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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-23) exists of draft-ietf-ospf-ospfv3-lsa-extend-10 ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 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: July 20, 2018 H. Gredler 6 Individual 7 M. Nanduri 8 ebay Corporation 9 L. Jalil 10 Verizon 11 January 16, 2018 13 OSPF Graceful Link shutdown 14 draft-ietf-ospf-link-overload-12 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 value on one side of the link is not sufficient 21 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 as being in a graceful-shutdown state to 25 indicate impending maintenance activity on the link. This 26 information can be used by the network devices to re-route the 27 traffic effectively. 29 This document describes the protocol extensions to disseminate 30 graceful-link-shutdown information in OSPFv2 and OSPFv3. 32 Requirements Language 34 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 35 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 36 document are to be interpreted as described in RFC 2119 [RFC2119]. 38 Status of This Memo 40 This Internet-Draft is submitted in full conformance with the 41 provisions of BCP 78 and BCP 79. 43 Internet-Drafts are working documents of the Internet Engineering 44 Task Force (IETF). Note that other groups may also distribute 45 working documents as Internet-Drafts. The list of current Internet- 46 Drafts is at https://datatracker.ietf.org/drafts/current/. 48 Internet-Drafts are draft documents valid for a maximum of six months 49 and may be updated, replaced, or obsoleted by other documents at any 50 time. It is inappropriate to use Internet-Drafts as reference 51 material or to cite them other than as "work in progress." 53 This Internet-Draft will expire on July 20, 2018. 55 Copyright Notice 57 Copyright (c) 2018 IETF Trust and the persons identified as the 58 document authors. All rights reserved. 60 This document is subject to BCP 78 and the IETF Trust's Legal 61 Provisions Relating to IETF Documents 62 (https://trustee.ietf.org/license-info) in effect on the date of 63 publication of this document. Please review these documents 64 carefully, as they describe your rights and restrictions with respect 65 to this document. Code Components extracted from this document must 66 include Simplified BSD License text as described in Section 4.e of 67 the Trust Legal Provisions and are provided without warranty as 68 described in the Simplified BSD License. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 73 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3 74 3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4 75 4. Graceful-Link-Shutdown sub-TLV . . . . . . . . . . . . . . . 4 76 4.1. OSPFv2 graceful-link-shutdown sub-TLV . . . . . . . . . . 4 77 4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 5 78 4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 5 79 4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV . . . . . . . . . . 6 80 4.5. BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . . 6 81 4.6. Distinguishing parallel links . . . . . . . . . . . . . . 7 82 5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 8 83 5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 8 84 5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 9 85 5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 9 86 5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 9 87 5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 10 88 6. Backward compatibility . . . . . . . . . . . . . . . . . . . 10 89 7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 10 90 7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 10 91 7.2. Controller based Traffic Engineering Deployments . . . . 11 92 7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 12 93 7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 13 94 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 95 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 96 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 97 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 98 11.1. Normative References . . . . . . . . . . . . . . . . . . 14 99 11.2. Informative References . . . . . . . . . . . . . . . . . 14 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 102 1. Introduction 104 When a node is being prepared for a planned maintenance or upgrade, 105 [RFC6987] provides mechanisms to advertise the node being in a 106 graceful-shutdown state by setting all outgoing link costs to 107 MaxLinkMetric (0xffff). These procedures are specific to the 108 maintenance activity on a node and cannot be used when a single link 109 on the node requires maintenance. 