idnits 2.17.00 (12 Aug 2021) /tmp/idnits64824/draft-ietf-idr-bgpls-sr-vtn-mt-00.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- -- The document date (4 February 2022) is 99 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC5029' is defined on line 349, but no explicit reference was found in the text == Unused Reference: 'I-D.dong-lsr-sr-enhanced-vpn' is defined on line 386, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-lsr-isis-srv6-extensions' is defined on line 410, but no explicit reference was found in the text == Unused Reference: 'RFC5120' is defined on line 426, but no explicit reference was found in the text == Unused Reference: 'RFC8667' is defined on line 432, but no explicit reference was found in the text == Outdated reference: A later version (-04) exists of draft-ietf-spring-resource-aware-segments-03 == Outdated reference: A later version (-02) exists of draft-ietf-spring-sr-for-enhanced-vpn-01 == Outdated reference: A later version (-04) exists of draft-dong-idr-bgpls-sr-enhanced-vpn-03 == Outdated reference: A later version (-10) exists of draft-ietf-teas-enhanced-vpn-09 Summary: 0 errors (**), 0 flaws (~~), 9 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR Working Group C. Xie 3 Internet-Draft C. Li 4 Intended status: Informational China Telecom 5 Expires: 8 August 2022 J. Dong 6 Z. Li 7 Huawei Technologies 8 4 February 2022 10 BGP-LS with Multi-topology for Segment Routing based Virtual Transport 11 Networks 12 draft-ietf-idr-bgpls-sr-vtn-mt-00 14 Abstract 16 Enhanced VPN (VPN+) aims to provide enhanced VPN service to support 17 some applications' needs of enhanced isolation and stringent 18 performance requirements. VPN+ requires integration between the 19 overlay VPN and the underlay network. A Virtual Transport Network 20 (VTN) is a virtual underlay network which consists of a subset of the 21 network topology and network resources allocated from the physical 22 network. A VTN could be used as the underlay for one or a group of 23 VPN+ services. 25 When Segment Routing is used as the data plane of VTNs, each VTN can 26 be allocated with a group of Segment Identifiers (SIDs) to identify 27 the topology and resource attributes of network segments in the VTN. 28 The association between the network topology, the network resource 29 attributes and the SR SIDs may need to be distributed to a 30 centralized network controller. For network scenarios where each VTN 31 can be associated with a unique logical network topology, this 32 document describes a mechanism to distribute the information of SR 33 based VTNs using BGP-LS with Multi-Topology. 35 Requirements Language 37 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 38 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 39 document are to be interpreted as described in RFC 2119 [RFC2119]. 41 Status of This Memo 43 This Internet-Draft is submitted in full conformance with the 44 provisions of BCP 78 and BCP 79. 46 Internet-Drafts are working documents of the Internet Engineering 47 Task Force (IETF). Note that other groups may also distribute 48 working documents as Internet-Drafts. The list of current Internet- 49 Drafts is at https://datatracker.ietf.org/drafts/current/. 51 Internet-Drafts are draft documents valid for a maximum of six months 52 and may be updated, replaced, or obsoleted by other documents at any 53 time. It is inappropriate to use Internet-Drafts as reference 54 material or to cite them other than as "work in progress." 56 This Internet-Draft will expire on 8 August 2022. 58 Copyright Notice 60 Copyright (c) 2022 IETF Trust and the persons identified as the 61 document authors. All rights reserved. 63 This document is subject to BCP 78 and the IETF Trust's Legal 64 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 65 license-info) in effect on the date of publication of this document. 66 Please review these documents carefully, as they describe your rights 67 and restrictions with respect to this document. Code Components 68 extracted from this document must include Revised BSD License text as 69 described in Section 4.e of the Trust Legal Provisions and are 70 provided without warranty as described in the Revised BSD License. 72 Table of Contents 74 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 75 2. Advertisement of SR VTN Topology Attribute . . . . . . . . . 