--- 1/draft-ietf-idr-bgp-ls-segment-routing-msd-17.txt 2020-05-08 15:13:21.007324385 -0700 +++ 2/draft-ietf-idr-bgp-ls-segment-routing-msd-18.txt 2020-05-08 15:13:21.027324658 -0700 @@ -1,26 +1,26 @@ IDR Working Group J. Tantsura Internet-Draft Apstra, Inc. Intended status: Standards Track U. Chunduri -Expires: October 28, 2020 Futurewei Technologies +Expires: November 9, 2020 Futurewei Technologies K. Talaulikar Cisco Systems G. Mirsky ZTE Corp. N. Triantafillis Amazon Web Services - April 26, 2020 + May 8, 2020 Signaling MSD (Maximum SID Depth) using Border Gateway Protocol - Link State - draft-ietf-idr-bgp-ls-segment-routing-msd-17 + draft-ietf-idr-bgp-ls-segment-routing-msd-18 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 28, 2020. + This Internet-Draft will expire on November 9, 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 @@ -59,30 +59,28 @@ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4 2. Advertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4 3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4 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 . . . . . . . . . . . . . . . . . 8 + 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 + 6. Manageability Considerations . . . . . . . . . . . . . . . . 6 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 + 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 + 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 + 10.2. 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 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. @@ -230,54 +228,35 @@ 1-octet MSD-Value. * MSD-Type : MSD-Type : one of the values defined in the "IGP MSD-Types" registry defined in [RFC8491]. * MSD-Value : a number in the range of 0-255. For all MSD-Types, 0 represents the lack of ability to impose an MSD stack of any depth; any other value represents that of the link when used as an outgoing interface. -5. 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 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. - - 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 - 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 in [RFC8491]. - -6. IANA Considerations +5. IANA Considerations This document requests assigning code-points from the registry "BGP- LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" based on table below. Early allocation for these code-points have been done by IANA. +------------+-----------------+---------------------------+-------------------+ | Code Point | Description | IS-IS TLV/Sub-TLV | Reference | +------------+-----------------+---------------------------+-------------------+ | 266 | Node MSD | 242/23 | This document | | 267 | Link MSD | (22,23,25,141,222,223)/15 | This document | +------------+-----------------+---------------------------+-------------------+ -7. Manageability Considerations +6. Manageability Considerations The new protocol extensions introduced in this document augment the existing IGP topology information that is distributed via [RFC7752]. Procedures and protocol extensions defined in this document do not affect the BGP protocol operations and management other than as discussed in the Manageability Considerations section of [RFC7752]. Specifically, the malformed attribute tests for syntactic checks in the Fault Management section of [RFC7752] now encompass the new BGP- LS Attribute TLVs defined in this document. The semantic or content checking for the TLVs specified in this document and their @@ -285,38 +264,38 @@ left to the consumer of the BGP-LS information (e.g. an application or a controller) and not the BGP protocol. A consumer of the BGP-LS information retrieves this information over a BGP-LS session (refer Section 1 and 2 of [RFC7752]). This document only introduces new Attribute TLVs and any syntactic error in them would result in the BGP-LS Attribute being discarded [RFC7752]. The MSD information introduced in BGP-LS by this specification, may be used by BGP-LS consumer applications like a SR - path computation engine (PCE) to learn the SR SID stack handling - capabilities of the nodes in the topology. This can enable the SR - 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. + PCE to learn the SR SID stack handling capabilities of the nodes in + the topology. This can enable the SR 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 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 +7. 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 supported by the head-end (the node performing the SID imposition) may occur. The presence of this information may also inform an attacker of how to induce any of the aforementioned conditions. The procedures and protocol extensions defined in this document do @@ -324,39 +303,40 @@ section of [RFC4271] for a discussion of BGP security. Also, refer to [RFC4272] and [RFC6952] for analyses of security issues for BGP. Security considerations for acquiring and distributing BGP-LS information are discussed in [RFC7752]. The TLVs introduced in this document are used to propagate the MSD IGP extensions defined in [RFC8476] [RFC8491]. It is assumed that the IGP instances originating these TLVs will support all the required security (as described in [RFC8476] [RFC8491]) in order to prevent any security issues when propagating the TLVs into BGP-LS. The advertisement of the node and link attribute information defined in this document - presents no additional risk beyond that associated with the existing - node and link attribute information already supported in [RFC7752]. + presents no significant additional risk beyond that associated with + the existing node and link attribute information already supported in + [RFC7752]. -9. Contributors +8. Contributors Siva Sivabalan Cisco Systems Inc. Canada Email: msiva@cisco.com -10. Acknowledgements +9. Acknowledgements We like to thank Acee Lindem, Stephane Litkowski, Bruno Decraene and Alvaro Retana for their reviews and valuable comments. -11. References +10. References -11.1. Normative References +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, . [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, @@ -369,21 +349,21 @@ [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, DOI 10.17487/RFC8476, December 2018, . [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, DOI 10.17487/RFC8491, November 2018, . -11.2. Informative References +10.2. Informative References [I-D.ietf-idr-bgp-model] Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP YANG Model for Service Provider Networks", draft-ietf-idr- bgp-model-08 (work in progress), February 2020. [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-