idnits 2.17.1 draft-dong-idr-bgpls-sr-enhanced-vpn-04.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 copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (4 March 2022) is 784 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'I-D.ietf-lsr-isis-srv6-extensions' is defined on line 907, but no explicit reference was found in the text == Outdated reference: A later version (-12) exists of draft-ietf-idr-bgp-ls-flex-algo-08 == Outdated reference: A later version (-14) exists of draft-ietf-idr-bgpls-srv6-ext-09 == Outdated reference: A later version (-17) exists of draft-ietf-idr-rfc7752bis-10 == Outdated reference: A later version (-08) exists of draft-ietf-spring-resource-aware-segments-03 == Outdated reference: A later version (-07) exists of draft-ietf-spring-sr-for-enhanced-vpn-01 ** Downref: Normative reference to an Informational draft: draft-ietf-spring-sr-for-enhanced-vpn (ref. 'I-D.ietf-spring-sr-for-enhanced-vpn') == Outdated reference: A later version (-17) exists of draft-ietf-teas-enhanced-vpn-09 ** Downref: Normative reference to an Informational draft: draft-ietf-teas-enhanced-vpn (ref. 'I-D.ietf-teas-enhanced-vpn') == Outdated reference: A later version (-25) exists of draft-ietf-teas-ietf-network-slices-05 ** Downref: Normative reference to an Informational draft: draft-ietf-teas-ietf-network-slices (ref. 'I-D.ietf-teas-ietf-network-slices') ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) == Outdated reference: A later version (-10) exists of draft-dong-lsr-sr-enhanced-vpn-07 == Outdated reference: A later version (-02) exists of draft-dong-teas-nrp-scalability-01 == Outdated reference: A later version (-26) exists of draft-ietf-lsr-flex-algo-18 == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-18 == Outdated reference: A later version (-03) exists of draft-li-mpls-enhanced-vpn-vtn-id-01 Summary: 4 errors (**), 0 flaws (~~), 14 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR Working Group J. Dong 3 Internet-Draft Z. Hu 4 Intended status: Standards Track Z. Li 5 Expires: 5 September 2022 Huawei Technologies 6 X. Tang 7 R. Pang 8 China Unicom 9 4 March 2022 11 BGP-LS Extensions for Scalable Segment Routing based Enhanced VPN 12 draft-dong-idr-bgpls-sr-enhanced-vpn-04 14 Abstract 16 Enhanced VPN (VPN+) aims to provide enhanced VPN services to support 17 some applications' needs of enhanced isolation and stringent 18 performance requirements. VPN+ requires integration between the 19 overlay VPN connectivity and the resources and characteristics 20 provided by the underlay network. A Virtual Transport Network (VTN) 21 is a virtual underlay network which can be used to support one or a 22 group of VPN+ services. In the context of network slicing, a VTN 23 could be instantiated as a network resource partition (NRP). 25 This document specifies the BGP-LS mechanisms with necessary 26 extensions to advertise the information of scalable Segment Routing 27 (SR) based NRPs to a centralized network controller. Each NRP can 28 have a customized topology and a set of network resources allocated 29 from the physical network. Multiple NRPs may shared the same 30 topology, and multiple NRPs may share the same set of network 31 resources on specific network segments. This allows flexible 32 combination of network topology and network resource attributes to 33 build a large number of NRPs with a relatively small number of 34 logical topologies. The proposed mechanism is applicable to both 35 segment routing with MPLS data plane (SR-MPLS) and segment routing 36 with IPv6 data plane (SRv6). 38 Requirements Language 40 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 41 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 42 document are to be interpreted as described in RFC 2119 [RFC2119]. 44 Status of This Memo 46 This Internet-Draft is submitted in full conformance with the 47 provisions of BCP 78 and BCP 79. 49 Internet-Drafts are working documents of the Internet Engineering 50 Task Force (IETF). Note that other groups may also distribute 51 working documents as Internet-Drafts. The list of current Internet- 52 Drafts is at https://datatracker.ietf.org/drafts/current/. 54 Internet-Drafts are draft documents valid for a maximum of six months 55 and may be updated, replaced, or obsoleted by other documents at any 56 time. It is inappropriate to use Internet-Drafts as reference 57 material or to cite them other than as "work in progress." 59 This Internet-Draft will expire on 5 September 2022. 61 Copyright Notice 63 Copyright (c) 2022 IETF Trust and the persons identified as the 64 document authors. All rights reserved. 66 This document is subject to BCP 78 and the IETF Trust's Legal 67 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 68 license-info) in effect on the date of publication of this document. 69 Please review these documents carefully, as they describe your rights 70 and restrictions with respect to this document. Code Components 71 extracted from this document must include Revised BSD License text as 72 described in Section 4.e of the Trust Legal Provisions and are 73 provided without warranty as described in the Revised BSD License. 75 Table of Contents 77 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 78 2. Advertisement of NRP Definition . . . . . . . . . . . . . . . 4 79 3. Advertisement of NRP Topology Attribute . . . . . . . . . . . 