SPRING Working Group X. Geng Internet-Draft M. Chen Intended status: Standards Track F. Yang, Ed. Expires: January 6, 2022 Huawei Technologies P. Camarillo Cisco Systems, Inc. G. Mishra Verizon Inc. July 05, 2021 Segment Routing for Redundancy Protection draft-geng-spring-sr-redundancy-protection-04 Abstract Redundancy protection provides a mechanism to achieve the high reliability of the service transmission in network. Specifically, packets of flows are replicated into two or more copies, which are transported through different paths in parallel. When copies of packets are merged at network node, the redundant packets are eliminated to guarantee one copy of the flow is successfully transmitted. This document extends the capabilities in SR paradigm to support redundancy protection function, including the definitions of new Segments and a variation of Segment Routing Policy. The new mechanism applies equally to both Segment Routing with MPLS data plane (SR-MPLS) and Segment Routing with IPv6 data plane (SRv6). 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 . 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 Geng, et al. Expires January 6, 2022 [Page 1] Internet-Draft Segment Routing for Redundancy Protection July 2021 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 January 6, 2022. Copyright Notice Copyright (c) 2021 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 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2.2. Terminology and Conventions . . . . . . . . . . . . . . . 4 3. Redundancy Protection in Segment Routing Scenario . . . . . . 4 4. Segment to Support Redundancy Protection . . . . . . . . . . 5 4.1. Redundancy Segment . . . . . . . . . . . . . . . . . . . 5 4.1.1. SR over MPLS . . . . . . . . . . . . . . . . . . . . 6 4.1.2. SRv6 . . . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Merging Segment . . . . . . . . . . . . . . . . . . . . . 7 4.2.1. SR over MPLS . . . . . . . . . . . . . . . . . . . . 7 4.2.2. SRv6 . . . . . . . . . . . . . . . . . . . . . . . . 7 5. Meta Data to Support Redundancy Protection . . . . . . . . . 8 6. Segment Routing Policy to Support Redundancy Protection . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 Geng, et al. Expires January 6, 2022 [Page 2] Internet-Draft Segment Routing for Redundancy Protection July 2021 1. Introduction Redundancy Protection provides a mechanism to achieve the high reliability of the service transmission in network. Specifically, packets of flows are replicated into two or more copies, which are transported through different paths in parallel. When copies of packets are merged at network node, the redundant packets are eliminated to guarantee one copy of the flow is successfully transmitted. Redundancy protection targets to the services especially requires ultra reliable transmission, for example 5G URLLC services including Cloud VR/Game, remote surgery, harbor crane lifting, and differential protection in electrical utilities etc. Redundancy protection can also be used as Packet Replication and Elimination Function for Deterministic Networking defined in [RFC8655]. At last, it also bring values to existing services in legacy network, for example IPTV service and financial private line in fixed broadband network, as well as the video service in data center interconnect. In this document, redundancy protection for point to point service is discussed, P2MP service stays out of scope. Segment Routing (SR) leverages the source routing paradigm. An ingress node steers a packet through an ordered list of instructions, called "segments". A segment can be associated to an arbitrary processing of the packet in the node identified by the segment. This document extends the Segment Routing capabilities to support the redundancy protection in an SR environment, including the definitions of new Segments and a variation of Segment Routing Policy. The new mechanism applies equally to both Segment Routing with MPLS data plane (SR-MPLS) [RFC8660] and Segment Routing with IPv6 data plane (SRv6) [RFC8986]. 2. Terminology 2.1. 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. Geng, et al. Expires January 6, 2022 [Page 3] Internet-Draft Segment Routing for Redundancy Protection July 2021 2.2. Terminology and Conventions SR: Segment Routing URLLC: Ultra-Reliable Low-Latency Communication VR: Virtual Reality Red Node: Redundancy Node Mer Node: Merging Node FID: Flow IDentification SN: Sequence Number 3. Redundancy Protection in Segment Routing Scenario | | |<------------- SRv6 Domain ------------->| | | | +---+ | | +-----+R3 +-----+ | | | +---+ | | +-+-+ +-+-+ +-+-+ +-+-+ -------+R1 +--------+Red| |Mer+--------+R2 +------- +---+ +-+-+ +-+-+ +---+ | +---+ | +-----+R4 +-----+ +---+ Figure 1: Example Scenario of Redundancy Protection in SRv6 Domain This figure shows an example of redundancy protection used in SRv6 domain. R1, R2, R3, R4, Red and Mer are SR-capable nodes. When a flow is sent into SRv6 domain, the process is: 1) R1 receives the traffic flow and encapsulates packets with a list of segments destined to R2, which is instantiated as an ordered list of SRv6 SIDs. 2) When the packet flow arrives at Red node, known as Redundancy Node, each packet is replicated into two or more copies. Each copy of the packet is encapsulated with a new segment list, which represents different disjoint forwarding paths. 