LSR Working Group A. Wang Internet-Draft China Telecom Intended status: Standards Track Z. Hu Expires: 24 April 2023 Huawei Technologies A. Lindem Cisco Systems G. Mishra Verizon Inc. J. Sun ZTE Corporation 21 October 2022 Advertisement of Stub Link Attributes draft-wang-lsr-stub-link-attributes-05 Abstract This document describes the mechanism that can be used to advertise the stub link attributes within the IS-IS or OSPF domain. 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 24 April 2023. 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 to this document. Code Components Wang, et al. Expires 24 April 2023 [Page 1] Internet-Draft Advertisement of Stub Link Attributes October 2022 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. Conventions used in this document . . . . . . . . . . . . . . 3 3. Consideration for Identifying Stub Link . . . . . . . . . . . 3 4. Protocol Extension for Stub Link Attributes . . . . . . . . . 3 4.1. OSPF Stub-Link TLV . . . . . . . . . . . . . . . . . . . 3 4.2. IS-IS Stub-link TLV . . . . . . . . . . . . . . . . . . . 4 4.3. IPv4 Prefix Sub-TLV . . . . . . . . . . . . . . . . . . . 5 4.4. IPv6 Prefix Sub-TLV . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Applied Scenarios . . . . . . . . . . . . . . . . . 9 A.1. Inter-AS topology recovery . . . . . . . . . . . . . . . 9 A.2. Egress Engineering for Anycast Servers . . . . . . . . . 11 A.3. Optimized BGP Next-hop Selection . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction Stub links are used commonly within enterprise or service provider networks. One common use case is the inter-AS routing scenario where there are no IGP adjacencies between the adjacent BGP domains, another use case is at the network boundary that the interfaces are used to connect to the application servers. For operators that have multiple ASes interconnecting with each other via the stub links, there is a requirement to obtain the inter-AS topology information as described in [I-D.ietf-idr-bgpls-inter-as-topology-ext]. To achieve such goal, it is required that the BGP-LS to be enabled on every router that has the stub links, which is challenging for the network operation. It is desirable to advertise the stub link info into the IGP to ease the deployment of BGP-LS on any router in the IGP domain. For stub links that are used to connect the servers, knowing the status of these stub links can facilitate the routers within the IGP to accomplish TE tasks in some scenarios. Wang, et al. Expires 24 April 2023 [Page 2] Internet-Draft Advertisement of Stub Link Attributes October 2022 But OSPF and IS-IS have no capability to identify such stub links and their associated attributes now. This document defines the protocol extension for OSPFv2/v3 and IS-IS to indicate the stub links and their associated attributes. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] . 3. Consideration for Identifying Stub Link OSPF[RFC5392] defines the Inter-AS-TE-v2 LSA and Inter-AS-TE-v3 LSA to carry the TE information about inter-AS links. IS-IS[RFC5316] defines the Inter-AS Reachability TLV to carry the TE information about inter-AS links. But they are normally being used under RSVP- TE, especially inter-domain RSVP-TE scenarios. As illustrated in the potential scenarios that described in Appendix A, there is still the need for a generic solution which also covers non inter-AS stub links. Then, to solve the problems that described in the applied scenarios, this document defines the Stub-Link TLV to identify the stub link and transmit the associated attributes for OSPF and IS-IS respectively. 