed MPLS Tunnel with Dynamic Control Plane . . . . . . . . . . . . . . . . . . 7 6. Applicability of BFD Demand Mode in SR-MPLS Domain . . . . . 7 7. Using BFD to Monitor Point-to-Multipoint SR Policy . . . . . 8 8. Use of Echo BFD in SR-MPLS . . . . . . . . . . . . . . . . . 8 9. Use of S-BFD in SR-MPLS . . . . . . . . . . . . . . . . . . . 9 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 10.1. Non-FEC Path TLV . . . . . . . . . . . . . . . . . . . . 9 10.2. Return Code . . . . . . . . . . . . . . . . . . . . . . 10 11. Implementation Status . . . . . . . . . . . . . . . . . . . . 11 12. Security Considerations . . . . . . . . . . . . . . . . . . . 12 13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 15.1. Normative References . . . . . . . . . . . . . . . . . . 12 15.2. Informative References . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 Mirsky, et al. Expires 2 February 2024 [Page 2] Internet-Draft BFD in SPRING MPLS August 2023 1. Introduction [RFC5880], [RFC5881], and [RFC5883] defined the operation of Bidirectional Forwarding Detection (BFD) protocol between the two systems over IP networks. [RFC5884] and [RFC7726] set rules for using BFD Asynchronous mode over point-to-point (p2p) Multiprotocol Label Switching (MPLS) Label Switched Path (LSP). These latter standards implicitly assume that the remote BFD system, which is at the egress Label Edge Router (LER), will use the shortest path route regardless of the path the BFD system at the ingress LER uses to send BFD Control packets towards it. Throughout this document, references to ingress LER and egress LER are used, respectively, as a shortened version of the "BFD system at the ingress/egress LER". This document defines the use of LSP Ping for Segment Routing networks over the MPLS data plane [RFC8287] to bootstrap and control path of a BFD session from the egress to ingress LER using Segment Routing tunnel with MPLS data plane (SR-MPLS). [RFC9256] defines the SR Policy architecture. When analyzing the applicability of a BFD-based mechanism for detecting network failures in a Segment Routing domain, it is essential to identify the SR Policy elements monitored by the BFD. Concluding from the definition of BFD in [RFC5880], in an SR domain, BFD, in its modes and functions, monitors not the SR Policy, as defined in [RFC9256], but a segment list that is a constituent of the candidate path of the particular SR Policy. That is the context used throughout the document. 1.1. Conventions 1.1.1. Terminology BFD: Bidirectional Forwarding Detection BSID: Binding Segment Identifier FEC: Forwarding Equivalence Class MPLS: Multiprotocol Label Switching SR-MPLS Segment Routing with MPLS data plane LSP: Label Switched Path LER Label Edge Router p2p Point-to-point Mirsky, et al. Expires 2 February 2024 [Page 3] Internet-Draft BFD in SPRING MPLS August 2023 p2mp Point-to-multipoint SID Segment Identifier SR Segment Routing S-BFD Seamless BFD 1.1.2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "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. 2. Bootstrapping BFD Session over Segment Routed Tunnel with MPLS Data Plane Use of an LSP Ping to bootstrap BFD over MPLS LSP is required, as documented in [RFC5884], to establish an association between a fault detection message, i.e., BFD Control message, and the Forwarding Equivalency Class (FEC) of a single label stack LSP in case of Penultimate Hop Popping or when the egress LER distributes the Explicit NULL label to the penultimate hop router. The Explicit NULL label is not advertised as a Segment Identifier (SID) by an SR node but, as demonstrated in section 3.1 [RFC8660] if the operation at the penultimate hop is NEXT; then the egress SR node will receive an IP encapsulated packet. Thus the conclusion is that LSP Ping MUST be used to bootstrap a BFD session in an SR-MPLS domain if there are no other means to bootstrap the BFD session, e.g., using an extension to a dynamic routing protocol as described in [RFC9026] and [RFC9186]. As demonstrated in [RFC8287], the introduction of Segment Routing network domains with an MPLS data plane requires three new sub-TLVs that MAY be used with Target FEC TLV. Section 6.1 addresses the use of the new sub-TLVs in Target FEC TLV in LSP ping and LSP traceroute. For the case of LSP ping, the [RFC8287] states that: The initiator, i.e., ingress LER, MUST include FEC(s) corresponding to the destination segment. The initiator MAY include FECs corresponding to some or all of segments imposed in the label stack by the ingress LER to communicate the segments traversed. Mirsky, et al. Expires 2 February 2024 [Page 4] Internet-Draft BFD in SPRING MPLS August 2023 It has