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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: January 13, 2022 J. Dong 6 Z. Li 7 Huawei Technologies 8 July 12, 2021 10 BGP-LS with Multi-topology for Segment Routing based Virtual Transport 11 Networks 12 draft-xie-idr-bgpls-sr-vtn-mt-03 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 January 13, 2022. 58 Copyright Notice 60 Copyright (c) 2021 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 65 (https://trustee.ietf.org/license-info) in effect on the date of 66 publication of this document. Please review these documents 67 carefully, as they describe your rights and restrictions with respect 68 to this document. Code Components extracted from this document must 69 include Simplified BSD License text as described in Section 4.e of 70 the Trust Legal Provisions and are provided without warranty as 71 described in the Simplified BSD License. 73 Table of Contents 75 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 76 2. Advertisement of SR VTN Topology Attribute . . . . . . . . . 3 77 2.1. Intra-domain Topology Advertisement . . . . . . . . . . . 4 78 2.2. Inter-Domain Topology Advertisement . . . . . . . . . . . 5 79 3. Advertisement of SR VTN Resource Attribute . . . . . . . . . 6 80 4. Scalability Considerations . . . . . . . . . . . . . . . . . 6 81 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 82 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 83 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 84 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 85 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 86 8.2. Informative References . . . . . . . . . . . . . . . . . 8 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 89 1. Introduction 91 Enhanced VPN (VPN+) is an enhancement to VPN services to support the 92 needs of new applications, particularly including the applications 93 that are associated with 5G services. These applications require 94 enhanced isolation and have more stringent performance requirements 95 than that can be provided with traditional overlay VPNs. Thus these 96 properties require integration between the overlay connectivity and 97 the characteristics provided by the underlay networks. 98 [I-D.ietf-teas-enhanced-vpn] specifies the framework of enhanced VPN 99 and describes the candidate component technologies in different 100 network planes and layers. An enhanced VPN can be used for 5G 101 network slicing, and will also be of use in more generic scenarios. 103 To meet the requirement of enhanced VPN services, a number of Virtual 104 Transport Networks (VTNs) need to be created, each consists of a 105 subset of the underlay network topology and a subset of network 106 resources allocated from the underlay network to meet the requirement 107 of one or a group of VPN+ services. 109 [I-D.ietf-spring-resource-aware-segments] introduces resource 110 awareness to Segment Routing (SR) [RFC8402]. The resource-aware SIDs 111 have additional semantics to identify the set of network resources 112 available for the packet processing action associated with the SIDs. 113 As described in [I-D.ietf-spring-sr-for-enhanced-vpn], the resource- 114 aware segments can be used to build SR based VTNs with the required 115 network topology and network resource attributes to support enhanced 116 VPN services. 118 To allow the network controller and network nodes to perform VTN- 119 specific explicit path computation and/or shortest path computation, 120 the group of resource-aware SIDs allocated by network nodes to each 121 VTN and the associated topology and resource attributes need to be 122 distributed in the control plane. When a centralized network 123 controller is used for VTN-specific path computation, especially when 124 a VTN spans multiple IGP areas or multiple Autonomous Systems (ASes), 125 BGP-LS is needed to advertise the VTN information in each IGP area or 126 AS to the network controller, so that the controller could use the 127 collected information to build the view of inter-area or inter-AS SR 128 VTNs. 130 In some network scenarios, each VTN can be associated with a unique 131 logical network topology, [I-D.ietf-lsr-isis-sr-vtn-mt] describes an 132 IGP mechanism to advertise the association between the topology, 133 resource attributes and the SR SIDs for each VTN. This document 134 describes a mechanism to distribute the information of SR based VTNs 135 to the network controller using BGP-LS with Multi-Topology. 