Inter-Domain Routing K. Talaulikar, Ed. Internet-Draft Arrcus Inc Intended status: Standards Track P. Psenak Expires: November 14, 2022 Cisco Systems J. Tantsura Microsoft May 13, 2022 Application-Specific Attributes Advertisement with BGP Link-State draft-ietf-idr-bgp-ls-app-specific-attr-11 Abstract New extensions have been defined for link-state routing protocols that enable distribution of application-specific link attributes for existing as well as newer applications such as Segment Routing. This document defines extensions to BGP-LS to enable the advertisement of these application-specific attributes as a part of the topology information from the network. 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 November 14, 2022. Copyright Notice Copyright (c) 2022 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 carefully, as they describe your rights and restrictions with respect Talaulikar, et al. Expires November 14, 2022 [Page 1] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Application Specific Link Attributes TLV . . . . . . . . . . 3 3. Application-Specific Link Attributes . . . . . . . . . . . . 4 4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Deployment Considerations . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Manageability Considerations . . . . . . . . . . . . . . . . 9 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 10.1. Normative References . . . . . . . . . . . . . . . . . . 10 10.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction BGP Link-State [RFC7752] enables the distribution of the link-state topology information from link-state routing protocols (viz., IS-IS [RFC1195], OSPFv2 [RFC2328] and OSPFv3 [RFC5340]) to an application like a controller or Path Computation Engine (PCE) via BGP. The controller/PCE gets the end-to-end topology information across IGP domains so it can perform path computations for use cases like end- to-end traffic engineering (TE). The link-state topology information distributed via BGP-LS includes link attributes that were originally defined for traditional MPLS Traffic Engineering (i.e., using RSVP-TE [RFC3209]) or GMPLS [RFC4202]) applications. In recent years new applications, such as Segment Routing (SR) Policy [RFC8402] and Loop-Free Alternates (LFA) [RFC5286], that also make use of link attributes have been introduced. [RFC8919] and [RFC8920] define extensions for IS-IS and OSPF respectively that enable advertising application-specific link attributes for these and other future applications. This has resulted in the need for a similar BGP-LS extension to include this additional link-state topology information from the link-state routing protocols. This document defines the BGP-LS extensions for the advertisement of application-specific link attributes. It describes the advertisement of these link attributes as top-level TLVs (i.e., as TLVs of the BGP- Talaulikar, et al. Expires November 14, 2022 [Page 2] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 LS Attribute) and as sub-TLVs of the new (top-level) Application Specific Link Attributes TLV. The document also describes the procedures for the advertisement of these attributes from the underlying IGPs and discusses their deployment aspects. 1.1. 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 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Application Specific Link Attributes TLV The BGP-LS [RFC7752] specifies the Link Network Layer Reachability Information (NLRI) for the advertisement of links and their attributes using the BGP-LS Attribute. The Application-Specific Link Attributes (ASLA) TLV is a new optional top-level BGP-LS Attribute TLV that is introduced for Link NLRIs. It is defined such that it may act as a container for certain existing and future link attributes that require application-specific definition. The format of this TLV is as follows and is similar to the corresponding ASLA sub-TLVs defined for OSPF and IS-IS in [RFC8920] and [RFC8919] respectively. 0 1 2 3 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SABM Length | UDABM Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Standard Application Identifier Bit Mask (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | User-Defined Application Identifier Bit Mask (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Attribute sub-TLVs // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Application-Specific Link Attributes TLV where: o Type: 1122 o Length: variable. Talaulikar, et al. Expires November 14, 2022 [Page 3] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 o SABM Length : Standard Application Identifier Bit Mask Length in octets as defined in [RFC8920]. o UDABM Length : User-Defined Application Identifier Bit Mask Length in octets as defined in [RFC8920]. o Standard Application Identifier Bit Mask : An optional set of