111 In traffic-engineering deployments, LSPs need to be diverted from the 112 link without disrupting the services. [RFC5817] describes 113 requirements and procedures for graceful shutdown of MPLS links. It 114 is useful to be able to advertise the impending maintenance activity 115 on the link and to have LSP re-routing policies at the ingress to 116 route the LSPs away from the link. 118 Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned 119 by means of pseudo-wires or L2-circuits. Prior to devices in the 120 underlying network going offline for maintenance, it is useful to 121 divert the traffic away from the node before the maintenance is 122 actually performed. Since the nodes in the underlying network are 123 not visible to OSPF, the existing stub router mechanism described in 124 [RFC6987] cannot be used. An application specific to this use case 125 is described in Section 7.1. 127 The procedures described in this draft may be used to divert the 128 traffic away from the link in other scenarios and is not restricted 129 to link-shutdown or link-replacement activity. 131 This document provides mechanisms to advertise graceful-link-shutdown 132 state in the flexible encodings provided by OSPFv2 Prefix/Link 133 Attribute Advertisement [RFC7684]. Throughout this document, OSPF is 134 used when the text applies to both OSPFv2 and OSPFv3. OSPFv2 or 135 OSPFv3 is used when the text is specific to one version of the OSPF 136 protocol. 138 2. Motivation 140 The motivation of this document is to reduce manual intervention 141 during maintenance activities. The following objectives help to 142 accomplish this in a range of deployment scenarios. 144 1. Advertise impending maintenance activity so that traffic from 145 both directions can be diverted away from the link. 147 2. Allow the solution to be backward compatible so that nodes that 148 do not understand the new advertisement do not cause routing 149 loops. 151 3. Advertise the maintenance activity to other nodes in the network 152 so that LSP ingress routers/controllers can learn about the 153 impending maintenance activity and apply specific policies to re- 154 route the LSPs for traffic-engineering based deployments. 156 4. Allow the link to be used as last resort link to prevent traffic 157 disruption when alternate paths are not available. 159 3. Flooding Scope 161 The graceful-link-shutdown information is flooded in area-scoped 162 Extended Link Opaque LSA [RFC7684]. The Graceful-Link-Shutdown sub- 163 TLV MAY be processed by the head-end nodes or the controller as 164 described in the Section 7. The procedures for processing the 165 Graceful-Link-Shutdown sub-TLV are described in Section 5. 167 4. Graceful-Link-Shutdown sub-TLV 169 4.1. OSPFv2 graceful-link-shutdown sub-TLV 171 The Graceful-Link-Shutdown sub-TLV identifies the link as being 172 gracefully shutdown. It is advertised in extended Link TLV of the 173 Extended Link Opaque LSA as defined in [RFC7684]. 175 0 1 2 3 176 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 1 177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 178 | Type | Length | 179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 Figure 1: Graceful-Link-Shutdown sub-TLV for OSPFv2 183 Type : TBA (suggested value 7) 185 Length: 0 187 4.2. Remote IPv4 Address Sub-TLV 189 This sub-TLV specifies the IPv4 address of remote endpoint on the 190 link. It is advertised in the Extended Link TLV as defined in 191 [RFC7684]. This sub-TLV is optional and MAY be advertised in area- 192 scoped Extended Link Opaque LSA to identify the link when there are 193 multiple parallel links between two nodes. 195 0 1 2 3 196 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 1 197 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 198 | Type | Length | 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 | Remote IPv4 address | 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 203 Figure 2: Remote IPv4 Address Sub-TLV 205 Type : TBA (suggested value 8) 207 Length: 4 209 Value: Remote IPv4 address. The remote IP4 address is used to 210 identify the particular link when there are multiple parallel links 211 between two nodes. 213 4.3. Local/Remote Interface ID Sub-TLV 215 This sub-TLV specifies local and remote interface identifiers. It is 216 advertised in the Extended Link TLV as defined in [RFC7684]. This 217 sub-TLV is optional and MAY be advertised in area-scoped Extended 218 Link Opaque LSA to identify the link when there are multiple parallel 219 unnumbered links between two nodes. The local interface-id is 220 generally readily available. One of the mechanisms to obtain remote 221 interface-id is described in [RFC4203]. 