been noted in [RFC5884] that a BFD session monitors for defects particular tuple. [RFC7726] clarified how to establish and operate multiple BFD sessions for the same tuple. Because only the ingress LER is aware of the SR-based explicit route, the egress LER can associate the LSP ping with BFD Discriminator TLV with only one of the FECs it advertised for the particular segment. Thus this document clarifies that: When LSP Ping is used to bootstrapping a BFD session for SR-MPLS tunnel the FEC corresponding to the segment to be associated with the BFD session MUST be as the very last sub-TLV in the Target FEC TLV. If the target segment is an anycast prefix segment ([I-D.ietf-spring-mpls-anycast-segments]) the corresponding Anycast SID MUST be included in the Target TLV as the very last sub-TLV. Also, for BFD Control packet the ingress SR node MUST use precisely the same label stack encapsulation, especially Entropy Label ([RFC6790]), as for the LSP ping with the BFD Discriminator TLV that bootstrapped the BFD session. Other operational aspects of using BFD to monitor the continuity of the path to the particular Anycast SID, advertised by a group of SR-MPLS capable nodes, will be considered in the future versions of the document. Encapsulation of a BFD Control packet in Segment Routing network with MPLS data plane MUST follow Section 7 [RFC5884] when the IP/UDP header used and MUST follow Section 3.4 [RFC6428] without IP/UDP header being used. 3. Use BFD Reverse Path TLV over Segment Routed MPLS Tunnel For BFD over MPLS LSP case, per [RFC5884], egress LER MAY send BFD Control packet to the ingress LER either over IP network or an MPLS LSP. Similarly, for the case of BFD over p2p SR-MPLS tunnel, the egress LER MAY route BFD Control packet over the IP network, as described in [RFC5883], or transmit over a segment tunnel, as described in Section 7 [RFC5884]. In some cases, there may be a need to direct egress LER to use a specific path for the reverse direction of the BFD session by using the BFD Reverse Path TLV and following all procedures as defined in [I-D.ietf-mpls-bfd-directed]. 4. Use Non-FEC Path TLV For the case of MPLS data plane, Segment Routing Architecture [RFC8402] explains that "a segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels." Mirsky, et al. Expires 2 February 2024 [Page 5] Internet-Draft BFD in SPRING MPLS August 2023 This document defines a new optional Non-FEC Path TLV. The format of the Non-FEC Path TLV is presented in Figure 1 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Non-FEC Path TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Non-FEC Path ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Non-FEC Path TLV Format Non-FEC Path TLV Type is two octets in length and has a value of TBD1 (to be assigned by IANA as requested in Section 10.1). Length field is two octets long and defines the length in octets of the Non-FEC Path field. Non-FEC Path field contains a sub-TLV. Any Non-FEC Path sub-TLV (defined in this document or to be defined in the future) for Non-FEC Path TLV type MAY be used in this field. None or one sub-TLV MAY be included in the Non-FEC Path TLV. If no sub-TLV has been found in the Non-FEC Path TLV, the egress LER MUST revert to using the reverse path selected based on its local policy. If there is more than one sub-TLV, then the Return Code in echo reply MUST be set to value TBD3 "Too Many TLVs Detected" (to be assigned by IANA as requested in Table 4). Non-FEC Path TLV MAY be used to specify the reverse path of the BFD session identified in the BFD Discriminator TLV. If the Non-FEC Path TLV is present in the echo request message the BFD Discriminator TLV MUST be present as well. If the BFD Discriminator TLV is absent when the Non-FEC Path TLV is included, then it MUST be treated as malformed Echo Request, as described in [RFC8029]. This document defines the Segment Routing MPLS Tunnel sub-TLV that MAY be used with the Non-FEC Path TLV. The format of the sub-TLV is presented in Figure 2. Mirsky, et al. Expires 2 February 2024 [Page 6] Internet-Draft BFD in SPRING MPLS August 2023 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SR MPLS Tunnel sub-TLV Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID Entry 1 (Top of Stack) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID Entry 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID Entry N (Bottom of Stack) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Segment Routing MPLS Tunnel sub-TLV The Segment Routing MPLS Tunnel sub-TLV Type is two octets in length, and has a value of TBD2 (to be assigned by IANA as requested in Section 10.1). The egress LER MUST use the Value field as label stack for BFD Control packets for the BFD session identified by the source IP address of the MPLS LSP Ping packet and the value in the BFD Discriminator TLV. Label Entries MUST be in network order. 