bits (of size 0, 4, or 8 octets as indicated by the SABML), where each bit represents a single standard application as defined in [RFC8919]. o User-Defined Application Identifier Bit Mask : An optional set of bits (of size 0, 4, or 8 octets as indicated by the UDABML), where each bit represents a single user-defined application as defined in [RFC8919]. o Link Attribute sub-TLVs : BGP-LS Attribute TLVs corresponding to the Link NLRI that are application-specific (including existing ones as specified in Section 3) are included as sub-TLVs of the ASLA TLV. The semantics associated with the standard and user-defined bit masks as well as the encoding scheme for application-specific attributes are as specified in [RFC8920]. The ASLA TLV and its sub-TLVs can only be added to the BGP-LS Attribute associated with the Link NLRI of the node that originates the underlying IGP link attribute TLVs/sub-TLVs. The procedures for originating link attributes in the ASLA TLV from underlying IGPs are specified in Section 4. 3. Application-Specific Link Attributes Several BGP-LS Attribute TLVs corresponding to the Link NLRI are defined in BGP-LS and more may be added in the future. Those attributes that have been determined to be, and advertised as application-specific in the underlying IGPs are also encoded in a similar manner in BGP-LS. The following table lists the currently defined BGP-LS Attributes TLVs corresponding to Link NLRI that can have application-specific semantics based on the underlying IGP specifications [RFC8919] [RFC8920]. These were originally defined with semantics for RSVP-TE and GMPLS applications in BGP-LS by the respective reference documents. Talaulikar, et al. Expires November 14, 2022 [Page 4] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 +---------------+-------------------------------+-------------------+ | TLV Code | Description | Reference | | Point | | Document | +---------------+-------------------------------+-------------------+ | 1088 | Administrative group (color) | [RFC7752] | | 1092 | TE Default Metric | [RFC7752] | | 1096 | Shared Risk Link Group | [RFC7752] | | 1114 | Unidirectional Link Delay | [RFC8571] | | 1115 | Min/Max Unidirectional Link | [RFC8571] | | | Delay | | | 1116 | Unidirectional Delay | [RFC8571] | | | Variation | | | 1117 | Unidirectional Link Loss | [RFC8571] | | 1118 | Unidirectional Residual | [RFC8571] | | | Bandwidth | | | 1119 | Unidirectional Available | [RFC8571] | | | Bandwidth | | | 1120 | Unidirectional Utilized | [RFC8571] | | | Bandwidth | | | 1173 | Extended Administrative Group | [RFC9104] | +---------------+-------------------------------+-------------------+ Table 1: Existing BGP-LS TLVs identified as Application-Specific All the BGP-LS Attribute TLVs defined in the table above are REQUIRED to be advertised as a top-level TLV in the BGP-LS Attribute for carrying link attributes specific to RSVP-TE. BGP-LS Attribute TLVs corresponding to Link NLRI that are identified as application-specific are REQUIRED to be encoded within an ASLA TLV. Link attributes that do not have application-specific semantics MUST NOT be advertised within the ASLA TLV. When the same application-specific link attributes are advertised both within the ASLA TLV and as top-level TLVs in the BGP-LS Attribute, the attributes advertised within the ASLA TLV take precedence for the applications indicated in the ASLA TLV encoding. 4. Procedures The BGP-LS originator learns of the association of an application- specific attribute to one or more applications from the underlying IGP protocol LSA/LSPs from which it is advertising the topology information. [RFC8920] and [RFC8919] specify the mechanisms for advertising application-specific link attributes in OSPF and IS-IS respectively. Talaulikar, et al. Expires November 14, 2022 [Page 5] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 Application-specific link attributes received from an IGP node without the use of ASLA encodings continue to be encoded using the respective BGP-LS top-level TLVs listed in Table 1 as specified in their respective reference documents. A BGP-LS originator node that is advertising link-state information from the underlying IGP using ASLA encodings determines their BGP-LS encoding based on the following rules: 1. Application-specific link attributes received from an OSPF node using ASLA sub-TLV or from an IS-IS node using either ASLA sub- TLV or ASLA SRLG TLV MUST be encoded in the BGP-LS ASLA TLV as sub-TLVs. Exceptions to this rule are specified in (2)(F) and (2)(G) below. 