--- 1/draft-ietf-ospf-segment-routing-msd-21.txt 2018-10-11 17:13:15.384119737 -0700 +++ 2/draft-ietf-ospf-segment-routing-msd-22.txt 2018-10-11 17:13:15.412120419 -0700 @@ -1,51 +1,51 @@ OSPF Working Group J. Tantsura -Internet-Draft Nuage Networks +Internet-Draft Apstra, Inc. Intended status: Standards Track U. Chunduri -Expires: March 29, 2019 Huawei Technologies +Expires: April 14, 2019 Huawei Technologies S. Aldrin Google, Inc P. Psenak Cisco Systems - September 25, 2018 + October 11, 2018 Signaling MSD (Maximum SID Depth) using OSPF - draft-ietf-ospf-segment-routing-msd-21 + draft-ietf-ospf-segment-routing-msd-22 Abstract This document defines a way for an Open Shortest Path First (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 can be supported in a given network. This - document defines only one type of MSD, but defines an encoding that - can support other MSD types. Here the term OSPF means both OSPFv2 - and OSPFv3. + Router to advertise multiple types of supported Maximum SID(Segment + Identifier) Depths (MSDs) at node and/or link granularity. Such + advertisements allow entities (e.g., centralized controllers) to + determine whether a particular SID stack can be supported in a given + network. This document defines only one type of MSD, but defines an + encoding that 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 March 29, 2019. + This Internet-Draft will expire on April 14, 2019. Copyright Notice Copyright (c) 2018 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 @@ -55,85 +55,99 @@ the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4 2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 3. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5 - 4. Using Node and Link MSD Advertisements . . . . . . . . . . . 6 + 4. Procedures for Defining and Using Node and Link MSD + Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 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) that can be imposed at each node/link on a given SR path - to insure that the SID stack depth of a computed path doesn't exceed - the number of SIDs the node is capable of imposing. + (Segment Identifier) Depth (MSD) that can be imposed at each node/ + link on a given SR path to ensure that the Segment Identifier (SID) + stack depth of a computed path doesn't exceed the number of SIDs the + node is capable of imposing. - Path Computation Element Protocol(PCEP) SR draft - [I-D.ietf-pce-segment-routing] signals MSD in SR Path Computation - Element Capability TLV and METRIC Object. However, if PCEP is not - supported/configured on the head-end of an 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. BGP-LS (Distribution - of Link-State and TE Information using Border Gateway Protocol) - [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-pce-segment-routing] defines how to signal MSD in the Path + Computation Element communication Protocol (PCEP). However, if PCEP + is not supported/configured on the head-end of an 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. BGP-LS + (Distribution of Link-State and TE Information using Border Gateway + Protocol) [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 necessarily act as head-ends. In order for BGP-LS to signal MSD for all the nodes and - links in the network where MSD is relevant, MSD capabilities should - be advertised by every OSPF router in the network. + links in the network MSD is relevant, MSD capabilities SHOULD be + advertised by 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 an Entropy Label (EL) at - a depth that can be read by transit nodes. + a depth that 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. In the future it - is expected, that new MSD types will be defined to signal additional + 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. - Although MSD advertisements are associated with Segment Routing, the - advertisements MAY be present even if Segment Routing itself is not - enabled. Note that in a non-SR MPLS network, label depth is what is - defined by the MSD advertisements. + + MSD advertisements MAY be useful even if Segment Routing itself is + not enabled. For example, in a non-SR MPLS network, MSD defines the + maximum label depth. 1.1. Terminology This memo makes use of the terms defined in [RFC7770] BGP-LS: Distribution of Link-State and TE Information using Border Gateway Protocol OSPF: Open Shortest Path First - MSD: Maximum SID Depth - the number of SIDs a node or one of its - links can support + MSD: Maximum SID Depth - the number of SIDs supported by a node or a + link on a node + + SID: Segment Identifier as defined in [RFC8402] + + Label Imposition: Imposition is the act of modifying and/or adding + labels to the outgoing label stack associated with a packet. This + includes: + + o replacing the label at the top of the label stack with a new label + + o pushing one or more new labels onto the label stack + + The number of labels imposed is then the sum of the number of labels + which are replaced and the number of labels which are pushed. See + [RFC3031] for further details. PCC: Path Computation Client PCE: Path Computation Element - PCEP: Path Computation Element Protocol SR: Segment Routing SID: Segment Identifier LSA: Link state advertisement RI: OSPF Router Information LSA @@ -186,22 +200,22 @@ scope of the advertisement is specific to the deployment. When multiple Node MSD TLVs are received from a given router, the receiver MUST use the first occurrence of the TLV in the Router Information LSA. If the Node MSD TLV appears in multiple Router Information LSAs that have different flooding scopes, the Node MSD TLV in the Router Information LSA with the area-scoped flooding scope MUST be used. If the Node MSD TLV appears in multiple Router Information LSAs that have the same flooding scope, the Node MSD TLV in the Router Information (RI) LSA with the numerically smallest - Instance ID MUST be used and subsequent instances of the Node MSD TLV - MUST be ignored. The RI LSA can be advertised at any of the defined + Instance ID MUST be used and other instances of the Node MSD TLV MUST + be ignored. The RI LSA can be advertised at any of the defined opaque flooding scopes (link, area, or Autonomous System (AS)). For the purpose of Node MSD TLV advertisement, area-scoped flooding is RECOMMENDED. 