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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: Standards Track China Telecom 5 Expires: January 14, 2021 J. Dong 6 Z. Li 7 Huawei Technologies 8 July 13, 2020 10 BGP-LS with Multi-topology for Segment Routing based Virtual Transport 11 Networks 12 draft-xie-idr-bgpls-sr-vtn-mt-01 14 Abstract 16 Enhanced VPN (VPN+) as defined in I-D.ietf-teas-enhanced-vpn aims to 17 provide enhanced VPN service to support applications's needs of 18 enhanced isolation and stringent performance requirements. VPN+ 19 requries integration between the overlay VPN and the underlay 20 network. A Virtual Transport Network (VTN) is a virtual network 21 which consists of a subset of the network toplogy and network 22 resources allocated from the underlay network. A VTN could be used 23 as the underlay for one or a group of VPN+ services. 25 I-D.dong-idr-bgpls-sr-enhanced-vpn defines the BGP-LS extensions to 26 distribute the information of Segment Routing (SR) based VTNs to 27 external entities, such as the network controllers. This document 28 describes a simplified mechanism to distribute the information of SR 29 based VTNs using BGP-LS with Multi-Topology. 31 Requirements Language 33 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 34 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 35 document are to be interpreted as described in RFC 2119 [RFC2119]. 37 Status of This Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at https://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on January 14, 2021. 54 Copyright Notice 56 Copyright (c) 2020 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (https://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 72 2. Advertisement of SR VTN Topology . . . . . . . . . . . . . . 3 73 2.1. Intra-domain Topology Advertisement . . . . . . . . . . . 3 74 2.2. Inter-Domain Topology Advertisement . . . . . . . . . . . 5 75 3. Advertisement of VTN Resource Attribute . . . . . . . . . . . 6 76 3.1. Advertising Topology specific TE attributes . . . . . . . 6 77 4. Scalability Considerations . . . . . . . . . . . . . . . . . 6 78 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 79 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 80 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 81 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 82 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 83 8.2. Informative References . . . . . . . . . . . . . . . . . 8 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 86 1. Introduction 88 Enhanced VPN (VPN+) is an enhancement to VPN services to support the 89 needs of new applications, particularly including the applications 90 that are associated with 5G services. These applications require 91 enhanced isolation and have more stringent performance requirements 92 than that can be provided with traditional overlay VPNs. These 93 properties cannot be met with pure overlay networks, as they require 94 integration between the underlay and the overlay networks. 95 [I-D.ietf-teas-enhanced-vpn] specifies the framework of enhanced VPN 96 and describes the candidate component technologies in different 97 network planes and layers. An enhanced VPN can be used for 5G 98 transport network slicing, and will also be of use in more generic 99 scenarios. 101 To meet the requirement of enhanced VPN services, a number of Virtual 102 Transport Networks (VTNs) need to be created, each with a subset of 103 the underlay network topology and a set of network resources 104 allocated to meet the requirement of a specific VPN+ service or a 105 group of VPN+ services. 107 [I-D.dong-spring-sr-for-enhanced-vpn] specifies how segment routing 108 (SR) [RFC8402] can be used to build virtual transport networks (VTNs) 109 with the required network topology and network resources, which could 110 be used as the underlay of enhanced VPN services. 