5 80 3.1. Intra-domain Topology Advertisement . . . . . . . . . . . 6 81 3.1.1. MTR based Topology Advertisement . . . . . . . . . . 6 82 3.1.2. Flex-Algo based Topology Advertisement . . . . . . . 7 83 3.2. Inter-Domain Topology Advertisement . . . . . . . . . . . 8 84 3.2.1. NRP IDs TLV . . . . . . . . . . . . . . . . . . . . . 9 85 4. Advertisement of NRP Resource Attribute . . . . . . . . . . . 10 86 4.1. Option 1: L2 Bundle based Approach . . . . . . . . . . . 11 87 4.2. Option 2: Per-NRP Link TE Attributes . . . . . . . . . . 12 88 5. Advertisement of NRP specific Data Plane Identifiers . . . . 13 89 5.1. NRP-specific SR-MPLS SIDs . . . . . . . . . . . . . . . . 13 90 5.1.1. NRP-specific Prefix-SID TLV . . . . . . . . . . . . . 13 91 5.1.2. NRP-specific Adj-SID TLV . . . . . . . . . . . . . . 14 92 5.2. NRP-specific SRv6 SIDs . . . . . . . . . . . . . . . . . 15 93 5.2.1. NRP-specific SRv6 Locators and End SIDs . . . . . . . 15 94 5.2.2. NRP-specific SRv6 End.X SID . . . . . . . . . . . . . 16 95 5.3. Dedicated NRP ID in Data Plane . . . . . . . . . . . . . 17 96 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 97 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 98 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 99 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 100 9.1. Normative References . . . . . . . . . . . . . . . . . . 18 101 9.2. Informative References . . . . . . . . . . . . . . . . . 20 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 104 1. Introduction 106 Enhanced VPN (VPN+) is an enhancement to VPN services to support the 107 needs of new applications, particularly the applications that are 108 associated with 5G services. These applications require enhanced 109 isolation and have more stringent performance requirements than that 110 can be provided with traditional overlay VPNs. These properties 111 require integration between the underlay and the overlay networks. 112 [I-D.ietf-teas-enhanced-vpn] specifies the framework of enhanced VPN 113 and describes the candidate component technologies in different 114 network planes and layers. An enhanced VPN can be used for 5G 115 network slicing, and will also be of use in more generic scenarios. 117 To meet the requirement of enhanced VPN services, a number of virtual 118 underlay networks need to be created, each with a subset of the 119 underlay network topology and a set of network resources allocated to 120 meet the requirement of a specific VPN+ service or a group of VPN+ 121 services. Such a virtual underlay network is called Virtual 122 Transport Network (VTN) in [I-D.ietf-teas-enhanced-vpn]. 123 [I-D.ietf-teas-ietf-network-slices] introduces the concept Network 124 Resource Partition (NRP) as a set of network resources that are 125 available to carry traffic and meet the SLOs and SLEs. In order to 126 allocate network resources to an NRP, the NRP is associated with a 127 network topology to define the set of links and nodes. Thus VTN and 128 NRP are similar concepts, and NRP can be seen as an instantiation of 129 VTN in the context of network slicing. For clarity, the rest of this 130 document uses NRP in the description of the proposed mechanisms and 131 protocol extensions. 133 [I-D.ietf-spring-resource-aware-segments] introduces resource- 134 awareness to Segment Routing (SR) [RFC8402] by associating existing 135 type of SIDs with network resource attributes (e.g. bandwidth, 136 processing or storage resources). These resource-aware SIDs retain 137 their original functionality, with the additional semantics of 138 identifying the set of network resources available for the packet 139 processing action. [I-D.ietf-spring-sr-for-enhanced-vpn] describes 140 the use of resource-aware segments to build SR based NRPs. To allow 141 the network controller and network nodes to perform NRP-specific 142 explicit path computation and/or shortest path computation, the group 143 of resource-aware SIDs allocated by network nodes to each NRP and the 144 associated topology and resource attributes need to be distributed in 145 the control plane. 147 When an NRP spans multiple IGP areas or multiple Autonomous Systems 148 (ASes), BGP-LS is needed to advertise the NRP information in each IGP 149 area or AS to the network controller, so that the controller could 150 use the collected information to build the view of inter-area or 151 inter-AS SR NRPs. 153 This document describes BGP-LS [RFC7752] based mechanism with 154 necessary extensions to advertise the topology and resource attribute 155 of inter-area and inter-domain SR based NRPs. Each NRP can have a 156 customized topology and a set of network resources allocated. 157 Multiple NRPs may shared the same topology, and some of the NRPs may 158 share the same set of network resources on specific network segments. 159 This allows flexible combination of network topology and network 160 resource attributes to build a large number of NRPs with a relatively 161 small number of logical topologies. The definition of NRP is 162 advertised as a node attribute using BGP-LS. The associated network 163 topology and resources attributes of a NRP are advertised as link 164 attributes using BGP-LS. 166 2. Advertisement of NRP Definition 168 According to [I-D.ietf-teas-ietf-network-slices], an NRP consists of 169 a set of dedicated or shared network resources, and is associated 170 with a customized network topology. Thus a NRP can be defined as the 171 combination of a set of network attributes, which include the 172 topology attribute and other attributes, such as the associated 173 network resources. 