SPRING Working Group C. Li Internet-Draft Huawei Technologies Intended status: Informational A. Sawaf Expires: 24 October 2022 Saudi Telecom Company R. Hu Z. Li Huawei Technologies 22 April 2022 A Framework for Constructing Service Function Chaining Systems Based on Segment Routing draft-li-spring-sr-sfc-control-plane-framework-06 Abstract Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of topological sub-paths, called "segments". Segment routing architecture can be implemented over an MPLS data plane as well as an IPv6 data plane. Service Function Chaining (SFC) provides support for the creation of composite services that consist of an ordered set of Service Functions (SF) that are to be applied to packets and/or frames selected as a result of classification. SFC can be implemented based on several technologies, such as Network Service Header (NSH) and SR. This document describes a framework for constructing SFC based on Segment Routing. The document reviews the control plane solutions for route distribution of service function instance and service function path, and steering packets into a service function chain. 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." Li, et al. Expires 24 October 2022 [Page 1] Internet-Draft SR based SFC Control Plane April 2022 This Internet-Draft will expire on 24 October 2022. Copyright Notice Copyright (c) 2022 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 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview of SR Based SFC Control Plane . . . . . . . . . . . 4 3. Stateless SR Based SFC . . . . . . . . . . . . . . . . . . . 7 3.1. Service Function Instance Route Distribution . . . . . . 7 3.2. Service Function Path Route Distribution . . . . . . . . 8 3.3. Steer Packets into SFC . . . . . . . . . . . . . . . . . 8 4. Stateful SR Based SFC . . . . . . . . . . . . . . . . . . . . 8 4.1. Service Function Route Distribution . . . . . . . . . . . 8 4.2. Service Function Path Route Distribution . . . . . . . . 9 4.3. Steer Packets into SFC . . . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. Introduction Segment routing (SR) [RFC8402] is a source routing paradigm that explicitly indicates the forwarding path for packets at the ingress node by inserting an ordered list of instructions, called segments. When segment routing is deployed on MPLS data plane, it is called SR- MPLS [RFC8660]. When segment routing is deployed on IPv6 data plane, it is called SRv6 [RFC8754]. Li, et al. Expires 24 October 2022 [Page 2] Internet-Draft SR based SFC Control Plane April 2022 Service Function Chaining (SFC) [RFC7665] provides an architecture that supports the creation of composite service that consist of an ordered set of Service Functions (SF) that are to be applied to packets and/or frames selected as a result of classification. SFC can be implemented based on Network Service Header [RFC8300]. In NSH-based SFC, per-SFC state, such as a mapping between Service Path Identifier (SPI) and Service Index (SI) to next-hop forwarding, needs to be maintained on nodes along the Service Function Path(SFP), and it can therefore, be termed as "stateful SFC". [I-D.ietf-bess-nsh-bgp-control-plane] defines the use of BGP as a control plane for networks that support SFC based on NSH and MPLS. The document introduces a new BGP address family called the SFC AFI/ SAFI with two route types: Service Function Instance Route (SFIR) and Service Function Path Route (SFPR). An NSH or MPLS based SFC can be constructed based on the information of SFIR and SFPR. SFC can also be instantiated based on SR. In SR, the forwarding path is explicitly encoded into the packets on the SR source node. In SR- based SFC, an SFC can be represented by a SID list explicitly indicated by the source SR node. The SID in SID list may need to be associated with service information in order to indicate network service, such as Deep Packet Inspection (DPI). Therefore, no per-SFC state needs to be maintained along with the SFP, and it can therefore be termed "stateless SFC". In order to construct SR-based SFC, several mechanisms are proposed, including the mechanisms of SFIR and SFPR distribution, as well as the mechanism of steering packets into an SFP. This document reviews these solutions to describe a framework for the construction of an SFC system based on Segment Routing. 1.1. 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. 1.2. Terminology MPLS: Multiprotocol Label Switching. Li, et al. Expires 24 October 2022 [Page 3] Internet-Draft SR based SFC Control Plane April 2022 SID: Segment Identifier. SR: Segment Routing. SR-MPLS: Segment Routing with MPLS data plane. SRH: Segment Routing Header. SFIR: Service Function Instance Route SFPR: Service Function Path Route Further, this document makes use of the terms defined in [RFC7665] and [I-D.ietf-spring-sr-service-programming]. 