Network Working Group M. Younsi Internet-Draft P. Francois Intended status: Standards Track INSA-Lyon Expires: 4 January 2025 P. Lucente NTT 3 July 2024 BMP Local Path-ID draft-younsi-grow-local-path-id-03 Abstract Intelligence is required to track BGP paths throughout the various RIBs and VRFs of a routing platform, due to potential attribute modifications and the use of BGP multipath. This document introduces the option to identify a path within a router in order to ease correlation in monitoring. A BMPv4 TLV is defined in order to communicate this locally significant identifier in monitoring messages. 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. 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 4 January 2025. Younsi, et al. Expires 4 January 2025 [Page 1] Internet-Draft local-path-id July 2024 Copyright Notice Copyright (c) 2024 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 to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Local Path ID . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Local Path ID Properties . . . . . . . . . . . . . . . . 3 2.2. Design Recommendation . . . . . . . . . . . . . . . . . . 4 3. Advertising the Local Path ID in BMP . . . . . . . . . . . . 4 3.1. Local Path ID TLV . . . . . . . . . . . . . . . . . . . . 5 3.2. Local Path ID TLV Sub-Types . . . . . . . . . . . . . . . 5 3.2.1. Local Path ID Value . . . . . . . . . . . . . . . . . 6 3.2.2. Unavailability Reason Codes . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5. Normative References . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction When using VRFs and/or BGP Multipath, multiple paths to the same destination may be shared among various routing information bases. From a collection perspective, tracking the identity of a path thus requires some form of modeling, which is subject to inaccuracy. This aspect is exacerbated as path attributes may be modified in the process. This is especially problematic when a PE using BGP multipath in VPN instances exports multiple paths for the same destination into the default VRF, which were learned from different peers. While BGP ADD-PATH [RFC7911] provides a way to identify paths in BGP multi-path scenarios, the scope of the ADD-PATH path-id is local to a single BGP peering session, and thus cannot be used to distinguish paths received over multiple sessions. Younsi, et al. Expires 4 January 2025 [Page 2] Internet-Draft local-path-id July 2024 This document introduces a way to identify paths globally within a router, allowing operators to not resort to modeling when monitoring BGP paths on a router. In Section 2, we introduce the concept of Local Path ID, which is an identifier of a path for a given NLRI, preserved through the import/export operations performed onto them. In Section 3, we introduce a BMPv4 TLV allowing to communicate the value of a Local Path ID on a BMP session. 2. Local Path ID In this section, we define an identifier called Local Path ID, which allows to uniquely identify a path for a given NLRI on a router. According to this specification, a path to be advertised by BMP is provided with an associated Local Path ID. The Local Path ID is an opaque numerical value with a few properties guaranteeing its utility. The exact approach to generate a Local Path ID is however left for the implementation. 2.1. Local Path ID Properties The Local Path ID of each path MUST be unique for a given NLRI. We scope the identifier space to each NLRI to keep it a small value. Indeed, most Internet routers have at most a few tens of paths for a given NLRI. While we put a minimum scope (the NLRI) for the identifier space, an implementor may decide to use a broader space for this unicity, as long as Local Path IDs are still unique for a given NLRI. For example, Local Path IDs can be unique accross VRFs, even though they will have to be larger, as this does not violate the rule. The Local Path ID only has a meaning local to the router generating it. Once generated, the Local Path ID MUST be preserved between VRFs, and Routing Information Bases. It is however not intended to be exchanged or synchronized between routers. To ensure traceability in monitoring, the Local Path ID SHOULD be transmitted when paths are redistributed between processes. If the Local Path ID is not transmitted then the process receiving the path SHOULD allocate one. The value of 0 for a Local Path ID is reserved. Younsi, et al. Expires 4 January 2025 [Page 3] Internet-Draft local-path-id July 2024 2.2. Design Recommendation In this section, we give general recommendations for the Local Path ID generation. These recommendations may or may not be applicable depending on the platform, the implementation of BGP, etc. The actual generation process of the Local Path ID does not matter as long as the the properties defined in Section 2.1 are respected. We recommend having the Local Path ID made of three concatenated parts: < process_id | vrf_id | path_discriminator >. The path_discriminator allows for differentiation between paths for a given NLRI, coming from the same table and process (with the same vrf_id and process_id). The process originating the path is in charge of guaranteeing the uniqueness of the path_discriminator it produces for each path of its NLRIs. The vrf_id represents a unique identifier for the VRF in which the path to the NLRI is contained. It allows leveraging the already existing routing table structures of most BGP implementations by having to guarantee the uniqueness of the path_discriminator only within the table. The process_id is the identifier of the process which produced, originated, or received a path. The process_id allows differentiation between path IDs generated in BGP from path IDs generated in other processes like an IGP. Redistributed IGP paths will then have a different Local Path ID no matter if BGP or another IGP has chosen the same path_discriminator value. Using the process_id avoids requiring interprocess synchronization of path_discriminators or the use of a Local Path ID management process. 