111 [I-D.dong-lsr-sr-enhanced-vpn] and [I-D.xie-lsr-isis-sr-vtn-mt] 112 specifies the IGP mechanism and extensions to build a set of SR based 113 VTNs. When a VTN spans multiple IGP areas or multiple Autonomous 114 Systems (ASes), BGP-LS is needed to advertise the VTN information in 115 each IGP area or AS to the network controller, so that the controller 116 could use the collected information to build the inter-area or inter- 117 AS SR VTNs. 119 [I-D.dong-idr-bgpls-sr-enhanced-vpn] defines the BGP-LS extensions to 120 distribute the information of Segment Routing (SR) based VTNs to 121 external entities, such as the network controllers, which allows 122 flexible combination of the topology and resource attribute to build 123 customized VTNs. While in some network scenarios, it is assumed that 124 each VTN has an independent topology and a set of dedicated network 125 resources. For such scenarios, this document describes a simplified 126 mechanism to distribute the information of SR based VTNs using BGP-LS 127 with Multi-Topology. 129 2. Advertisement of SR VTN Topology 131 [I-D.xie-lsr-isis-sr-vtn-mt] describes the ISIS Multi-topology 132 mechanisms to distribute the topology attributes of SR based VTNs. 133 This section describes the corresponding BGP-LS mechanism to 134 distribute both the intra-domain and inter-domain topology attributes 135 of SR based VTNs. 137 2.1. Intra-domain Topology Advertisement 139 In section 3.2.1.5 of [RFC7752], Multi-Topology Identifier (MT-ID) 140 TLV is defined, which can contain one or more IS-IS or OSPF Multi- 141 Topology IDs. The MT-ID TLV MAY be present in a Link Descriptor, a 142 Prefix Descriptor, or the BGP-LS Attribute of a Node NLRI. 144 [I-D.ietf-idr-bgp-ls-segment-routing-ext] defines the BGP-LS 145 extensions to carry the segment routing information using TLVs of 146 BGP-LS Attribute. When MTR is used with SR-MPLS data plane, 147 topology-specific prefix-SIDs and topology-specific Adj-SIDs can be 148 carried in the BGP-LS Attribute associated with the prefix NLRI and 149 link NLRI respectively, the MT-ID TLV is carried in the prefix 150 descriptor and link descriptor to identify the corresponding topology 151 of the SIDs. 153 [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to 154 advertise SRv6 segments along with their functions and attributes. 155 When MTR is used with SRv6 data plane, the SRv6 Locator TLV is 156 carried in the BGP-LS Attribute associated with the prefix-NLRI, the 157 MT-ID TLV can be carried in the prefix descriptor to identify the 158 corresponding topology of the SRv6 Locator. The SRv6 End.X SIDs are 159 carried in the BGP-LS Attribute associated with the link NLRI, the 160 MT-ID TLV can be carried in the link descriptor to identify the 161 corresponding topology of the End.X SIDs. The SRv6 SID NLRI is 162 defined to advertise other types of SRv6 SIDs, in which the SRv6 SID 163 Descriptors can include the MT-ID TLV so as to advertise topology- 164 specific SRv6 SIDs. 166 [RFC7752] also defines the rules of the usage of MT-ID TLV: 168 "In a Link or Prefix Descriptor, only a single MT-ID TLV containing 169 the MT-ID of the topology where the link or the prefix is reachable 170 is allowed. In case one wants to advertise multiple topologies for a 171 given Link Descriptor or Prefix Descriptor, multiple NLRIs need to be 172 generated where each NLRI contains an unique MT-ID. In the BGP-LS 173 attribute of a Node NLRI, one MT-ID TLV containing the array of MT- 174 IDs of all topologies where the node is reachable is allowed." 176 Editor's note: the above rules indicates that only one MT-ID is 177 allowed to be carried the Link or Prefix descriptors. When a link or 178 prefix participates in multiple topologies, multiple NLRIs needs to 179 be generated to report all the topologies a link or prefix 180 participates in, together with the topology-specific segment routing 181 information. This would increase the number of BGP Updates and may 182 introduce additional processing burden to both the sending BGP 183 speaker and the receiving network controller. When the number of 184 topologies in a network is not a small number, some optimization may 185 be introduced for the reporting of multi-topology information and the 186 associated segment routing information in BGP-LS. Based on the WG's 187 opinion, this will be elaborated in a future version. 189 2.2. Inter-Domain Topology Advertisement 191 [I-D.ietf-idr-bgpls-segment-routing-epe] and 192 [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions for 193 advertisement of BGP topology information between ASes and the BGP 194 Peering Segment Identifiers. Such information could be used by a 195 network controller for the computation and instantiation of inter-AS 196 traffic engineering SR paths. 