Network Working Group C. Xie Internet-Draft C. Li Intended status: Informational China Telecom Expires: January 9, 2020 S. Peng Z. Li Y. Xiao Huawei Technologies July 8, 2019 SRv6 Network Migration draft-xie-spring-srv6-network-migration-00 Abstract SRv6 has significant advantages over SR-MPLS which has attracted more and more attentions and interests from operators and verticals. The smooth network migration towards SRv6 is a key focal point for the SRv6 deployers. This document provides network migration guidance and recommendations on solutions in various scenarios. 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 RFC 2119 [RFC2119]. 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 January 9, 2020. Xie, et al. Expires January 9, 2020 [Page 1] Internet-Draft SRv6 Network Migration July 2019 Copyright Notice Copyright (c) 2019 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Advantages of SRv6 . . . . . . . . . . . . . . . . . . . . . 3 2.1. IP Route Aggregation . . . . . . . . . . . . . . . . . . 3 2.2. End-to-end Service Auto-start . . . . . . . . . . . . . . 4 2.3. On-Demand Upgrade . . . . . . . . . . . . . . . . . . . . 5 3. Incremental Deployment Guidance for SRv6 Migration . . . . . 6 4. Migration Guidance for SRv6/SR-MPLS Co-existence Scenario . . 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction SRv6 [I-D.ietf-spring-srv6-network-programming] has significant advantages over SR-MPLS and has attracted more and more attentions and interests from operators and verticals. The smooth network migration towards SRv6 is a key focal point for the SRv6 deployers. SRv6 is the Segment Routing deployed on the IPv6 data plane[RFC8200]. Therefore, in order to support SRv6, the network needs to support IPv6 first. As being actively promoted all over the world, the deployments of IPv6 have been ever-increasing which provides the strong base for the deployments of SRv6. With the IPv6 as its data plane, for network migration towards SRv6, both software and hardware need to be upgraded. Compared with other new protocols, only IGP and BGP need to be extended to support SRv6, which significantly simplifies the software upgrade required. While Xie, et al. Expires January 9, 2020 [Page 2] Internet-Draft SRv6 Network Migration July 2019 in the hardware it needs to support the new SRv6 header SRH[I-D.ietf-6man-segment-routing-header], the design of SRv6 assures the compatibility with the existing IPv6 network. An SRv6 SID is designed as an IPv6 address with 128bits long. From the encapsulation aspect an SRv6 packet is the same as an IPv6 packet. When only L3VPN over SRv6 BE (Best-Effort) is deployed, there will be no SRH. Therefore, no additional hardware capabilities are required but only software upgrade for protocol extensions. As the services supported by SRv6 increase, e.g. SFC, network slicing, more SIDs in the SRH may impose new requirements on the hardware. Besides hardware upgrading, various solutions [I-D.peng-spring-srv6-compatibility] have already been proposed to relief the imposed pressure on the hardware, such as BSID etc. to guarantee the compatibility with the existing network. On the other hand SRv6 has much more advantages over SR-MPLS for the network migration to support new services. This document summarizes the advantages and provides network migration guidance and recommendations on solutions in various scenarios. 2. Advantages of SRv6 Compared with SR-MPLS, SRv6 has significant advantages especially in the large scale networking scenario. 