2. In the case of IS-IS, the following specific procedures are to be followed: A. When application-specific link attributes are received from a node with the L bit set in the ASLA sub-TLV and application bits other than RSVP-TE are set in the application bit masks then the application-specific link attributes advertised in the corresponding legacy IS-IS TLVs/sub-TLVs MUST be encoded within the BGP-LS ASLA TLV as sub-TLVs with the application bits, other than the RSVP-TE bit, copied from the IS-IS ASLA sub-TLV. The link attributes advertised in the legacy IS-IS TLVs/sub-TLVs are also advertised in BGP-LS top-level TLVs as per [RFC7752] [RFC8571] [RFC9104]. The same procedure also applies for the advertisement of the SRLG values from the IS- IS ASLA SRLG TLV. B. When the ASLA sub-TLV has the RSVP-TE application bit set, then the link attributes for the corresponding ASLA sub-TLV MUST be encoded using the respective BGP-LS top-level TLVs as per [RFC7752] [RFC8571] [RFC9104]. Similarly, when the ASLA SRLG TLV has the RSVP-TE application bit set, then the SRLG values within it MUST be encoded using the top-level BGP-LS SRLG TLV (1096) as per [RFC7752]. C. The SRLGs advertised in IS-IS SRLG ASLA TLVs and the other link attributes advertised in IS-IS ASLA sub-TLVs are REQUIRED to be collated, on a per-application basis, for all applications that have their bit set in the SABM/UDABM in at least one of the aforementioned TLV types. When performing this collation, only the TLVs with the application's bit set in SABM/UDABM MUST be used when such TLVs are available from either TLV types. If the bit for an application is set in the SABM/UDABM of only one of the TLV types, then the Talaulikar, et al. Expires November 14, 2022 [Page 6] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 attributes from the other TLV type with zero-length application bit mask MUST be also collated for that application, if such TLV is available. Such collated link attributes are advertised in a per-application instance of the BGP-LS ASLA TLV. D. If the resulting set of collated link attributes and SRLG values is common across multiple applications, they MAY be advertised in a common BGP-LS ASLA TLV instance where the bits for all such applications would be set in the application bit mask. E. Both the SRLG values from IS-IS ASLA SRLG TLVs and the link attributes from IS-IS ASLA sub-TLVs, with the zero-length application bit mask, MUST be advertised into a BGP-LS ASLA TLV with a zero-length application bit mask, independent of the collation described above. F. [RFC8919] allows the advertisement of the Maximum Link Bandwidth within an ASLA sub-TLV even though it is not an application-specific attribute. However, when originating the Maximum Link Bandwidth into BGP-LS, the attribute MUST be encoded only in the top-level BGP-LS Maximum Link Bandwidth TLV (1089) and MUST NOT be advertised within the BGP-LS ASLA TLV. G. [RFC8919] also allows the advertisement of the Maximum Reservable Link Bandwidth and the Unreserved Bandwidth within an ASLA sub-TLV even though these attributes are specific to RSVP-TE application. However, when originating the Maximum Reservable Link Bandwidth and Unreserved Bandwidth into BGP- LS, these attributes MUST be encoded only in the BGP-LS top- level Maximum Reservable Link Bandwidth TLV (1090) and Unreserved Bandwidth TLV (1091) respectively and not within the BGP-LS ASLA TLV. These rules ensure that a BGP-LS originator performs the advertisement for all application-specific link attributes from the IGP nodes that support or do not support the ASLA extension. Furthermore, it also ensures that the top-level BGP-LS TLVs defined for RSVP-TE and GMPLS applications continue to be used for advertisement of their application-specific attributes. A BGP-LS speaker would normally advertise all the application- specific link attributes corresponding to RSVP-TE and GMPLS applications as existing top-level BGP-LS TLVs while for other applications they are encoded in ASLA TLV(s) with appropriate applicable bit mask setting. The application-specific attribute Talaulikar, et al. Expires November 14, 2022 [Page 7] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 value received via sub-TLVs within the ASLA TLV have preference over the value received via the top-level TLVs. 5. Deployment Considerations BGP-LS sources the link-state topology information (including the extensions introduced by this document) from the underlying link- state IGP protocols. The various deployment aspects related to the advertisement and use of application-specific link attributes are discussed in the Deployment Considerations sections of [RFC8920] and [RFC8919]. The IGP backward compatibility aspects described in those documents associated with application-specific link attributes along with the BGP-LS procedures specified in this document enable backward compatibility in deployments of existing implementations of [RFC7752] [RFC8571] [RFC9104] for applications such as RSVP-TE, SR Policy, and LFA. It is recommended that nodes supporting this specification are selected as originators of BGP-LS information when