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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (February 22, 2021) is 1157 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'I-D.ietf-spring-srv6-network-programming' is defined on line 342, but no explicit reference was found in the text == Outdated reference: A later version (-26) exists of draft-ietf-lsr-flex-algo-13 == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-11 == Outdated reference: A later version (-08) exists of draft-ietf-spring-resource-aware-segments-01 ** Downref: Normative reference to an Informational draft: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 'I-D.ietf-spring-sr-for-enhanced-vpn') == Outdated reference: A later version (-10) exists of draft-dong-lsr-sr-enhanced-vpn-04 == Outdated reference: A later version (-17) exists of draft-ietf-teas-enhanced-vpn-06 Summary: 1 error (**), 0 flaws (~~), 8 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 LSR Working Group Y. Zhu 3 Internet-Draft China Telecom 4 Intended status: Standards Track J. Dong 5 Expires: August 26, 2021 Z. Hu 6 Huawei Technologies 7 February 22, 2021 9 Using Flex-Algo for Segment Routing based VTN 10 draft-zhu-lsr-isis-sr-vtn-flexalgo-02 12 Abstract 14 Enhanced VPN (VPN+) aims to provide enhanced VPN service to support 15 some application's needs of enhanced isolation and stringent 16 performance requirements. VPN+ requires integration between the 17 overlay VPN connectivity and the characteristics provided the 18 underlay network. A Virtual Transport Network (VTN) is a virtual 19 underlay network which has a customized network topology and a set of 20 network resources allocated from the physical network. A VTN could 21 be used as the underlay for one or a group of VPN+ services. 23 In some network scenarios, each VTN can be associated with a unique 24 Flex-Algo Identifier. This document describes a mechanism to build 25 the SR based VTNs using SR Flex-Algo and IGP L2 bundle with minor 26 extensions. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on August 26, 2021. 45 Copyright Notice 47 Copyright (c) 2021 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 63 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 64 2. Advertisement of SR VTN Topology Attribute . . . . . . . . . 3 65 3. Advertisement of SR VTN Resource Attribute . . . . . . . . . 4 66 4. Forwarding Plane Operations . . . . . . . . . . . . . . . . . 5 67 5. Scalability Considerations . . . . . . . . . . . . . . . . . 6 68 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 69 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 70 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 71 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 72 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 73 9.2. Informative References . . . . . . . . . . . . . . . . . 8 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 76 1. Introduction 78 Enhanced VPN (VPN+) is an enhancement to VPN services to support the 79 needs of new applications, particularly including the applications 80 that are associated with 5G services. These applications require 81 enhanced isolation and have more stringent performance requirements 82 than that can be provided with traditional overlay VPNs. Thus these 83 properties require integration between the underlay and the overlay 84 networks. [I-D.ietf-teas-enhanced-vpn] specifies the framework of 85 enhanced VPN and describes the candidate component technologies in 86 different network planes and layers. An enhanced VPN may be used for 87 5G transport network slicing, and will also be of use in other 88 generic scenarios. 90 To meet the requirement of enhanced VPN services, a number of virtual 91 transport networks (VTN) can be created, each with a subset of the 92 underlay network topology and a set of network resources allocated 93 from the underlay network to meet the requirement of a specific VPN+ 94 service or a group of VPN+ services. Another possible approach is to 95 create a set of point-to-point paths, each with a set of network 96 resource reserved along the path, such paths are called Virtual 97 Transport Paths (VTPs). Although using a set of dedicated VTPs can 98 provide similar characteristics as VTN, it has some scalability 99 issues due to the per-path state in the network. 101 [I-D.ietf-spring-resource-aware-segments] introduces resource 102 awareness to Segment Routing (SR) [RFC8402]. As described in 103 [I-D.ietf-spring-sr-for-enhanced-vpn], the resource-aware SIDs can be 104 used to build virtual transport networks (VTNs) with the required 105 network topology and network resource attributes to support enhanced 106 VPN services. With segment routing based data plane, Segment 107 Identifiers (SIDs) can be used to represent both the topology and the 108 set of network resources allocated by network nodes to a VTN. The 109 SIDs of each VTN and the associated topology and resource attributes 110 need to be distributed using control plane. 112 [I-D.dong-lsr-sr-enhanced-vpn] defines the IGP mechanisms with 113 necessary extensions to build a set of Segment Routing (SR) based 114 VTNs. The VTNs could be used as the underlay of the enhanced VPN 115 service. The mechanism described in [I-D.dong-lsr-sr-enhanced-vpn] 116 allows flexible combination of the topology and resource attribute to 117 build customized VTNs. In some network scenarios, each VTN can be 118 associated with a unique Flex-Algo and allocated with a set of 119 dedicated network resources. This document describes a mechanism to 120 build the SR based VTNs using SR Flex-Algo and IGP L2 bundle with 121 minor extensions. 