OSPF Working Group J. Tantsura Internet-Draft Nuage Networks Intended status: Standards Track U. Chunduri Expires: August 30, 2018 Huawei Technologies S. Aldrin Google, Inc P. Psenak Cisco Systems February 26, 2018 Signaling MSD (Maximum SID Depth) using OSPF draft-ietf-ospf-segment-routing-msd-09 Abstract This document defines a way for an OSPF Router to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity. Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular SID stack is supportable in a given network. This document only defines one type of MSD (maximum label imposition) - but defines an encoding which can support other MSD types. Here the term OSPF means both OSPFv2 and OSPFv3. 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 August 30, 2018. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. Tantsura, et al. Expires August 30, 2018 [Page 1] Internet-Draft February 2018 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 1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5 5. Using Node and Link MSD Advertisements . . . . . . . . . . . 5 6. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 11.1. Normative References . . . . . . . . . . . . . . . . . . 7 11.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction When Segment Routing(SR) paths are computed by a centralized controller, it is critical that the controller learns the Maximum SID Depth(MSD) which can be imposed at the node/link a given SR path is applied so as to insure that the SID stack depth of a computed path doesn't exceed the number of SIDs the node is capable of imposing. PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD in SR PCE Capability TLV and METRIC Object. However, if PCEP is not supported/configured on the head-end of a SR tunnel or a Binding-SID anchor node and controller does not participate in IGP routing, it has no way to learn the MSD of nodes and links which has been configured. BGP-LS [RFC7752] defines a way to expose topology and associated attributes and capabilities of the nodes in that topology to a centralized controller. MSD signaling by BGP-LS has been defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is configured on a small number of nodes, that do not Tantsura, et al. Expires August 30, 2018 [Page 2] Internet-Draft February 2018 necessarily act as head-ends. In order, for BGP-LS to signal MSD for all the nodes and links in the network MSD is relevant, MSD capabilites should be advertised to every OSPF router in the network. Other types of MSD are known to be useful. For example, [I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability (RLDC) that is used by a head-end to insert Entropy Label (EL) at appropriate depth, so it could be read by transit nodes. This document defines an extension to OSPF used to advertise one or more types of MSD at node and/or link granularity. It also creates an IANA registry for assigning MSD type identifiers. It also defines one MSD type called Base MPLS Imposition MSD. In the future it is expected that new MSD types will be defined to signal additional capabilities e.g., entropy labels, SIDs that can be imposed through recirculation, or SIDs associated with another dataplane e.g., IPv6. 1.1. Conventions used in this document 1.1.1. Terminology BGP-LS: Distribution of Link-State and TE Information using Border Gateway Protocol BMI: Base MPLS Imposition is the number of MPLS labels which can be imposed inclusive of any service/transport labels OSPF: Open Shortest Path First MSD: Maximum SID Depth - the number of SIDs a node or a link on a node can support PCC: Path Computation Client PCE: Path Computation Element PCEP: Path Computation Element Protocol SID: Segment Identifier SR: Segment Routing 1.2. 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]. Tantsura, et al. Expires August 30, 2018 [Page 3] Internet-Draft February 2018 2. Terminology This memo makes use of the terms defined in [RFC4970]. 3. Node MSD TLV A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD TLV is defined to carry the provisioned SID depth of the router originating the RI LSA. Node MSD is the lowest MSD supported by the node. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Type and Value ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 1: Node MSD TLV The Type (2 bytes) of this TLV has value of 12. Length is variable (minimum of 2, multiple of 2 octets) and represents the total length of value field. Value field consists of a 1 octet sub-type (IANA Registry) and 1 octet value. Sub-Type 1 (IANA Section), MSD and the Value field contains maximum MSD of the router originating the RI LSA. Node Maximum MSD is a number in the range of 0-254. 0 represents lack of the ability to impose MSD stack of any depth; any other value represents that of the node. This value SHOULD represent the lowest value supported by node. Other Sub-types other than defined above are reserved for future extensions. This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is optional. The scope of the advertisement is specific to the deployment. Tantsura, et al. Expires August 30, 2018 [Page 4] Internet-Draft February 2018 4. Link MSD sub-TLV A new sub-TLV called Link MSD sub-TLV is defined to carry the provisioned SID depth of the interface associated with the link. