--- 1/draft-ietf-ospf-segment-routing-msd-17.txt 2018-08-28 11:13:15.462245365 -0700 +++ 2/draft-ietf-ospf-segment-routing-msd-18.txt 2018-08-28 11:13:15.486245947 -0700 @@ -1,23 +1,23 @@ OSPF Working Group J. Tantsura Internet-Draft Nuage Networks Intended status: Standards Track U. Chunduri -Expires: February 22, 2019 Huawei Technologies +Expires: March 1, 2019 Huawei Technologies S. Aldrin Google, Inc P. Psenak Cisco Systems - August 21, 2018 + August 28, 2018 Signaling MSD (Maximum SID Depth) using OSPF - draft-ietf-ospf-segment-routing-msd-17 + draft-ietf-ospf-segment-routing-msd-18 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 @@ -31,21 +31,21 @@ 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 February 22, 2019. + This Internet-Draft will expire on March 1, 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 @@ -95,39 +95,36 @@ head-ends. In order for BGP-LS to signal MSD for all the nodes and 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. This document defines an extension to OSPF used to advertise one or - 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 + 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 + 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. + enabled. Note that in a non-SR MPLS network, label depth is what is + defined by the MSD advertisements. 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 - BMI: Base MPLS Imposition is the number of MPLS labels that can be - imposed inclusive of all service/transport/special labels - OSPF: Open Shortest Path First MSD: Maximum SID Depth - the number of SIDs a node or one of its links can support PCC: Path Computation Client PCE: Path Computation Element PCEP: Path Computation Element Protocol @@ -161,21 +158,21 @@ 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Node MSD TLV - The Type: TBD1 + Type: TBD1 Length: variable (multiple of 2 octets) and represents the total length of value field in octets. Value: consists of one or more pairs of a 1 octet MSD-type and 1 octet MSD-Value. MSD-Type: one of the values defined in the IGP MSD Types registry defined in [I-D.ietf-isis-segment-routing-msd]. @@ -214,25 +211,25 @@ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Link MSD Sub-TLV Type: - For OSPFv2, the Link level MSD value is advertised as an optional + 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 a type of TBD2. - For OSPFv3, the Link level MSD value is advertised as an optional + 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 a type of TBD3. Length: variable and same as defined in Section 2. Value: consists of one or more pairs of a 1 octet MSD-type and 1 octet MSD-Value. MSD-Type: one of the values defined in the MSD Types registry defined in [I-D.ietf-isis-segment-routing-msd]. @@ -253,24 +250,24 @@ 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 is used by receiving OSPF routers. This situation MAY be logged as a warning. 4. 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 Link - MSD type MUST be considered as the corresponding Node MSD type value. + 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 + 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 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.