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'I-D.dong-spring-sr-for-enhanced-vpn') == Outdated reference: A later version (-26) exists of draft-ietf-lsr-flex-algo-11 == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-09 == Outdated reference: A later version (-08) exists of draft-ietf-spring-resource-aware-segments-00 == Outdated reference: A later version (-10) exists of draft-dong-lsr-sr-enhanced-vpn-04 == Outdated reference: A later version (-28) exists of draft-ietf-spring-srv6-network-programming-18 == Outdated reference: A later version (-17) exists of draft-ietf-teas-enhanced-vpn-06 Summary: 1 error (**), 0 flaws (~~), 9 warnings (==), 1 comment (--).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: March 15, 2021 Z. Hu 6 Huawei Technologies 7 September 11, 2020 9 Using Flex-Algo for Segment Routing based VTN 10 draft-zhu-lsr-isis-sr-vtn-flexalgo-01 12 Abstract 14 As defined in I-D.ietf-teas-enhanced-vpn, enhanced VPN (VPN+) aims to 15 provide enhanced VPN service to support the needs of enhanced 16 isolation and stringent performance requirements. VPN+ requires 17 integration between the overlay VPN and the underlay network. A 18 Virtual Transport Network (VTN) is a virtual network which consists 19 of a subset of network topology and network resources allocated from 20 the underlay network. A VTN could be used as the underlay for one or 21 a group of VPN+ services. 23 I-D.dong-lsr-sr-enhanced-vpn defines the IGP mechanisms with 24 necessary extensions to build a set of Segment Routing (SR) based 25 VTNs. This document describes a simplified mechanism to build the SR 26 based VTNs using SR Flex-Algo together with minor extensions to IGP 27 L2 bundle. 29 Requirements Language 31 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 32 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 33 document are to be interpreted as described in RFC 2119 [RFC2119]. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at https://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on March 15, 2021. 51 Copyright Notice 53 Copyright (c) 2020 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (https://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 69 2. Advertisement of SR VTN Topology Attribute . . . . . . . . . 3 70 3. Advertisement of SR VTN Resource Attribute . . . . . . . . . 4 71 4. Forwarding Plane Operations . . . . . . . . . . . . . . . . . 5 72 5. Scalability Considerations . . . . . . . . . . . . . . . . . 5 73 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 74 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 75 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 76 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 77 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 78 9.2. Informative References . . . . . . . . . . . . . . . . . 7 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 81 1. Introduction 83 Enhanced VPN (VPN+) is an enhancement to VPN services to support the 84 needs of new applications, particularly including the applications 85 that are associated with 5G services. These applications require 86 enhanced isolation and have more stringent performance requirements 87 than that can be provided with traditional overlay VPNs. Thus these 88 properties require integration between the underlay and the overlay 89 networks. [I-D.ietf-teas-enhanced-vpn] specifies the framework of 90 enhanced VPN and describes the candidate component technologies in 91 different network planes and layers. An enhanced VPN may be used for 92 5G transport network slicing, and will also be of use in other 93 generic scenarios. 95 To meet the requirement of enhanced VPN services, a number of virtual 96 transport networks (VTN) can be created, each with a subset of the 97 underlay network topology and a set of network resources allocated 98 from the underlay network to meet the requirement of a specific VPN+ 99 service or a group of VPN+ services. Another possible approach is to 100 create a set of point-to-point paths, each with a set of network 101 resource reserved along the path, such paths are called Virtual 102 Transport Paths (VTPs). Although using a set of dedicated VTPs can 103 provide similar characteristics as VTN, it has some scalability 104 issues due to the per-path state in the network. 106 [I-D.ietf-spring-resource-aware-segments] introduces resource 107 awareness to Segment Routing (SR) [RFC8402]. As described in 108 [I-D.dong-spring-sr-for-enhanced-vpn], the resource-aware SIDs can be 109 used to build virtual transport networks (VTNs) with the required 110 network topology and network resource attributes to support enhanced 111 VPN services. With segment routing based data plane, Segment 112 Identifiers (SIDs) can be used to represent both the topology and the 113 set of network resources allocated by network nodes to a virtual 114 network. The SIDs of each VTN and the associated topology and 115 resource attributes need to be distributed using control plane. 