Network Working Group W. Cheng Internet Draft L. Gong Intended status: Informational China Mobile Expires: October 02, 2025 C. Lin New H3C Technologies R. Chen ZTE Corporation April 02, 2025 IGP Color-Aware Shortcut draft-cheng-lsr-igp-shortcut-enhancement-08 Abstract IGP shortcut mechanism allows calculating routes to forward traffic over Traffic Engineering tunnels. This document specifies the enhancement of IGP shortcut which can steer routes onto TE-tunnels based on colors. 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 October 02, 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 (http://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 Cheng, et al. Expires October 02, 2025 [Page 1] Internet-Draft IGP Color-Aware Shortcut April 2025 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 1.1. Requirements Language.....................................3 2. Colors of IGP Prefixes.........................................3 3. Colors of TE-Tunnels...........................................4 4. IGP Color-Aware Shortcut.......................................4 5. Use Case.......................................................5 6. Management Considerations......................................5 7. Security Considerations........................................6 8. IANA Considerations............................................6 9. References.....................................................6 9.1. Normative References......................................6 9.2. Informational References..................................7 Authors' Addresses................................................7 1. Introduction [RFC3906] describes how IGP calculate routes to forward traffic over Traffic Engineering tunnels. Such mechanism is also referred to as IGP shortcut. The granularity of IGP shortcut is based on nodes. If the first-hop of a node is determined to be a TE-tunnel during the SPF computation, all routes to IP prefixes advertised by that node will be over that TE-tunnel. For example, in the following topology, X1 and X2 are IP prefixes advertised by rtrC, and Y1 and Y2 are IP prefixes advertised by rtrD. Using IGP shortcut, all routes to X1, X2, Y1 and Y2 will be steered onto T1 since T1 has the lowest cost. === T1(10) ===> === T2(15) ===> rtrA -- rtrB -- rtrC -- rtrD 10 10 | 10 | X1,X2 Y1,Y2 However, in some scenarios, there may be requirements to steer the routes to different prefixes of the same node onto different TE- tunnels. For example, the traffic flows to X1 and Y1 need to be forwarded over low-cost tunnel T1, but the traffic flows to X2 and Y2 need to be forwarded over low-delay tunnel T2. Cheng, et al. Expires October 02, 2025 [Page 2] Internet-Draft IGP Color-Aware Shortcut April 2025 In the BGP-based service, "color" is often used to indicate the intent of forwarding [RFC9012] [RFC9252]. The Color Extended Community can be attached to BGP routes, and the associated flows will be steered into tunnels with the same color. This document specifies the enhancement of IGP shortcut which can steer routes onto TE-tunnels based on colors. In [RFC3906], the term "TE-tunnel" mainly refers to Label Switched Path, such as MPLS RSVP-TE tunnel. With the development of Segment Routing (SR) technology, SR Policy [RFC9256] becomes a useful tool for Traffic Engineering. In the context of this document, SR Policies are also included as TE-tunnels. 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. Colors of IGP Prefixes A prefix can be associated with one or more colors. Administrative tags are used to advertising the colors for IGP prefixes. For IS-IS, the 32-bit Administrative Tag Sub-TLV defined in [RFC5130] can be used to associate one or more 32-bit tags with a prefix. For OSPFv2 and OSPFv3, the 32-bit Administrative Tag Sub-TLV defined in [I-D.ietf-lsr-ospf-admin-tags] provides the similar function. Since multiple tags for different applications may be attached to one prefix, there has to be a mechanism for a receiver to know which tags are used as colors. For example, the tag space can be split and some of it can be used to signal colors. The value of a tag and the value of color indicated by that tag can simply be equal. Alternatively, there can be a mapping relationship between them. For example, the value of color can be calculated from the value of tag by applying a mask over it. How to obtain the color(s) of a prefix from the associated tags, is governed by local policy and uniform within the same IGP domain. Cheng, et al. Expires October 02, 2025 [Page 3] Internet-Draft IGP Color-Aware Shortcut April 2025 3. Colors of TE-Tunnels The main idea of this document is to steer the flows to colored prefixes into tunnels with the same color. Some kinds of TE-tunnels, such as SR Policy [RFC9256], have inherent color values which can be directly used to match the colors of prefixes. For the TE-tunnels which have no inherent color, the color values may be determined by local configurations. 