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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: 13 July 2022 J. Dong 6 Z. Li 7 Huawei Technologies 8 9 January 2022 10 BGP-LS with Multi-topology for Segment Routing based Virtual Transport 11 Networks 12 draft-xie-idr-bgpls-sr-vtn-mt-04 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 13 July 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 [I-D.ietf-idr-bgp-ls-segment-routing-ext] defines the BGP-LS 153 extensions to carry the segment routing information using TLVs of 154 BGP-LS Attribute. When Multi-Topology is used with SR-MPLS data 155 plane, topology-specific prefix-SIDs and topology-specific Adj-SIDs 156 can be carried in the BGP-LS Attribute associated with the prefix 157 NLRI and link NLRI respectively, the MT-ID TLV is carried in the 158 prefix descriptor or link descriptor to identify the corresponding 159 topology of the SIDs. 161 [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to 162 advertise SRv6 segments along with their functions and attributes. 163 When Multi-Topology is used with SRv6 data plane, the SRv6 Locator 164 TLV is carried in the BGP-LS Attribute associated with the prefix- 165 NLRI, the MT-ID TLV can be carried in the prefix descriptor to 166 identify the corresponding topology of the SRv6 Locator. The SRv6 167 End.X SIDs are carried in the BGP-LS Attribute associated with the 168 link NLRI, the MT-ID TLV can be carried in the link descriptor to 169 identify the corresponding topology of the End.X SIDs. The SRv6 SID 170 NLRI is defined to advertise other types of SRv6 SIDs, in which the 171 SRv6 SID Descriptors can include the MT-ID TLV so as to advertise 172 topology-specific SRv6 SIDs. 174 [I-D.ietf-idr-rfc7752bis] also defines the rules of the usage of MT- 175 ID TLV: 177 "In a Link or Prefix Descriptor, only a single MT-ID TLV containing 178 the MT-ID of the topology where the link or the prefix is reachable 179 is allowed. In case one wants to advertise multiple topologies for a 180 given Link Descriptor or Prefix Descriptor, multiple NLRIs MUST be 181 generated where each NLRI contains a single unique MT-ID." 182 Editor's note: the above rules indicates that only one MT-ID is 183 allowed to be carried the Link or Prefix descriptors. When a link or 184 prefix needs to be advertised in multiple topologies, multiple NLRIs 185 needs to be generated to report all the topologies the link or prefix 186 participates in, together with the topology-specific segment routing 187 information and link attributes. This may increase the number of BGP 188 Updates needed for advertising MT-specific topology attributes, and 189 may introduce additional processing burden to both the sending BGP 190 speaker and the receiving network controller. When the number of 191 topologies in a network is not a small number, some optimization may 192 be needed for the reporting of multi-topology information and the 193 associated segment routing information in BGP-LS. Based on the WG's 194 opinion, this may be elaborated in a future version. 196 2.2. Inter-Domain Topology Advertisement 198 [I-D.ietf-idr-bgpls-segment-routing-epe] and 199 [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions for 200 advertisement of BGP inter-domain topology information and the BGP 201 Egress Peering Segment Identifiers. Such information could be used 202 by a network controller for the computation and instantiation of 203 inter-AS traffic engineering SR paths. 205 In some network scenarios, there are needs to create VTNs which span 206 multiple ASes. The inter-domain VTNs could have different inter- 207 domain connectivity, and may be associated with different set of 208 network resources in each domain and also on the inter-domain links. 209 In order to build the multi-domain SR based VTNs, it is necessary to 210 advertise the topology and resource attribute of each VTN and the 211 associated BGP Peering SIDs on the inter-domain links. 213 Depending on the requirement of inter-domain VTNs, different 214 mechanism can be used on the inter-domain connection: 216 * One EBGP session between two ASes can be established over multiple 217 underlying links. In this case, different underlying links can be 218 used for different inter-domain VTNs which requires link isolation 219 between each other. In another similar case, the EBGP session is 220 established over a single link, while the network resource (e.g. 221 bandwidth) on this link can be partitioned into several pieces, 222 each of which can be considered as a virtual member link. A VTN 223 is associated with one of the physical or virtual member links. 