117 [I-D.dong-lsr-sr-enhanced-vpn] defines the IGP mechanisms with 118 necessary extensions to build a set of Segment Routing (SR) based 119 VTNs. The VTNs could be used as the underlay of the enhanced VPN 120 service. The mechanism described in [I-D.dong-lsr-sr-enhanced-vpn] 121 allows flexible combination of the topology and resource attribute to 122 build customized VTNs. In some network scenarios, it is assumed that 123 each VTN can have an independent topology and a set of dedicated 124 network resources, and the number of the VTNs required is limited. 125 This document describes a simplified mechanism to build the SR based 126 VTNs in those scenarios. 128 2. Advertisement of SR VTN Topology Attribute 130 [I-D.ietf-lsr-flex-algo] specifies the mechanism to provide 131 distributed constraint-path computation, and the usage of SR-MPLS 132 prefix-SIDs and SRv6 locators for steering traffic along the 133 constrained paths. 135 The Flex-Algo definition consists of the topological constraints for 136 path computation. According to the network nodes' participation of a 137 Flex-Algo, and the rules of including or excluding Admin Groups (i.e. 138 colors) and Shared Risk Link Groups (SRLGs), thus the topology 139 attribute of a VTN can be described using the associated Flex-Algo. 140 And when each VTN has an independent set of network topology 141 constraints, the Flex-Algo identifier could be reused as the 142 identifier of the VTN in control plane. 144 With the mechanisms defined in[RFC8667] [I-D.ietf-lsr-flex-algo], SR- 145 MPLS prefix-SID advertisement can be associated with a specific 146 topology and a specific algorithm, which can be a Flex-Algo. This 147 allows the nodes to use the prefix-SIDs to steer traffic along 148 distributed computed constraint paths according to the identified 149 Flex-Algo in the associated topology. 151 [I-D.ietf-lsr-isis-srv6-extensions] specifies the IS-IS extensions to 152 support SRv6 data plane, in which the SRv6 locators advertisement can 153 be associated with a specific topology and a specific algorithm, 154 which can be a Flex-Algo. This allows the nodes to used the SRv6 155 locators to steer traffic along distributed computed constraint paths 156 according to the identified Flex-Algo in the associated topology. In 157 addition, topology/algorithm specific SRv6 End SIDs and End.X SIDs 158 can be used to enforce traffic over the Loop-Free Alternatives (LFA) 159 computed backup paths. 161 3. Advertisement of SR VTN Resource Attribute 163 Each VTN may have customized network resource attributes. In order 164 to perform constraint based path computation for each VTN on network 165 controller and the ingress nodes, the resource attribute of each VTN 166 also needs to be advertised. 168 [RFC8668] was defined to advertise the link attributes of the Layer 2 169 bundle member links. In this section, it is extended to advertise 170 the network resource attributes associated with different VTNs on a 171 Layer 3 link. 173 The Layer 3 link may or may not be a Layer 2 link bundle, as long as 174 it has the capability of allocating different subsets of link 175 resources to different VTNs it participates in. A subset of the link 176 resource can be considered as a virtual Layer 2 member link (or sub- 177 interface) of the Layer 3 link. If the Layer 3 interface is a Layer 178 2 link bundle, it is possible that the subset of link resource 179 allocated to a specific VTN is provided by one of the physical Layer 180 2 member links. 182 A new flag "V" (Virtual) is defined in the flag field of the Parent 183 L3 Neighbor Descriptor in the L2 Bundle Member Attributes TLV (25). 185 0 1 2 3 4 5 6 7 186 +-+-+-+-+-+-+-+-+ 187 |P|V| | 188 +-+-+-+-+-+-+-+-+ 190 V flag: When the V flag is set, it indicates the advertised member 191 links under the Parent L3 link are virtual Layer 2 member links. 193 When the V flag is clear, it indicates the member links are physical 194 member links. 196 For each virtual or physical member link, the TE attributes defined 197 in [RFC5305] such as the Maximum Link Bandwidth and Admin Groups 198 SHOULD be advertised using the mechanism as defined in [RFC8668]. 199 The Adj-SIDs or SRv6 End.X SIDs associated with each of the virtual 200 or physical member links of an L2 bundle SHOULD also be advertised. 202 In order to correlate the virtual or physical member links with the 203 corresponding VTNs, each member link SHOULD be assigned with a 204 dedicated Admin Group or Extended Admin Group, which is included in 205 the definition of the Flex-Algo of the corresponding VTN. Note that 206 in this case the Admin Group or Extended Admin Group of the Layer 3 207 link SHOULD be set to the union of all the Admin Groups or Extended 208 Admin Groups of its virtual or physical member links. This is to 209 ensure that the Layer 3 link is always included in the Flex-Algo 210 specific constraint path computation of the VTNs it participates in. 212 4. Forwarding Plane Operations 214 For SR-MPLS data plane, a prefix SID is associated with the paths 215 calculated using the corresponding Flex-Algo of a VTN. An outgoing 216 Layer 3 interface is determined for each path. In addition, the 217 prefix-SID also steers the traffic to use the virtual or physical 218 member link which is associated with the VTN on the