4 76 2.1. Intra-domain Topology Advertisement . . . . . . . . . . . 4 77 2.2. Inter-Domain Topology Advertisement . . . . . . . . . . . 5 78 3. Advertisement of SR VTN Resource Attribute . . . . . . . . . 6 79 4. Scalability Considerations . . . . . . . . . . . . . . . . . 7 80 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 81 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 82 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 83 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 84 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 85 8.2. Informative References . . . . . . . . . . . . . . . . . 9 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 88 1. Introduction 90 Enhanced VPN (VPN+) is an enhancement to VPN services to support the 91 needs of new applications, particularly including the applications 92 that are associated with 5G services. These applications require 93 enhanced isolation and have more stringent performance requirements 94 than that can be provided with traditional overlay VPNs. Thus these 95 properties require integration between the overlay connectivity and 96 the characteristics provided by the underlay networks. 97 [I-D.ietf-teas-enhanced-vpn] specifies the framework of enhanced VPN 98 and describes the candidate component technologies in different 99 network planes and layers. An enhanced VPN can be used for 5G 100 network slicing, and will also be of use in more generic scenarios. 102 To meet the requirement of enhanced VPN services, a number of Virtual 103 Transport Networks (VTNs) need to be created, each consists of a 104 subset of the underlay network topology and a subset of network 105 resources allocated from the underlay network to meet the requirement 106 of one or a group of VPN+ services. 108 [I-D.ietf-spring-resource-aware-segments] introduces resource 109 awareness to Segment Routing (SR) [RFC8402]. The resource-aware SIDs 110 have additional semantics to identify the set of network resources 111 available for the packet processing action associated with the SIDs. 112 As described in [I-D.ietf-spring-sr-for-enhanced-vpn], the resource- 113 aware segments can be used to build SR based VTNs with the required 114 network topology and network resource attributes to support enhanced 115 VPN services. 117 To allow the network controller and network nodes to perform VTN- 118 specific explicit path computation and/or shortest path computation, 119 the group of resource-aware SIDs allocated by network nodes to each 120 VTN and the associated topology and resource attributes need to be 121 distributed in the control plane. When a centralized network 122 controller is used for VTN-specific path computation, especially when 123 a VTN spans multiple IGP areas or multiple Autonomous Systems (ASes), 124 BGP-LS is needed to advertise the VTN information in each IGP area or 125 AS to the network controller, so that the controller could use the 126 collected information to build the view of inter-area or inter-AS SR 127 VTNs. 129 In some network scenarios, each VTN can be associated with a unique 130 logical network topology, [I-D.ietf-lsr-isis-sr-vtn-mt] describes an 131 IGP mechanism to advertise the association between the topology, 132 resource attributes and the SR SIDs for each VTN. This document 133 describes a mechanism to distribute the information of SR based VTNs 134 to the network controller using BGP-LS with Multi-Topology. 136 2. Advertisement of SR VTN Topology Attribute 138 [I-D.ietf-lsr-isis-sr-vtn-mt] describes the IS-IS Multi-topology 139 based mechanisms to distribute the topology attributes of SR based 140 VTNs. This section describes the corresponding BGP-LS mechanism to 141 distribute both the intra-domain and inter-domain topology attributes 142 of SR based VTNs. 144 2.1. Intra-domain Topology Advertisement 146 In section 4.2.2.1 of [I-D.ietf-idr-rfc7752bis], Multi-Topology 147 Identifier (MT-ID) TLV is defined, which can contain one or more IS- 148 IS or OSPF Multi-Topology IDs. The MT-ID TLV MAY be present in a 149 Link Descriptor, a Prefix Descriptor, or the BGP-LS Attribute of a 150 Node NLRI. 152 [RFC9085] defines the BGP-LS extensions to carry the segment routing 153 information using TLVs of BGP-LS Attribute. When Multi-Topology is 154 used with SR-MPLS data plane, topology-specific prefix-SIDs and 155 topology-specific Adj-SIDs can be carried in the BGP-LS Attribute 156 associated with the prefix NLRI and link NLRI respectively, the MT-ID 157 TLV is carried in the prefix descriptor or link descriptor to 158 identify the corresponding topology of the SIDs. 160 [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to 161 advertise SRv6 segments along with their functions and attributes. 