123 1.1. Requirements Language 125 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 126 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 127 "OPTIONAL" in this document are to be interpreted as described in 128 BCP14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they 129 appear in all capitals, as shown here. 131 2. Advertisement of SR VTN Topology Attribute 133 [I-D.ietf-lsr-flex-algo] specifies the mechanism to provide 134 distributed constraint-path computation, and the usage of SR-MPLS 135 prefix-SIDs and SRv6 locators for steering traffic along the 136 constrained paths. 138 The Flex-Algo definition is the combination of calculation-type, 139 metric-type and the topological constraints used for path 140 computation. According to the network nodes' participation of a 141 Flex-Algo, and the rules of including or excluding Admin Groups (i.e. 142 colors) and Shared Risk Link Groups (SRLGs), the topology attribute 143 of a VTN can be described using the associated Flex-Algo. If each 144 VTN is associated with a unique Flex-Algo, the Flex-Algo identifier 145 could be reused as the identifier of the VTN in the control plane. 147 With the mechanisms defined in[RFC8667] [I-D.ietf-lsr-flex-algo], SR- 148 MPLS prefix-SID advertisement can be associated with a specific 149 topology and a specific algorithm, which can be a Flex-Algo. This 150 allows the nodes to use the prefix-SIDs to steer traffic along 151 distributed computed constraint paths according to the associated 152 Flex-Algo in a particular topology. 154 [I-D.ietf-lsr-isis-srv6-extensions] specifies the IS-IS extensions to 155 support SRv6 data plane, in which the SRv6 locators advertisement can 156 be associated with a topology and a specific algorithm, which can be 157 a Flex-Algo. This allows the nodes to used the SRv6 locators to 158 steer traffic along distributed computed constraint paths according 159 to the associated Flex-Algo in a particular topology. In addition, 160 topology/algorithm specific SRv6 End SIDs and End.X SIDs can be used 161 to enforce traffic over the Loop-Free Alternatives (LFA) computed 162 backup paths. 164 3. Advertisement of SR VTN Resource Attribute 166 Each VTN can be allocated with a set of dedicated network resources. 167 In order to perform constraint based path computation for each VTN on 168 network controller and the ingress nodes, the resource attribute of 169 each VTN also needs to be advertised. 171 [RFC8668] was defined to advertise the link attributes of the Layer-2 172 bundle member links. In this section, it is extended to advertise 173 the set of network resource attributes associated with different VTNs 174 on a shared Layer-3 link. 176 The Layer-3 link may or may not be a Layer-2 link bundle, as long as 177 it has the capability of allocating different subsets of link 178 resources to different VTNs it participates in. A subset of the link 179 resources can be considered as a virtual Layer-2 member link (or sub- 180 interface) of the Layer-3 link. If the Layer-3 interface is a 181 Layer-2 link bundle, it is possible that the subset of link resource 182 allocated to a specific VTN is provided by one of the physical 183 Layer-2 member links. 185 A new flag "V" (Virtual) is defined in the flag field of the Parent 186 L3 Neighbor Descriptor in the L2 Bundle Member Attributes TLV (25). 188 0 1 2 3 4 5 6 7 189 +-+-+-+-+-+-+-+-+ 190 |P|V| | 191 +-+-+-+-+-+-+-+-+ 193 V flag: When the V flag is set, it indicates the advertised member 194 links under the Parent Layer-3 link are virtual Layer-2 member links. 195 When the V flag is clear, it indicates the member links are physical 196 member links. This flag may be used to determine whether the member 197 links share fates with the parent interface. 199 For each virtual or physical member link, the TE attributes defined 200 in [RFC5305] such as the Maximum Link Bandwidth and Admin Groups 201 SHOULD be advertised using the mechanism as defined in [RFC8668]. 202 The Adj-SIDs or SRv6 End.X SIDs associated with each of the virtual 203 or physical Layer-2 member links SHOULD also be advertised. 205 In order to correlate the virtual or physical member links with the 206 Flex-Algo used to identify the VTN, each VTN SHOULD be assigned with 207 a unique Admin Group (AG) or Extended Admin Group (EAG), and the 208 virtual or physical member link associated with this VTN SHOULD be 209 configured with the AG or EAG assigned to the VTN. The AG or EAG of 210 the Layer 3 link SHOULD be set to the union of all the AGs or EAGs of 211 its virtual or physical member links. In the definition of the Flex- 212 Algo corresponding to the VTN, It MUST use the Include-Any Admin 213 Group rule with only the AG or EAG assigned to the VTN as the link 214 constraints, the Include-All Admin Goup rule or the Exclude Admin 215 Group rule MUST NOT be used. This ensures that the Layer-3 link is 216 included in the Flex-Algo specific constraint path computation for 217 each VTN it participates in. 219 4. Forwarding Plane Operations 221 For SR-MPLS data plane, a prefix SID is associated with the paths 222 calculated using the corresponding Flex-Algo of a VTN. An outgoing 223 Layer-3 interface is determined for each path. In addition, the 224 prefix-SID also steers the traffic to use the