5. BFD Reverse Path TLV over Segment Routed MPLS Tunnel with Dynamic Control Plane When Segment Routed domain with MPLS data plane uses distributed tunnel computation BFD Reverse Path TLV MAY use Target FEC sub-TLVs defined in [RFC8287]. 6. Applicability of BFD Demand Mode in SR-MPLS Domain Sections 6.6 and 6.18.4 of [RFC5880] define how Demand mode of BFD can be used to monitor uni-directional MPLS LSP. Similar procedures can be following in SR-MPLS to monitor uni-directional SR tunnels: * an ingress SR node bootstraps BFD session over SR-MPLS in Async BFD mode; * once BFD session is Up, the ingress SR node switches the egress LER into the Demand mode by setting D field in BFD Control packet it transmits; * if the egress LER detects the failure of the BFD session, it sends its BFD Control packet to the ingress SR node over the IP network with a Poll sequence; Mirsky, et al. Expires 2 February 2024 [Page 7] Internet-Draft BFD in SPRING MPLS August 2023 * if the ingress SR node receives a BFD Control packet from the remote node in a Demand mode with Poll sequence and Diag field indicating the failure, the ingress SR node transmits BFD Control packet with Final over IP and switches the BFD over SR-MPLS back into Async mode, sending BFD Control packets one per second. 7. Using BFD to Monitor Point-to-Multipoint SR Policy [I-D.ietf-spring-sr-replication-segment] defined variants of SR Policy to deliver point-to-multipoint (p2mp) services. For the given p2mp segment [RFC8562] can be used if, for example, leaves have an alternative source of the multicast service flow to select. In such a scenario, a leaf may switch to using the alternative flow after p2mp BFD detects the failure in the working multicast path. For scenarios where it is required for the root to monitor the state of the multicast tree [RFC8563] can be used. The root may use the detection of the failure of the multicast tree to the particular leaf to restore the path for that leaf or re-instantiate the whole multicast tree. An essential part of using p2mp BFD is the bootstrapping the BFD session at all the leaves. The root, acting as the MultipointHead, MAY use LSP Ping with the BFD Discriminator TLV. Alternatively, extensions to routing protocols, e.g., BGP, or management plane, e.g., Path Computation Element Protocol, MAY be used to associate the particular p2mp segment with MultipointHead's Discriminator. Extensions for routing protocols and management plane are for further study. 8. Use of Echo BFD in SR-MPLS Echo-BFD [RFC5880] can be used to monitor a segment list of the particular SR Policy between the local and the remote BFD peers. As defined in [RFC5880], the remote BFD system does not process the payload of an Echo BFD. Thus it is the local system that demultiplexes the Echo BFD packet matching it to the appropriate BFD session and detects missing Echo BFD packets. A BFD Control packet MAY be used as the payload of Echo BFD. This specification defines the use of Echo BFD in SR-MPLS network with BFD Control packet as the payload. The use of other types of Echo BFD payload is outside the scope of this document. Because the remote BFD system does not process Echo BFD, the value of the Your Discriminator field MUST be set to the discriminator the local BFD system assigned to the given BFD session. My Discriminator field MUST be zeroed. Authentication MUST be set according to the configuration of the BFD session. To ensure that the Echo BFD packet is returned to the sender without being processed, the sender MAY use a Binding SID (BSID) [RFC8402] that has been bound with the SR Policy that ensures the return of a Mirsky, et al. Expires 2 February 2024 [Page 8] Internet-Draft BFD in SPRING MPLS August 2023 packet to that particular node. A BSID MAY be associated with the SR Policy that is the reverse to the SR Policy programmed onto the BFD Echo packet by the sender. 