175 The Network Resource Partition Definition (NRPD) TLV is a new TLV of 176 the optional BGP-LS Attribute which is associated with the node NLRI. 178 The format of NRPD TLV is as follows: 180 0 1 2 3 181 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 1 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 | Type | Length | 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 | NRP ID | 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 | MT-ID | Algorithm | Flags | 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 | Sub-TLVs | 190 ~ ... ~ 191 | | 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 194 Where: 196 * Type: To be assigned by IANA. 198 * Length: the length of the value field of the TLV. It is variable 199 dependent on the included Sub-TLVs. 201 * NRP ID: A global significant 32-bit identifier which is used to 202 identify an NRP. 204 * MT-ID: 16-bit identifier which contains the multi-topology 205 identifier of the IGP topology. 207 * Algorithm: 8-bit identifier which indicates the algorithm which 208 applies to this virtual transport network. It can be either a 209 normal algorithm in [RFC8402] or a Flex-Algorithm 210 [I-D.ietf-lsr-flex-algo]. 212 * Flags: 8-bit flags. Currently all the flags are reserved for 213 future use. They SHOULD be set to zero on transmission and MUST 214 be ignored on receipt. 216 * Sub-TLVs: optional sub-TLVs to specify the additional attributes 217 of an NRP. Currently no sub-TLV is defined in this document. 219 3. Advertisement of NRP Topology Attribute 221 [I-D.dong-lsr-sr-enhanced-vpn] describes the IGP mechanisms to 222 distribute the topology attributes of SR based NRPs. This section 223 describes the BGP-LS mechanism to distribute both the intra-domain 224 and inter-domain topology attributes of SR based NRPs. 226 3.1. Intra-domain Topology Advertisement 228 The intra-domain topology attribute of an NRP can be determined by 229 the MT-ID and/or the algorithm ID included in the NRP definition. In 230 practice, it could be described using two optional approaches. 232 The first approach is to use Multi-Topology Routing (MTR) [RFC4915] 233 [RFC5120] with the segment routing extensions to advertise the 234 topology associated with the SR based NRPs. Different algorithms MAY 235 be used to further specify the computation algorithm or the metric 236 type used for path computation within the topology. Multiple NRPs 237 can be associated with the same tupple, and the 238 IGP computation with the tuple can be shared by 239 these NRPs. 241 The second approach is to use Flex-Algo [I-D.ietf-lsr-flex-algo] to 242 describe the topological constraints of SR based NRPs on a network 243 topology (e.g. the default topology). Multiple NRPs can be 244 associated with the same Flex-Algo, and the IGP computation result 245 with this Flex-Algo can be shared. 247 This section describes the two optional approaches to advertise the 248 intra-domain topology of an NRP using BGP-LS. 250 3.1.1. MTR based Topology Advertisement 252 In section 4.2.2.1 of [I-D.ietf-idr-rfc7752bis], Multi-Topology 253 Identifier (MT-ID) TLV is defined, which can contain one or more IS- 254 IS or OSPF Multi-Topology IDs. The MT-ID TLV MAY be present in a 255 Link Descriptor, a Prefix Descriptor, or the BGP-LS Attribute of a 256 Node NLRI. 258 [RFC9085] defines the BGP-LS extensions to carry the segment routing 259 information using TLVs of BGP-LS Attribute. When MTR is used with 260 SR-MPLS data plane, topology-specific prefix-SIDs and topology- 261 specific Adj-SIDs can be carried in the BGP-LS Attribute associated 262 with the prefix NLRI and link NLRI respectively, the MT-ID TLV is 263 carried in the prefix descriptor or link descriptor to identify the 264 corresponding topology of the SIDs. 266 [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to 267 advertise SRv6 segments along with their functions and attributes. 268 When MTR is used with SRv6 data plane, the SRv6 Locator TLV is 269 carried in the BGP-LS Attribute associated with the prefix-NLRI, the 270 MT-ID TLV can be carried in the prefix descriptor to identify the 271 corresponding topology of the SRv6 Locator. The SRv6 End.X SIDs are 272 carried in the BGP-LS Attribute associated with the link NLRI, the 273 MT-ID TLV can be carried in the link descriptor to identify the 274 corresponding topology of the End.X SIDs. The SRv6 SID NLRI is 275 defined to advertise other types of SRv6 SIDs, in which the SRv6 SID 276 Descriptors can include the MT-ID TLV so as to advertise topology- 277 specific SRv6 SIDs. 279 [I-D.ietf-idr-rfc7752bis] also defines the rules of the usage of MT- 280 ID TLV: 282 "In a Link or Prefix Descriptor, only a single MT-ID TLV containing 283 the MT-ID of the topology where the link or the prefix is reachable 284 is allowed. In case one wants to advertise multiple topologies for a 285 given Link Descriptor or Prefix Descriptor, multiple NLRIs MUST be 286 generated where each NLRI contains a single unique MT-ID." 288 Editor's note: the above rules indicates that only one MT-ID is 289 allowed to be carried the Link or Prefix descriptors. When a link or 290 prefix needs to be advertised in multiple topologies, multiple NLRIs 291 needs to be generated to report all the topologies the link or prefix 292 participates in, together with the topology-specific segment routing 293 information and link attributes. This may increase the number of BGP 294 Updates needed for advertising MT-specific topology attributes, and 295 may introduce additional processing burden to both the sending BGP 296 speaker and the receiving network controller. When the number of 297 topologies in a network is not a small number, some optimization may 298 be needed for the reporting of multi-topology information and the 299 associated segment routing information in BGP-LS. Based on the WG's 300 opinion, this will be elaborated in a future version. 