OSPF Working Group J. Tantsura Internet-DraftU. ChunduriIndividual Intended status: Standards TrackIndividualU. Chunduri Expires:May 20,September 9, 2017 Huawei Technologies S. Aldrin Google, Inc P. Psenak Cisco Systems March 8, 2017November 16, 2016Signaling MSD (Maximum SID Depth) using OSPFdraft-ietf-ospf-segment-routing-msd-00draft-ietf-ospf-segment-routing-msd-01 Abstract This document proposes a way toexposesignal Maximum SID Depth (MSD) supported by a node at node and/or linklevelgranularity by an OSPF Router. In a Segment Routing (SR) enabled network a centralized controller that programs SR tunnelsat the head-end nodeneeds to know the MSDinformationsupported by the head-end at nodeleveland/or linklevelgranularity to push thelabelSID stack of an appropriatedepth .depth. MSD is relevant to the head-end of a SR tunnel or Binding-SID anchor node where Binding-SID expansions might result in creation of a new SID stack. 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 http://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 onMay 20,September 9, 2017. Copyright Notice Copyright (c)20162017 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 (http://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 . . . . . . . . . . . . . . . . . .34 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . .34 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . .34 4. LINK MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . .45 5. Node MSD vs Link MSD conflict resolution . . . . . . . . . .46 6.Acknowledgements .IANA Considerations . . . . . . . . . . . . . . . . . . . . .46 7.IANASecurity Considerations . . . . . . . . . . . . . . . . . . . 6 8. Contributors . .4 8. Security Considerations. . . . . . . . . . . . . . . . . . .5. . . 6 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 10. References . . . . . . . . . . . . . . . . . . . . . . . . .5 9.1.7 10.1. Normative References . . . . . . . . . . . . . . . . . .5 9.2.7 10.2. Informative References . . . . . . . . . . . . . . . . .57 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .68 1. Introduction When Segment Routing tunnels are computed by a centralized controller, it iscrucialcritical that the controllerknowslearns the MSD "Maximum SID Depth" of the node or link SR tunnel exits over, soit doesn't download a path withthe SID(label stack)stack depth of adepth more thanpath computed doesn't exceed the number of SIDs the nodeor link usedis capable of imposing. This document describes how to use OSPF toexposesignal the MSD ofthea node or link to a centralized controller. PCEP SR extensions draft [I-D.ietf-pce-segment-routing]has defined MSD, to signalsignals MSD in SR PCE CapabilityTLV,TLV and METRIC Object. However,Ifif PCEP is notsupported by a node (head-end ofsupported/configured on the head-end of a SRtunnel)tunnel or a Binding-SID anchor node and controller does not participate in IGProutingrouting, it has no way to learn the MSD ofthe node or linknodes and links which has been configured. BGP-LS [RFC7752] defines a way to expose topology and associateddifferent attributes,attributes and capabilities of the nodes in that topology to a centralizedcontroller andcontroller. MSD signaling by BGP-LS has been defined in[I-D.tantsura-bgp-ls-segment-routing-msd]. For this information[I-D.tantsura-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is configured on a small number of nodes, that do not necessarily act as head-ends. In order, for BGP-LS tobe advertised by BGPsignal MSD for the all nodes and linksofin thenetwork, where thisnetwork MSD isprovisioned,relevant, MSD capabilites SHOULD be distributed to every OSPFmodule should have this informationrouter in theLSDB.network. [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. MSD in contrary signals ability to push SID's stack of a particular depth. MSD of type 1 (IANA Registry) is used to signal the number of SIDs a node is capable of imposing, to be used by a path computation element/controller and is only relevant to the part of the stack created as the result of the computation. In case, there are additional labels (e.g. service) that are to be pushed to the stack - MSD SHOULD be adjusted to reflect that. In the future, new MSD types could be defined to signal additional capabilities: entropy labels, labels that can be pushed thru recirculation, or another dataplane e.g IPv6. [I-D.ietf-ospf-mpls-elc] defines,RLSDCRLDC which indicates how many labels a node can read to take a decision to insert an Entropy Label (EL) and is different than how many labels a node can push as defined by MSD in this draft. 