198 In some network scenarios, there are needs to create VTNs which span 199 multiple ASes. The inter-domain VTNs could have different inter- 200 domain connectivity, and may be associated with different set of 201 network resources in each domain and also on the inter-domain links. 202 In order to build the multi-domain VTNs using segment routing, it is 203 necessary to advertise the topology and resource attribute of VTN on 204 the inter-domain links and the associated BGP Peering SIDs. 206 Depending on the requirement of inter-domain VTNs, different 207 mechanism can be used on the inter-domain connection: 209 o One EBGP session between two ASes can be established over multiple 210 underlying links. In this case, different underlying links can be 211 used for different inter-domain VTNs which requires link isolation 212 between each other. In another similar case, the EBGP session is 213 established over a single link, while the network resource (e.g. 214 bandwidth) on this link can be partitioned into several pieces, 215 each of which can be considered as a virtual member link. In both 216 cases, different BGP Peer-Adj-SIDs SHOULD be allocated to each 217 underlying physical or virtual member link, and ASBRs SHOULD 218 advertise the VTN identifier associated with each BGP Peer-Adj- 219 SID. 221 o For inter-domain connection between two ASes, multiple EBGP 222 sessions can be established between different set of peering 223 ASBRs. It is possible that some of these BGP sessions are used 224 for one multi-domain VTN, while some other BGP sessions are used 225 for another multi-domain VTN. In this case, different BGP peer- 226 node-SIDs are allocated to each BGP session, and ASBRs SHOULD 227 advertise the VTN identifier associated with each BGP Peer-node- 228 SIDs. 230 o At the AS-level topology, different multi-domain VTNs may have 231 different inter-domain connectivity. Different BGP Peer-Set-SIDs 232 can be allocated to represent the groups of BGP peers which can be 233 used for load-balancing in each multi-domain VTN. 235 When MT-ID is used consistently in multiple ASes covered by a VTN, 236 the topology-specific BGP peering SIDs can be advertised with the MT- 237 ID carried in the corresponding Link NLRI. This can be achieved with 238 the existing mechanisms as defined in 239 [RFC7752][I-D.ietf-idr-bgpls-segment-routing-epe] and 240 [I-D.ietf-idr-bgpls-srv6-ext]. 242 In network scenarios where consistent usage of MT-ID among multiple 243 ASes can not be expected, then a global-significant VTN ID needs to 244 be introduced to define the AS level topologies. Within each domain, 245 the MT based mechanism could be used for intra-domain topology 246 advertisement. The detailed mechanism is specified in 247 [I-D.dong-idr-bgpls-sr-enhanced-vpn]. 249 3. Advertisement of VTN Resource Attribute 251 [I-D.xie-lsr-isis-sr-vtn-mt] specifies the mechanism to advertise the 252 resource information associated with each VTN. This section 253 describes the corresponding BGP-LS mechanisms. 255 3.1. Advertising Topology specific TE attributes 257 The information of the network resources associated with a VTN can be 258 specified by carrying the Link TE attribute TLVs [RFC7752] in BGP-LS 259 Attribute, with the associated MT-ID carried in the corresponding 260 Link NLRI. 262 When Maximum Link Bandwidth sub-TLV is carried in the MT-ISN TLV, it 263 indicates the amount of link bandwidth allocated to the corresponding 264 VTN. The bandwidth allocated to a VTN can be exclusive for services 265 carried in the corresponding VTN. The usage of other TE attribute 266 TLVs in topology-specific TLVs is for further study. 268 4. Scalability Considerations 270 The mechanism described in this document requires that each VTN has 271 an independent topology, and for inter-domain VTNs, the MT-ID used in 272 each involved domain is consistent. While this brings the benefits 273 of simplicity, it also has some limitations. For example, it means 274 that even if multiple VTNs may have the same topology attribute, they 275 would still need to be identified using different MT-IDs in the 276 control plane. This requires that for each VTN, independent path 277 computation would be executed. The number of VTNs supported in a 278 network may be dependent on the number of topologies supported, which 279 is related to the control plane computation overhead. 