302 3.1.2. Flex-Algo based Topology Advertisement 304 The Flex-Algo definition [I-D.ietf-lsr-flex-algo] can be used to 305 describe the calculation-type, the metric-type and the topological 306 constraints for path computation on a network topology. As specified 307 in [I-D.dong-lsr-sr-enhanced-vpn], the topology of a NRP can be 308 determined by applying Flex-Algo constraints on a network topology. 310 BGP-LS extensions for Flex-Algo [I-D.ietf-idr-bgp-ls-flex-algo] 311 provide the mechanisms to advertise the Flex-Algo definition 312 information. BGP-LS extensions for SR-MPLS [RFC9085] and SRv6 313 [I-D.ietf-idr-bgpls-srv6-ext] provide the mechanism to advertise the 314 algorithm-specific segment routing information. 316 In [RFC9085], algorithm-specific prefix-SIDs can be advertised in 317 BGP-LS attribute associated with Prefix NLRI. In 318 [I-D.ietf-idr-bgpls-srv6-ext], algorithm-specific SRv6 Locators can 319 be advertised in BGP-LS Attribute associated with the corresponding 320 Prefix NLRI, and algorithm-specific End.X SID can be advertised in 321 BGP-LS Attribute associated with the corresponding Link NLRI. Other 322 types of SRv6 SIDs can also be algorithm-specific and are advertised 323 using the SRv6 SID NLRI. 325 3.2. Inter-Domain Topology Advertisement 327 In some network scenarios, an NRP which spans multiple areas or ASes 328 needs to be created. The multi-domain NRP could have different 329 inter-domain connectivity, and may be associated with different set 330 of network resources in each domain and also on the inter-domain 331 links. In order to build the multi-domain NRPs using segment 332 routing, it is necessary to advertise the topology and resource 333 attribute of NRP on the inter-domain links and the associated BGP 334 Peering SIDs. 336 [RFC9086] and [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS 337 extensions for advertisement of BGP topology information between ASes 338 and the associated BGP Peering Segment Identifiers. Such information 339 could be used by a network controller for the computation and 340 instantiation of inter-AS traffic engineering SR paths. 342 Depending on the network scenarios and the requirement of inter- 343 domain NRPs, different mechanisms can be used to specify the inter- 344 domain connections of NRPs. 346 * One EBGP session between two ASes can be established over multiple 347 underlying links. In this case, different underlying links can be 348 used for different inter-domain NRPs which requires link isolation 349 between each other. In another similar case, the EBGP session is 350 established over a single link, while the network resource (e.g. 351 bandwidth) on this link can be partitioned into different pieces, 352 each of which can be considered as a virtual member link. In both 353 cases, different BGP Peer-Adj-SIDs SHOULD be allocated to each 354 underlying physical or virtual member link, and ASBRs SHOULD 355 advertise the NRP identifier associated with each BGP Peer-Adj- 356 SID. 358 * For inter-domain connection between two ASes, multiple EBGP 359 sessions can be established between different set of peering 360 ASBRs. It is possible that some of these BGP sessions are used 361 for one inter-domain NRP, while some other BGP sessions are used 362 for another inter-domain NRP. In this case, different BGP peer- 363 node-SIDs are allocated to each BGP session, and ASBRs SHOULD 364 advertise the NRP identifier associated with each BGP Peer-node- 365 SIDs. 367 * At the AS-level topology, different inter-domain NRPs may have 368 different inter-domain connectivity. Different BGP Peer-Set-SIDs 369 can be allocated to represent the groups of BGP peers which can be 370 used for load-balancing in each inter-domain NRP. 372 In network scenarios where the MT-ID or Flex-Algo is used 373 consistently in multiple areas or ASes covered by a NRP. the 374 approaches to advertise topology-specific BGP peering SIDs are 375 described as below: 377 * Using MT-based mechanism, the topology-specific BGP peering SIDs 378 can be advertised with the MT-ID associated with the NRP carried 379 in the corresponding link NLRI. This can be supported with the 380 existing mechanisms defined in [RFC7752][RFC9086] and 381 [I-D.ietf-idr-bgpls-srv6-ext]. 383 * Using Flex-Algo based mechanism, the topology-specific BGP peering 384 SIDs can be advertised together with the Admin Group (color) of 385 the corresponding Flex-Algo in the BGP-LS attribute. 387 In network scenarios where consistent usage of MT-ID or Flex-Algo 388 among multiple ASes can not be expected, then the global-significant 389 NRP-ID can be used to define the AS level topologies. Within each 390 domain, the MT or Flex-Algo based mechanism could still be used for 391 topology advertisement. 