Network Working Group C. Lin Internet Draft New H3C Technologies Intended status: Standards Track Y. Liu Expires: 20 October 2025 China Mobile 16 April 2025 LDP Extensions for Flex-Algo draft-lin-mpls-ldp-flex-algo-00 Abstract This document specifies extensions to LDP to support the use Flex- Algo, enabling Label Switched Paths (LSPs) to follow a specific Flex-Algo. 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 20 October 2025. Copyright Notice Copyright (c) 2025 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. Lin, et al. Expires 20 October 2025 [Page 1] Internet-Draft LDP Extensions for Flex-Algo April 2025 Table of Contents 1. Introduction...................................................2 1.1. Terminology...............................................3 2. Signaling Extensions...........................................3 2.1. New Address Families: FA IP/FA IPv6.......................3 2.2. LDP FEC Elements with FA IP AF............................4 2.3. IGP IPA Mapping and Translation...........................5 2.4. LDP Flex-Algo Capability Advertisement....................5 2.4.1. Protocol Extension...................................5 2.4.2. Procedures...........................................6 3. FA Applicability on FEC-Based Features.........................7 3.1. Typed Wildcard FEC Element................................7 3.2. LSP Ping..................................................7 3.2.1. New FEC Sub-Types....................................7 3.2.2. FA LDP IPv4 FEC Sub-TLV..............................7 3.2.3. FA LDP IPv6 FEC Sub-TLV..............................8 3.2.4. Operation Considerations.............................8 4. Error Handling.................................................9 4.1. Error Notification for Invalid IPA ID.....................9 5. IANA Considerations............................................9 5.1. FA Capability TLV.........................................9 5.2. New Status Code...........................................9 5.3. New address families......................................9 6. References....................................................10 6.1. Normative References.....................................10 6.2. Informative References...................................10 Authors' Addresses...............................................10 1. Introduction Multi-Topology Routing (MTR) is a technology that enables service differentiation within an IP network. The Flexible Algorithm (FA) is another mechanism for creating a sub-topology within a topology using defined topology constraints and computation algorithms. To deploy Label Distribution Protocol (LDP) in a network that supports Flex-Algo, or other methods of signaling non-default IGP Algorithms (IPAs), it is necessary for LDP to become algorithm aware. This document specifies extensions to LDP to support the use of IPAs, enabling Label Switched Paths (LSPs) to follow a specific algorithm. [RFC7307] describes how to extend the LDP protocol to support Multi- Topology (MT), but it only uses one byte to carry the MT-ID and does not support IPAs. This document updates RFC 7307 by allowing LSPs to follow a specific topology and algorithm. This document defines how LDP can utilize a specific combination of topology and algorithm, referred to as Topology-Algorithm(TA). In Lin, et al. Expires 20 October 2025 [Page 2] Internet-Draft LDP Extensions for Flex-Algo April 2025 this context, LDP's functionality is enhanced to ensure that the LSPs are constructed and maintained according to the specified TA parameters, thus optimizing the routing and resource utilization in diverse network environments. These enhancements to LDP provide the flexibility needed to support advanced topological and algorithmic configurations, making it a robust choice for modern, dynamic network infrastructures. 1.1. Terminology This document uses terminologies defined in [RFC7307]. o MT-ID: A 16-bit value used to represent the Multi-Topology ID. o Algorithm: A 1-octet value from the IGP Algorithm Types registry under IGP Parameters registry. 2. Signaling Extensions 2.1. New Address Families: FA IP/FA IPv6 [RFC7307] defines MT IP and MT IPv6 address families, which are used to specify IPv4 and IPv6 prefixes within a topology scope, but they can only carry MT-ID information. To extend IP address families for Flex-Algo, two new Address Families named "FA IP" and "FA IPv6" are used to specify IPv4 and IPv6 prefixes within a Flex-Algo scope. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | IPA | MT-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: FA IP Address Family Format Lin, et al. Expires 20 October 2025 [Page 3] Internet-Draft LDP Extensions for Flex-Algo April 2025 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 Address | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | IPA | MT-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: FA IPv6 Address Family Format IPA: A 1-octet value from the IGP Algorithm Types registry under IGP Parameters registry. MT-ID: A 2-octet field MT-ID (see Section 3.7 of [RFC4915], Section 7 of [RFC5120]) to special the topology. If this field is set to zero, it means the default topology. 2.2. LDP FEC Elements with FA IP AF The following section specifies the format extensions of the existing LDP FEC elements to support Flex-Algo. The "Address Family" of these FEC elements will be set to "FA IP" or "FA IPv6". The encoding of the Flex-Algo Prefix FEC element is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix (2) | Address Family(FA IP/IPv6) | PreLen | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Lin, et al. Expires 20 October 2025 [Page 4] Internet-Draft LDP Extensions for Flex-Algo April 2025 | Prefix | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | IPA | MT-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: FA Prefix FEC Element Format The Flex-Algo Typed Wildcard FEC element encoding is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Typed Wcard (5)| FEC Type | Len = 6 | AF = FA IP | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | or FA IPv6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | IPA | MT-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Flex-Algo Typed Wildcard FEC Element 2.3. IGP IPA Mapping and Translation The non-reserved non-special IGP IPA values can be used and