Network Working Group W. Cheng Internet Draft L. Gong Intended status: Standards Track China Mobile Expires: March 6, 2024 C. Lin M. Chen New H3C Technologies September 6, 2023 IGP Shortcut Enhancement draft-cheng-lsr-igp-shortcut-enhancement-02 Abstract IGP shortcut mechanism allows calculating routes to forward traffic over Traffic Engineering tunnels. This document describes 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), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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. 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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. Extensions for IGP.............................................3 2.1. IS-IS Color Sub-TLV.......................................3 2.2. OSPF Color Sub-TLV........................................4 3. SPF Computation................................................5 4. Color Values of TE-Tunnels.....................................5 5. Backward Compatibility.........................................6 6. Security Considerations........................................6 7. IANA Considerations............................................6 8. References.....................................................6 8.1. Normative References......................................6 8.2. Informational References..................................7 Authors' Addresses................................................8 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. Cheng, et al. Expires March 6, 2024 [Page 2] Internet-Draft IGP Shortcut Enhancement September 2023 === 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. 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 describes the enhancement of IGP shortcut which can steer routes onto TE-tunnels based on colors. It also defines the extensions for IGP to advertise colors for prefixes. 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. Extensions for IGP 2.1. IS-IS Color Sub-TLV The IS-IS Color Sub-TLV is defined in this document to advertise colors for prefixes in IS-IS. The Sub-TLV has the following format: Cheng, et al. Expires March 6, 2024 [Page 3] Internet-Draft IGP Shortcut Enhancement September 2023 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 | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Color | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Type: TBD. o Length: 1 octet. The length value is variable. o Flags: 2 octets. No flags are defined in this document. Undefined flags MUST be set to 0 by the sender, and any unknown flags MUST be ignored by the receiver. o Color: 4 octets. Contains color value associated with the prefix. The IS-IS Color Sub-TLV is applicable to TLVs 27, 135, 235, 236, and 237. 2.2. OSPF Color Sub-TLV The OSPF Color Sub-TLV is defined in this document to advertise colors for prefixes in OSPFv2 and OSPFv3. The Sub-TLV has the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Color | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Color (cont.) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Type: TBD. o Length: 1 octet. The length value is variable. o Flags: 2 octets. No flags are defined in this document. Undefined flags MUST be set to 0 by the sender, and any unknown flags MUST be ignored by the receiver. o Color: 4 octets. Contains color value associated with the prefix. Cheng, et al. Expires March 6, 2024 [Page 4] Internet-Draft IGP Shortcut Enhancement September 2023 The OSPF Color Sub-TLV is applicable to OSPFv2 Extended Prefix TLV OSPFv3 Inter-Area-Prefix TLV OSPFv3 Intra-Area-Prefix TLV OSPFv3 External-Prefix TLV. 3. SPF Computation 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. 4. Color Values of TE-Tunnels The main idea of this document is to steer the flows to colored prefixes into tunnels with the same color values. Cheng, et al. Expires March 6, 2024 [Page 5] Internet-Draft IGP Shortcut Enhancement September 2023 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, which is out of the scope of this document. 5. Backward Compatibility If a head-end node does not support the Color Sub-TLV, it will calculate routes ignoring the colors. As a result, the behavior would be the same as without this specification. 6. Security Considerations TBD. 7. IANA Considerations This document defines the following new Sub-TLV in IS-IS: TBD - IS-IS Color Sub-TLV This document defines the following new Sub-TLV in OSPFv2 and OSPFv3: TBD - OSPF Color Sub-TLV 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, May 2017 [RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway Protocol (IGP) Routes Over Traffic Engineering Tunnels", RFC 3906, DOI 10.17487/RFC3906, October 2004, . [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, Cheng, et al. Expires March 6, 2024 [Page 6] Internet-Draft IGP Shortcut Enhancement September 2023 8.2. 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, . Cheng, et al. Expires March 6, 2024 [Page 7] Internet-Draft IGP Shortcut Enhancement September 2023 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 Mengxiao Chen New H3C Technologies China Email: chen.mengxiao@h3c.com Cheng, et al. Expires March 6, 2024 [Page 8]