2.1. IP Route Aggregation It has been many years that the operators are troubled by the complexity of the service deployments, especially in the large scale networking scenario. With the solutions such as multi-segment PW and Option A, the service-touch points are increased, and the services or OAM cannot be deployed end-to-end. o With Seamless MPLS or SR-MPLS, since the MPLS label itself does not have reachability information, it must be attached to a routable address. The 32-bit host route needs to leak across domains. For an extreme case, as shown in Figure 1a, in a large scale networking scenario, millions of host routes LSPs might need to be imported, which places big challenges on the capabilities of the edge nodes. o With SRv6, owning to its native IP feature of route aggregatability as shown in Figure 1b, the aggregated routes can be imported across network domains. For the large scale networking, only very few aggregated routes are needed in order to Xie, et al. Expires January 9, 2020 [Page 3] Internet-Draft SRv6 Network Migration July 2019 start end-to-end services, which also reduces the scalability requirements on the edge nodes. /------Metro------\ /----Core----\ /------Metro-------\ LB PE1 ASBR ASBR PE2 LB 1.1.1.1 2.2.2.2 +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ |A | |B | |ER| | | |PE| | | |PE| | | |ER| |B | |A | +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ SR-LSP SR-LSP SR-LSP SR-LSP SR-LSP |<--->|<---------->| |<--------->| |<--------->|<--->| BGP-LSP |<---------------------------------------------------------->| +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +IP + +IP + +IP + +IP + +IP + +IP + +IP + +IP + +IP + +ETH+ +VPN+ +VPN+ +VPN+ +VPN+ +VPN+ +VPN+ +VPN+ +ETH+ +---+ +BGP+ +BGP+ +BGP+ +BGP+ +BGP+ +BGP+ +BGP+ +---+ +SR + +SR + +ETH+ +SR + +ETH+ +SR + +SR + +ETH+ +ETH+ +---+ +ETH+ +---+ +ETH+ +ETH+ +---+ +---+ +---+ +---+ +---+ (a) SR-MPLS /------Metro------\ /----Core----\ /------Metro-------\ LOC PE1 ASBR ASBR PE2 LOC A1::100:: A2::200:: +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ |A | |B | |ER| | | |PE| | | |PE| | | |ER| |B | |A | +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ \_____A1::/80____/ \__A0::/80__/ \____A2::/80____/ Aggregated Route Aggregated Route Aggregated Route +---+ +----------+ +----------+ +----------+ +---+ +IP + + IP + + IP + + IP + +IP + +ETH + +w./wo.SRH + +w./wo.SRH + +w./wo.SRH + +ETH+ +---+ + ETH + + ETH + + ETH + +---+ +----------+ +----------+ +----------+ (b) SRv6 Figure 1. Large-scale Networking with (a) SR-MPLS vs. (b) SRv6 2.2. End-to-end Service Auto-start In the SR cross-domain scenario, in order to set up end-to-end SR tunnels, the SIDs in each domain needs to be imported to other domains. Xie, et al. Expires January 9, 2020 [Page 4] Internet-Draft SRv6 Network Migration July 2019 o With SR-MPLS, SRGB and Node SID need the overall network-wide planning. However, in the cross-domain scenario, it is difficult or sometimes even impossible to perform the overall planning. The node SIDs in different domains may collide. BGP Prefix SID can be used for the cross-domain SID import, but it must be careful when converting the SID to avoid the SID collision. Moreover, the pre- allocated SRGB within each domain needs to consider the total number of devices in all other domains, which raises the difficulties of the network-wide planning. o With SRv6，owning to its native IP feature of route reachability, as long as the IPv6 address space is carefully planned, and the aggregated routes are imported by using BGP4+, the services will auto-start in the cross-domain scenario. 