223 0 1 2 3 224 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 1 225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 226 | Type | Length | 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 228 | Local Interface ID | 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | Remote Interface ID | 231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 Figure 3: Local/Remote Interface ID Sub-TLV 235 Type : TBA (suggested value 9) 237 Length: 8 239 Value: 4 octets of Local Interface ID followed by 4 octets of Remote 240 interface ID. 242 4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV 244 The Graceful-Link-Shutdown sub-TLV is carried in the Router-Link TLV 245 as defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The 246 Router-Link TLV contains the neighbour interface-id and can uniquely 247 identify the link on the remote node. 249 0 1 2 3 250 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 1 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 | Type | Length | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 Figure 4: Graceful-Link-Shutdown sub-TLV for OSPFv3 257 Type : TBA (Suggested value 7) 259 Length: 0 261 4.5. BGP-LS Graceful-Link-Shutdown TLV 263 BGP-LS as defined in [RFC7752] is a mechanism to distribute network 264 information to external entities using BGP routing protocol. 265 Graceful-link-shutdown is an imporatant link information that the 266 external entities can use for various use cases as defined in 267 Section 7. BGP Link NLRI is used to carry the link information. A 268 new TLV called Graceful-Link-Shutdown is defined to describe the link 269 attribute corresponding to graceful-link-shutdown state. 271 4.6. Distinguishing parallel links 273 ++++++++++I.w I.y +++++++++ 274 |Router A|------------------|Router B | 275 | |------------------| | 276 ++++++++++I.x I.z++++++++++ 278 Figure 5: Parallel Linkls 280 Consider two routers A and B connected with two parallel point-to- 281 point interfaces. I.w and I.x represent the Interface address on 282 Router A's side and I.y and I.z represent Interface addresses on 283 Router B's side. The extended link opaque LSA as described in 284 [RFC7684] describes links using link-type, Link-ID and Link-data. 285 For ex. Link with address I.w is described as below on Router A. 287 Link-type = Point-to-point 289 Link-ID: Router-ID B 291 Link-Data = I.w 293 A third node (controller or head-end) in the network cannot 294 distinguish the Interface on router B which is connected to this 295 particular Interface with the above information. Interface with 296 address I.y or I.z could be chosen due to this ambiguity. In such 297 cases Remote-IPv4 Address sub-TLV should be originated and added to 298 the extended link-TLV. The use cases as described in Section 7 299 require controller or head-end nodes to interpret the graceful-link- 300 shutdown information and hence the need for the RemoteIPv4 address 301 sub-TLV. I.y is carried in the extended-link-TLV which unambiguously 302 identifies the interface on the remote side. OSPFv3 Router-link-TLV 303 as described in [I-D.ietf-ospf-ospfv3-lsa-extend] contains Interface 304 ID and neighbor's Interface-ID which can uniquely identify connecting 305 interface on the remote side and hence OSPFv3 does not require 306 seperate Remote-IPv6 address to be advertised along with OSPFv3- 307 Graceful-Link-Shutdown sub-TLV. 309 5. Elements of procedure 311 As defined in [RFC7684] every link on the node will have a separate 312 Extended Link Opaque LSA. The node that has the link to be taken out 313 of service SHOULD advertise the Graceful-Link-Shutdown sub-TLV in the 314 Extended Link TLV of the Extended Link Opaque LSA as defined in 315 [RFC7684] for OSPFv2. The Graceful-Link-Shutdown sub-TLV indicates 316 that the link identified by the sub-TLV is subjected to maintenance. 317 The Graceful-Link-Shutdown information is advertised as a property of 318 the link and is flooded across the area. This information can be 319 used by ingress routers or controllers to take special actions. An 320 application specific to this use case is described in Section 7.2. 322 The precise action taken by the remote node at the other end of the 323 link identified for graceful-shutdown depends on the link type. 325 5.1. Point-to-point links 327 The node that has the link to be taken out of service MUST set metric 328 of the link to MaxLinkMetric (0xffff) and re-originate its router- 329 LSA. MAX-TE-METRIC is a constant defined by this draft and set to 330 0xfffffffe. The TE metric SHOULD be set to MAX-TE-METRIC 331 (0xfffffffe) and the node SHOULD re-originate the corresponding TE 332 Link Opaque LSAs. When a Graceful-Link-Shutdown sub-TLV is received 333 for a point-to-point link, the remote node MUST identify the local 334 link which corresponds to the graceful-shutdown link and set the 335 metric to MaxLinkMetric (0xffff) and the remote node MUST re- 336 originate its router-LSA with the changed metric. The TE metric 337 SHOULD be set to MAX-TE-METRIC (0xfffffffe) and the TE opaque LSA for 338 the link SHOULD be re-originated with new value. 340 The Extended link opaque LSAs and the Extended link TLV are not 341 scoped for multi-topology [RFC4915]. In multi-topology deployments 342 [RFC4915], the Graceful-Link-Shutdown sub-TLV advertised in an 343 Extended Link opaque LSA corresponds to all the topologies which 344 include the link. The receiver node SHOULD change the metric in the 345 reverse direction for all the topologies which include the remote 346 link and re-originate the router-LSA as defined in [RFC4915]. 