9. Use of S-BFD in SR-MPLS Seamless BFD (S-BFD), defined in [RFC7880], maintains essential characteristics and elements of the base BFD mechanism described in [RFC5880] with a lighter approach to instantiating a BFD session between BFD peers. Similar to the BFD Asynchronous mode, S-BFD is capable of monitoring a segment list of a p2p SR Policy. Considering that a particular SR Policy can include multiple candidate paths, which, in turn, have one or more segment lists, it could be beneficial to monitor each segment list independently. To achieve that, S-BFD Reflector advertises My Discriminator value. Then, the S-BFD Initiator uses the advertised My Discriminator value as Your Discriminator value in the BFD Control messages transmitted over the segment list of the SR Policy. Furthermore, the S-BFD Initiator assigns a unique My Discriminator for each S-BFD session monitoring a segment list. S-BFD Reflector transmits BFD Control messages as IP/UDP packets, taking advantage of the available resilience mechanisms of the IP network. From that point, to minimize the detection of failures in the IP network that do not affect the monitored segment list, it is reasonable not to use defect detection intervals that are close to the IP network repair time. Instead, having an S-BFD detection interval three times longer than the IP network repair time is practical. 10. IANA Considerations 10.1. Non-FEC Path TLV IANA is requested to assign new TLV type from the from Standards Action range of the registry "Multiprotocol Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" as defined in Table 1. +=======+==================+===============+ | Value | TLV Name | Reference | +=======+==================+===============+ | TBD1 | Non-FEC Path TLV | This document | +-------+------------------+---------------+ Table 1: New Non-FEC Path TLV IANA is requested to create new Non-FEC Path sub-TLV registry for the Non-FEC Path TLV, as described in Table 2. Mirsky, et al. Expires 2 February 2024 [Page 9] Internet-Draft BFD in SPRING MPLS August 2023 +=============+===============+=====================================+ | Range | Registration | Note | | | Procedures | | +=============+===============+=====================================+ | 0-16383 | Standards | This range is for mandatory | | | Action | TLVs or for optional TLVs | | | | that require an error | | | | message if not recognized. | +-------------+---------------+-------------------------------------+ | 16384-31743 | Specification | Experimental RFC needed | | | Required | | +-------------+---------------+-------------------------------------+ | 32768-49161 | Standards | This range is for optional | | | Action | TLVs that can be silently | | | | dropped if not recognized. | +-------------+---------------+-------------------------------------+ | 49162-64511 | Specification | Experimental RFC needed | | | Required | | +-------------+---------------+-------------------------------------+ | 64512-65535 | Private Use | | +-------------+---------------+-------------------------------------+ Table 2: Non-FEC Path sub-TLV registry IANA is requested to allocate the following values from the Non-FEC Path sub-TLV registry as defined in Table 3. +=======+=====================================+===============+ | Value | Description | Reference | +=======+=====================================+===============+ | 0 | Reserved | This document | +-------+-------------------------------------+---------------+ | TBD2 | Segment Routing MPLS Tunnel sub-TLV | This document | +-------+-------------------------------------+---------------+ | 65535 | Reserved | This document | +-------+-------------------------------------+---------------+ Table 3: New Segment Routing Tunnel sub-TLV 10.2. Return Code IANA is requested to create Non-FEC Path sub-TLV sub-registry for the new Non-FEC Path TLV and assign a new Return Code value from the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry, "Return Codes" sub-registry, as follows using a Standards Action value. Mirsky, et al. Expires 2 February 2024 [Page 10] Internet-Draft BFD in SPRING MPLS August 2023 +========+=========================+===============+ | Value | Description | Reference | +========+=========================+===============+ | X TBD3 | Too Many TLVs Detected. | This document | +--------+-------------------------+---------------+ Table 4: New Return Code 11. Implementation Status Note to RFC Editor: This section MUST be removed before publication of the document. This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit". - The organization responsible for the implementation: ZTE Corporation. - The implementation's name ROSng SW empowers traditional routers, e.g., ZXCTN 6000. - A brief general description: A list of SIDs can be specified as the Return Path for an SR-MPLS tunnel. - The implementation's level of maturity: production. - Coverage: complete - Version compatibility: draft-mirsky-spring-bfd-06. Mirsky, et al. Expires 2 February 2024 [Page 11] Internet-Draft BFD in SPRING MPLS August 2023 - Licensing: proprietary. - Implementation experience: Appreciate Early Allocation of values for Non-FEC TLV and Segment Routing MPLS Tunnel sub-TLV (using Private Use code points). - Contact information: Qian Xin qian.xin2@zte.com.cn - The date when information about this particular implementation was last updated: 12/16/2019 12. Security Considerations Security considerations discussed in [RFC5880], [RFC5884], [RFC7726], and [RFC8029] apply to this document. 