outgoing Layer 3 219 interface for packet forwarding. The Adj-SIDs associated with the 220 virtual or physical member links of a VTN MAY be used with the 221 prefix-SIDs of the same VTN together to build SR-MPLS paths with the 222 topological and resource constraints of the VTN. 224 For SRv6 data plane, an SRv6 Locator is a prefix which is associated 225 with the paths calculated using the corresponding Flex-Algo of a VTN. 226 An outgoing Layer 3 interface is determined for each path. In 227 addition, the SRv6 Locator prefix also steers the traffic to use the 228 virtual or physical member link which is associated with the VTN on 229 the outgoing Layer 3 interface for packet forwarding. The End.X SIDs 230 associated with the virtual or physical member links of a VTN MAY be 231 used with the SRv6 Locator prefix of the same VTN together to build 232 SRv6 paths with the topological and resource constraints of the VTN. 234 5. Scalability Considerations 236 The mechanism described in this document requires that each VTN 237 associated with an independent Flex-Algo, so that the VTNs can be 238 identified using the corresponding Flex-Algo ID. While this brings 239 the benefits of simplicity, it also has some limitations. For 240 example, it means that even if multiple VTNs share the same topology 241 constraints, they would still need to be identified using different 242 Flex-Algos in the control plane. This means independent path 243 computation would be executed for each VTN. The number of VTNs 244 supported in a network may be dependent on the number of Flex-Algos 245 supported, which is related to the control plane computation 246 overhead. 248 Another aspect which may impact the number of VTNs supported with 249 this mechanism is that at most 128 Flex-Algos can be used in a 250 network. 252 6. Security Considerations 254 This document introduces no additional security vulnerabilities to 255 IS-IS. 257 The mechanism proposed in this document is subject to the same 258 vulnerabilities as any other protocol that relies on IGPs. 260 7. IANA Considerations 262 This document does not request any IANA actions. 264 8. Acknowledgments 266 The authors would like to thank Zhenbin Li for the review and 267 discussion of this document. 269 9. References 271 9.1. Normative References 273 [I-D.dong-spring-sr-for-enhanced-vpn] 274 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 275 Z., and F. Clad, "Segment Routing based Virtual Transport 276 Network for Enhanced VPN", draft-dong-spring-sr-for- 277 enhanced-vpn-10 (work in progress), August 2020. 279 [I-D.ietf-lsr-flex-algo] 280 Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and 281 A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex- 282 algo-11 (work in progress), September 2020. 284 [I-D.ietf-lsr-isis-srv6-extensions] 285 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 286 Z. Hu, "IS-IS Extension to Support Segment Routing over 287 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-09 288 (work in progress), September 2020. 290 [I-D.ietf-spring-resource-aware-segments] 291 Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, 292 Z., and F. Clad, "Introducing Resource Awareness to SR 293 Segments", draft-ietf-spring-resource-aware-segments-00 294 (work in progress), July 2020. 296 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 297 Requirement Levels", BCP 14, RFC 2119, 298 DOI 10.17487/RFC2119, March 1997, 299 . 301 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 302 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 303 2008, . 305 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 306 Decraene, B., Litkowski, S., and R. Shakir, "Segment 307 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 308 July 2018, . 310 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 311 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 312 Extensions for Segment Routing", RFC 8667, 313 DOI 10.17487/RFC8667, December 2019, 314 . 316 [RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri, 317 M., and E. Aries, "Advertising Layer 2 Bundle Member Link 318 Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668, 319 December 2019, . 321 9.2. Informative References 323 [I-D.dong-lsr-sr-enhanced-vpn] 324 Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L., 325 and S. Bryant, "IGP Extensions for Segment Routing based 326 Enhanced VPN", draft-dong-lsr-sr-enhanced-vpn-04 (work in 327 progress), June 2020. 329 [I-D.ietf-spring-srv6-network-programming] 330 Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., 331 Matsushima, S., and Z. Li, "SRv6 Network Programming", 332 draft-ietf-spring-srv6-network-programming-18 (work in 333 progress), August 2020. 335 [I-D.ietf-teas-enhanced-vpn] 336 Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A 337 Framework for Enhanced Virtual Private Networks (VPN+) 338 Service", draft-ietf-teas-enhanced-vpn-06 (work in 339 progress), July 2020. 341 Authors' Addresses 343 Yongqing Zhu 344 China Telecom 346 Email: zhuyq8@chinatelecom.cn 348 Jie Dong 349 Huawei Technologies 351 Email: jie.dong@huawei.com 353 Zhibo Hu 354 Huawei Technologies 356 Email: huzhibo@huawei.com