137 2. Advertisement of SR VTN Topology Attribute 139 [I-D.ietf-lsr-isis-sr-vtn-mt] describes the IS-IS Multi-topology 140 based mechanisms to distribute the topology attributes of SR based 141 VTNs. This section describes the corresponding BGP-LS mechanism to 142 distribute both the intra-domain and inter-domain topology attributes 143 of SR based VTNs. 145 2.1. Intra-domain Topology Advertisement 147 In section 4.2.2.1 of [I-D.ietf-idr-rfc7752bis], Multi-Topology 148 Identifier (MT-ID) TLV is defined, which can contain one or more IS- 149 IS or OSPF Multi-Topology IDs. The MT-ID TLV MAY be present in a 150 Link Descriptor, a Prefix Descriptor, or the BGP-LS Attribute of a 151 Node NLRI. 153 [I-D.ietf-idr-bgp-ls-segment-routing-ext] defines the BGP-LS 154 extensions to carry the segment routing information using TLVs of 155 BGP-LS Attribute. When Multi-Topology is used with SR-MPLS data 156 plane, topology-specific prefix-SIDs and topology-specific Adj-SIDs 157 can be carried in the BGP-LS Attribute associated with the prefix 158 NLRI and link NLRI respectively, the MT-ID TLV is carried in the 159 prefix descriptor or link descriptor to identify the corresponding 160 topology of the SIDs. 162 [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to 163 advertise SRv6 segments along with their functions and attributes. 164 When Multi-Topology is used with SRv6 data plane, the SRv6 Locator 165 TLV is carried in the BGP-LS Attribute associated with the prefix- 166 NLRI, the MT-ID TLV can be carried in the prefix descriptor to 167 identify the corresponding topology of the SRv6 Locator. The SRv6 168 End.X SIDs are carried in the BGP-LS Attribute associated with the 169 link NLRI, the MT-ID TLV can be carried in the link descriptor to 170 identify the corresponding topology of the End.X SIDs. The SRv6 SID 171 NLRI is defined to advertise other types of SRv6 SIDs, in which the 172 SRv6 SID Descriptors can include the MT-ID TLV so as to advertise 173 topology-specific SRv6 SIDs. 175 [I-D.ietf-idr-rfc7752bis] also defines the rules of the usage of MT- 176 ID TLV: 178 "In a Link or Prefix Descriptor, only a single MT-ID TLV containing 179 the MT-ID of the topology where the link or the prefix is reachable 180 is allowed. In case one wants to advertise multiple topologies for a 181 given Link Descriptor or Prefix Descriptor, multiple NLRIs MUST be 182 generated where each NLRI contains a single unique MT-ID." 184 Editor's note: the above rules indicates that only one MT-ID is 185 allowed to be carried the Link or Prefix descriptors. When a link or 186 prefix needs to be advertised in multiple topologies, multiple NLRIs 187 needs to be generated to report all the topologies the link or prefix 188 participates in, together with the topology-specific segment routing 189 information and link attributes. This may increase the number of BGP 190 Updates needed for advertising MT-specific topology attributes, and 191 may introduce additional processing burden to both the sending BGP 192 speaker and the receiving network controller. When the number of 193 topologies in a network is not a small number, some optimization may 194 be needed for the reporting of multi-topology information and the 195 associated segment routing information in BGP-LS. Based on the WG's 196 opinion, this may be elaborated in a future version. 198 2.2. Inter-Domain Topology Advertisement 200 [I-D.ietf-idr-bgpls-segment-routing-epe] and 201 [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions for 202 advertisement of BGP inter-domain topology information and the BGP 203 Egress Peering Segment Identifiers. Such information could be used 204 by a network controller for the computation and instantiation of 205 inter-AS traffic engineering SR paths. 207 In some network scenarios, there are needs to create VTNs which span 208 multiple ASes. The inter-domain VTNs could have different inter- 209 domain connectivity, and may be associated with different set of 210 network resources in each domain and also on the inter-domain links. 211 In order to build the multi-domain SR based VTNs, it is necessary to 212 advertise the topology and resource attribute of each VTN and the 213 associated BGP Peering SIDs on the inter-domain links. 215 Depending on the requirement of inter-domain VTNs, different 216 mechanism can be used on the inter-domain connection: 218 o One EBGP session between two ASes can be established over multiple 219 underlying links. In this case, different underlying links can be 220 used for different inter-domain VTNs which requires link isolation 221 between each other. In another similar case, the EBGP session is 222 established over a single link, while the network resource (e.g. 223 bandwidth) on this link can be partitioned into several pieces, 224 each of which can be considered as a virtual member link. A VTN 225 is associated with one of the physical or virtual member links. 