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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Open Shortest Path First IGP S. Hegde 3 Internet-Draft Juniper Networks, Inc. 4 Intended status: Standards Track P. Sarkar 5 Expires: October 21, 2017 H. Gredler 6 Individual 7 M. Nanduri 8 Microsoft Corporation 9 L. Jalil 10 Verizon 11 April 19, 2017 13 OSPF Link Overload 14 draft-ietf-ospf-link-overload-06 16 Abstract 18 When a link is being prepared to be taken out of service, the traffic 19 needs to be diverted from both ends of the link. Increasing the 20 metric to the highest metric on one side of the link is not 21 sufficient to divert the traffic flowing in the other direction. 23 It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be 24 able to advertise a link being in an overload state to indicate 25 impending maintenance activity on the link. This information can be 26 used by the network devices to re-route the traffic effectively. 28 This document describes the protocol extensions to disseminate link- 29 overload information in OSPFv2 and OSPFv3. 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 http://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 October 21, 2017. 54 Copyright Notice 56 Copyright (c) 2017 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 (http://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 . . . . . . . . . . . . . . . . . . . . . . . . 3 72 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 73 3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4 74 3.1. Area scope flooding . . . . . . . . . . . . . . . . . . . 4 75 3.2. Link scope flooding . . . . . . . . . . . . . . . . . . . 4 76 4. Link-Overload sub-TLV . . . . . . . . . . . . . . . . . . . . 4 77 4.1. OSPFv2 Link-overload sub-TLV . . . . . . . . . . . . . . 4 78 4.2. Remote IPv4 address sub-TLV . . . . . . . . . . . . . . . 5 79 4.3. Local/Remote Interface ID . . . . . . . . . . . . . . . . 6 80 4.4. OSPFv3 Link-Overload sub-TLV . . . . . . . . . . . . . . 6 81 5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 7 82 5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 7 83 5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 8 84 5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 8 85 5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 8 86 5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 9 87 6. Backward compatibility . . . . . . . . . . . . . . . . . . . 9 88 7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 9 89 7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 9 90 7.2. Controller based Traffic Engineering Deployments . . . . 10 91 7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 11 92 7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 11 93 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 94 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 95 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 96 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 97 11.1. Normative References . . . . . . . . . . . . . . . . . . 12 98 11.2. Informative References . . . . . . . . . . . . . . . . . 13 99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 101 1. Introduction 103 When a node is being prepared for a planned maintenance or upgrade, 104 [RFC6987] provides mechanisms to advertise the node being in an 105 overload state by setting all outgoing link costs to MAX-METRIC 106 (0xffff). These procedures are specific to the maintenance activity 107 on a node and cannot be used when a single link attached to the node 108 requires maintenance. 110 In traffic-engineering deployments, LSPs need to be diverted from the 111 link without disrupting the services. It is useful to be able to 112 advertise the impending maintenance activity on the link and to have 113 LSP re-routing policies at the ingress to route the LSPs away from 114 the link. 116 Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned 117 by means of pseudo-wires or L2-circuits. Prior to devices in the 118 underlying network going offline for maintenance, it is useful to 119 divert the traffic away from the node before the maintenance is 120 actually scheduled. Since the nodes in the underlying network are 121 not visible to OSPF, the existing stub router mechanism described in 122 [RFC6987] cannot be used. An application specific to this use case 123 is described in Section 7.1 125 This document provides mechanisms to advertise link-overload state in 126 the flexible encodings provided by OSPFv2 Prefix/Link Attribute 127 Advertisement([RFC7684]) and RI LSA ([RFC7770]). Throughout this 128 document, OSPF is used when the text applies to both OSPFv2 and 129 OSPFv3. OSPFv2 or OSPFv3 is used when the text is specific to one 130 version of the OSPF protocol. 