393 3.2.1. NRP IDs TLV 395 A new NRP IDs TLV is defined to describe the identifiers of one or 396 more NRPs an intra-domain or inter-domain link belongs to. It can be 397 carried in BGP-LS attribute which is associated with a Link NLRI, or 398 it could be carried as a sub-TLV in the L2 Bundle Member Attribute 399 TLV. 401 The format of NRP IDs TLV is as below: 403 0 1 2 3 404 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 1 405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 406 | Type | Length | 407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 408 | Flags | Reserved | 409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 410 | NRP ID-1 | 411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 412 ~ ... ~ 413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 414 | NRP ID-n | 415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 417 Where: 419 * Type: To be assigned by IANA. 421 * Length: The length of the value field of the sub-TLV. It is 422 variable dependent on the number of NRP IDs included. 424 * Flags: 16 bit flags. All the bits are reserved, which MUST be set 425 to 0 on transmission and SHOULD be ignored on receipt. 427 * Reserved: this field is reserved for future use. MUST be set to 0 428 on transmission and SHOULD be ignored on receipt. 430 * NRP IDs: One or more 32-bit identifiers to specify the NRPs this 431 link belongs to. 433 4. Advertisement of NRP Resource Attribute 435 [I-D.dong-lsr-sr-enhanced-vpn] specifies the optional mechanism to 436 advertise the resource information associated with each NRP. One 437 approach is to use the L2 bundle mechanism [RFC8668] to advertise the 438 set of link resources allocated to an NRP as a L2 physical or virtual 439 member link. Another approach is to advertise the set of network 440 resources as per NRP link TE attributes. This section defines the 441 corresponding BGP-LS extensions for both approaches. 443 Two new TLVs are defined to carry the NRP ID and the link attribute 444 flags of either a Layer-3 link or the L2 bundle member links. The 445 NRP ID TLV is defined in section 3.2.1 of this document, and a new 446 Link Attribute Flags TLV is defined in this section. The TE 447 attributes of each Layer 3 link or the L2 bundle member link, such as 448 the bandwidth and the SR SIDs, can be advertised using the mechanism 449 as defined in [RFC9085][RFC9086] and [I-D.ietf-idr-bgpls-srv6-ext]. 451 4.1. Option 1: L2 Bundle based Approach 453 On an Layer-3 interface, each NRP can be allocated with a subset of 454 link resources (e.g. bandwidth). A subset of link resources may be 455 dedicated to an NRP, or may be shared by a group of NRPs. Each 456 subset of link resource can be instantiated as a virtual layer-2 457 member link under the Layer-3 interface, and the Layer-3 interface is 458 considered as a virtual Layer-2 bundle. The Layer-3 interface may 459 also be a physical Layer 2 link bundle, in this case a subset of link 460 resources allocated to an NRP may be provided by one of the physical 461 Layer-2 member links. 463 The NRP ID TLV defined in section 3.2.1 of this document is used to 464 carry the NRP IDs associated with the L2 bundle member links. The TE 465 attributes of the L2 bundle member links, such as the maximum link 466 bandwidth, and the SR SIDs, can be advertised using the mechanism as 467 defined in [RFC9085][RFC9086] and [I-D.ietf-idr-bgpls-srv6-ext]. 469 A new Link attribute Flags TLV is defined to specify the 470 characteristics of a link. It can be carried in BGP-LS attribute 471 which is associated with a Link NLRI, or it could be carried as a 472 sub-TLV in the L2 Bundle Member Attribute TLV. The format of the 473 sub-TLV is as below: 475 0 1 2 3 476 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 1 477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 478 | Type | Length | 479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 480 | Flags | 481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 483 Where: 485 Type: TBD 487 Length: 4 octets. 489 Flags: 16-bit flags. This field is consistent with the Flag field 490 in IS-IS Link Attribute sub-TLV in [RFC5029]. In addition to the 491 flags defined in [RFC5029], A new Flag "E" is defined in this 492 document. 494 - Link excluded from load balancing. When the flag is set, it 495 indicates this link is only used for the associated NRPs. 497 . 499 4.2. Option 2: Per-NRP Link TE Attributes 501 An Layer-3 interface can participate in multiple NRPs, each of which 502 is allocated with a subset of the resources of the interface. For 503 each NRP, the associated resources can be described using per-NRP TE 504 attributes. A new NRP-specific TE attribute TLV is defined to 505 advertise the link attributes associated with an NRP. This sub-TLV 506 MAY be carried in the BGP-LS Attribute associated with a Link NLRI. 507 The format of the NRP-specific TE attribute TLV is shown as below: 509 0 1 2 3 510 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 1 511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 512 | Type | Length | 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 514 | Flags | Reserved | 515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 516 | NRP IDs Sub-TLV | 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 518 ~ Other Sub-TLVs ~ 519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 Where: 523 * Type: To be assigned by IANA. 525 * Length: The length of the value field of the TLV. It is variable 526 dependent on the length of the Sub-TLVs field. 