2.3. On-Demand Upgrade The MPLS label itself does not hold any reachability information, so it must be attached to a routable address, which means that the matching relationship between the label and FEC needs to be maintained along the path. SR-MPLS uses the MPLS data plane. When the network migrates to SR- MPLS, there are two ways, as shown in Figure 2: 1. MPLS/SR-MPLS Dual stack: the entire network is upgraded first and then deploy SR-MPLS. 2. MPLS and SR-MPLS interworking: mapping servers are deployed at some of the intermediate nodes and then removed once the entire network is upgraded With either way, big changes in a wide area are required at the initial stage therefore causes a long time-to-market. On the contrary, the network can be migrated to SRv6 on demand. Wherever the services need to turn on, only the relevant devices need to be upgraded to enable SRv6, and all other devices only need to support IPv6 forwarding and need not to be aware of SRv6. When the TE services are needed, only the key nodes along the path needs to be upgraded to support SRv6. Xie, et al. Expires January 9, 2020 [Page 5] Internet-Draft SRv6 Network Migration July 2019 (~~~~~~MPLS/SR-MPLS~~~~~~~) ( +---+ +---+ +---+ ) MPLS Migration Options Option 1 ( |SM | |SM | |SM | ) --->( +---+ +---+ +---+ ) / ( +---+ +---+ +---+ ) (~~~~~~~~~~MPLS~~~~~~~~~~~) / ( |SM | |SM | |SM | ) ( +---+ +---+ +---+ ) / ( +---+ +---+ +---+ ) ( | M | | M | | M | ) / ~~~~~~~~~~~~~~~~~~~~~~~~~~ ( +---+ +---+ +---+ ) \ ( +---+ +---+ +---+ ) \ (~~MPLS~~|~~~~~SR-MPLS~~~~~) ( | M | | M | | M | ) \ ( +---+ | +---+ +---+ ) ( +---+ +---+ +---+ ) \ ( | M | | |SM | |SM | ) ~~~~~~~~~~~~~~~~~~~~~~~~~~ --->( +---+ | +---+ +---+ ) Option 2 ( +---+ | +---+ +---+ ) ( | M | | |SM | |SM | ) ( +---+ | +---+ +---+ ) ~~~~~~~~~~~~~~~~~~~~~~~~~~ SRv6 Migration (~~~~~~~~~~MPLS~~~~~~~~~~~) (~~~~~~SRv6 on demand~~~~~) ( +---+ +---+ +---+ ) ( +---+ +---+ +---+ ) ( | M | | M | | M | ) ( |S6 | | M | | M | ) ( +---+ +---+ +---+ ) ----------> ( +---+ +---+ +---+ ) ( +---+ +---+ +---+ ) ( +---+ +---+ +---+ ) ( | M | | M | | M | ) ( | M | | M | |S6 | ) ( +---+ +---+ +---+ ) ( +---+ +---+ +---+ ) ~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~ Figure 2. MPLS Domain Migration vs. SRv6 On-Demand Upgrade 3. Incremental Deployment Guidance for SRv6 Migration The incremental deployment is the key for smooth migration to SRv6. In order to quickly launch SRv6 network services and enjoy the benefits brought by SRv6, the recommended incremental SRv6 deployment steps are given as follows. These are based on the practical deployment experience earned from the cases such as China Telecom described in [I-D.matsushima-spring-srv6-deployment-status]. The referenced network topology is shown in Figure 3. Xie, et al. Expires January 9, 2020 [Page 6] Internet-Draft SRv6 Network Migration July 2019 /---- Path 1 ----\ +------+ +----+ +---/--+ +---\--+ +----+ +------+ |Site 1|----|PE 1|----|ASBR 1| IP Core |ASBR 2|----|PE 2|----|Site 2| +------+ +----+ +---\--+ +---/--+ +----+ +------+ \---- Path 2 ----/ Figure 3. Reference Network Topology Step1. All the network devices are upgraded to support IPv6. Step 2. According to service demands, only a set of selected PE devices are upgraded to support SRv6 in order to immediately deploy SRv6 overlay VPN services. For instance, in Figure 3, PE1 and PE2 are SRv6-enabled. Step 3. Besides the PE devices, some P devices are upgraded to support SRv6 in order to deploy loose TE which enables network path adjustment and optimization. SFC is also the possible service provided by upgrading part of network devices. Step 4. All the network devices are upgraded to support SRv6. In this case, it is able to deploy strict TE, which enables the deterministic network and other strict security inspection. 4. Migration Guidance for SRv6/SR-MPLS Co-existence Scenario As the network migration to SRv6 is progressing, in most cases SRv6-based services and SR-MPLS-based services will coexist. As shown in Figure 4, in the Non-Standalone (NSA) case specified by 3GPP Release 15 that 5G networks will be supported by existing 4G infrastructure. 