281 5. Security Considerations 283 This document introduces no additional security vulnerabilities to 284 BGP-LS. 286 The mechanism proposed in this document is subject to the same 287 vulnerabilities as any other protocol that relies on BGP-LS. 289 6. IANA Considerations 291 This document does not request any IANA actions. 293 7. Acknowledgments 295 The authors would like to thank Shunwan Zhuang for the review and 296 discussion of this document. 298 8. References 300 8.1. Normative References 302 [I-D.dong-spring-sr-for-enhanced-vpn] 303 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., and 304 Z. Li, "Segment Routing for Resource Guaranteed Virtual 305 Networks", draft-dong-spring-sr-for-enhanced-vpn-08 (work 306 in progress), June 2020. 308 [I-D.ietf-idr-bgp-ls-segment-routing-ext] 309 Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., 310 and M. Chen, "BGP Link-State extensions for Segment 311 Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16 312 (work in progress), June 2019. 314 [I-D.ietf-idr-bgpls-segment-routing-epe] 315 Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray, 316 S., and J. Dong, "BGP-LS extensions for Segment Routing 317 BGP Egress Peer Engineering", draft-ietf-idr-bgpls- 318 segment-routing-epe-19 (work in progress), May 2019. 320 [I-D.ietf-idr-bgpls-srv6-ext] 321 Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., 322 daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link 323 State Extensions for SRv6", draft-ietf-idr-bgpls- 324 srv6-ext-03 (work in progress), July 2020. 326 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 327 Requirement Levels", BCP 14, RFC 2119, 328 DOI 10.17487/RFC2119, March 1997, 329 . 331 [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link 332 Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, 333 September 2007, . 335 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 336 S. Ray, "North-Bound Distribution of Link-State and 337 Traffic Engineering (TE) Information Using BGP", RFC 7752, 338 DOI 10.17487/RFC7752, March 2016, 339 . 341 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 342 Decraene, B., Litkowski, S., and R. Shakir, "Segment 343 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 344 July 2018, . 346 8.2. Informative References 348 [I-D.dong-idr-bgpls-sr-enhanced-vpn] 349 Dong, J., Hu, Z., Li, Z., Tang, X., and R. Pang, "BGP-LS 350 Extensions for Segment Routing based Enhanced VPN", draft- 351 dong-idr-bgpls-sr-enhanced-vpn-02 (work in progress), June 352 2020. 354 [I-D.dong-lsr-sr-enhanced-vpn] 355 Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L., 356 and S. Bryant, "IGP Extensions for Segment Routing based 357 Enhanced VPN", draft-dong-lsr-sr-enhanced-vpn-04 (work in 358 progress), June 2020. 360 [I-D.ietf-lsr-isis-srv6-extensions] 361 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 362 Z. Hu, "IS-IS Extension to Support Segment Routing over 363 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08 364 (work in progress), April 2020. 366 [I-D.ietf-teas-enhanced-vpn] 367 Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A 368 Framework for Enhanced Virtual Private Networks (VPN+) 369 Services", draft-ietf-teas-enhanced-vpn-05 (work in 370 progress), February 2020. 372 [I-D.xie-lsr-isis-sr-vtn-mt] 373 Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi- 374 Topology (MT) for Segment Routing based Virtual Transport 375 Network", draft-xie-lsr-isis-sr-vtn-mt-00 (work in 376 progress), March 2020. 378 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 379 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 380 Extensions for Segment Routing", RFC 8667, 381 DOI 10.17487/RFC8667, December 2019, 382 . 384 Authors' Addresses 386 Chongfeng Xie 387 China Telecom 388 China Telecom Beijing Information Science & Technology, Beiqijia 389 Beijing 102209 390 China 392 Email: xiechf@chinatelecom.cn 394 Cong Li 395 China Telecom 396 China Telecom Beijing Information Science & Technology, Beiqijia 397 Beijing 102209 398 China 400 Email: licong@chinatelecom.cn 402 Jie Dong 403 Huawei Technologies 404 Huawei Campus, No. 156 Beiqing Road 405 Beijing 100095 406 China 408 Email: jie.dong@huawei.com 410 Zhenbin Li 411 Huawei Technologies 412 Huawei Campus, No. 156 Beiqing Road 413 Beijing 100095 414 China 416 Email: lizhenbin@huawei.com