162 When Multi-Topology is used with SRv6 data plane, the SRv6 Locator 163 TLV is carried in the BGP-LS Attribute associated with the prefix- 164 NLRI, the MT-ID TLV can be carried in the prefix descriptor to 165 identify the corresponding topology of the SRv6 Locator. The SRv6 166 End.X SIDs are carried in the BGP-LS Attribute associated with the 167 link NLRI, the MT-ID TLV can be carried in the link descriptor to 168 identify the corresponding topology of the End.X SIDs. The SRv6 SID 169 NLRI is defined to advertise other types of SRv6 SIDs, in which the 170 SRv6 SID Descriptors can include the MT-ID TLV so as to advertise 171 topology-specific SRv6 SIDs. 173 [I-D.ietf-idr-rfc7752bis] also defines the rules of the usage of MT- 174 ID TLV: 176 "In a Link or Prefix Descriptor, only a single MT-ID TLV containing 177 the MT-ID of the topology where the link or the prefix is reachable 178 is allowed. In case one wants to advertise multiple topologies for a 179 given Link Descriptor or Prefix Descriptor, multiple NLRIs MUST be 180 generated where each NLRI contains a single unique MT-ID." 181 Editor's note: the above rules indicates that only one MT-ID is 182 allowed to be carried the Link or Prefix descriptors. When a link or 183 prefix needs to be advertised in multiple topologies, multiple NLRIs 184 needs to be generated to report all the topologies the link or prefix 185 participates in, together with the topology-specific segment routing 186 information and link attributes. This may increase the number of BGP 187 Updates needed for advertising MT-specific topology attributes, and 188 may introduce additional processing burden to both the sending BGP 189 speaker and the receiving network controller. When the number of 190 topologies in a network is not a small number, some optimization may 191 be needed for the reporting of multi-topology information and the 192 associated segment routing information in BGP-LS. Based on the WG's 193 opinion, this may be elaborated in a future version. 195 2.2. Inter-Domain Topology Advertisement 197 [RFC9086] and [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS 198 extensions for advertisement of BGP inter-domain topology information 199 and the BGP Egress Peering Segment Identifiers. Such information 200 could be used by a network controller for the computation and 201 instantiation of inter-AS traffic engineering SR paths. 203 In some network scenarios, there are needs to create VTNs which span 204 multiple ASes. The inter-domain VTNs could have different inter- 205 domain connectivity, and may be associated with different set of 206 network resources in each domain and also on the inter-domain links. 207 In order to build the multi-domain SR based VTNs, it is necessary to 208 advertise the topology and resource attribute of each VTN and the 209 associated BGP Peering SIDs on the inter-domain links. 211 Depending on the requirement of inter-domain VTNs, different 212 mechanism can be used on the inter-domain connection: 214 * One EBGP session between two ASes can be established over multiple 215 underlying links. In this case, different underlying links can be 216 used for different inter-domain VTNs which requires link isolation 217 between each other. In another similar case, the EBGP session is 218 established over a single link, while the network resource (e.g. 219 bandwidth) on this link can be partitioned into several pieces, 220 each of which can be considered as a virtual member link. A VTN 221 is associated with one of the physical or virtual member links. 