--- 1/draft-ietf-ospf-segment-routing-msd-12.txt 2018-05-17 04:13:20.662309383 -0700 +++ 2/draft-ietf-ospf-segment-routing-msd-13.txt 2018-05-17 04:13:20.686309956 -0700 @@ -1,23 +1,23 @@ OSPF Working Group J. Tantsura Internet-Draft Nuage Networks Intended status: Standards Track U. Chunduri -Expires: November 10, 2018 Huawei Technologies +Expires: November 18, 2018 Huawei Technologies S. Aldrin Google, Inc P. Psenak Cisco Systems - May 09, 2018 + May 17, 2018 Signaling MSD (Maximum SID Depth) using OSPF - draft-ietf-ospf-segment-routing-msd-12 + draft-ietf-ospf-segment-routing-msd-13 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 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. @@ -30,21 +30,21 @@ 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 November 10, 2018. + This Internet-Draft will expire on November 18, 2018. 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 @@ -60,56 +60,55 @@ 1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1.1. 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 5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 - 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 + 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 - 10.2. Informative References . . . . . . . . . . . . . . . . . 9 + 10.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 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. The 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 an SR tunnel or a - Binding-SID anchor node and controller does not participate in IGP + Binding-SID anchor node and controller do not participate in IGP routing, it has no way to learn the MSD of nodes and links. 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 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 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. 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 + more types of MSD at node and/or link granularity. It also defines the Base MPLS Imposition MSD type. 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. Although MSD advertisements are associated with Segment Routing, the advertisements MAY be present even if Segment Routing itself is not enabled. 1.1. Conventions used in this document @@ -133,21 +132,21 @@ PCE: Path Computation Element PCEP: Path Computation Element Protocol SR: Segment Routing SID: Segment Identifier LSA: Link state advertisement - RI: Router Information LSA + RI: OSPF Router Information LSA 1.2. 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 BCP14 [RFC2119], [RFC8174] when, and only when they appear in all capitals, as shown here . 2. Node MSD Advertisement @@ -167,30 +166,31 @@ | MSD Type and Value ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 1: Node MSD TLV The Type: TBD1 Length: variable (minimum of 2, multiple of 2 octets) and represents the total length of value field. - Value: consists of one or more pairs of a 1 octet type (IANA - Registry) and 1 octet value. + Value: consists of one or more pairs of a 1 octet MSD-type and 1 + octet MSD-Value. - MSD Type 1 (IANA Section), MSD and the Value field contains the MSD - of the originating router. Node MSD is a number in the range of - 0-255. 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 minimum value supported by a node. + MSD-Type: one of the values defined in the MSD Types registry defined + in [I-D.ietf-isis-segment-routing-msd]. - Other MSD Types are reserved for future extensions. + MSD-Value: a number in the range of 0-255. For all MSD-Types, 0 + represents lack of the ability to impose MSD stack of any depth; any + other value represents that of the node. This value MUST represent + the lowest value supported by any link configured for use by the + advertising OSPF instance. This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is optional. The 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 @@ -225,28 +225,32 @@ For OSPFv2, the Link level MSD value is advertised as an optional Sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], and has value of TBD2. For OSPFv3, the Link level MSD value is advertised as an optional Sub-TLV of the E-Router-LSA TLV as defined in [RFC8362], and has value of TBD3. Length: variable and similar to that, defined in Section 2. - Value: consists of one or more pairs of a 1 octet MSD Type (IANA - Registry) and 1 octet value. + Value: consists of one or more pairs of a 1 octet MSD-type and 1 + octet MSD-Value. - MSD 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 0-255. 0 - represents lack of the ability to impose MSD stack of any depth; any - other value represents that of the particular link MSD value. + MSD-Type: one of the values defined in the MSD Types registry defined + in [I-D.ietf-isis-segment-routing-msd]. + + MSD-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 0-255. For all MSD-Types, 0 represents lack + of the ability to impose MSD stack of any depth; any other value + represents that of the particular link when used as an outgoing + interface. Other MSD Types are reserved for future extensions. If this TLV is advertised multiple times in the same OSPFv2 Extended Link Opaque LSA, only the first instance of the TLV is used by receiving OSPFv2 routers. This situation SHOULD be logged as an error. If this TLV is advertised multiple times for the same link in different OSPFv2 Extended Link Opaque LSAs originated by the same @@ -273,50 +277,34 @@ specified when an MSD type is defined. 5. Base MPLS Imposition MSD The Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS labels a node is capable of imposing, including all service/transport/special labels. Absence of BMI-MSD advertisements indicates solely that the advertising node does not support advertisement of this capability. + Assignment of MSD-Type for BMI-MSD is defined in + [I-D.ietf-isis-segment-routing-msd]. 6. IANA Considerations This document requests IANA to allocate TLV type (TBD1) from the OSPF Router Information (RI) TLVs Registry as defined by [RFC4970]. IANA has allocated the value 12 through the early assignment process. Also, this document requests IANA to allocate a sub-TLV type (TBD2) from the OSPFv2 Extended Link TLV Sub-TLVs registry. IANA has allocated the the value 6 through the early assignment process. Finally, this document requests IANA to allocate a sub-TLV type (TBD3) from the OSPFv3 Extended-LSA Sub-TLV registry. - This document requests creation of an IANA managed registry under a - new category of "Interior Gateway Protocol (IGP) Parameters" IANA - registries to identify MSD types as proposed in Section 2, Section 3. - The registration procedure is "Expert Review" as defined in - [RFC8126]. The 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 - 7. Security Considerations Security concerns for OSPF are addressed in [RFC7474]. Further security analysis for OSPF protocol is done in [RFC6863] including analysis of both the above documents. Security considerations, as specified by [RFC7770], [RFC7684] and [RFC8362] are applicable to this document. Advertisement of an incorrect MSD value may result: in a path computation failing and the service unavailable or instantiation of a @@ -321,32 +309,38 @@ Advertisement of an incorrect MSD value may result: in a path computation failing and the service unavailable or instantiation of a path that can't be supported by the head-end (the node performing the imposition). 8. Contributors The following people contributed to this document: Les Ginsberg + Email: ginsberg@cisco.com 9. Acknowledgements - The authors would like to thank Acee Lindem, Ketan Talaulikar, - Stephane Litkowski and Bruno Decraene for their reviews and valuable - comments. + The authors would like to thank Acee Lindem, Ketan Talaulikar, Tal + Mizrahi, Stephane Litkowski and Bruno Decraene for their reviews and + valuable comments. 10. References - 10.1. 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-12 (work in progress), May + 2018. + [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, .