13. Contributors Xiao Min ZTE Corp. Email: xiao.min2@zte.com.cn 14. Acknowledgments Authors express their sincere gratitude to Alexander "Sasha" Vainshtein for his helpful comments and thought-inspiring discussion of SR Policies and BFD-based mechanisms. Authors greatly appreciate the help of Qian Xin, who provided the information about the implementation of this specification. 15. References 15.1. Normative References [I-D.ietf-mpls-bfd-directed] Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen, "Bidirectional Forwarding Detection (BFD) Directed Return Path for MPLS Label Switched Paths (LSPs)", Work in Progress, Internet-Draft, draft-ietf-mpls-bfd-directed-24, 2 July 2023, . Mirsky, et al. Expires 2 February 2024 [Page 12] Internet-Draft BFD in SPRING MPLS August 2023 [I-D.ietf-spring-sr-replication-segment] Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z. J. Zhang, "SR Replication segment for Multi-point Service Delivery", Work in Progress, Internet-Draft, draft-ietf- spring-sr-replication-segment-16, 31 July 2023, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, . [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, DOI 10.17487/RFC5881, June 2010, . [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, June 2010, . [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, "Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, June 2010, . [RFC6428] Allan, D., Ed., Swallow, G., Ed., and J. Drake, Ed., "Proactive Connectivity Verification, Continuity Check, and Remote Defect Indication for the MPLS Transport Profile", RFC 6428, DOI 10.17487/RFC6428, November 2011, . [RFC7726] Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S. Aldrin, "Clarifying Procedures for Establishing BFD Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726, DOI 10.17487/RFC7726, January 2016, . [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures", RFC 8029, DOI 10.17487/RFC8029, March 2017, . Mirsky, et al. Expires 2 February 2024 [Page 13] Internet-Draft BFD in SPRING MPLS August 2023 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8287] Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya, N., Kini, S., and M. Chen, "Label Switched Path (LSP) Ping/Traceroute for Segment Routing (SR) IGP-Prefix and IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017, . [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, . [RFC8562] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky, Ed., "Bidirectional Forwarding Detection (BFD) for Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562, April 2019, . [RFC8563] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky, Ed., "Bidirectional Forwarding Detection (BFD) Multipoint Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019, . [RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing with the MPLS Data Plane", RFC 8660, DOI 10.17487/RFC8660, December 2019, . 15.2. Informative References [I-D.ietf-spring-mpls-anycast-segments] Sarkar, P., Gredler, H., Filsfils, C., Previdi, S., Decraene, B., and M. Horneffer, "Anycast Segments in MPLS based Segment Routing", Work in Progress, Internet-Draft, draft-ietf-spring-mpls-anycast-segments-03, 27 April 2020, . [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, DOI 10.17487/RFC6790, November 2012, . Mirsky, et al. Expires 2 February 2024 [Page 14] Internet-Draft BFD in SPRING MPLS August 2023 [RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. Pallagatti, "Seamless Bidirectional Forwarding Detection (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016, . [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, July 2016, . [RFC9026] Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed., "Multicast VPN Fast Upstream Failover", RFC 9026, DOI 10.17487/RFC9026, April 2021, . [RFC9186] Mirsky, G. and X. Ji, "Fast Failover in Protocol Independent Multicast - Sparse Mode (PIM-SM) Using Bidirectional Forwarding Detection (BFD) for Multipoint Networks", RFC 9186, DOI 10.17487/RFC9186, January 2022, . [RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, July 2022, . Authors' Addresses Greg Mirsky Ericsson Email: gregimirsky@gmail.com Jeff Tantsura NVDIA Email: jefftant.ietf@gmail.com Ilya Varlashkin Google Email: imv@google.com Mach(Guoyi) Chen Huawei Email: mach.chen@huawei.com Mirsky, et al. Expires 2 February 2024 [Page 15] Internet-Draft BFD in SPRING MPLS August 2023 Jiang Wenying CMCC Email: jiangwenying@chinamobile.com Mirsky, et al. Expires 2 February 2024 [Page 16]