132 2. Motivation 134 The motivation of this document is to reduce manual intervention 135 during maintenance activities. The following objectives help to 136 accomplish this in a range of deployment scenarios. 138 1. Advertise impending maintenance activity so that traffic from 139 both directions can be diverted away from the link. 141 2. Allow the solution to be backward compatible so that nodes that 142 do not understand the new advertisement do not cause routing 143 loops. 145 3. Advertise the maintenance activity to other nodes in the network 146 so that LSP ingress routers/controllers can learn of the 147 impending maintenance activity and apply specific policies to re- 148 route the LSPs for traffic-engineering based deployments. 150 4. Allow the link to be used as last resort link to prevent traffic 151 disruption when alternate paths are not available. 153 3. Flooding Scope 155 The link-overload information can be flooded in area scoped extended 156 link LSA [RFC7684] or a link scoped RI LSA [RFC7770] or both based on 157 the needs of the application. Section 7 describes applications 158 requiring area scope as well as link scope link-overload information. 160 3.1. Area scope flooding 162 For OSPFv2, Link-Overload sub-TLV is carried in the extended Link TLV 163 as defined in [RFC7684]. 165 3.2. Link scope flooding 167 The link local scope RI LSA MAY carry the Link-Overload sub-TLV as 168 defined in Section 4. The link local scope RI-LSA corresponds to the 169 link on which the LSA arrives and there is no need to explicitly 170 specify the remote IPv4 address. The remote IPv4 address field MAY 171 be zero when the Link-Overload sub-TLV is carried in the link local 172 RI LSA. The Link-Overload sub-TLV MAY appear in any instance of the 173 link local RI-LSA. The Link-Overload sub-TLV is carried in the RI- 174 LSA for both OSPFv2 and OSPFv3. 176 4. Link-Overload sub-TLV 178 4.1. OSPFv2 Link-overload sub-TLV 180 The Link-Overload sub-TLV identifies the link being in overload 181 state. It is carried in extended Link TLV as defined in [RFC7684] or 182 link local scope RI LSA as defined in [RFC7770]. 184 0 1 2 3 185 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 1 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 | Type | Length | 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 190 Figure 1: Link-Overload sub-TLV for OSPFv2 192 Type : TBA (suggested value 5) 194 Length: 0 196 4.2. Remote IPv4 address sub-TLV 198 This sub-TLV specifies the IPv4 address of the link on remote side. 199 It is carried in extended Link TLV as defined in [RFC7684].This sub- 200 TLV is optional and MAY be advertised in area scoped Extended Link 201 Opaque LSA to identify the link when there are multiple parallel 202 interfaces between two nodes. 204 0 1 2 3 205 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 1 206 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 207 | Type | Length | 208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 | Remote IPv4 address | 210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 Figure 2: Remote IPv4 address sub-TLV 214 Type : TBA (suggested value 4) 216 Length: 4 218 Value: Remote IPv4 address. The remote IP4 address is used to 219 identify the particular link when there are multiple parallel links 220 between two nodes. 222 4.3. Local/Remote Interface ID 224 This sub-TLV specifies local and remote interface identifiers. It is 225 carried in extended Link TLV as defined in [RFC7684].This sub-TLV is 226 optional and MAY be advertised in area scoped Extended Link Opaque 227 LSA to identify the link when there are multiple parallel unnumbered 228 interfaces between two nodes. The procedures to originate this sub- 229 TLV is defined in [RFC4203] 231 0 1 2 3 232 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 1 233 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 234 | Type | Length | 235 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 236 | Local Interface ID | 237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 238 | Remote Interface ID | 239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 241 Figure 3: Local/Remote Interface ID sub-TLV 243 Type : TBA (suggested value 11) 245 Length: 8 247 Value: 4 octets of Local Interface ID followed by 4 octets of Remote 248 interface ID. 250 4.4. OSPFv3 Link-Overload sub-TLV 252 The OSPFv3 Link-Overload sub-TLV is carried in the link local scope 253 OSPFv3 RI LSA as defined in [RFC7770]. 255 0 1 2 3 256 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 1 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 258 | Type | Length | 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 261 Figure 4: Link-Overload sub-TLV for OSPFv3 263 Type : TBA (Suggested value 4) 264 Length: 0 266 The area scope advertisement of Link-Overload sub-TLV for OSPFv3 will 267 be described in a separate document. 