528 * Flags: 16-bit flags. All the 16 bits are reserved for future use, 529 which SHOULD be set to 0 on transmission and MUST be ignored on 530 receipt. 532 * Reserved: 16-bit field reserved for future use, SHOULD be set to 0 533 on transmission and MUST be ignored on receipt. 535 The NRP IDs TLV as defined in section 3.2.1 is used as the NRP IDs 536 Sub-TLV in the per-NRP Link TE Attribute TLV. 538 Other Sub-TLVs are optional and can be used to carry the TE 539 attributes associated with the NRPs. The existing Link TE Attribute 540 TLVs as defined in [I-D.ietf-idr-rfc7752bis] can be reused as sub- 541 TLVs here. New sub-TLVs may be defined in the future. 543 5. Advertisement of NRP specific Data Plane Identifiers 545 In network scenarios where each NRP is associated with an independent 546 topology or Flex-Algo, the topology or Flex-Algo specific SR SIDs or 547 Locators could be used to identify the NRP in data plane, so that the 548 set of network resources associated with the NRP can be determined. 549 In network scenarios where multiple NRPs share the same topology or 550 Flex-Algo, additional data plane identifiers are needed to identify 551 different NRPs. 553 This section describes the mechanisms to advertise the NRP 554 identifiers with different data plane encapsulations. 556 5.1. NRP-specific SR-MPLS SIDs 558 With SR-MPLS data plane, the NRP identifier can be implicitly 559 determined by the SR SIDs associated with the NRP. Each node SHOULD 560 allocate NRP-specific Prefix-SIDs for each NRP it participates in. 561 Similarly, NRP-specific Adj-SIDs MAY be allocated for each link which 562 participates in the NRP. 564 5.1.1. NRP-specific Prefix-SID TLV 566 A new NRP-specific Prefix-SID TLV is defined to advertise the 567 relationship between the prefix-SID and its associated NRP. It is 568 derived from NRP-specific Prefix-SID sub-TLV of IS-IS 569 [I-D.dong-lsr-sr-enhanced-vpn]. The format of the sub-TLV is as 570 below: 572 0 1 2 3 573 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 1 574 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 575 | Type | Length | 576 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 577 | Flags | Reserved | 578 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 579 | NRP ID | 580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 581 | SID/Index/Label(Variable) | 582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 584 Where: 586 * Type: TBD 588 * Length: The length of the value field of the sub-TLV. It is 589 variable dependent on the length of the SID/Index/Label field. 591 * Flags: 16-bit flags. The high-order 8 bits are the same as in the 592 Prefix-SID sub-TLV defined in [RFC8667]. The lower-order 8 bits 593 are reserved for future use, which SHOULD be set to 0 on 594 transmission and MUST be ignored on receipt. 596 * Reserved: 16-bit field reserved for future use, SHOULD be set to 0 597 on transmission and MUST be ignored on receipt. 599 * NRP ID: A 32-bit local identifier to identify the NRP this prefix- 600 SID is associated with. 602 * SID/Index/Label: The same as defined in [RFC8667]. 604 One or more of NRP-specific Prefix-SID TLVs MAY be carried in BGP-LS 605 attribute of the associated Prefix NLRI. The MT-ID in the Prefix 606 descriptors SHOULD be the same as the MT-ID in the definition of the 607 NRP. 609 5.1.2. NRP-specific Adj-SID TLV 611 A new NRP-specific Adj-SID TLV is defined to advertise between the 612 Adj-SID and its associated NRP. It is derived from NRP specific Adj- 613 SID sub-TLV of IS-IS [I-D.dong-lsr-sr-enhanced-vpn]. The format of 614 the sub-TLV is as below: 616 0 1 2 3 617 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 1 618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 619 | Type | Length | 620 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 621 | Flags | Reserved | 622 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 623 | NRP ID | 624 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 625 | SID/Index/Label(Variable) | 626 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 628 Where: 630 * Type: TBD 632 * Length: The length of the value field of the sub-TLV. It is 633 variable dependent on the length of the SID/Index/Label field. 635 * Flags: 16-bit flags. The high-order 8 bits are the same as in the 636 Adj-SID sub-TLV defined in [RFC8667]. The lower-order 8 bits are 637 reserved for future use, which SHOULD be set to 0 on transmission 638 and MUST be ignored on receipt. 640 * Reserved: 16-bit field reserved for future use, SHOULD be set to 0 641 on transmission and MUST be ignored on receipt. 643 * NRP ID: A 32-bit global unique identifier to identify the NRP this 644 Adj-SID is associated with. 646 * SID/Index/Label: The same as defined in [RFC8667]. 