224 In both cases, different BGP Peer-Adj-SIDs or SRv6 End.X SID 225 SHOULD be allocated to each underlying physical or virtual member 226 link, the association between the BGP Peer Adj-SID/End.X SID and 227 the identifier of the VTN SHOULD be advertised by the ASBR. 229 * For inter-domain connection between two ASes, multiple EBGP 230 sessions can be established between different set of peering 231 ASBRs. It is possible that some of these BGP sessions are used 232 for one multi-domain VTN, while some other BGP sessions are used 233 for another multi-domain VTN. In this case, different BGP Peer 234 Node SIDs are allocated to each BGP session and are advertised 235 using the mechanism in [I-D.ietf-idr-bgpls-segment-routing-epe] 236 and [I-D.ietf-idr-bgpls-srv6-ext], the association between the BGP 237 Peer Node SIDs and the identifier of the VTN SHOULD be advertised 238 by the ASBR. 240 * At the AS-level topology, different multi-domain VTNs may have 241 different inter-domain connectivity. Different BGP Peer Set SIDs 242 MAY be allocated to represent the groups of BGP peers which can be 243 used for load-balancing in each multi-domain VTN. 245 When MT-ID is used consistently in multiple ASes covered by a VTN, 246 the topology-specific BGP peering SIDs can be advertised with the MT- 247 ID carried in the corresponding Link NLRI. This can be achieved with 248 the existing mechanisms as defined in 249 [RFC7752][I-D.ietf-idr-bgpls-segment-routing-epe] and 250 [I-D.ietf-idr-bgpls-srv6-ext]. 252 In network scenarios where consistent usage of MT-ID among multiple 253 domains can not be expected, a global-significant VTN-ID needs to be 254 introduced to define the inter-domain topologies. Within each 255 domain, the MT based mechanism could be reused for intra-domain 256 topology advertisement. The detailed mechanism is specified in 257 [I-D.dong-idr-bgpls-sr-enhanced-vpn]. 259 3. Advertisement of SR VTN Resource Attribute 261 [I-D.ietf-lsr-isis-sr-vtn-mt] specifies the mechanism to advertise 262 the resource information associated with each VTN. This section 263 describes the corresponding BGP-LS mechanisms. 265 The information of the network resources associated with a VTN can be 266 specified by carrying the TE Link attribute TLVs in BGP-LS Attribute 267 [RFC7752], with the associated MT-ID carried in the corresponding 268 Link NLRI. 270 When Maximum Link Bandwidth sub-TLV is carried in the BGP-LS 271 attribute associated with the Link NLRI of a VTN, it indicates the 272 amount of link bandwidth resource allocated to the corresponding VTN 273 on the link. The bandwidth allocated to a VTN can be exclusive for 274 traffic in the corresponding VTN. The advertisement of other TE 275 attributes in BGP-LS for each VTN is for further study. 277 4. Scalability Considerations 279 The mechanism described in this document requires that each VTN 280 mapped to an independent topology, and for the inter-domain VTNs, the 281 MT-IDs used in each involved domain need to be consistent. Reusing 282 MT-IDs as the identifier of VTN can avoid introducing new identifiers 283 in the control plane, while it also has some limitations. For 284 example, when multiple VTNs shares the same topology, each VTN still 285 need to be identified using different MT-IDs in the control plane, 286 thus independent path computation needs be executed for each VTN. 287 The number of VTNs supported in a network may be dependent on the 288 number of topologies supported, which is related to the control plane 289 overhead. The mechanism described in this document is applicable to 290 network scenarios where the number of required VTN is relatively 291 small. A detailed analysis about the VTN scalability and the 292 possible optimizations for supporting a large number of VTNs is 293 described in [I-D.dong-teas-enhanced-vpn-vtn-scalability]. 295 5. Security Considerations 297 This document introduces no additional security vulnerabilities to 298 BGP-LS. 300 The mechanism proposed in this document is subject to the same 301 vulnerabilities as any other protocol that relies on BGP-LS. 303 6. IANA Considerations 305 This document does not request any IANA actions. 307 7. Acknowledgments 309 The authors would like to thank Shunwan Zhuang for the review and 310 discussion of this document. 312 8. References 314 8.1. Normative References 316 [I-D.ietf-idr-bgp-ls-segment-routing-ext] 317 Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., 318 and M. Chen, "Border Gateway Protocol - Link State (BGP- 319 LS) Extensions for Segment Routing", Work in Progress, 320 Internet-Draft, draft-ietf-idr-bgp-ls-segment-routing-ext- 321 18, 15 April 2021, . 