269 5. Elements of procedure 271 The Link-Overload sub-TLV indicates that the link identified by the 272 sub-TLV is overloaded. The node that has the link to be taken out of 273 service SHOULD originate the Link-Overload sub-TLV in the Extended 274 Link TLV in the Extended Link Opaque LSA as defined in [RFC7684] for 275 OSPFv2. The Link-Overload information is carried as a property of 276 the link and is flooded across the area. This information can be 277 used by ingress routers or controllers to take special actions. An 278 application specific to this use case is described in Section 7.2. 280 The precise action taken by the remote node at the other end of the 281 link identified as overloaded depends on the link type. 283 5.1. Point-to-point links 285 The node that has the link to be taken out of service SHOULD set 286 metric of the link to MAX-METRIC (0xffff) and re- originate the 287 Router-LSA. The TE metric SHOULD be set to MAX-TE-METRIC -1 288 (0xfffffffe) and the node SHOULD re-originate the TE Link Opaque 289 LSAs. When a Link-Overload sub-TLV is received for a point-to-point 290 link, the remote node SHOULD identify the local link which 291 corresponds to the overloaded link and set the metric to MAX-METRIC 292 (0xffff)and the remote node SHOULD re-originate the router-LSA with 293 the changed metric. The TE metric SHOULD be set to MAX-TE-METRIC -1 294 (0xfffffffe) and the TE opaque LSA for the link SHOULD be re- 295 originated with new value. 297 Extended link opaque LSAs and the Extended link TLV are not scoped 298 for multi-topology [RFC4915]. In multi-topology deployments 299 [RFC4915], the Link-Overload sub-TLV carried in an Extended Link 300 opaque LSA corresponds to all the topologies the link belongs to. 301 The receiver node SHOULD change the metric in the reverse direction 302 corresponding to all the topologies to which the reverse link belongs 303 and re-originate the Router LSA as defined in [RFC4915]. 305 When the originator of the Link-Overload sub-TLV purges the Extended 306 Link Opaque LSA or re-originates it without the Link-Overload sub- 307 TLV, the remote node must re-originate the appropriate LSAs with the 308 metric and TE metric values set to their original values. 310 5.2. Broadcast/NBMA links 312 Broadcast or NBMA networks in OSPF are represented by a star topology 313 where the Designated Router (DR) is the central point to which all 314 other routers on the broadcast or NBMA network connect logically. As 315 a result, routers on the broadcast or NBMA network advertise only 316 their adjacency to the DR. Routers that do not act as DR do not form 317 or advertise adjacencies with each other. For the Broadcast links, 318 the MAX-METRIC on the remote link cannot be changed since all the 319 neighbours are on same link. Setting the link cost to MAX-METRIC 320 would impact paths going via all neighbours. 322 The node that has the link to be taken out of service SHOULD set 323 metric of the link to MAX-METRIC(0xffff) and re-originate the Router- 324 LSA. The TE metric SHOULD be set to MAX-TE-METRIC -1(0xfffffffe) and 325 the node SHOULD re-originate the TE Link Opaque LSAs. For a 326 broadcast link, the two part metric as described in [RFC8042] is 327 used. The node originating the Link-Overload sub-TLV MUST set the 328 metric in the Network-to-Router Metric sub-TLV to MAX-METRIC 0xffff 329 for OSPFv2 and OSPFv3 and re-originate the LSAs the TLV is carried- 330 in. The nodes that receive the two part metric should follow the 331 procedures described in [RFC8042]. The backward compatibility 332 procedures described in [RFC8042] should be followed to ensure loop 333 free routing. 335 5.3. Point-to-multipoint links 337 Operation for the point-to-multipoint links is similar to the point- 338 to-point links. When a Link-Overload sub-TLV is received for a 339 point-to-multipoint link the remote node SHOULD identify the 340 neighbour which corresponds to the overloaded link and set the metric 341 to MAX-METRIC (0xffff). The remote node MUST re-originate the 342 Router-LSA with the changed metric and flood into the OSPF area. 344 5.4. Unnumbered interfaces 346 Unnumbered interface do not have a unique IP addresses and borrow 347 address from other interfaces. [RFC2328] describes procedures to 348 handle unnumbered interfaces in the context of the Router LSA. We 349 apply a similar procedure to the Extended Link TLV carrying the Link- 350 Overload sub-TLV in to handle unnumbered interfaces. The link-data 351 field in the Extended Link TLV carries the Local interface-id instead 352 of the IP address. The Local/Remote Interface ID sub-TLV MUST be 353 originated when there are multiple parallel unnumbered interfaces 354 between two nodes. Procedures to obtain interface-id of the remote 355 side are defined in [RFC4203]. 