virtual or physical 225 member link which is associated with the VTN on the outgoing Layer-3 226 interface for packet forwarding. The Adj-SIDs associated with the 227 virtual or physical member links of a VTN MAY be used with the 228 prefix-SIDs of the same VTN together to build SR-MPLS paths with the 229 topological and resource constraints of the VTN. 231 For SRv6 data plane, an SRv6 Locator is a prefix which is associated 232 with the paths calculated using the corresponding Flex-Algo of a VTN. 233 An outgoing Layer-3 interface is determined for each path. In 234 addition, the SRv6 Locator prefix also steers the traffic to use the 235 virtual or physical member link which is associated with the VTN on 236 the outgoing Layer-3 interface for packet forwarding. The End.X SIDs 237 associated with the virtual or physical member links of a VTN MAY be 238 used with the SRv6 Locator prefix of the same VTN together to build 239 SRv6 paths with the topological and resource constraints of the VTN. 241 5. Scalability Considerations 243 The mechanism described in this document assumes that each VTN is 244 associated with an unique Flex-Algo, so that the Flex-Algo IDs can be 245 reused to identify the VTNs in the control plane. While this brings 246 the benefit of simplicity, it also has some limitations. For 247 example, it means that even if multiple VTNs share the same 248 topological constraints, they would still need to be identified using 249 different Flex-Algo IDs in the control plane, then independent path 250 computation needs to be executed for each VTN. The number of VTNs 251 supported in a network may be dependent on the number of Flex-Algos 252 supported, which is related to the control plane computation 253 overhead. Another aspect which may impact the number of VTNs 254 supported with this mechanism is that at most 128 Flex-Algos can be 255 used in a network. 257 Based on the above considerations, this mechanism may be suitable for 258 networks where a relatively small number of VTNs are needed. 260 6. Security Considerations 262 This document introduces no additional security vulnerabilities to 263 IS-IS. 265 The mechanism proposed in this document is subject to the same 266 vulnerabilities as any other protocol that relies on IGPs. 268 7. IANA Considerations 270 This document does not request any IANA actions. 272 8. Acknowledgments 274 The authors would like to thank Zhenbin Li and Peter Psenak for the 275 review and discussion of this document. 277 9. References 279 9.1. Normative References 281 [I-D.ietf-lsr-flex-algo] 282 Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and 283 A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex- 284 algo-13 (work in progress), October 2020. 286 [I-D.ietf-lsr-isis-srv6-extensions] 287 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 288 Z. Hu, "IS-IS Extension to Support Segment Routing over 289 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11 290 (work in progress), October 2020. 292 [I-D.ietf-spring-resource-aware-segments] 293 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 294 Z., and F. Clad, "Introducing Resource Awareness to SR 295 Segments", draft-ietf-spring-resource-aware-segments-01 296 (work in progress), January 2021. 298 [I-D.ietf-spring-sr-for-enhanced-vpn] 299 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 300 Z., and F. Clad, "Segment Routing based Virtual Transport 301 Network (VTN) for Enhanced VPN", February 2021, 302 . 305 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 306 Requirement Levels", BCP 14, RFC 2119, 307 DOI 10.17487/RFC2119, March 1997, 308 . 310 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 311 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 312 2008, . 314 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 315 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 316 May 2017, . 318 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 319 Decraene, B., Litkowski, S., and R. Shakir, "Segment 320 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 321 July 2018, . 323 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 324 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 325 Extensions for Segment Routing", RFC 8667, 326 DOI 10.17487/RFC8667, December 2019, 327 . 329 [RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri, 330 M., and E. Aries, "Advertising Layer 2 Bundle Member Link 331 Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668, 332 December 2019, . 334 9.2. Informative References 336 [I-D.dong-lsr-sr-enhanced-vpn] 337 Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L., 338 and S. Bryant, "IGP Extensions for Segment Routing based 339 Enhanced VPN", draft-dong-lsr-sr-enhanced-vpn-04 (work in 340 progress), June 2020. 342 [I-D.ietf-spring-srv6-network-programming] 343 Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., 344 Matsushima, S., and Z. Li, "SRv6 Network Programming", 345 draft-ietf-spring-srv6-network-programming-28 (work in 346 progress), December 2020. 348 [I-D.ietf-teas-enhanced-vpn] 349 Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A 350 Framework for Enhanced Virtual Private Networks (VPN+) 351 Service", draft-ietf-teas-enhanced-vpn-06 (work in 352 progress), July 2020. 354 Authors' Addresses 356 Yongqing Zhu 357 China Telecom 359 Email: zhuyq8@chinatelecom.cn 361 Jie Dong 362 Huawei Technologies 364 Email: jie.dong@huawei.com 366 Zhibo Hu 367 Huawei Technologies 369 Email: huzhibo@huawei.com