3. Advertising the Local Path ID in BMP The Local Path ID is to be included in BMPv4 Route Monitoring messages [I-D.ietf-grow-bmp-tlv] as a BMPv4 TLV, called "Local Path ID TLV". This TLV can carry multiple types of data which are discriminated by the "TLV Sub-Type" field. The "TLV Sub-Type" field can take the values given in Table 1. When a Local Path ID is allocated for a path, the router includes it using the "TLV Sub-Type" value 0x00 (Local Path ID Value). When a Local Path ID is not allocated, the router includes a "TLV Sub-Type" value 0x01 (Unavailability Reason Code) that describes why the Local Path ID is not available for the path. In practice, this means that a Local Path ID enabled router SHOULD always associate a Path ID TLV with a path advertised in BMP. Younsi, et al. Expires 4 January 2025 [Page 4] Internet-Draft local-path-id July 2024 On the collector side, a path should be identified using the Local Path ID Value when provided, and only resort to network modeling when the Local Path ID is not available. 3.1. Local Path ID TLV The encoding of the "Local Path ID TLV" is illustrated in Figure 1. 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 (2 octets) | Length (2 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Index (2 octets) | Sub-Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Value (variable) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 Type: set to TBD1 Length: the length of the "TLV Sub-Type" field + the length of the "Value" field, in bytes Index: index of the NLRI in the BGP Update PDU as described by [I-D.ietf-grow-bmp-tlv]. The Index MUST refer to a single NLRI (no Group TLV). Sub-Type: a one byte TLV Sub-Type, as listed in Table 1 Value: the value corresponding to the TLV Sub-Type as described in Section 3.2 3.2. Local Path ID TLV Sub-Types The Table 1 defines the list of TLV Sub-Types and references the section defining their associated values. Younsi, et al. Expires 4 January 2025 [Page 5] Internet-Draft local-path-id July 2024 +======+============================+==========+===============+ | Code | Name | Length | Section | +======+============================+==========+===============+ | 0x00 | Local Path ID Value | Variable | Section 3.2.1 | +------+----------------------------+----------+---------------+ | 0x01 | Unavailability Reason Code | 2 bytes | Section 3.2.2 | +------+----------------------------+----------+---------------+ Table 1: Local Path ID TLV Sub-Types 3.2.1. Local Path ID Value When the Local Path ID is available for a path, the router exports the Local Path ID using a "Local Path ID TLV" with "TLV Sub-Type" = 0x00. The Local Path ID Value contains the raw bytes of the generated Local Path ID (Section 2). The Length field is thus set to the length, in bytes, of the Local Path ID, plus one (for the TLV Sub-Type field). 3.2.2. Unavailability Reason Codes An implementation enabled for Local Path ID usage MUST notify if a Local Path ID is unavailable (for any reason) by using the "TLV Sub- Type" = 0x01. When "TLV Sub-Type" is 0x01, the TLV Value is a 2-byte error code from Table 2. The Length field of the "Local Path ID TLV" is thus set to 3 in this case. Younsi, et al. Expires 4 January 2025 [Page 6] Internet-Draft local-path-id July 2024 +======+================+=====================================+ | Code | Reason | Description | +======+================+=====================================+ | 0x00 | Unknown Reason | A unknown error occurred during the | | | | allocation of the Local Path ID | +------+----------------+-------------------------------------+ | 0x01 | Origin process | A path is imported from another | | | did not | process, the latter does not | | | provide a | provide a Local Path ID for the | | | Local Path ID. | imported path and the receiving | | | | process did not allocate one either | +------+----------------+-------------------------------------+ | 0x02 | All Local Path | A Local Path ID could not be | | | ID have been | allocated for a path because the | | | allocated. | entire range of Local Path IDs is | | | | in use | +------+----------------+-------------------------------------+ Table 2: Local Path ID Unavailability Reason Codes 4. IANA Considerations This document requests that IANA assigns the following new parameters to the "BMP Route Monitoring TLVs" [I-D.ietf-grow-bmp-tlv] registry * Type = TBD1: Local Path ID TLV type. The value of this TLV is defined in Section 3 This document also requests the definition of a "Local Path ID Reason Codes" registry in the "BMP Parameters" namespace, seeded as follows: * Type = 0: Unknown Reason. Set to 0 when an unknown error occurred during the allocation of the Local Path ID. * Type = 1: Origin Process did not provide a Local Path ID. Set to 1 when a path is imported from another process, the latter does not provide a Local Path ID for the imported path and the receiving process did not allocate one either. * Type = 2: All Local Path ID have been allocated. Set to 2 when a Local Path ID could not be allocated for a path because the entire range of Local Path IDs is in use. 5. Normative References Younsi, et al. Expires 4 January 2025 [Page 7] Internet-Draft local-path-id July 2024 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, "Advertisement of Multiple Paths in BGP", RFC 7911, DOI 10.17487/RFC7911, July 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [I-D.ietf-grow-bmp-tlv] Lucente, P. and Y. Gu, "BMP v4: TLV support for BMP Route Monitoring and Peer Down Messages", Work in Progress, Internet-Draft, draft-ietf-grow-bmp-tlv-13, 23 October 2023, . Authors' Addresses Maxence Younsi INSA-Lyon Villeurbanne France Email: maxence.younsi@insa-lyon.fr Pierre Francois INSA-Lyon Villeurbanne France Email: pierre.francois@insa-lyon.fr Paolo Lucente NTT Siriusdreef 70-72 Hoofddorp, WT 2132 Netherlands Email: paolo@ntt.net Younsi, et al. 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