2. Overview of SR Based SFC Control Plane As per [RFC7665], the architecture of SFC consists of classifiers, Service Function Forwarders (SFFs), Service Functions (SFs) and SFC Proxies. This is illustrated in Figure 1. +-----+ +-----+ +-----+ | | | SFC | | | | SF1 | |Proxy|---| SF2 | +-----+ +-----+ +-----+ | | +--------------+ | | | Service | SFC +------+ +------+ |Classification| Encapsulation | SFF1 | | SFF2 | --->| Function |+---------------->| |--------| |-------> | | | | | | +--------------+ +------+ +------+ SFC-enabled Domain Figure 1. SFC Architecture In order to construct an SFC, SFIR and SFPR should be distributed to classifiers and SFFs. Also, the rules of steering packets into specific SFPs should be configured at the classifier. [I-D.ietf-bess-nsh-bgp-control-plane]. Li, et al. Expires 24 October 2022 [Page 4] Internet-Draft SR based SFC Control Plane April 2022 In SR, a source node can explicitly indicate the forwarding path for packets by inserting an ordered list of instructions. These packet steering policies, known as SR policy, can be installed by a central controller via BGP [I-D.ietf-idr-segment-routing-te-policy] or other mechanisms. When SFC is constructed based on SR, SFPR and packet steering rules can be installed by SR policy at the ingress node, which plays the role of classifier in the SFC architecture. In other words, SFPR does not need to be distributed to all the nodes along the SFP. The architecture of SR based SFC is illustrated in Figure 2. +-----+ +-----+ +-----+ +-----+ | | | | | SR | | | |SR-C | | SF1 | |Proxy|---| SF2 | +-----+ +-----+ +-----+ +-----+ | | | | | | +--------------+ +------+ +------+ | | SFC Encap/SR | SFF1/| | SFF2/| --->|CF/SR ingress |+---------------->| SR |--------| SR |-------> | | | | | | +--------------+ +------+ +------+ SFC-enabled Domain Figure 2. SR based SFC architecture. * CF/SR ingress: an SR ingress node plays the role of Classifier in the SFC architecture, and it connects to an SR controller, where the SR policies originate. * SR-C: SR Controller (SR-C) is connected to the SR ingress node, and may be attached to any node in the network. SR-C is capable of discovering topology, and calculating constrained paths for SFCs. * SFF/SR nodes: the SFF component in SFC architecture, which enables SR to steer packets to SFs. * SFn: Service Functions, can be SR-aware or SR-unaware. If an SF is SR-unaware then SR proxy is needed. * SR proxy: A proxy between SFF/SR nodes and SR-unaware SF. Li, et al. Expires 24 October 2022 [Page 5] Internet-Draft SR based SFC Control Plane April 2022 There are two solutions to encode SFC in the SR data plane. [I-D.ietf-spring-sr-service-programming] defines data plane functionality required to implement service segments and achieve service programming in SR-enabled MPLS and IP networks. It can be termed "Stateless SFC" since no per-SFC state is maintained on the SR nodes along the SFP. The second solution can be termed "Stateful SFC" [I-D.ietf-spring-nsh-sr], since it still maintains per-SFC state on nodes. [I-D.ietf-spring-nsh-sr]describes two modes of operation: * NSH-based SFC with SR-based transport tunnel: SR is used as the transport tunnel to route packets between classifier and SFF or SFFs. Service plane routing relies on NSH. * SR-based SFC with Integrated NSH Service Plane: The SFP is encoded within the SR segment-list, while the NSH only maintains the service plane context information, which will be used at NSH-aware SFs, and at SFFs as a pointer to cache SR segment-lists. In order to support these data plane encodings, control plane mechanisms are required. The existing control plane mechanisms are shown in table 1. +------------------------------------------------------------+ | SR based SFC | SFIR | SFPR | Steering policy| +-------------------+-----------+-----------+----------------+ | | BGP | BGP | BGP | |Stateless | BGP-LS | PCEP | PCEP | | | IGP | | | +-------------------+-----------+-----------+----------------+ |NSH-based SFC | BGP | BGP | BGP | |with SR-based | | PCEP | | |transport tunnel | | | | | | | | | | | | | | +-------------------+-----------+-----------+----------------+ |SR-based SFC | BGP | BGP | BGP | |with Integrated | BGP-LS | PCEP | PCEP | |NSH Service Plane | IGP | | | | | | | | +-------------------+-----------+-----------+----------------+ Table 1. SR based SFC Control Plane Solutions Li, et al. Expires 24 October 2022 [Page 6] Internet-Draft SR based SFC Control Plane April 2022 3. Stateless SR Based SFC As describe in [I-D.ietf-spring-sr-service-programming], service instances are associated with a segment, called a service SID. These service SIDs are leveraged as part of a SID-list to steer packets through the corresponding services 3.1. Service Function