222 In both cases, different BGP Peer-Adj-SIDs or SRv6 End.X SID 223 SHOULD be allocated to each underlying physical or virtual member 224 link, the association between the BGP Peer Adj-SID/End.X SID and 225 the identifier of the VTN SHOULD be advertised by the ASBR. 227 * For inter-domain connection between two ASes, multiple EBGP 228 sessions can be established between different set of peering 229 ASBRs. It is possible that some of these BGP sessions are used 230 for one multi-domain VTN, while some other BGP sessions are used 231 for another multi-domain VTN. In this case, different BGP Peer 232 Node SIDs are allocated to each BGP session and are advertised 233 using the mechanism in [RFC9086] and 234 [I-D.ietf-idr-bgpls-srv6-ext], the association between the BGP 235 Peer Node SIDs and the identifier of the VTN SHOULD be advertised 236 by the ASBR. 238 * At the AS-level topology, different multi-domain VTNs may have 239 different inter-domain connectivity. Different BGP Peer Set SIDs 240 MAY be allocated to represent the groups of BGP peers which can be 241 used for load-balancing in each multi-domain VTN. 243 When MT-ID is used consistently in multiple ASes covered by a VTN, 244 the topology-specific BGP peering SIDs can be advertised with the MT- 245 ID carried in the corresponding Link NLRI. This can be achieved with 246 the existing mechanisms as defined in [RFC7752][RFC9086] and 247 [I-D.ietf-idr-bgpls-srv6-ext]. 249 In network scenarios where consistent usage of MT-ID among multiple 250 domains can not be expected, a global-significant VTN-ID needs to be 251 introduced to define the inter-domain topologies. Within each 252 domain, the MT based mechanism could be reused for intra-domain 253 topology advertisement. The detailed mechanism is specified in 254 [I-D.dong-idr-bgpls-sr-enhanced-vpn]. 256 3. Advertisement of SR VTN Resource Attribute 258 [I-D.ietf-lsr-isis-sr-vtn-mt] specifies the mechanism to advertise 259 the resource information associated with each VTN. This section 260 describes the corresponding BGP-LS mechanisms. 262 The information of the network resources associated with a VTN can be 263 specified by carrying the TE Link attribute TLVs in BGP-LS Attribute 264 [RFC7752], with the associated MT-ID carried in the corresponding 265 Link NLRI. 267 When Maximum Link Bandwidth sub-TLV is carried in the BGP-LS 268 attribute associated with the Link NLRI of a VTN, it indicates the 269 amount of link bandwidth resource allocated to the corresponding VTN 270 on the link. The bandwidth allocated to a VTN can be exclusive for 271 traffic in the corresponding VTN. The advertisement of other TE 272 attributes in BGP-LS for each VTN is for further study. 274 4. Scalability Considerations 276 The mechanism described in this document requires that each VTN 277 mapped to an independent topology, and for the inter-domain VTNs, the 278 MT-IDs used in each involved domain need to be consistent. Reusing 279 MT-IDs as the identifier of VTN can avoid introducing new identifiers 280 in the control plane, while it also has some limitations. For 281 example, when multiple VTNs shares the same topology, each VTN still 282 need to be identified using different MT-IDs in the control plane, 283 thus independent path computation needs be executed for each VTN. 284 The number of VTNs supported in a network may be dependent on the 285 number of topologies supported, which is related to the control plane 286 overhead. The mechanism described in this document is applicable to 287 network scenarios where the number of required VTN is relatively 288 small. A detailed analysis about the VTN scalability and the 289 possible optimizations for supporting a large number of VTNs is 290 described in [I-D.dong-teas-enhanced-vpn-vtn-scalability]. 292 5. Security Considerations 294 This document introduces no additional security vulnerabilities to 295 BGP-LS. 297 The mechanism proposed in this document is subject to the same 298 vulnerabilities as any other protocol that relies on BGP-LS. 300 6. IANA Considerations 302 This document does not request any IANA actions. 304 7. Acknowledgments 306 The authors would like to thank Shunwan Zhuang for the review and 307 discussion of this document. 309 8. References 311 8.1. Normative References 313 [I-D.ietf-idr-bgpls-srv6-ext] 314 Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., 315 Bernier, D., and B. Decraene, "BGP Link State Extensions 316 for SRv6", Work in Progress, Internet-Draft, draft-ietf- 317 idr-bgpls-srv6-ext-09, 10 November 2021, 318 . 321 [I-D.ietf-idr-rfc7752bis] 322 Talaulikar, K., "Distribution of Link-State and Traffic 323 Engineering Information Using BGP", Work in Progress, 324 Internet-Draft, draft-ietf-idr-rfc7752bis-10, 10 November 325 2021, . 