348 When the originator of the Graceful-Link-Shutdown sub-TLV purges the 349 Extended Link Opaque LSA or re-originates it without the Graceful- 350 Link-Shutdown sub-TLV, the remote node must re-originate the 351 appropriate LSAs with the metric and TE metric values set to their 352 original values. 354 5.2. Broadcast/NBMA links 356 Broadcast or NBMA networks in OSPF are represented by a star topology 357 where the Designated Router (DR) is the central point to which all 358 other routers on the broadcast or NBMA network logically connect. As 359 a result, routers on the broadcast or NBMA network advertise only 360 their adjacency to the DR. Routers that do not act as DR do not form 361 or advertise adjacencies with each other. For the Broadcast links, 362 the MaxLinkMetric on the remote link cannot be changed since all the 363 neighbors are on same link. Setting the link cost to MaxLinkMetric 364 would impact paths going via all neighbors. 366 The node that has the link to be taken out of service MUST set metric 367 of the link to MaxLinkMetric (0xffff) and re-originate the Router- 368 LSA. The TE metric SHOULD be set to MAX-TE-METRIC( 0xfffffffe) and 369 the node SHOULD re-originate the corresponding TE Link Opaque LSAs. 370 For a broadcast link, the two part metric as described in [RFC8042] 371 is used. The node originating the Graceful-Link-Shutdown sub-TLV 372 MUST set the metric in the Network-to-Router Metric sub-TLV to 373 MaxLinkMetric (0xffff) for OSPFv2 and OSPFv3 and re-originate the 374 corresponding LSAs. The nodes that receive the two-part metric 375 should follow the procedures described in [RFC8042]. The backward 376 compatibility procedures described in [RFC8042] should be followed to 377 ensure loop free routing. 379 5.3. Point-to-multipoint links 381 Operation for the point-to-multipoint links is similar to the point- 382 to-point links. When a Graceful-Link-Shutdown sub-TLV is received 383 for a point-to-multipoint link the remote node MUST identify the 384 neighbour which corresponds to the graceful-shutdown link and set the 385 metric to MaxLinkMetric (0xffff). The remote node MUST re-originate 386 the router-LSA with the changed metric for the correponding neighbor. 388 5.4. Unnumbered interfaces 390 Unnumbered interface do not have a unique IP address and borrow their 391 address from other interfaces. [RFC2328] describes procedures to 392 handle unnumbered interfaces in the context of the router-LSA. We 393 apply a similar procedure to the Extended Link TLV advertising the 394 Graceful-Link-Shutdown sub-TLV in order to handle unnumbered 395 interfaces. The link-data field in the Extended Link TLV includes 396 the Local interface-id instead of the IP address. The Local/Remote 397 Interface ID sub-TLV MUST be advertised when there are multiple 398 parallel unnumbered interfaces between two nodes. One of the 399 mechanisms to obtain the interface-id of the remote side are defined 400 in [RFC4203]. 402 5.5. Hybrid Broadcast and P2MP interfaces 404 Hybrid Broadcast and P2MP interfaces represent a broadcast network 405 modeled as P2MP interfaces. [RFC6845] describes procedures to handle 406 these interfaces. Operation for the Hybrid interfaces is similar to 407 the P2MP interfaces. When a Graceful-Link-Shutdown sub-TLV is 408 received for a hybrid link, the remote node MUST identify the 409 neighbor which corresponds to the graceful-shutdown link and set the 410 metric to MaxLinkMetric (0xffff). All the remote nodes connected to 411 originator MUST re-originate the router-LSA with the changed metric 412 for the neighbor. 414 6. Backward compatibility 416 The mechanisms described in the document are fully backward 417 compatible. It is required that the node adverting the Graceful- 418 Link-Shutdown sub-TLV as well as the node at the remote end of the 419 graceful-shutdown link support the extensions described herein for 420 the traffic to diverted from the graceful-shutdown link. If the 421 remote node doesn't support the capability, it will still use the 422 graceful-shutdown link but there are no other adverse effects. In 423 the case of broadcast links using two-part metrics, the backward 424 compatibility procedures as described in [RFC8042] are applicable. 426 7. Applications 428 7.1. Pseudowire Services 430 Many service providers offer pseudo-wire services to customers using 431 L2 circuits. The IGP protocol that runs in the customer network 432 would also run over the pseudo-wire to create a seamless private 433 network for the customer. Service providers want to offer graceful- 434 shutdown functionality when the PE device is taken-out for 435 maintenance. The provider should guarantee that the PE is taken out 436 for maintenance only after the service is successfully diverted on an 437 alternate path. There can be large number of customers attached to a 438 PE node and the remote end-points for these pseudo-wires are spread 439 across the service provider's network. It is a tedious and error- 440 prone process to change the metric for all pseudo-wires in both 441 directions. The graceful-link-shutdown feature simplifies the 442 process by increasing the metric on the link in the reverse direction 443 as well so that traffic in both directions is diverted away from the 444 PE undergoing maintenance. The Graceful-Link-Shutdown feature allows 445 the link to be used as a last resort link so that traffic is not 446 disrupted when alternative paths are not available. 