--- 1/draft-ietf-idr-bgp-ls-segment-routing-msd-16.txt 2020-04-26 14:13:05.884066471 -0700 +++ 2/draft-ietf-idr-bgp-ls-segment-routing-msd-17.txt 2020-04-26 14:13:05.908067084 -0700 @@ -1,26 +1,26 @@ IDR Working Group J. Tantsura Internet-Draft Apstra, Inc. Intended status: Standards Track U. Chunduri -Expires: October 1, 2020 Futurewei Technologies +Expires: October 28, 2020 Futurewei Technologies K. Talaulikar Cisco Systems G. Mirsky ZTE Corp. N. Triantafillis Amazon Web Services - March 30, 2020 + April 26, 2020 Signaling MSD (Maximum SID Depth) using Border Gateway Protocol - Link State - draft-ietf-idr-bgp-ls-segment-routing-msd-16 + draft-ietf-idr-bgp-ls-segment-routing-msd-17 Abstract This document defines a way for a Border Gateway Protocol - Link State (BGP-LS) speaker 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 Segment Identifier (SID) stack can be supported in a given network. @@ -33,21 +33,21 @@ 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 October 1, 2020. + This Internet-Draft will expire on October 28, 2020. Copyright Notice Copyright (c) 2020 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 @@ -68,38 +68,38 @@ 4. Link MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Procedures for Defining and Using Node and Link MSD Advertisements . . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Manageability Considerations . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 - 11.2. Informative References . . . . . . . . . . . . . . . . . 9 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 + 11.2. Informative References . . . . . . . . . . . . . . . . . 8 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction When Segment Routing (SR) [RFC8402] paths are computed by a - centralized controller, it is critical that the controller learn the + 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. This ensures that the Segment Identifier (SID) stack depth of a computed path doesn't exceed the number of SIDs the node is capable of imposing. [RFC8664] defines how to signal MSD in the Path Computation Element Protocol (PCEP). The OSPF and IS-IS extensions for signaling of MSD are defined in [RFC8476] and [RFC8491] respectively. 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 + tunnel or a Binding-SID anchor node, and the controller does not participate in IGP routing, it has no way of learning 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. This document defines extensions to BGP-LS to advertise one or more types of MSDs at node and/or link granularity. Other types of MSD are known to be useful. For example, [I-D.ietf-ospf-mpls-elc] and [I-D.ietf-isis-mpls-elc] define Readable Label Depth Capability (RLDC) that is used by a head-end to insert an Entropy Label (EL) at @@ -112,22 +112,20 @@ not enabled. For example, in a non-SR MPLS network, MSD defines the maximum label depth. 1.1. Conventions used in this document 1.1.1. Terminology MSD: Maximum SID Depth - the number of SIDs supported by a node or a link on a node - PCC: Path Computation Client - PCE: Path Computation Element PCEP: Path Computation Element Protocol SID: Segment Identifier as defined in [RFC8402] SR: Segment Routing Label Imposition: Imposition is the act of modifying and/or adding labels to the outgoing label stack associated with a packet. This @@ -300,21 +297,21 @@ PCE to perform path computations taking into consideration the size of SID stack that the specific head-end node may be able to impose. Errors in the encoding or decoding of the MSD information may result in the unavailability of such information to the SR PCE or incorrect information being made available to it. This may result in the head- end node not being able to instantiate the desired SR path in its forwarding and provide the SR based optimization functionality. The handling of such errors by applications like SR PCE may be implementation specific and out of scope of this document. - The extensions specified in this document, do not specify any new + The extensions specified in this document do not specify any new configuration or monitoring aspects in BGP or BGP-LS. The specification of BGP models is an ongoing work based on the [I-D.ietf-idr-bgp-model]. 8. Security Considerations The 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 @@ -388,22 +385,22 @@ [I-D.ietf-isis-mpls-elc] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S., and M. Bocci, "Signaling Entropy Label Capability and Entropy Readable Label Depth Using IS-IS", draft-ietf- isis-mpls-elc-11 (work in progress), March 2020. [I-D.ietf-ospf-mpls-elc] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S., and M. Bocci, "Signaling Entropy Label Capability and - Entropy Readable Label-stack Depth Using OSPF", draft- - ietf-ospf-mpls-elc-12 (work in progress), October 2019. + Entropy Readable Label Depth Using OSPF", draft-ietf-ospf- + mpls-elc-13 (work in progress), April 2020. [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001, . [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, .