4. Protocol Extension for Stub Link Attributes The following sections define the protocol extension to indicate the stub link and its associated attributes in OSPFv2/v3 and IS-IS. 4.1. OSPF Stub-Link TLV This document defines the Stub-Link TLV to describe stub link of a single router. For OSPFv2, the newly defined Stub-Link TLV is named as OSPFv2 Extended Stub-Link TLV, which is included in the OSPFv2 Extended Link Opaque LSA [RFC7684] For OSPFv3, the newly defined Stub-Link TLV is named as Router-Stub- Link TLV, which is included in the OSPFv3 Router-LSA [RFC8362] OSPFv2 Extended Stub-Link TLV and OSPFv3 Router-Stub-Link TLV has the following same format: Wang, et al. Expires 24 April 2023 [Page 3] Internet-Draft Advertisement of Stub Link Attributes October 2022 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(Stub-Link) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U| Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Prefix Sub-TLVs | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Existing Sub-TLVs (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: OSPF Stub-Link TLV Type: The TLV type. The value is 2(TBD) for OSPFv2 Extended Link Stub-Link TLV under the IANA codepoint "OSPFv2 Extended Link Opaque LSA TLVs", and is 10(TBD) for OSPFv3 Router-Stub-Link TLV under the IANA codepoint "OSPFv3 Extended-LSA TLVs" Length: Variable, dependent on sub-TLVs Flags: Define the type of the stub-link: * U bit(bit 0): Identify the unnumbered stub link if this bit is set. * bit 1-bit 15: Reserved Link Prefix Sub-TLV: The prefix of the stub-link. It's format is defined in Section 4.3 and Section 4.4. Existing Sub-TLVs: Sub-TLV that defined within "OSPFv2 Extended Link TLV Sub-TLVs" and "OSPFv3 Extended-LSA Sub-TLVs" can be included if necessary. If the stub-link is identified as unnumbered stub link (U bit is set), then the "Remote IPv4 Address sub-TLV" or "Remote Interface IPv6 Address sub-TLV", which should be set to the identifier value of remote router, SHOULD be included to facilitate the pairing of inter- AS link. This document creates a registry for Stub-Link attributes in Section 6. 4.2. IS-IS Stub-link TLV This document defines the IS-IS Stub-Link TLV to describes stub link of a single router. Wang, et al. Expires 24 April 2023 [Page 4] Internet-Draft Advertisement of Stub Link Attributes October 2022 The IS-IS Stub-Link 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(Stub-Link) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U| Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Prefix Sub-TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Existing Sub-TLVs(Variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: IS-IS Stub-Link TLV Type: IS-IS TLV codepoint. Value is 151 (TBD) for stub-link TLV. Length: Variable, dependent on sub-TLVs Flags: Define the type of the stub-link: * 0: U bit(bit 0): Identify the unnumbered stub link if this bit is set. * bit 1-bit 15: Reserved Link Prefix Sub-TLV: The prefix of the stub-link. It's format is defined in Section 4.3 and Section 4.4. Existing Sub-TLVs: Sub-TLVs that defined within "IS-IS Sub-TLVs for TLVs Advertising Neighbor Information " can be included if necessary. If the stub-link is identified as unnumbered stub link type (U bit is set), then the "IPv4 Remote ASBR ID" or "IPv6 Remote ASBR ID" sub-TLV SHOULD be included to facilitate the pairing of inter-AS link. 4.3. IPv4 Prefix Sub-TLV The IPv4 Prefix 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: IPv4 Prefix Sub-TLV Wang, et al. Expires 24 April 2023 [Page 5] Internet-Draft Advertisement of Stub Link Attributes October 2022 Type: IPv4 Prefix Sub-TLV codepoint. Value is 25(TBD) for OSPFv2 (under "OSPFv2 Extended Link Sub-TLVs" ) 30(TBD) for OSPFv3(under OSPFv3 Extended-LSA Sub-TLVs) 45(TBD) for IS-IS(under "IS-IS Sub-TLVs for TLVs Advertising Neighbor Information") Length: Netmask length value of the IPv4 Prefix. Value should be in 2-32. IPv4 Prefix: The value of 4-octet IPv4 Prefix address, the host part should be zero. 4.4. IPv6 Prefix Sub-TLV The IPv6 Prefix 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: IPv6 Prefix Sub-TLV Type: IPv6 Prefix Sub-TLV codepoint. Value is 31(TBD) for OSPFv3.(under OSPFv3 Extended-LSA Sub-TLVs) 46(TBD) for IS-IS(under "IS-IS Sub-TLVs for TLVs Advertising Neighbor Information") Length: Netmask length value of the IPv6 Prefix. Value should be in 2-128. IPv6 Prefix: The value of 16-octet IPv6 Prefix address, the host part should be zero. Wang, et al. Expires 24 April 2023 [Page 6] Internet-Draft Advertisement of Stub Link Attributes October 2022 5. Security Considerations Security concerns for IS-IS are addressed in [RFC5304] and[RFC5310] Security concern for OSPFv3 is addressed in [RFC4552] Advertisement of the additional information defined in this document introduces no new security concerns. 