226 In both cases, different BGP Peer-Adj-SIDs or SRv6 End.X SID 227 SHOULD be allocated to each underlying physical or virtual member 228 link, the association between the BGP Peer Adj-SID/End.X SID and 229 the identifier of the VTN SHOULD be advertised by the ASBR. 231 o For inter-domain connection between two ASes, multiple EBGP 232 sessions can be established between different set of peering 233 ASBRs. It is possible that some of these BGP sessions are used 234 for one multi-domain VTN, while some other BGP sessions are used 235 for another multi-domain VTN. In this case, different BGP Peer 236 Node SIDs are allocated to each BGP session and are advertised 237 using the mechanism in [I-D.ietf-idr-bgpls-segment-routing-epe] 238 and [I-D.ietf-idr-bgpls-srv6-ext], the association between the BGP 239 Peer Node SIDs and the identifier of the VTN SHOULD be advertised 240 by the ASBR. 242 o At the AS-level topology, different multi-domain VTNs may have 243 different inter-domain connectivity. Different BGP Peer Set SIDs 244 MAY be allocated to represent the groups of BGP peers which can be 245 used for load-balancing in each multi-domain VTN. 247 When MT-ID is used consistently in multiple ASes covered by a VTN, 248 the topology-specific BGP peering SIDs can be advertised with the MT- 249 ID carried in the corresponding Link NLRI. This can be achieved with 250 the existing mechanisms as defined in 251 [RFC7752][I-D.ietf-idr-bgpls-segment-routing-epe] and 252 [I-D.ietf-idr-bgpls-srv6-ext]. 254 In network scenarios where consistent usage of MT-ID among multiple 255 domains can not be expected, a global-significant VTN-ID needs to be 256 introduced to define the inter-domain topologies. Within each 257 domain, the MT based mechanism could be reused for intra-domain 258 topology advertisement. The detailed mechanism is specified in 259 [I-D.dong-idr-bgpls-sr-enhanced-vpn]. 261 3. Advertisement of SR VTN Resource Attribute 263 [I-D.ietf-lsr-isis-sr-vtn-mt] specifies the mechanism to advertise 264 the resource information associated with each VTN. This section 265 describes the corresponding BGP-LS mechanisms. 267 The information of the network resources associated with a VTN can be 268 specified by carrying the TE Link attribute TLVs in BGP-LS Attribute 269 [RFC7752], with the associated MT-ID carried in the corresponding 270 Link NLRI. 272 When Maximum Link Bandwidth sub-TLV is carried in the BGP-LS 273 attribute associated with the Link NLRI of a VTN, it indicates the 274 amount of link bandwidth resource allocated to the corresponding VTN 275 on the link. The bandwidth allocated to a VTN can be exclusive for 276 traffic in the corresponding VTN. The advertisement of other TE 277 attributes in BGP-LS for each VTN is for further study. 279 4. Scalability Considerations 281 The mechanism described in this document requires that each VTN 282 mapped to an independent topology, and for the inter-domain VTNs, the 283 MT-IDs used in each involved domain need to be consistent. Reusing 284 MT-IDs as the identifier of VTN can avoid introducing new identifiers 285 in the control plane, while it also has some limitations. For 286 example, when multiple VTNs shares the same topology, each VTN still 287 need to be identified using different MT-IDs in the control plane, 288 thus independent path computation needs be executed for each VTN. 289 The number of VTNs supported in a network may be dependent on the 290 number of topologies supported, which is related to the control plane 291 overhead. The mechanism described in this document is applicable to 292 network scenarios where the number of required VTN is relatively 293 small. A detailed analysis about the VTN scalability and the 294 possible optimizations for supporting a large number of VTNs is 295 described in [I-D.dong-teas-enhanced-vpn-vtn-scalability]. 297 5. Security Considerations 299 This document introduces no additional security vulnerabilities to 300 BGP-LS. 302 The mechanism proposed in this document is subject to the same 303 vulnerabilities as any other protocol that relies on BGP-LS. 305 6. IANA Considerations 307 This document does not request any IANA actions. 309 7. Acknowledgments 311 The authors would like to thank Shunwan Zhuang for the review and 312 discussion of this document. 