1.1. Conventions used in this document 1.1.1. Terminology BGP-LS: Distribution of Link-State and TE Information using Border Gateway Protocol OSPF: Open Shortest Path First MSD: Maximum SID Depth 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]. 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 isTBD.12 (Suggested value - to be assigned by IANA). Length is variable (minimum of 2, multiple of 2bytes,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 push MSD 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. 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 the value is 5 (Suggested value - to be assigned by IANA) For OSPFv3, the Link level MSD value isTBD.advertised as an optional Sub-TLV of the Router-Link TLV as defined in [I-D.ietf-ospf-ospfv3-lsa-extend], and the value is 3 (Suggested value - to be assigned by IANA). Length is2 bytes,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 forOSPFv3OSPFv2 and OSPFv3. Link MSD is a number in the range of 0-254. 0 represents lack of the ability to push MSD of any depth; any other value represents that of the particular link MSD value.For OSPFv2, the Link level MSD value is advertised as an optional Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684]. For OSPFv3, the Link level MSD value is advertised as an optional Sub-TLV of the Router-Link TLV asOther Sub-types other than definedin [I-D.ietf-ospf-ospfv3-lsa-extend].above are reserved for future extensions. 5. Node MSD vs Link MSD conflict resolution When both Node MSD and Link MSD are present, the value in the Link MSD MUST be used. 6.Acknowledgements TBD 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]. Also for link MSD, we request IANA to allocate new sub-TLV codes as proposed in Section 4 from OSPFv2 Extended Link Opaque LSAs Extended Link TLV registry and from Router-Link TLV defined in OSPFv3 Extend- LSA Sub-TLV registry.8.This document also request IANA to create a new Sub-type registry as proposed in Section 3, Section 4. Value Name Reference ----- --------------------- ------------- 0 Reserved This document 1 MSD This document 2-250 Unassigned This document 251-254 Experimental This document 255 Reserved This document Figure 3: MSD Sub-type Codepoints Registry 7. Security Considerations This document describes a mechanismfor advertisingto signal Segment RoutingSID depthMSD supported at nodeandand/or linklevel informationgranularity through OSPFLSAsLSA's and does not introduce any new security issues. 8. Contributors The following people contributed to this document: Les Ginsberg Email: ginsberg@cisco.com 9. Acknowledgements The authors would like to thank Stephane Litkowski and Bruno Decraene for their reviews and valuable comments. 10. References9.1.10.1. 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, <http://www.rfc-editor.org/info/rfc2119>. [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, <http://www.rfc-editor.org/info/rfc4970>.9.2.10.2. Informative References [I-D.ietf-ospf-mpls-elc] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability Using OSPF",draft-ietf-ospf-mpls-elc-03draft-ietf-ospf-mpls-elc-04 (work in progress),OctoberNovember 2016. [I-D.ietf-ospf-ospfv3-lsa-extend] Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-13 (work in progress), October 2016. [I-D.ietf-pce-segment-routing] Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and J. Hardwick, "PCEP Extensions for Segment Routing", draft- ietf-pce-segment-routing-08 (work in progress), October 2016.[I-D.tantsura-bgp-ls-segment-routing-msd][I-D.tantsura-idr-bgp-ls-segment-routing-msd] Tantsura, J., Chunduri, U., Mirsky, G.,Sivabalan, S.,andU. Chunduri,S. Sivabalan, "Signaling Maximum SID Depth using Border Gateway Protocol Link-State",draft-tantsura-bgp-ls-segment-routing-msd-02draft-tantsura-idr-bgp-ls-segment-routing- msd-02 (work in progress), January2016.2017. [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, <http://www.rfc-editor.org/info/rfc5838>. [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, <http://www.rfc-editor.org/info/rfc7684>. [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, <http://www.rfc-editor.org/info/rfc7752>. Authors' Addresses Jeff Tantsura Individual Email: jefftant.ietf@gmail.com Uma ChunduriIndividualHuawei Technologies Email: uma.chunduri@huawei.com Sam Aldrin Google, Inc Email: aldrin.ietf@gmail.com Peter Psenak Cisco Systems Email:uma.chunduri@gmail.comppsenak@cisco.com