3. Link MSD sub-TLV The link sub-TLV is defined to carry the MSD of the interface associated with the link. MSD values may be learned via a hardware API or may be provisioned. @@ -246,43 +260,38 @@ TLV MUST be used by receiving OSPF routers. This situation SHOULD be logged as an error. If this sub-TLV is advertised multiple times for the same link in different OSPF Extended Link Opaque LSAs/E-Router-LSAs originated by the same OSPF router, the OSPFv2 Extended Link TLV in the OSPFv2 Extended Link Opaque LSA with the smallest Opaque ID or in the OSPFv3 E-Router-LSA with the smallest Link State ID MUST be used by receiving OSPF routers. This situation MAY be logged as a warning. -4. Using Node and Link MSD Advertisements +4. Procedures for Defining and Using Node and Link MSD Advertisements - When Link MSD is present for a given MSD type, the value of the Link - MSD MUST take preference over the Node MSD. When a Link MSD type is - not signalled but the Node MSD type is, then the value of that Node - MSD type MUST be considered as the corresponding Link MSD type value. - In order to increase flooding efficiency, it is RECOMMENDED, that - routers with homogenous Link MSD values advertise just the Node MSD - value. + When Link MSD is present for a given MSD-type, the value of the Link + MSD MUST take precedence over the Node MSD. When a Link MSD-type is + not signaled but the Node MSD-type is, then the Node MSD-type value + MUST be considered as the MSD value for that link. - Information received in an MSD advertisements is to to ensure that - the controller learns the Maximum SID Depth (MSD) that can be imposed - at each node/link on a given SR path so that the SID stack depth of a - computed path doesn't exceed the number of SIDs the node is capable - of imposing + In order to increase flooding efficiency, it is RECOMMENDED that + routers with homogenous link MSD values advertise just the Node MSD + value. 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 + 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 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. + MSD-type is not supported. The correct interpretation MUST be + specified when an MSD-type is defined. 5. IANA Considerations This document requests IANA to allocate TLV type (TBD1) from the OSPF Router Information (RI) TLVs Registry as defined by [RFC7770]. IANA has allocated the value 12 through the early assignment process. Value Description Reference ----- --------------- ------------- 12 Node MSD This document @@ -316,33 +326,29 @@ [RFC7684] and [RFC8362] are applicable to this document. Implementations MUST assure that malformed TLV and Sub-TLV defined in this document are detected and do not provide a vulnerability for attackers to crash the OSPF router or routing process. Reception of malformed TLV or Sub-TLV SHOULD be counted and/or logged for further analysis. Logging of malformed TLVs and Sub-TLVs SHOULD be rate- limited to prevent a Denial of Service (DoS) attack (distributed or otherwise) from overloading the OSPF control plane. - Advertisement of an incorrect MSD value may result: - - If the value is smaller than supported - path computation failing to - compute a viable path. - - If the value is larger than supported - instantiation of a path that - can't be supported by the head-end (the node performing the SID - imposition). + Advertisement of an incorrect MSD value may have negative + consequences. If the value is smaller than supported, path + computation may fail to compute a viable path. If the value is + larger than supported, an attempt to instantiate a path that can't be + supported by the head-end (the node performing the SID imposition) + may occur. - The MSD discloses capabilities of the nodes (how many SIDs it - supports), which could provide an indication of the abilities or even - types of the nodes being used. This information could be used to - gain intelligence about devices in the network. + The presence of this information also may inform an attacker of how + to induce any of the aforementioned conditions. There's no Denial of Service risk specific to this extension, and it is not vulnerable to replay attacks. 7. Contributors The following people contributed to this document: Les Ginsberg @@ -354,47 +360,57 @@ Mizrahi, Stephane Litkowski and Bruno Decraene for their reviews and valuable comments. 9. References 9.1. Normative References [I-D.ietf-isis-segment-routing-msd] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling MSD (Maximum SID Depth) using IS-IS", draft- - ietf-isis-segment-routing-msd-16 (work in progress), - September 2018. + ietf-isis-segment-routing-msd-19 (work in progress), + October 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . + [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol + Label Switching Architecture", RFC 3031, + DOI 10.17487/RFC3031, January 2001, + . + [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, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and F. Baker, "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 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, . + 9.2. Informative References [I-D.ietf-idr-bgp-ls-segment-routing-msd] Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, "Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link-State", draft-ietf-idr-bgp-ls-segment- routing-msd-02 (work in progress), August 2018. [I-D.ietf-ospf-mpls-elc] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. @@ -430,28 +446,27 @@ [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, . Authors' Addresses Jeff Tantsura - Nuage Networks + Apstra, Inc. Email: jefftant.ietf@gmail.com 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