314 8. References 316 8.1. Normative References 318 [I-D.ietf-idr-bgp-ls-segment-routing-ext] 319 Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., 320 and M. Chen, "BGP Link-State extensions for Segment 321 Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-18 322 (work in progress), 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, "BGP-LS extensions for Segment Routing 327 BGP Egress Peer Engineering", draft-ietf-idr-bgpls- 328 segment-routing-epe-19 (work in progress), May 2019. 330 [I-D.ietf-idr-bgpls-srv6-ext] 331 Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., 332 Bernier, D., and B. Decraene, "BGP Link State Extensions 333 for SRv6", draft-ietf-idr-bgpls-srv6-ext-07 (work in 334 progress), March 2021. 336 [I-D.ietf-idr-rfc7752bis] 337 Talaulikar, K., "Distribution of Link-State and Traffic 338 Engineering Information Using BGP", draft-ietf-idr- 339 rfc7752bis-05 (work in progress), November 2020. 341 [I-D.ietf-spring-resource-aware-segments] 342 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 343 Z., and F. Clad, "Introducing Resource Awareness to SR 344 Segments", draft-ietf-spring-resource-aware-segments-02 345 (work in progress), February 2021. 347 [I-D.ietf-spring-sr-for-enhanced-vpn] 348 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 349 Z., and F. Clad, "Segment Routing based Virtual Transport 350 Network (VTN) for Enhanced VPN", draft-ietf-spring-sr-for- 351 enhanced-vpn-00 (work in progress), February 2021. 353 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 354 Requirement Levels", BCP 14, RFC 2119, 355 DOI 10.17487/RFC2119, March 1997, 356 . 358 [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link 359 Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, 360 September 2007, . 362 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 363 S. Ray, "North-Bound Distribution of Link-State and 364 Traffic Engineering (TE) Information Using BGP", RFC 7752, 365 DOI 10.17487/RFC7752, March 2016, 366 . 368 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 369 Decraene, B., Litkowski, S., and R. Shakir, "Segment 370 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 371 July 2018, . 373 8.2. Informative References 375 [I-D.dong-idr-bgpls-sr-enhanced-vpn] 376 Dong, J., Hu, Z., Li, Z., Tang, X., and R. Pang, "BGP-LS 377 Extensions for Segment Routing based Enhanced VPN", draft- 378 dong-idr-bgpls-sr-enhanced-vpn-03 (work in progress), 379 February 2021. 381 [I-D.dong-lsr-sr-enhanced-vpn] 382 Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L., 383 and S. Bryant, "IGP Extensions for Segment Routing based 384 Enhanced VPN", draft-dong-lsr-sr-enhanced-vpn-05 (work in 385 progress), February 2021. 387 [I-D.dong-teas-enhanced-vpn-vtn-scalability] 388 Dong, J., Li, Z., Qin, F., Yang, G., and J. N. Guichard, 389 "Scalability Considerations for Enhanced VPN (VPN+)", 390 draft-dong-teas-enhanced-vpn-vtn-scalability-02 (work in 391 progress), February 2021. 393 [I-D.ietf-lsr-isis-sr-vtn-mt] 394 Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi- 395 Topology (MT) for Segment Routing based Virtual Transport 396 Network", draft-ietf-lsr-isis-sr-vtn-mt-00 (work in 397 progress), March 2021. 399 [I-D.ietf-lsr-isis-srv6-extensions] 400 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 401 Z. Hu, "IS-IS Extension to Support Segment Routing over 402 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-14 403 (work in progress), April 2021. 405 [I-D.ietf-teas-enhanced-vpn] 406 Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A 407 Framework for Enhanced Virtual Private Network (VPN+) 408 Services", draft-ietf-teas-enhanced-vpn-07 (work in 409 progress), February 2021. 411 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 412 Topology (MT) Routing in Intermediate System to 413 Intermediate Systems (IS-ISs)", RFC 5120, 414 DOI 10.17487/RFC5120, February 2008, 415 . 417 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 418 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 419 Extensions for Segment Routing", RFC 8667, 420 DOI 10.17487/RFC8667, December 2019, 421 . 423 Authors' Addresses 424 Chongfeng Xie 425 China Telecom 426 China Telecom Beijing Information Science & Technology, Beiqijia 427 Beijing 102209 428 China 430 Email: xiechf@chinatelecom.cn 432 Cong Li 433 China Telecom 434 China Telecom Beijing Information Science & Technology, Beiqijia 435 Beijing 102209 436 China 438 Email: licong@chinatelecom.cn 440 Jie Dong 441 Huawei Technologies 442 Huawei Campus, No. 156 Beiqing Road 443 Beijing 100095 444 China 446 Email: jie.dong@huawei.com 448 Zhenbin Li 449 Huawei Technologies 450 Huawei Campus, No. 156 Beiqing Road 451 Beijing 100095 452 China 454 Email: lizhenbin@huawei.com