4. IGP Color-Aware Shortcut The SPF computation of IGP shortcut is described in Section 2 of [RFC3906]. The key idea is to determine the first-hop information of a node with consideration of TE-tunnels: o Examine the list of tail-end routers directly reachable via a TE- tunnel. If there is a TE-tunnel to this node, we use the TE- tunnel as the first-hop. o If there is no TE-tunnel, and the node is directly connected, we use the first-hop information from the adjacency database. o If the node is not directly connected, and is not directly reachable via a TE-tunnel, we copy the first-hop information from the parent node(s) to the new node. This document makes the following changes to the first step of the above algorithm: o If there is a TE-tunnel to this node, we add the TE-tunnel into the first-hop information (without deleting the previous ones). This document also adds the following steps when calculating next- hops for prefixes advertised by a node: o If a prefix is colored, we look up the first-hop information of the advertiser node for TE-tunnels with the same color. - If there are eligible TE-tunnels, we compare the costs of paths over those TE-tunnels, and use the next-hop of the TE- tunnel with the lowest path cost. - If there is no eligible TE-tunnel, we use the native adjacency next-hop. o If a prefix has no color, we use the next-hop with the lowest path cost. Cheng, et al. Expires October 02, 2025 [Page 4] Internet-Draft IGP Color-Aware Shortcut April 2025 5. Use Case TE-tunnel1(SR Policy1) =============================== (color100, low delay) |SLA requirements: | +-------------------------+ | Prefix-1,3: low delay | | 10 | | Prefix-2,4: high bandwidth | |TE-tunnel2(SR Policy2) | =============================== |(Color200,high bandwidth)| | +------------------+ | Prefix-3 | | 15 | | Prefix-4 ++--++ ++--++ +----+ +----+ | R1 +-----------------+ R2 +--------+ R3 +--------+ R4 | +----+ 10 +----+ 10 +----+ 10 +----+ Prefix-1 Prefix-2 Routing calculation on R1: Traditional Shortcut: Prefix-1,2,3,4 Next-hop: SR Policy 1 Color Aware Shortcut: Prefix-1,3 Next-hop: SR Policy 1 Prefix-2,4 Next-hop: SR Policy 2 Between R1 and R3, there are two SP policies: SR Policy 1, which has a color of 100 and corresponds to a low-latency SLA (Service-level Agreement) required path, and SR Policy 2, which has a color of 200 and corresponds to a high-bandwidth SLA-required path. In the case of a traditional TE Shortcut, after R1's route calculation, the next hops for Prefix-1, Prefix-2, Prefix-3, and Prefix-4 all point to SR Policy 1. In the case of a Color-aware TE Shortcut, the next hops for Prefix-1 and Prefix-3 point to SR Policy 1, while the next hops for Prefix-2 and Prefix-4 point to SR Policy 2. 6. Management Considerations Implementations MAY allow configuration of policies that: o Assign color values to prefixes. Cheng, et al. Expires October 02, 2025 [Page 5] Internet-Draft IGP Color-Aware Shortcut April 2025 o Map these colors to prefix tags for advertisement [RFC5130][I- D.ietf-lsr-ospf-admin-tags]. During prefix calculation, implementations MAY support local conversion of prefix tags to colors through configuration. When a TE tunnel is not associated with a color, implementations MAY permit manual configuration of the color attribute. Furthermore, implementations MAY support: o Color-based TE tunnel matching during IGP shortcut computation. o Policy-based control over which prefixes are included in the computation. 7. Security Considerations This document does not change the security aspects of IS-IS or OSPF. Security considerations specific to each protocol still apply. 8. IANA Considerations This document has no IANA actions. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway Protocol (IGP) Routes Over Traffic Engineering Tunnels", RFC 3906, DOI 10.17487/RFC3906, October 2004, . [RFC5130] Previdi, S., Shand, M., Ed., and C. Martin, "A Policy Control Mechanism in IS-IS Using Administrative Tags", RFC 5130, DOI 10.17487/RFC5130, February 2008, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, May 2017 Cheng, et al. Expires October 02, 2025 [Page 6] Internet-Draft IGP Color-Aware Shortcut April 2025 [RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, July 2022, [I-D.ietf-lsr-ospf-admin-tags] Lindem, A., Psenak, P., and Y. Qu, "Extensions to OSPF for Advertising Prefix Administrative Tags", Work in Progress, Internet-Draft, draft-ietf-lsr- ospf-admin-tags-29, 04 March 2025, . 9.2. Informational References [RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder, "The BGP Tunnel Encapsulation Attribute", RFC 9012, DOI 10.17487/RFC9012, April 2021, . [RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene, B., Zhuang, S., and J. Rabadan, "BGP Overlay Services Based on Segment Routing over IPv6 (SRv6)", RFC 9252, DOI 10.17487/RFC9252, July 2022, . Authors' Addresses Weiqiang Cheng China Mobile China Email: chengweiqiang@chinamobile.com Liyan Gong China Mobile China Email: gongliyan@chinamobile.com Changwang Lin New H3C Technologies China Email: linchangwang.04414@h3c.com Ran Chen ZTE Corporation Email: chen.ran@zte.com.cn Cheng, et al. Expires October 02, 2025 [Page 7]