6. IANA Considerations IANA is requested to the allocation in following registries: +====================================+======+=============================+ | Registry | Type | Meaning | +====================================+======+=============================+ |OSPFv2 Extended Link Opaque LSA TLVs| 2 |OSPFv2 Extended Stub-Link TLV| +------------------------------------+------+-----------------------------+ |OSPFv3 Extended-LSA TLVs | 10 |Router-Stub-Link TLV | +------------------------------------+------+-----------------------------+ |IS-IS Top-Level TLV | 151 |IS-IS Stub-Link TLV | +------------------------------------+------+-----------------------------+ |OSPFv2 Extended Link TLV | 25 | IPv4 Prefix Sub-TLV | +------------------------------------+------+-----------------------------+ |OSPFv3 Extended-LSA Sub-TLVs | 30 | IPv4 Prefix Sub-TLV | +------------------------------------+------+-----------------------------+ |OSPFv3 Extended-LSA Sub-TLVs | 31 | IPv6 Prefix Sub-TLV | +------------------------------------+------+-----------------------------+ |IS-IS Sub-TLVs for TLVs | | | |Advertising Neighbor Information | 45 | IPv4 Prefix Sub-TLV | +------------------------------------+------+-----------------------------+ |IS-IS Sub-TLVs for TLVs | | | |Advertising Neighbor Information | 46 | IPv6 Prefix Sub-TLV | +------------------------------------+------+-----------------------------+ Figure 5: IANA Allocation for newly defined TLVs and Sub-TLVs 7. Acknowledgement Thanks Ketan Talaulikar, Shunwan Zhang, Peter Psenak, Tony Li, Les Ginsberg, Dhruv Dhody, Jeff Tantsura and Robert Raszuk for their suggestions and comments on this idea. 8. References 8.1. Normative References Wang, et al. Expires 24 April 2023 [Page 7] Internet-Draft Advertisement of Stub Link Attributes October 2022 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, . [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2008, . [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2009, . [RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316, December 2008, . [RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering", RFC 5392, DOI 10.17487/RFC5392, January 2009, . [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 2015, . [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and F. Baker, "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, DOI 10.17487/RFC8362, April 2018, . 8.2. Informative References [I-D.ietf-idr-bgpls-inter-as-topology-ext] Wang, A., Chen, H., Talaulikar, K., and S. Zhuang, "BGP-LS Extension for Inter-AS Topology Retrieval", Work in Progress, Internet-Draft, draft-ietf-idr-bgpls-inter-as- topology-ext-11, 12 May 2022, . Wang, et al. Expires 24 April 2023 [Page 8] Internet-Draft Advertisement of Stub Link Attributes October 2022 Appendix A. Applied Scenarios The following sections describe the scenarios that knowing the stub link related attributes information can help solve the corresponding necessity in questions. A.1. Inter-AS topology recovery Figure 1 describes the scenario that the necessity of inter-AS topology recovery for Native IP point-to-point stub link scenario. R10, R11 and R12 are located in AS1. R20, R21,R22 are located in AS2. The controller runs BGP-LS with R10 in AS1 and R20 in AS2 respectively. There is one BGP session among the border router R11 and R21, which are connected by several stub links(passive interfaces) between them. The situation within the R21 and R22 are the same. Since the links between the border routers are passive, there will be no IGP neighbors between them. The BGP-LS information carried in each AS will not report these stub links,and the controller can't recovery the inter-AS topology automatically. Wang, et al. Expires 24 April 2023 [Page 9] Internet-Draft Advertisement of Stub Link Attributes October 2022 +----------+ +--------------+Controller+--------------+ ^ +----------+ ^ | | BGP-LS| |BGP-LS | +---+BGP+----+ | +-----------------+ +-------------------+ | | | | | | | | +---+-+ +-+---+ | | | | | +--------+ | | | | +--------+R11 |--------| R21+----------+ | | | | +--------+ | | | | | +---+-+ +-+---+ | | | +--+--+ | | +--+--+ | | | | | | | | | | |R10 | | | |R20 | | | | | | | | | | | +--+--+ +---+-+ +-+---+ +--+--+ | | | | +--------+ | | | | +--------+R12 |--------| R22+----------+ | | | +--------+ | | | +---+-+ +-+---+ | | | | | +--------AS1------+ +----------AS2------+ +---+BGP+----+ Figure 1: Inter-AS Topology Recovery(P2P Scenario) Figure 2 describes the similar situation but in LAN environment. The border routers of AS1, AS2 and AS3 are connected via one LAN interfaces(that is to say, the corresponding interfaces on R1, R2 and R3 are on the same subnet). There are three different BGP sessions from the loopback address of the border routers among them respectively. It is necessary to recovery the underlying inter-AS topology automatically. Wang, et al. Expires 24 April 2023 [Page 10] Internet-Draft Advertisement of Stub Link Attributes October 2022 +---------+ +---------+ | | | | | +--+--+ +--+--+ | | | | | | | | |R1 +-------+ +------+R2 | | | | | | | | | | | +--+--+ | | +--+--+ | | | | | | | +---AS1---+ | | +----AS2--+ +-+-+-+ | | | SW | | | +--+--+ | +--+--+ +--+ +--+ | | R3 | | | +-----+ | | | | | +-----AS3---+ Figure 2: Inter-AS Topology Recovery(LAN Scenario) A.2. Egress Engineering for Anycast Servers Figure 3 describes the scenario that the stub link information can be used for egress engineering for Anycast servers that connected to the network. In the example, the R1, R2 and R3 are border routers which are connected directly the server S1, S2 and S3 that have the same IP address IPa. The characteristics of the stub links that connected to these Anycast servers are different. It will be help for the router R0, to know the attributes of the stub links and select the optimal Anycast server to serve the customer's application. Wang, et al. Expires 24 April 2023 [Page 11] Internet-Draft Advertisement of Stub Link Attributes October 2022 +----------------+ | | | +---+-+ +-----+ | | | | S1 | | +-------+R1 +------+ | | | | | |(IPa)| | | +---+-+ +-----+ | | | | +--+--+ +---+-+ +-----+ | | | | | | S2 | | |R0 +----+R2 +------+ | | | | | | |(IPa)| | +--+--+ +---+-+ +-----+ | | | | | +---+-+ +-----+ | | | | | S3 | | +-------+R3 +------+ | | | | |(IPa)| | +---+-+ +-----+ | | +----------------+ Figure 3: Egress Engineering for Anycast Server A.3. Optimized BGP Next-hop Selection Figure 4 describes the scenario that the stub link information can facilitate the optimized BGP next hop selection. The router R10 and R20 which are located in different AS establish the BGP session directly, with the explicit route set on each other which point to the egress stub interface between the border routers. The attributes of the stub links among the border routers are vary. It is certainly will be helpful for the router R10 and R20 to select the optimized BGP next hop, that is via the stub links among them, to reach each other. Wang, et al. Expires 24 April 2023 [Page 12] Internet-Draft Advertisement of Stub Link Attributes October 2022 |<---------------+BGP+------------------>| | | | | +-----------------+ +-------------------+ | | | | | | | | +---+-+ +-+---+ | | | | | +--------+ | | | | +--------+R11 |--------| R21+----------+ | | | | +--------+ | | | | | +---+-+ +-+---+ | | | +--+--+ | | +--+--+ | | | | | | | | | | |R10 | | | |R20 | | | | | | | | | | | +--+--+ +---+-+ +-+---+ +--+--+ | | | | +--------+ | | | | +--------+R12 |--------| R22+----------+ | | | +--------+ | | | +---+-+ +-+---+ | | | | | +-------+AS1+-----+ +---------+AS2+-----+ Figure 4: Optimized BGP next hop selection Authors' Addresses Aijun Wang China Telecom Beiqijia Town, Changping District Beijing 102209 China Email: wangaj3@chinatelecom.cn Zhibo Hu Huawei Technologies Huawei Bld., No.156 Beiqing Rd. Beijing 100095 China Email: huzhibo@huawei.com Wang, et al. Expires 24 April 2023 [Page 13] Internet-Draft Advertisement of Stub Link Attributes October 2022 Acee Lindem Cisco Systems No. 301 Midenhall Way Cary, NC 27513 United States of America Email: acee@cisco.com Gyan S. Mishra Verizon Inc. 13101 Columbia Pike Silver Spring, MD 20904 United States of America Email: gyan.s.mishra@verizon.com Jinsong Sun ZTE Corporation No. 68, Ziijnhua Road Nan Jing 210012 China Email: sun.jinsong@zte.com.cn Wang, et al. Expires 24 April 2023 [Page 14]