328 [I-D.ietf-spring-resource-aware-segments] 329 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 330 Z., and F. Clad, "Introducing Resource Awareness to SR 331 Segments", Work in Progress, Internet-Draft, draft-ietf- 332 spring-resource-aware-segments-03, 12 July 2021, 333 . 336 [I-D.ietf-spring-sr-for-enhanced-vpn] 337 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 338 Z., and F. Clad, "Segment Routing based Virtual Transport 339 Network (VTN) for Enhanced VPN", Work in Progress, 340 Internet-Draft, draft-ietf-spring-sr-for-enhanced-vpn-01, 341 12 July 2021, . 344 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 345 Requirement Levels", BCP 14, RFC 2119, 346 DOI 10.17487/RFC2119, March 1997, 347 . 349 [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link 350 Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, 351 September 2007, . 353 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 354 S. Ray, "North-Bound Distribution of Link-State and 355 Traffic Engineering (TE) Information Using BGP", RFC 7752, 356 DOI 10.17487/RFC7752, March 2016, 357 . 359 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 360 Decraene, B., Litkowski, S., and R. Shakir, "Segment 361 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 362 July 2018, . 364 [RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler, 365 H., and M. Chen, "Border Gateway Protocol - Link State 366 (BGP-LS) Extensions for Segment Routing", RFC 9085, 367 DOI 10.17487/RFC9085, August 2021, 368 . 370 [RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K., 371 Ray, S., and J. Dong, "Border Gateway Protocol - Link 372 State (BGP-LS) Extensions for Segment Routing BGP Egress 373 Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August 374 2021, . 376 8.2. Informative References 378 [I-D.dong-idr-bgpls-sr-enhanced-vpn] 379 Dong, J., Hu, Z., Li, Z., Tang, X., and R. Pang, "BGP-LS 380 Extensions for Segment Routing based Enhanced VPN", Work 381 in Progress, Internet-Draft, draft-dong-idr-bgpls-sr- 382 enhanced-vpn-03, 22 February 2021, 383 . 386 [I-D.dong-lsr-sr-enhanced-vpn] 387 Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L., 388 and S. Bryant, "IGP Extensions for Scalable Segment 389 Routing based Enhanced VPN", Work in Progress, Internet- 390 Draft, draft-dong-lsr-sr-enhanced-vpn-07, 29 January 2022, 391 . 394 [I-D.dong-teas-enhanced-vpn-vtn-scalability] 395 Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N., 396 Mishra, G., and F. Qin, "Scalability Considerations for 397 Enhanced VPN (VPN+)", Work in Progress, Internet-Draft, 398 draft-dong-teas-enhanced-vpn-vtn-scalability-04, 25 399 October 2021, . 402 [I-D.ietf-lsr-isis-sr-vtn-mt] 403 Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi- 404 Topology (MT) for Segment Routing based Virtual Transport 405 Network", Work in Progress, Internet-Draft, draft-ietf- 406 lsr-isis-sr-vtn-mt-02, 13 January 2022, 407 . 410 [I-D.ietf-lsr-isis-srv6-extensions] 411 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 412 Z. Hu, "IS-IS Extensions to Support Segment Routing over 413 IPv6 Dataplane", Work in Progress, Internet-Draft, draft- 414 ietf-lsr-isis-srv6-extensions-18, 20 October 2021, 415 . 418 [I-D.ietf-teas-enhanced-vpn] 419 Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A 420 Framework for Enhanced Virtual Private Network (VPN+) 421 Services", Work in Progress, Internet-Draft, draft-ietf- 422 teas-enhanced-vpn-09, 25 October 2021, 423 . 426 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 427 Topology (MT) Routing in Intermediate System to 428 Intermediate Systems (IS-ISs)", RFC 5120, 429 DOI 10.17487/RFC5120, February 2008, 430 . 432 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 433 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 434 Extensions for Segment Routing", RFC 8667, 435 DOI 10.17487/RFC8667, December 2019, 436 . 438 Authors' Addresses 440 Chongfeng Xie 441 China Telecom 442 China Telecom Beijing Information Science & Technology, Beiqijia 443 Beijing 444 102209 445 China 447 Email: xiechf@chinatelecom.cn 449 Cong Li 450 China Telecom 451 China Telecom Beijing Information Science & Technology, Beiqijia 452 Beijing 453 102209 454 China 456 Email: licong@chinatelecom.cn 457 Jie Dong 458 Huawei Technologies 459 Huawei Campus, No. 156 Beiqing Road 460 Beijing 461 100095 462 China 464 Email: jie.dong@huawei.com 466 Zhenbin Li 467 Huawei Technologies 468 Huawei Campus, No. 156 Beiqing Road 469 Beijing 470 100095 471 China 473 Email: lizhenbin@huawei.com