carried in LDP without the need for translation. However, there is a need for translating reserved or special IGP IPA values to corresponding LDP IPAs. 2.4. LDP Flex-Algo Capability Advertisement 2.4.1. Protocol Extension We specify a new LDP capability, named "Flex-Algo (FA)", which is defined in accordance with the LDP capability guidelines [RFC5561]. Lin, et al. Expires 20 October 2025 [Page 5] Internet-Draft LDP Extensions for Flex-Algo April 2025 The LDP "FA" capability can be advertised by an LDP speaker to its peers either during the LDP session initialization or after the LDP session is set up. The advertisement is to announce the capability of the Label Switching Router (LSR) to support FA for the given IP address family. An LDP speaker MUST NOT send messages containing FA FEC elements unless the peer has said it can handle it. The format of the FA Capability TLV is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| Flex-Algo Cap.(IANA) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |S| Reserved | | +-+-+-+-+-+-+-+-+ | ~ Typed Wildcard FEC element(s) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: Flex-Algo Capability TLV Format Where: o Flex-Algo Capability: Capability TLV type (IANA assigned) 2.4.2. Procedures To announce its Flex-Algo capability for an IP address family, LDP FEC type, an LDP speaker sends an "FA Capability" including the exact Typed Wildcard FEC element with the corresponding "AddressFamily" field (i.e., set to "FA IP" for IPv4 and set to "FA IPv6" for IPv6 address family), corresponding "FEC Type" field (i.e., set to "Prefix"), and corresponding "IPA". To announce its Flex-Algo capability for both the IPv4 and IPv6 address family, or for multiple FEC types, or for multiple Flex-Algos, an LDP speaker sends an "FA Capability" with one or more FA Typed FEC elements in it. Lin, et al. Expires 20 October 2025 [Page 6] Internet-Draft LDP Extensions for Flex-Algo April 2025 3. FA Applicability on FEC-Based Features 3.1. Typed Wildcard FEC Element [RFC5918] extends base LDP and defines the Typed Wildcard FEC element framework. The Typed Wildcard FEC element can be used in any LDP message to specify a wildcard operation/action for a given type of FEC. The FA extensions defined in this document do not require any extension to procedures for the Typed Wildcard FEC element, and these procedures apply as is to FA wildcarding. The FA extensions, though, allow use of "FA IP" or "FA IPv6" in the Address Family field of the Typed Wildcard FEC element in order to use wildcard operations in the context of a given Flex-Algo. The use of FA- scoped address family also allows us to specify Flex-Algo in these operations. 3.2. LSP Ping 3.2.1. New FEC Sub-Types We define two new FEC types for LSP ping: o FA LDP IPv4 FEC o FA LDP IPv6 FEC 3.2.2. FA LDP IPv4 FEC Sub-TLV The format of the "FA LDP IPv4 FEC" sub-TLV to be used in a "Target FEC Stack" [RFC4379] is: 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 (FA LDP IPv4 FEC) | Length = 12 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | IPA | MT-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Lin, et al. Expires 20 October 2025 [Page 7] Internet-Draft LDP Extensions for Flex-Algo April 2025 Figure 5: FA LDP IPv4 FEC Sub-TLV 3.2.3. FA LDP IPv6 FEC Sub-TLV The format of the "FA LDP IPv6 FEC" sub-TLV to be used in a "Target FEC Stack" [RFC4379] is: 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 (FA LDP IPv6 FEC) | Length = 24 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | IPv6 prefix | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | IPA | MT-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: FA LDP IPv6 FEC Sub-TLV 3.2.4. Operation Considerations To detect data-plane failures using LSP ping for a specific Flex- Algo, the router will initiate an LSP ping request with the target FEC stack TLV containing the LDP FA IP Prefix Sub-TLV in the Echo Request packet. The Echo Request packet is sent with the label bound to the IP Prefix in the Flex-Algo. Once the Echo Request packet reaches the target router, it will process the packet and perform checks for the LDP FA IP Prefix sub-TLV present in the Target FEC Stack as described in [RFC4379] and respond according to the processing rules in [RFC4379]. For the case that the LSP ping with return path is not specified, the reply packet must go through the default Flex-Algo instead of the Flex-Algo where the Echo Request goes through. Lin, et al. Expires 20 October 2025 [Page 8] Internet-Draft LDP Extensions for Flex-Algo April 2025 4. Error Handling 4.1. Error Notification for Invalid IPA ID An LSR should respond with an "Invalid IPA ID" status code in the LDP Notification message when it receives an LDP message with a FEC element specifying an IPA that is not locally known or not supported. The LSR MUST also discard the entire message before sending the Notification message. 5. IANA Considerations 5.1. FA Capability TLV New LDP Capability TLV "Flex-Algo Capability" TLV is requested from the LDP Parameters registry "TLV Type Name Space". 5.2. New Status Code A new status code, "Invalid IPA ID," was requested from the LDP Parameters registry "Status Code Name Space". Registry: Range/Value Description -------------- ------------------------------ TBD1 Invalid IPA ID 5.3. New address families New address families under the IANA registry "Address Family Numbers": Number Description -------- ------------------------------------ TBD2 FA IP: Flex-Algo IP version 4 TBD3 FA IPv6: Flex-Algo IP version 6 Lin, et al. Expires 20 October 2025 [Page 9] Internet-Draft LDP Extensions for Flex-Algo April 2025 6. References 6.1. Normative References [RFC7307] Q. Zhao, Huawei Technology, K. Raza, C. Zhou, Cisco Systems, L. Fang, Microsoft, L. Li, China Mobile, D. King, Old Dog Consulting, "LDP Extensions for Multi-Topology", RFC 5286,DOI 10.17487/RFC7307, July 2014,. [RFC9658] IJ. Wijnands, Individual, M. Mishra, Ed., K. Raza, Cisco Systems, Inc., Z. Zhang, Juniper Networks, A. Gulko, Edward Jones, "Multipoint LDP Extensions for Multi- Topology Routing", RFC 9658,DOI 10.17487/RFC9658, October 2024,. 6.2. Informative References TBD Authors' Addresses Changwang Lin New H3C Technologies China Email: linchangwang.04414@h3c.com Yisong Liu China Mobile China Email: liuyisong@chinamobile.com Lin, et al. Expires 20 October 2025 [Page 10]