4G eNB connects to CSG 2, 5G gNB connects to CSG 1, and EPC connects to RSG 1. For supporting the 4G services, network services need to be provided between CSG 2 and RSG 1 for interconnecting 4G eNB and EPC, while for the 5G services, network services need to be deployed between CSG 1 and RSG 1 for interconnecting 5G gNB and EPC. Meanwhile, for supporting X2 interface between the eNB and gNB, network services also need to be deployed between the CSG 1 and CSG 2. Xie, et al. Expires January 9, 2020 [Page 7] Internet-Draft SRv6 Network Migration July 2019 +-----+ | eNB |------\ +-----+ \ +-----+ |CSG 2|-------+-----+ +-----+ +-----+ /+-----+ |ASG 1|-------------|RSG 1|------| EPC | +-----+ +--/--+ +-----+ +-----+ +-----+ | gNB |-----|CSG 1| Domain 1 | Domain 2 | +-----+ +--\--+ +-----+ +-----+ \+-----+ |ASG 2|-------------|RSG 2| |CSG 3|-------+-----+ +-----+ +-----+ Figure 4. A 3GPP Non-Standalone deployment case As shown in Figure 4, in most of the current network deployments, MPLS-based network services may have already existed between CSG 2 and RSG 1 for interconnecting 4G eNB and EPC for 4G sevices. When 5G services are to be supported, more stringent network services are required, e.g. low latency and high bandwidth. SRv6-based network services could be deployed between CSG 1 and RSG 1 for interconnecting 5G gNB and EPC. In order to perform smooth network migration, dual-stack solution can be adopted which deploy both SRv6 and MPLS stack in one node. With the dual-stack solution, only CSG 1 and RSG 1 need to be upgraded with SRv6/MPLS dual stack. In this case, CSG 1 can immediately start SRv6-based network services to RSG 1 for supporting 5G services, but continue to using MPLS-based services to CSG 2 for X2 interface communications. The upgrade at CSG 1 will not affect the existing 4G services supported by the MPLS-based network services between CSG 2 and RSG 1. RSG1 can provide MPLS services to CSG2 for 4G services as well as SRv6 services to CSG 1 for 5G services. 5. IANA Considerations There are no IANA considerations in this document. 6. Security Considerations TBD. Xie, et al. Expires January 9, 2020 [Page 8] Internet-Draft SRv6 Network Migration July 2019 7. References 7.1. Normative References [I-D.ietf-6man-segment-routing-header] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-segment-routing- header-21 (work in progress), June 2019. [I-D.ietf-spring-srv6-network-programming] Filsfils, C., Camarillo, P., Leddy, J., daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6 Network Programming", draft-ietf-spring-srv6-network- programming-01 (work in progress), July 2019. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . 7.2. Informative References [I-D.matsushima-spring-srv6-deployment-status] Matsushima, S., Filsfils, C., Ali, Z., and Z. Li, "SRv6 Implementation and Deployment Status", draft-matsushima- spring-srv6-deployment-status-01 (work in progress), May 2019. [I-D.peng-spring-srv6-compatibility] Peng, S. and Z. Li, "SRv6 Compatibility with Legacy Devices", draft-peng-spring-srv6-compatibility-00 (work in progress), October 2018. Authors' Addresses Xie, et al. Expires January 9, 2020 [Page 9] Internet-Draft SRv6 Network Migration July 2019 Chongfeng Xie China Telecom China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District Beijing 102209 China Phone: +86-10-50902116 Email: xiechf.bri@chinatelecom.cn Cong Li China Telecom China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District Beijing 102209 China Phone: +86-10-50902556 Email: licong.bri@chinatelecom.cn Shuping Peng Huawei Technologies Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: pengshuping@huawei.com Zhenbin Li Huawei Technologies Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: lizhenbin@huawei.com Yaqun Xiao Huawei Technologies Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: xiaoyaqun@huawei.com Xie, et al. Expires January 9, 2020 [Page 10]