648 Multiple NRP-specific Adj-SID TLVs MAY be carried in BGP-LS attribute 649 of the associated Link NLRI. The MT-ID in the Link descriptors 650 SHOULD be the same as the MT-ID in the definition of these NRPs. 652 5.2. NRP-specific SRv6 SIDs 654 5.2.1. NRP-specific SRv6 Locators and End SIDs 656 With SRv6 data plane, the NRP identifier can be implicitly or 657 explicitly determined using the SRv6 Locators associated with the 658 NRP, this is to ensure that all network nodes (including both the 659 SRv6 End nodes and Transit nodes) can identify the NRP to which a 660 packet belongs. Network nodes SHOULD allocate NRP-specific Locators 661 for each NRP it participates in. The NRP-specific Locators are used 662 as the covering prefix of NRP-specific SRv6 End SIDs, End.X SIDs and 663 other types of SIDs. 665 Each NRP-specific SRv6 Locator MAY be advertised in a separate Prefix 666 NLRI. If multiple NRPs share the same topology/algorithm, the 667 topology/algorithm specific Locator is the covering prefix of a group 668 of NRP-specific Locators. Then the advertisement of NRP-specific 669 locators can be optimized to reduce the amount of information 670 advertised in the control plane. 672 A new NRP locator-block sub-TLV under the SRv6 Locator TLV is defined 673 to advertise a set of sub-blocks which follows the topology/algorithm 674 specific Locator. Each NRP locator-block value is assigned to one of 675 the NRPs which share the same topology/algorithm. 677 0 1 2 3 678 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 1 679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 680 | Type | Length | 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | Number of NRPs| Block Length | Reserved | 683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 684 | NRP ID #1 | 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 686 ~ Locator Block Value ~ 687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 688 ~ ... ~ 689 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 690 | NRP ID #n | 691 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 692 ~ Locator Block Value ~ 693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 695 Where: 697 * Type: TBD 699 * Length: The length of the value field of the sub-TLV. It is 700 variable dependent on the number of NRPs and the Block Length. 702 * Number of NRPs: The number of NRPs which share the same topology/ 703 algorithm specific Locator as the covering prefix. 705 * Block Length: The length of the NRP locator-block which follows 706 the length of the topology/algorithm specific Locator. 708 * NRP ID: A 32-bit identifier to identify the NRP the locator-block 709 is associated with. 711 * Block Value: The value of the NRP locator-block for each NRP. 713 With the NRP locator-block sub-TLV, the NRP-specific Locator can be 714 obtained by concatenating the topology/algorithm specific locator and 715 the locator-block value advertised for the NRP. 717 5.2.2. NRP-specific SRv6 End.X SID 719 The SRv6 End.X SIDs are advertised in the BGP-LS attribute with Link 720 NLRI.In order to distinguish the End.X SIDs which belong to different 721 NRPs, a new "NRP ID Sub-TLV" is introduced under the SRv6 End.X SID 722 TLV and SRv6 LAN End.X SID TLV defined in 723 [I-D.ietf-idr-bgpls-srv6-ext]. Its format is shown as below: 725 0 1 2 3 726 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 1 727 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 728 | Type | Length | 729 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 730 | NRP ID | 731 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 733 Where: 735 * Type: TBD. 737 * Length: the length of the Value field of the TLV. It is set to 4. 739 * NRP ID: A 32-bit global identifier to identify the NRP this End.X 740 SID is associated with. 742 5.3. Dedicated NRP ID in Data Plane 744 As the number of NRPs increases, with the mechanism described in 745 [I-D.ietf-spring-sr-for-enhanced-vpn], the number of SR SIDs and SRv6 746 Locators allocated for different NRPs would also increase. In 747 network scenarios where the number of SIDs or Locators becomes a 748 concern, some data plane optimization may be needed to reduce the 749 amount of SR SIDs and Locators allocated. As described in 750 [I-D.dong-teas-nrp-scalability], one approach is to decouple the data 751 plane identifiers used for topology based forwarding and the 752 identifiers used for the NRP-specific processing. Thus a new data 753 plane global NRP-ID could be introduced and encapsulated in the 754 packet. One possible encapsulation of NRP-ID in IPv6 data plane is 755 proposed in [I-D.dong-6man-enhanced-vpn-vtn-id]. One possible 756 encapsulation of NRP-ID in MPLS data plane is proposed in 757 [I-D.li-mpls-enhanced-vpn-vtn-id]. 759 In that case, the NRP ID encapsulated in data packet can be the same 760 value as the NRP ID used in the control protocols, so that the 761 overhead of advertising the mapping relationship between the NRP IDs 762 in the control plane and the corresponding data plane identifiers 763 could be saved. 765 6. Security Considerations 767 This document introduces no additional security vulnerabilities to 768 BGP-LS. 770 The mechanism proposed in this document is subject to the same 771 vulnerabilities as any other protocol that relies on BGP-LS. 773 7. IANA Considerations 775 TBD 777 8. Acknowledgments 779 The authors would like to thank Shunwan Zhuang and Zhenbin Li for the 780 review and discussion of this document. 782 9. References 784 9.1. Normative References 786 [I-D.ietf-idr-bgp-ls-flex-algo] 787 Talaulikar, K., Psenak, P., Zandi, S., and G. Dawra, 788 "Flexible Algorithm Definition Advertisement with BGP 789 Link-State", Work in Progress, Internet-Draft, draft-ietf- 790 idr-bgp-ls-flex-algo-08, 10 November 2021, 791 . 794 [I-D.ietf-idr-bgpls-srv6-ext] 795 Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., 796 Bernier, D., and B. Decraene, "BGP Link State Extensions 797 for SRv6", Work in Progress, Internet-Draft, draft-ietf- 798 idr-bgpls-srv6-ext-09, 10 November 2021, 799 . 