3) Meta data information such as flow identification (FID) and sequence number (SN) is used to facilitate the packet elimination on Geng, et al. Expires January 6, 2022 [Page 4] Internet-Draft Segment Routing for Redundancy Protection July 2021 Merging node (Mer). Flow identification identifies the specific flow, and sequence number distinguishes the packet sequence of a flow. Meta data is either carried in the packet before it arrives at Red node, or added to each of the replicas at Red node. 4) The multiple replicas go through different paths until the Mer node. The first received packet of the flow is transmitted from Merging Node to R2, and the redundant packets are eliminated. 5) When there is any failures or packet loss in one path, the service continues undisrupted through the other path without break. 6) Sometimes, the packet will arrive out of order because of redundancy protection, the function of reordering may be also necessary on Merging Node. In such case the Merging node may include a reordering function, which is implementation specific and out of the scope of this document. In this example, service protection is supported by utilizing two packet flows transmitted over two forwarding paths. It is noted that there is no limitation of the number of replicas. For a unidirectional flow, Red node supports replication function, and Mer node supports elimination function. Reordering function MAY be required in combination of elimination function on merging node. To minimize the jitter caused by random packet loss, the disjoint paths are recommended to have similar path forwarding delay. 4. Segment to Support Redundancy Protection To achieve the packet replication and elimination functions, Redundancy Segment and Merging Segment, as well as the SR over MPLS forwarding behavior and SRv6 Endpoint Behavior are introduced. 4.1. Redundancy Segment Redundancy Segment is the identifier of packets which need the replication function on redundancy node. It is also a variation of Binding SID, and associated with a Redundancy Policy to provide segment lists of disjoint paths. Thus, Redundancy segment is associated with service instructions, indicating the following operations: o Steers the packet into the corresponding redundancy policy o Encapsulates flow identification and sequence number in packets if the two information is not carried in packets Geng, et al. Expires January 6, 2022 [Page 5] Internet-Draft Segment Routing for Redundancy Protection July 2021 o Packet replication and segment encapsulation based on the information of redundancy policy, e.g., the number of replication copies, an ordered list of segments with a topological instruction 4.1.1. SR over MPLS In the case of SR over MPLS, IETF Deterministic Networking working group has defined Packet Replication/Elimination/Ordering Functions in DetNet MPLS data plane [RFC8964]. The support of redundancy segment in SR over MPLS data plane keeps consistent with PRF function defined in [RFC8964]. 4.1.2. SRv6 In the case of SRv6, a new behavior End.R for Redundancy Segment is defined. An instance of a redundancy SID is associated with a redundancy policy B and a source address A. In the following description, End.R behavior is specified in the encapsulation mode. The End.R behavior in the insertion mode is for further study. When an SRv6-capable node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as an SRv6 SID (S), and S is a Redundancy SID, N does: S01. When an SRH is processed { S02. If (Segments Left>0) { S03. Decrement IPv6 Hop Limit by 1 S04. Decrement Segments Left by 1 S05. Update IPv6 DA with Segment List[Segments Left] S06. Add flow identification and sequence number if indicated* S07. Duplicate the packets (as number of active SID lists in B) S08. Push the new IPv6 headers to each replica. The IPv6 header contains an SRH with the SID list in B S09. Set the outer IPv6 SA to A S10. Set the outer IPv6 DA to the first SID of new SRH SL S11. Set the outer Payload Length, Traffic Class, Flow Label, Hop Limit and Next-Header fields S12. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination S13. } S14. } * Adding flow identification and sequence number is an optional behavior for Redundancy Segment. The instruction execution is determined and explicitly indicated by SR policy or Segment itself. Geng, et al. Expires January 6, 2022 [Page 6] Internet-Draft Segment Routing for Redundancy Protection July 2021 4.2. Merging Segment Merging Segment is associated with service instructions, indicates the following operations: o Packet merging and elimination: forward the first received packets and eliminate the redundant packets In order to eliminate the redundant packet of a flow, merging node utilizes sequence number to evaluate the redundant status of a packet. Note that implementation specific mechanism could be applied to control the amount of state monitored on sequence number, so that system memory usage can be limited at a reasonable level. As merging node needs to maintain the state of flows, a centralized controller should have a knowledge of merging nodes capability, and never provision the redundancy policy to redundancy node when the computation result goes beyond the flow recovery capability of merging node. The capability advertisement of merging node will be specified separately elsewhere, which is not within the scope of this document. 4.2.1. SR over MPLS In the case of SR over MPLS, the support of merging segment in SR over MPLS data plane keeps consistent with the PEF function defined in [RFC8964]. 4.2.2. SRv6 In the case of SRv6, a new behavior End.M for Merging Segment is defined. When an SRv6-capable node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as an SRv6 SID (S), and S is a Merging SID, N does: Geng, et al. Expires January 6, 2022 [Page 7] Internet-Draft Segment Routing for Redundancy Protection July 2021 S01. When an SRH is processed { S02. If (Segments Left> or ==0) { S03. Acquire the sequence number of received packet and look it up in table S04. If (this sequence number does not exist in the table) { S05. Store this sequence number in table S06. Remove the outer IPv6+SRH header S07. Decrement IPv6 Hop Limit by 1 in inner SRH S08. Decrement Segments Left by 1 in inner SRH S09. Update IPv6 DA with Segment List[Segments Left] in inner SRH S10. Submit the packet to the egress IPv6 FIB lookup and transmit S11. } S12. ELSE { S13. Drop the packet S14. } S15. } S16. } 5. Meta Data to Support Redundancy Protection To support the redundancy protection function, flow identification and sequence number are required. Flow identification identifies one specific flow of redundancy protection, and is usually allocated from centralized controller to the headend or redundancy node in SR network. Sequence number distinguishes the packets within a flow by specifying the order of packets, and is usually generated locally on SR node itself. Thus, the encapsulation of flow identification and sequence number is required in both SR over MPLS and SRv6 data plane. 6. Segment Routing Policy to Support Redundancy Protection Redundancy Policy is a variation of SR Policy to conduct the replicas to multiple disjoint paths for redundancy protection. It extends SR policy to include more than one ordered lists of segments between redundancy node and merging node, and all the ordered lists of segments are used at the same time to steer the copies of flow into different disjoint paths. 7. IANA Considerations This document requires registration of End.R behavior and End.M behavior in "SRv6 Endpoint Behaviors" sub-registry of "Segment Routing Parameters" registry. Geng, et al. Expires January 6, 2022 [Page 8] Internet-Draft Segment Routing for Redundancy Protection July 2021 8. Security Considerations TBD 9. Acknowledgements The authors would like to thank Bruno Decraene, Ron Bonica, James Guichard, Jeffrey Zhang, Balazs Varga for their valuable comments and discussions. 10. References 10.1. 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, . [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, . [RFC8964] Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant, S., and J. Korhonen, "Deterministic Networking (DetNet) Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January 2021, . [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 (SRv6) Network Programming", RFC 8986, DOI 10.17487/RFC8986, February 2021, . 10.2. Informative References [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, "Deterministic Networking Architecture", RFC 8655, DOI 10.17487/RFC8655, October 2019, . Geng, et al. Expires January 6, 2022 [Page 9] Internet-Draft Segment Routing for Redundancy Protection July 2021 Authors' Addresses Xuesong Geng Huawei Technologies China Email: gengxuesong@huawei.com Mach(Guoyi) Chen Huawei Technologies China Email: mach.chen@huawei.com Fan Yang Huawei Technologies China Email: shirley.yangfan@huawei.com Pablo Camarillo Garvia Cisco Systems, Inc. Spain Email: pcamaril@cisco.com Gyan Mishra Verizon Inc. Email: gyan.s.mishra@verizon.com Geng, et al. Expires January 6, 2022 [Page 10]