357 5.5. Hybrid Broadcast and P2MP interfaces 359 Hybrid Broadcast and P2MP interfaces represent a broadcast network 360 modeled as P2MP interfaces. [RFC6845] describes procedures to handle 361 these interfaces. Operation for the Hybrid interfaces is similar to 362 the P2MP interfaces. When a Link-Overload sub-TLV is received for a 363 hybrid link the remote node SHOULD identify the neighbour which 364 corresponds to the overloaded link and set the metric to MAX-METRIC 365 (0xffff). All the remote nodes connected to originator MUST re- 366 originate the Router-LSA with the changed metric and flood into the 367 OSPF area. 369 6. Backward compatibility 371 The mechanism described in the document is fully backward compatible. 372 It is required that the originator of the Link-Overload sub-TLV as 373 well as the node at the remote end of the link identified as 374 overloaded understand the extensions defined in this document. In 375 the case of broadcast links, the backward compatibility procedures as 376 described in [RFC8042] are applicable. 378 7. Applications 380 7.1. Pseudowire Services 382 Many service providers offer pseudo-wire services to customers using 383 L2 circuits. The IGP protocol that runs in the customer network 384 would also run over the pseudo-wire to create seamless private 385 network for the customer. Service providers want to offer overload 386 kind of functionality when the PE device is taken-out for 387 maintenance. The provider should guarantee that the PE is taken out 388 for maintenance only after the service is successfully diverted on an 389 alternate path. There can be large number of customers attached to a 390 PE node and the remote end-points for these pseudo-wires are spread 391 across the service provider's network. It is a tedious and error- 392 prone process to change the metric for all pseudo-wires in both 393 directions. The link-overload feature simplifies the process by 394 increasing the metric on the link in the reverse direction as well so 395 that traffic in both directions is diverted away from the PE 396 undergoing maintenance. The Link-Overload feature allows the link to 397 be used as a last resort link so that traffic is not disrupted when 398 alternative paths are not available. 400 Private VLAN 401 ======================================= 402 | | 403 | | 404 | ------PE3---------------PE4------CE3 405 | / \ 406 | / \ 407 CE1---------PE1----------PE2---------CE2 408 | \ 409 | \ 410 | ------CE4 411 | | 412 | | 413 | | 414 ================================= 415 Private VLAN 417 Figure 5: Pseudowire Services 419 In the example shown in Figure 5, when the PE1 node is going for 420 maintenance, service providers set the PE1 to overload state. The 421 PE1 going in overload state triggers all the CEs (In this example 422 CE1)connected to the PE to set their pseudowire links passing via PE1 423 to link-overload state. The mechanisms used to communicate between 424 PE1 and CE1 is outside the scope of this document. CE1 sets the 425 link-overload state on its private VLAN connecting CE3, CE2 and CE4 426 and modifies the metric to MAX_METRIC and floods the information, the 427 remote end of the link at CE3, CE2, and CE4 also set the metric on 428 the link to MAX-METRIC and the traffic from both directions gets 429 diverted away from the link. 431 7.2. Controller based Traffic Engineering Deployments 433 In controller-based deployments where the controller participates in 434 the IGP protocol, the controller can also receive the link-overload 435 information as a warning that link maintenance is imminent. Using 436 this information, the controller can find alternate paths for traffic 437 which use the affected link. The controller can apply various 438 policies and re-route the LSPs away from the link undergoing 439 maintenance. If there are no alternate paths satisfying the traffic 440 engineering constraints, the controller might temporarily relax those 441 constraints and put the service on a different path. 443 _____________ 444 | | 445 -------------| Controller |-------------- 446 | |____________ | | 447 | | 448 |--------- Primary Path ------------------| 449 PE1---------P1----------------P2---------PE2 450 | | 451 | | 452 |________P3________| 454 Alternate Path 456 Figure 6: Controller based Traffic Engineering 458 In the above example, PE1->PE2 LSP is set-up to satisfy a constraint 459 of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have 460 only 1 Gbps capacity and there is no alternate path satisfying the 461 bandwidth constraint of 10GB. When P1->P2 link is being prepared for 462 maintenance, the controller receives the link-overload information, 463 as there is no alternate path available which satisfies the 464 constraints, controller chooses a path that is less optimal and 465 temporarily sets up an alternate path via P1->P3->P2. Once the 466 traffic is diverted, the P1->P2 link can be taken out of service for 467 maintenance/upgrade. 