802 [I-D.ietf-idr-rfc7752bis] 803 Talaulikar, K., "Distribution of Link-State and Traffic 804 Engineering Information Using BGP", Work in Progress, 805 Internet-Draft, draft-ietf-idr-rfc7752bis-10, 10 November 806 2021, . 809 [I-D.ietf-spring-resource-aware-segments] 810 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 811 Z., and F. Clad, "Introducing Resource Awareness to SR 812 Segments", Work in Progress, Internet-Draft, draft-ietf- 813 spring-resource-aware-segments-03, 12 July 2021, 814 . 817 [I-D.ietf-spring-sr-for-enhanced-vpn] 818 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 819 Z., and F. Clad, "Segment Routing based Virtual Transport 820 Network (VTN) for Enhanced VPN", Work in Progress, 821 Internet-Draft, draft-ietf-spring-sr-for-enhanced-vpn-01, 822 12 July 2021, . 825 [I-D.ietf-teas-enhanced-vpn] 826 Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A 827 Framework for Enhanced Virtual Private Network (VPN+) 828 Services", Work in Progress, Internet-Draft, draft-ietf- 829 teas-enhanced-vpn-09, 25 October 2021, 830 . 833 [I-D.ietf-teas-ietf-network-slices] 834 Farrel, A., Gray, E., Drake, J., Rokui, R., Homma, S., 835 Makhijani, K., Contreras, L. M., and J. Tantsura, 836 "Framework for IETF Network Slices", Work in Progress, 837 Internet-Draft, draft-ietf-teas-ietf-network-slices-05, 25 838 October 2021, . 841 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 842 Requirement Levels", BCP 14, RFC 2119, 843 DOI 10.17487/RFC2119, March 1997, 844 . 846 [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link 847 Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, 848 September 2007, . 850 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 851 S. Ray, "North-Bound Distribution of Link-State and 852 Traffic Engineering (TE) Information Using BGP", RFC 7752, 853 DOI 10.17487/RFC7752, March 2016, 854 . 856 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 857 Decraene, B., Litkowski, S., and R. Shakir, "Segment 858 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 859 July 2018, . 861 [RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler, 862 H., and M. Chen, "Border Gateway Protocol - Link State 863 (BGP-LS) Extensions for Segment Routing", RFC 9085, 864 DOI 10.17487/RFC9085, August 2021, 865 . 867 [RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K., 868 Ray, S., and J. Dong, "Border Gateway Protocol - Link 869 State (BGP-LS) Extensions for Segment Routing BGP Egress 870 Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August 871 2021, . 873 9.2. Informative References 875 [I-D.dong-6man-enhanced-vpn-vtn-id] 876 Dong, J., Li, Z., Xie, C., Ma, C., and G. Mishra, 877 "Carrying Virtual Transport Network (VTN) Identifier in 878 IPv6 Extension Header", Work in Progress, Internet-Draft, 879 draft-dong-6man-enhanced-vpn-vtn-id-06, 24 October 2021, 880 . 883 [I-D.dong-lsr-sr-enhanced-vpn] 884 Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L., 885 and S. Bryant, "IGP Extensions for Scalable Segment 886 Routing based Enhanced VPN", Work in Progress, Internet- 887 Draft, draft-dong-lsr-sr-enhanced-vpn-07, 29 January 2022, 888 . 891 [I-D.dong-teas-nrp-scalability] 892 Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N., 893 Mishra, G., Qin, F., Saad, T., and V. P. Beeram, 894 "Scalability Considerations for Network Resource 895 Partition", Work in Progress, Internet-Draft, draft-dong- 896 teas-nrp-scalability-01, 7 February 2022, 897 . 900 [I-D.ietf-lsr-flex-algo] 901 Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and 902 A. Gulko, "IGP Flexible Algorithm", Work in Progress, 903 Internet-Draft, draft-ietf-lsr-flex-algo-18, 25 October 904 2021, . 907 [I-D.ietf-lsr-isis-srv6-extensions] 908 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 909 Z. Hu, "IS-IS Extensions to Support Segment Routing over 910 IPv6 Dataplane", Work in Progress, Internet-Draft, draft- 911 ietf-lsr-isis-srv6-extensions-18, 20 October 2021, 912 . 915 [I-D.li-mpls-enhanced-vpn-vtn-id] 916 Li, Z. and J. Dong, "Carrying Virtual Transport Network 917 Identifier in MPLS Packet", Work in Progress, Internet- 918 Draft, draft-li-mpls-enhanced-vpn-vtn-id-01, 14 April 919 2021, . 922 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 923 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 924 RFC 4915, DOI 10.17487/RFC4915, June 2007, 925 . 927 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 928 Topology (MT) Routing in Intermediate System to 929 Intermediate Systems (IS-ISs)", RFC 5120, 930 DOI 10.17487/RFC5120, February 2008, 931 . 933 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 934 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 935 Extensions for Segment Routing", RFC 8667, 936 DOI 10.17487/RFC8667, December 2019, 937 . 939 [RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri, 940 M., and E. Aries, "Advertising Layer 2 Bundle Member Link 941 Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668, 942 December 2019, . 944 Authors' Addresses 946 Jie Dong 947 Huawei Technologies 948 Email: jie.dong@huawei.com 950 Zhibo Hu 951 Huawei Technologies 952 Email: huzhibo@huawei.com 954 Zhenbin Li 955 Huawei Technologies 956 Email: lizhenbin@huawei.com 958 Xiongyan Tang 959 China Unicom 960 Email: tangxy@chinaunicom.cn 962 Ran Pang 963 China Unicom 964 Email: pangran@chinaunicom.cn