advertising the link-state information from the IGPs. BGP-LS consumers that do not support this specification can continue to use the existing top-level TLVs for link attributes for existing applications as discussed above. They would, however, not be able to support neither the application-specific link attributes nor newer applications that may be encoded only using the ASLA TLV. 6. IANA Considerations IANA has assigned, through the early allocation process, the following code-point from the "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry. This document requests that the allocation be made permanent. The column "IS-IS TLV/Sub-TLV" defined in the registry does not require any value and should be left empty. +------------+--------------------------------------+---------------+ | Code Point | Description | Reference | +------------+--------------------------------------+---------------+ | 1122 | Application-Specific Link Attributes | this document | +------------+--------------------------------------+---------------+ Table 2: ASLA TLV Code-Point Allocation Talaulikar, et al. Expires November 14, 2022 [Page 8] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 7. Manageability Considerations The new protocol extensions introduced in this document augment the existing IGP topology information defined in [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 NLRIs attribute tests in the Fault Management section of [RFC7752] now encompasses the BGP-LS TLVs defined in 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 [I-D.ietf-idr-bgp-model]. 8. Security Considerations Security considerations for acquiring and distributing BGP-LS information are discussed in [RFC7752]. The TLVs introduced in this document are used to propagate the application-specific link attributes IGP extensions defined in [RFC8919] and [RFC8920]. It is assumed that the IGP instances originating these TLVs will support all the required security (as described in [RFC8919] and [RFC8920]) to prevent any security issues when propagating the TLVs into BGP-LS. This document defines a new way to advertise link attributes. Tampering with the information defined in this document may affect applications using it, including impacting traffic engineering, which uses various link attributes for its path computation. As the advertisements defined in this document limit the scope to specific applications, the impact of tampering is similarly limited in scope. The advertisement of the link attribute information defined in this document presents no significant additional risk beyond that associated with the existing link attribute information already supported in [RFC7752]. 9. Acknowledgements The authors would like to thank Les Ginsberg, Baalajee S, Amalesh Maity, Acee Lindem, Keyur Patel, Paul Wouters, Rudy Selderslaghs, and Kristy Paine for their review and feedback on this document. The authors would also like to thank Alvaro Retana for his very detailed AD review and comments for improving this document. Talaulikar, et al. Expires November 14, 2022 [Page 9] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 10. 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of IGP Traffic Engineering Performance Metric Extensions", RFC 8571, DOI 10.17487/RFC8571, March 2019, . [RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and J. Drake, "IS-IS Application-Specific Link Attributes", RFC 8919, DOI 10.17487/RFC8919, October 2020, . [RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura, J., and J. Drake, "OSPF Application-Specific Link Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020, . [RFC9104] Tantsura, J., Wang, Z., Wu, Q., and K. Talaulikar, "Distribution of Traffic Engineering Extended Administrative Groups Using the Border Gateway Protocol - Link State (BGP-LS)", RFC 9104, DOI 10.17487/RFC9104, August 2021, . 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-13 (work in progress), March 2022. Talaulikar, et al. Expires November 14, 2022 [Page 10] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, DOI 10.17487/RFC1195, December 1990, . [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, . [RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005, . [RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for IP Fast Reroute: Loop-Free Alternates", RFC 5286, DOI 10.17487/RFC5286, September 2008, . [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, . [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, . Authors' Addresses Ketan Talaulikar (editor) Arrcus Inc India Email: ketant.ietf@gmail.com Peter Psenak Cisco Systems Slovakia Email: ppsenak@cisco.com Talaulikar, et al. Expires November 14, 2022 [Page 11] Internet-Draft BGP-LS Extns for App Specific Attributes May 2022 Jeff Tantsura Microsoft Email: jefftant.ietf@gmail.com Talaulikar, et al. Expires November 14, 2022 [Page 12]