324 [I-D.ietf-idr-bgpls-segment-routing-epe] 325 Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray, 326 S., and J. Dong, "Border Gateway Protocol - Link State 327 (BGP-LS) Extensions for Segment Routing BGP Egress Peer 328 Engineering", Work in Progress, Internet-Draft, draft- 329 ietf-idr-bgpls-segment-routing-epe-19, 16 May 2019, 330 . 333 [I-D.ietf-idr-bgpls-srv6-ext] 334 Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., 335 Bernier, D., and B. Decraene, "BGP Link State Extensions 336 for SRv6", Work in Progress, Internet-Draft, draft-ietf- 337 idr-bgpls-srv6-ext-09, 10 November 2021, 338 . 341 [I-D.ietf-idr-rfc7752bis] 342 Talaulikar, K., "Distribution of Link-State and Traffic 343 Engineering Information Using BGP", Work in Progress, 344 Internet-Draft, draft-ietf-idr-rfc7752bis-10, 10 November 345 2021, . 348 [I-D.ietf-spring-resource-aware-segments] 349 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 350 Z., and F. Clad, "Introducing Resource Awareness to SR 351 Segments", Work in Progress, Internet-Draft, draft-ietf- 352 spring-resource-aware-segments-03, 12 July 2021, 353 . 356 [I-D.ietf-spring-sr-for-enhanced-vpn] 357 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 358 Z., and F. Clad, "Segment Routing based Virtual Transport 359 Network (VTN) for Enhanced VPN", Work in Progress, 360 Internet-Draft, draft-ietf-spring-sr-for-enhanced-vpn-01, 361 12 July 2021, . 364 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 365 Requirement Levels", BCP 14, RFC 2119, 366 DOI 10.17487/RFC2119, March 1997, 367 . 369 [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link 370 Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, 371 September 2007, . 373 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 374 S. Ray, "North-Bound Distribution of Link-State and 375 Traffic Engineering (TE) Information Using BGP", RFC 7752, 376 DOI 10.17487/RFC7752, March 2016, 377 . 379 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 380 Decraene, B., Litkowski, S., and R. Shakir, "Segment 381 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 382 July 2018, . 384 8.2. Informative References 386 [I-D.dong-idr-bgpls-sr-enhanced-vpn] 387 Dong, J., Hu, Z., Li, Z., Tang, X., and R. Pang, "BGP-LS 388 Extensions for Segment Routing based Enhanced VPN", Work 389 in Progress, Internet-Draft, draft-dong-idr-bgpls-sr- 390 enhanced-vpn-03, 22 February 2021, 391 . 394 [I-D.dong-lsr-sr-enhanced-vpn] 395 Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L., 396 and S. Bryant, "IGP Extensions for Scalable Segment 397 Routing based Enhanced VPN", Work in Progress, Internet- 398 Draft, draft-dong-lsr-sr-enhanced-vpn-06, 11 July 2021, 399 . 402 [I-D.dong-teas-enhanced-vpn-vtn-scalability] 403 Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N., 404 Mishra, G., and F. Qin, "Scalability Considerations for 405 Enhanced VPN (VPN+)", Work in Progress, Internet-Draft, 406 draft-dong-teas-enhanced-vpn-vtn-scalability-04, 25 407 October 2021, . 410 [I-D.ietf-lsr-isis-sr-vtn-mt] 411 Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi- 412 Topology (MT) for Segment Routing based Virtual Transport 413 Network", Work in Progress, Internet-Draft, draft-ietf- 414 lsr-isis-sr-vtn-mt-01, 12 July 2021, 415 . 418 [I-D.ietf-lsr-isis-srv6-extensions] 419 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 420 Z. Hu, "IS-IS Extensions to Support Segment Routing over 421 IPv6 Dataplane", Work in Progress, Internet-Draft, draft- 422 ietf-lsr-isis-srv6-extensions-18, 20 October 2021, 423 . 426 [I-D.ietf-teas-enhanced-vpn] 427 Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A 428 Framework for Enhanced Virtual Private Network (VPN+) 429 Services", Work in Progress, Internet-Draft, draft-ietf- 430 teas-enhanced-vpn-09, 25 October 2021, 431 . 434 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 435 Topology (MT) Routing in Intermediate System to 436 Intermediate Systems (IS-ISs)", RFC 5120, 437 DOI 10.17487/RFC5120, February 2008, 438 . 440 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 441 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 442 Extensions for Segment Routing", RFC 8667, 443 DOI 10.17487/RFC8667, December 2019, 444 . 446 Authors' Addresses 448 Chongfeng Xie 449 China Telecom 450 China Telecom Beijing Information Science & Technology, Beiqijia 451 Beijing 452 102209 453 China 455 Email: xiechf@chinatelecom.cn 457 Cong Li 458 China Telecom 459 China Telecom Beijing Information Science & Technology, Beiqijia 460 Beijing 461 102209 462 China 464 Email: licong@chinatelecom.cn 465 Jie Dong 466 Huawei Technologies 467 Huawei Campus, No. 156 Beiqing Road 468 Beijing 469 100095 470 China 472 Email: jie.dong@huawei.com 474 Zhenbin Li 475 Huawei Technologies 476 Huawei Campus, No. 156 Beiqing Road 477 Beijing 478 100095 479 China 481 Email: lizhenbin@huawei.com