Instance Route Distribution To associate a segment with a service, service information, such as Service Function Type (SFT), should be included in segment distribution. [I-D.dawra-idr-bgp-ls-sr-service-segments] specifies the extensions to BGP-LS for discovery and advertisement of service segments to enable setup of service programming paths using Segment Routing. [I-D.dawra-idr-bgp-ls-sr-service-segments] extends SRv6 Node SID TLV [I-D.ietf-idr-bgpls-srv6-ext] and SR-MPLS SID/ Label TLV [I-D.ietf-idr-bgp-ls-segment-routing-ext] to associate the Service SID Value with Service-related Information using Service Chaining Sub-TLV. The Service Chaining Sub-TLV contains information of Service SID value, Function Identifier (Static Proxy, Dynamic Proxy, Shared Memory Proxy, Masquerading Proxy, SR Aware Service Etc.), Service Type (DPI, Firewall, Classifier, LB etc.), Traffic Type (IPv4 OR IPv6 OR Ethernet) and Opaque Data (such as brand and version, other extra information). This extension works for both SR- MPLS and SRv6. [I-D.ietf-bess-nsh-bgp-control-plane] proposes a BGP-based SFC control plane solution, and it works for SR-MPLS as well. Service function instance route distribution can use SFIR in SFC AFI/SAFI. SFPR and steering rules for the classifier can be distributed by SR policy, which is defined in [I-D.ietf-idr-segment-routing-te-policy]. BGP control plane of SRv6-based SFC still needs to be defined. IGP extensions are proposed by [I-D.xu-isis-service-function-adv] and [I-D.xu-ospf-service-function-adv]. In IS-IS solution, SFFs within the SFC domain need to advertise each SF they are offering by using a new sub-TLV of the IS-IS Router CAPABILITY TLV [RFC4971]. This new sub-TLV is called Service Function sub-TLV, and it can appear multiple times within a given IS-IS Router CAPABILITY TLV or when more than one SF needs to be advertised. OSPF extensions are similar, and use the OSPF Router Information (RI) Opaque LSA [RFC4970] to carry Service Function sub-TLV. However, due to IGP flooding issues, IGP extensions are not very appropriate, and the drafts have expired for a long time. Li, et al. Expires 24 October 2022 [Page 7] Internet-Draft SR based SFC Control Plane April 2022 3.2. Service Function Path Route Distribution With SR, the SFPR does not need to be distributed to nodes along the SFP but only to the ingress node. SFPR and steering rules for the classifier can be distributed by SR policy. The BGP extension is defined in [I-D.ietf-idr-segment-routing-te-policy]. The PCEP extension is defined in [I-D.ietf-pce-segment-routing-policy-cp]. 3.3. Steer Packets into SFC In SR, packet steering rules are learned through SR policy. Thus, there is no need to install other rules in the classifier, which is the SR source node. 4. Stateful SR Based SFC "Stateful SFC" [I-D.ietf-spring-nsh-sr] proposes two modes of SR based SFC: * NSH-based SFC with SR-based transport tunnel * SR-based SFC with Integrated NSH Service Plane 4.1. Service Function Route Distribution For NSH-based SFC with SR-based transport tunnel, service information is maintained by NSH while SR is only used for transport between SFFs, so [I-D.ietf-bess-nsh-bgp-control-plane] can be used for this mode. To indicate NSH, an SFF label [I-D.ietf-mpls-sfc-encapsulation] should be inserted as the last label in the label stack in SR-MPLS. The control plane of SFF is also described in [I-D.ietf-bess-nsh-bgp-control-plane]. For choosing/configuring SR as the transport tunnel, BGP route of SFF's BGP Tunnel Encapsulation Attribute Type should be "SR TE Policy Type" [I-D.ietf-idr-segment-routing-te-policy]. For SR-based SFC with Integrated NSH Service Plane, there is no control plane solution as yet defined. Li, et al. Expires 24 October 2022 [Page 8] Internet-Draft SR based SFC Control Plane April 2022 4.2. Service Function Path Route Distribution Same as SFIR distribution, SFPR BGP distribution in NSH-based SFC with SR-based transport tunnel is identical to the mechanism defined in [I-D.ietf-bess-nsh-bgp-control-plane]. PCEP extension for SFPR distribution can reuse the NSH based SFC extension defined in [I-D.wu-pce-traffic-steering-sfc]. For SR-based SFC with Integrated NSH Service Plane, control plane solution is to be added in other documents. 4.3. Steer Packets into SFC For NSH-based SFC with SR-based transport tunnel, it is the same with the NSH based SFC. The Classifier is responsible for determining to which packet flow a packet belongs (usually by inspecting the packet header), imposing an NSH, and initializing the NSH with the SPI of the selected SFP and the SI of its first hop [I-D.ietf-bess-nsh-bgp-control-plane]. For SR-based SFC with Integrated NSH Service Plane, control plane solution is to be added in other document. 5. IANA Considerations This document does not require any IANA actions. 