469 7.3. L3VPN Services and sham-links 471 Many service providers offer L3VPN services to customers and CE-PE 472 links run OSPF [RFC4577]. When PE goes for maintenance, all the 473 links on the PE can be set to link-overlaod state which will gurantee 474 that the traffic from CEs also gets diverted. The interaction 475 between OSPF and BGP is outside the scope of this document. 477 Another useful usecase is when ISPs provide sham-link services to 478 customers [RFC4577].When PE goes for maintenance, all sham-links on 479 the PE can be set to link-overload state and traffic can be divered 480 from both ends without having to touch the configurations on the 481 remote end of the sham-links. 483 7.4. Hub and spoke deployment 485 OSPF is largely deployed in Hub and Spoke deployments with a number 486 of spokes connecting to the Hub. It is a general practice to deploy 487 multiple Hubs with all spokes connecting to these Hubs to achieve 488 redundancy. When a Hub node goes down for maintenance, all links on 489 the Hub can be set to link-overload state and traffic gets divered 490 from spoke sites as well without having to make configuration changes 491 on the spokes. 493 8. Security Considerations 495 This document does not introduce any further security issues other 496 than those discussed in [RFC2328] and [RFC5340]. 498 9. IANA Considerations 500 This specification updates one OSPF registry: 502 OSPF Extended Link TLVs Registry 504 i) TBD - Link-Overload sub-TLV 506 OSPFV3 Router Link TLV Registry 508 i) TBD - Link-Overload sub-TLV 510 OSPF RI TLV Registry 512 i) TBD - Link-Overload sub-TLV 514 BGP-LS Link NLRI Registry [RFC7752] 516 i)TBD - Link-Overload sub-TLV 518 10. Acknowledgements 520 Thanks to Chris Bowers for valuable inputs and edits to the document. 521 Thanks to Jeffrey Zhang and Acee Lindem for inputs. Thanks to 522 Karsten Thomann for careful review and inputs on the applications 523 where link-overload is useful. 525 11. References 527 11.1. Normative References 529 [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast 530 and Point-to-Multipoint Interface Type", RFC 6845, 531 DOI 10.17487/RFC6845, January 2013, 532 . 534 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 535 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 536 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 537 2015, . 539 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 540 S. Ray, "North-Bound Distribution of Link-State and 541 Traffic Engineering (TE) Information Using BGP", RFC 7752, 542 DOI 10.17487/RFC7752, March 2016, 543 . 545 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 546 S. Shaffer, "Extensions to OSPF for Advertising Optional 547 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 548 February 2016, . 550 [RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part 551 Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016, 552 . 554 11.2. Informative References 556 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 557 Requirement Levels", BCP 14, RFC 2119, 558 DOI 10.17487/RFC2119, March 1997, 559 . 561 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 562 DOI 10.17487/RFC2328, April 1998, 563 . 565 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 566 Support of Generalized Multi-Protocol Label Switching 567 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 568 . 570 [RFC4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the 571 Provider/Customer Edge Protocol for BGP/MPLS IP Virtual 572 Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577, 573 June 2006, . 575 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 576 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 577 RFC 4915, DOI 10.17487/RFC4915, June 2007, 578 . 580 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 581 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 582 . 584 [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. 585 McPherson, "OSPF Stub Router Advertisement", RFC 6987, 586 DOI 10.17487/RFC6987, September 2013, 587 . 589 Authors' Addresses 591 Shraddha Hegde 592 Juniper Networks, Inc. 593 Embassy Business Park 594 Bangalore, KA 560093 595 India 597 Email: shraddha@juniper.net 599 Pushpasis Sarkar 600 Individual 602 Email: pushpasis.ietf@gmail.com 604 Hannes Gredler 605 Individual 607 Email: hannes@gredler.at 609 Mohan Nanduri 610 Microsoft Corporation 611 One Microsoft Way 612 Redmond, WA 98052 613 US 615 Email: mnanduri@microsoft.com 617 Luay Jalil 618 Verizon 620 Email: luay.jalil@verizon.com