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Type and Value ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 2: Link MSD Sub-TLV The Type (2 bytes) of this TLV: For OSPFv2, the Link level MSD value is advertised as an optional Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684], and has value of 6. For OSPFv3, the Link level MSD value is advertised as an optional Sub-TLV of the Router-Link TLV as defined in [I-D.ietf-ospf-ospfv3-lsa-extend], and has value of 16 (Suggested value - to be assigned by IANA). Length is variable and similar to what is defined in Section 3. Value field consists of a 1 octet sub-type (IANA Registry) and 1 octet value. Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD of the router originating the corresponding LSA as specified for OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0 represents lack of the ability to impose MSD stack of any depth; any other value represents that of the particular link MSD value. Other Sub-types other than defined above are reserved for future extensions. 5. Using Node and Link MSD Advertisements When Link MSD is present for a given MSD type, the value of the Link MSD MUST be used in preference to the Node MSD. Tantsura, et al. Expires August 30, 2018 [Page 5] Internet-Draft February 2018 The meaning of the absence of both Node and Link MSD advertisements for a given MSD type is specific to the MSD type. Generally it can only be inferred that the advertising node does not support advertisement of that MSD type. However, in some cases the lack of advertisement might imply that the functionality associated with the MSD type is not supported. The correct interpretation MUST be specified when an MSD type is defined. 6. Base MPLS Imposition MSD Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS labels a node is capable of imposing, including any service/transport labels. Absence of BMI-MSD advertisements indicates only that the advertising node does not support advertisement of this capability. 7. IANA Considerations This document includes a request to IANA to allocate TLV type codes for the new TLV proposed in Section 3 of this document from OSPF Router Information (RI) TLVs Registry as defined by [RFC4970]. For the link MSD, we request IANA to allocate new sub-TLV codes as proposed in Section 4 from OSPFv2 Extended Link TLV Sub-TLVs registry and from Router-Link TLV defined in OSPFv3 Extend-LSA Sub-TLV registry. This document requests creation of a new IANA managed registry under a new category of "Interior Gateway Protocol (IGP) Parameters" IANA registries to identify MSD types as proposed in Section 3, Section 4. The registration procedure is "Expert Review" as defined in [RFC8126]. Suggested registry name is "MSD types". Types are an unsigned 8 bit number. The following values are defined by this document Value Name Reference ----- --------------------- ------------- 0 Reserved This document 1 Base MPLS Imposition MSD This document 2-250 Unassigned This document 251-254 Experimental This document 255 Reserved This document Figure 3: MSD Types Codepoints Registry Tantsura, et al. Expires August 30, 2018 [Page 6] Internet-Draft February 2018 8. Security Considerations Security considerations, as specified by [RFC7770] are applicable to this document 9. Contributors The following people contributed to this document: Les Ginsberg Email: ginsberg@cisco.com 10. Acknowledgements The authors would like to thank Stephane Litkowski and Bruno Decraene for their reviews and valuable comments. 11. References 11.1. 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, . [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, . [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, February 2016, . 11.2. Informative References [I-D.ietf-idr-bgp-ls-segment-routing-msd] Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, "Signaling Maximum SID Depth using Border Gateway Protocol Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 (work in progress), October 2017. Tantsura, et al. Expires August 30, 2018 [Page 7] Internet-Draft February 2018 [I-D.ietf-ospf-mpls-elc] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Readable Label-stack Depth Using OSPF", draft-ietf-ospf- mpls-elc-05 (work in progress), January 2018. [I-D.ietf-ospf-ospfv3-lsa-extend] Lindem, A., Roy, A., Goethals, D., Vallem, V., and F. Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3- lsa-extend-23 (work in progress), January 2018. [I-D.ietf-pce-segment-routing] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., and J. Hardwick, "PCEP Extensions for Segment Routing", draft-ietf-pce-segment-routing-11 (work in progress), November 2017. [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and R. Aggarwal, "Support of Address Families in OSPFv3", RFC 5838, DOI 10.17487/RFC5838, April 2010, . [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 2015, . [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, . [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . Authors' Addresses Jeff Tantsura Nuage Networks Email: jefftant.ietf@gmail.com Tantsura, et al. Expires August 30, 2018 [Page 8] Internet-Draft February 2018 Uma Chunduri Huawei Technologies Email: uma.chunduri@huawei.com Sam Aldrin Google, Inc Email: aldrin.ietf@gmail.com Peter Psenak Cisco Systems Email: ppsenak@cisco.com Tantsura, et al. Expires August 30, 2018 [Page 9]