6. Security Considerations This document does not introduce additional security requirements and mechanisms. 7. Acknowledgements TBA 8. References 8.1. 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, . Li, et al. Expires 24 October 2022 [Page 9] Internet-Draft SR based SFC Control Plane April 2022 8.2. Informative References [I-D.dawra-idr-bgp-ls-sr-service-segments] Dawra, G., Filsfils, C., Talaulikar, K., Clad, F., Bernier, D., Uttaro, J., Decraene, B., Elmalky, H., Xu, X., Guichard, J., and C. Li, "BGP-LS Advertisement of Segment Routing Service Segments", Work in Progress, Internet-Draft, draft-dawra-idr-bgp-ls-sr-service- segments-06, 17 August 2021, . [I-D.ietf-bess-nsh-bgp-control-plane] Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L. Jalil, "BGP Control Plane for the Network Service Header in Service Function Chaining", Work in Progress, Internet- Draft, draft-ietf-bess-nsh-bgp-control-plane-18, 21 August 2020, . [I-D.ietf-idr-bgp-ls-segment-routing-ext] Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., and M. Chen, "Border Gateway Protocol - Link State (BGP- LS) Extensions for Segment Routing", Work in Progress, Internet-Draft, draft-ietf-idr-bgp-ls-segment-routing-ext- 18, 15 April 2021, . [I-D.ietf-idr-bgpls-srv6-ext] Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., Bernier, D., and B. Decraene, "BGP Link State Extensions for SRv6", Work in Progress, Internet-Draft, draft-ietf- idr-bgpls-srv6-ext-09, 10 November 2021, . [I-D.ietf-idr-segment-routing-te-policy] Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., Jain, D., and S. Lin, "Advertising Segment Routing Policies in BGP", Work in Progress, Internet-Draft, draft- ietf-idr-segment-routing-te-policy-17, 14 April 2022, . [I-D.ietf-mpls-sfc-encapsulation] Malis, A. G., Bryant, S., Halpern, J. M., and W. Henderickx, "MPLS Transport Encapsulation for the Service Function Chaining (SFC) Network Service Header (NSH)", Li, et al. Expires 24 October 2022 [Page 10] Internet-Draft SR based SFC Control Plane April 2022 Work in Progress, Internet-Draft, draft-ietf-mpls-sfc- encapsulation-04, 24 March 2019, . [I-D.ietf-pce-segment-routing-policy-cp] Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H. Bidgoli, "PCEP extension to support Segment Routing Policy Candidate Paths", Work in Progress, Internet-Draft, draft- ietf-pce-segment-routing-policy-cp-07, 21 April 2022, . [I-D.ietf-spring-nsh-sr] Guichard, J. N. and J. Tantsura, "Integration of Network Service Header (NSH) and Segment Routing for Service Function Chaining (SFC)", Work in Progress, Internet- Draft, draft-ietf-spring-nsh-sr-11, 20 April 2022, . [I-D.ietf-spring-sr-service-programming] Clad, F., Xu, X., Filsfils, C., Bernier, D., Li, C., Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and S. Salsano, "Service Programming with Segment Routing", Work in Progress, Internet-Draft, draft-ietf-spring-sr- service-programming-05, 10 September 2021, . [I-D.wu-pce-traffic-steering-sfc] Wu, Q., Dhody, D., Boucadair, M., Jacquenet, C., and J. Tantsura, "PCEP Extensions for Service Function Chaining (SFC)", Work in Progress, Internet-Draft, draft-wu-pce- traffic-steering-sfc-12, 30 June 2017, . [I-D.xu-isis-service-function-adv] Xu, X., Wu, N., Shah, H., and L. M. Contreras, "Advertising Service Functions Using IS-IS", Work in Progress, Internet-Draft, draft-xu-isis-service-function- adv-05, 10 May 2017, . [I-D.xu-ospf-service-function-adv] Xu, X., Wu, N., Shah, H., and L. M. Contreras, "Advertising Service Functions Using OSPF", Work in Li, et al. Expires 24 October 2022 [Page 11] Internet-Draft SR based SFC Control Plane April 2022 Progress, Internet-Draft, draft-xu-ospf-service-function- adv-02, 29 June 2014, . [RFC4970] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July 2007, . [RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed., "Intermediate System to Intermediate System (IS-IS) Extensions for Advertising Router Information", RFC 4971, DOI 10.17487/RFC4971, July 2007, . [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015, . [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, January 2018, . [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, . [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, . [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, . Authors' Addresses Cheng Li Huawei Technologies Email: c.l@huawei.com Li, et al. Expires 24 October 2022 [Page 12] Internet-Draft SR based SFC Control Plane April 2022 Ahmed El Sawaf Saudi Telecom Company Riyadh Saudi Arabia Email: aelsawaf.c@stc.com.sa Ruizhao Hu Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: huruizhao@huawei.com Zhenbin Li Huawei Technologies Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China Email: lizhenbin@huawei.com Li, et al. Expires 24 October 2022 [Page 13]