448 Private VLAN 449 ======================================= 450 | | 451 | | 452 | ------PE3---------------PE4------CE3 453 | / \ 454 | / \ 455 CE1---------PE1----------PE2---------CE2 456 | \ 457 | \ 458 | ------CE4 459 | | 460 | | 461 | | 462 ================================= 463 Private VLAN 465 Figure 6: Pseudowire Services 467 In the example shown in Figure 6, when the PE1 node is going out of 468 service for maintenance, service providers set the PE1 to graceful- 469 link-shutdown state. The PE1 going in to maintenance state triggers 470 all the CEs connected to the PE (CE1 in this case) to set their 471 pseudowire links passing via PE1 to graceful-link-shutdown state. 472 The mechanisms used to communicate between PE1 and CE1 is outside the 473 scope of this document. CE1 sets the graceful-link-shutdown state on 474 its private VLAN connecting CE3, CE2 and CE4 and changes the metric 475 to MAX_METRIC and re-originates the corresponding LSA. The remote 476 end of the link at CE3, CE2, and CE4 also set the metric on the link 477 to MaxLinkMetric and the traffic from both directions gets diverted 478 away from the pseudowires. 480 7.2. Controller based Traffic Engineering Deployments 482 In controller-based deployments where the controller participates in 483 the IGP protocol, the controller can also receive the graceful-link- 484 shutdown information as a warning that link maintenance is imminent. 485 Using this information, the controller can find alternate paths for 486 traffic which uses the affected link. The controller can apply 487 various policies and re-route the LSPs away from the link undergoing 488 maintenance. If there are no alternate paths satisfying the traffic 489 engineering constraints, the controller might temporarily relax those 490 constraints and put the service on a different path. Increasing the 491 link metric alone does not specify the maintenance activity as the 492 metric could increase in events such as LDP-IGP synchronisation. An 493 explicit indication from the router using the graceful-link-shutdown 494 sub-TLV is needed to inform the Controller or head-end routers. 496 _____________ 497 | | 498 -------------| Controller |-------------- 499 | |____________ | | 500 | | 501 |--------- Primary Path ------------------| 502 PE1---------P1----------------P2---------PE2 503 | | 504 | | 505 |________P3________| 507 Alternate Path 509 Figure 7: Controller based Traffic Engineering 511 In the above example, PE1->PE2 LSP is set-up to satisfy a constraint 512 of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have 513 only 1 Gbps capacity and there is no alternate path satisfying the 514 bandwidth constraint of 10Gbps. When P1->P2 link is being prepared 515 for maintenance, the controller receives the graceful-link-shutdown 516 information, as there is no alternate path available which satisfies 517 the constraints, the controller chooses a path that is less optimal 518 and temporarily sets up an alternate path via P1->P3->P2. Once the 519 traffic is diverted, the P1->P2 link can be taken out of service for 520 maintenance/upgrade. 522 7.3. L3VPN Services and sham-links 524 Many service providers offer L3VPN services to customers and CE-PE 525 links run OSPF [RFC4577]. When PE is taken out of service for 526 maintenance, all the links on the PE can be set to graceful-link- 527 shutdown state which will gurantee that the traffic to/from dual- 528 homed CEs gets diverted. The interaction between OSPF and BGP is 529 outside the scope of this document. [RFC6987] based mechanism with 530 summaries and externals advertised with high metrics could also be 531 used to achieve the same functionality when implementations support 532 high metrics advertisement for summaries and externals. 534 Another useful usecase is when ISPs provide sham-link services to 535 customers [RFC4577]. When PE goes out of service for maintenance, 536 all sham-links on the PE can be set to graceful-link-shutdown state 537 and traffic can be divered from both ends without having to touch the 538 configurations on the remote end of the sham-links. 540 7.4. Hub and spoke deployment 542 OSPF is largely deployed in Hub and Spoke deployments with a large 543 number of spokes connecting to the Hub. It is a general practice to 544 deploy multiple Hubs with all spokes connecting to these Hubs to 545 achieve redundancy. The [RFC6987] mechanism can be used to divert 546 the spoke-to-spoke traffic from the overloaded hub router. The 547 traffic that flows from spokes via the hub into an external network 548 may not be diverted in certain scenarios.When a Hub node goes down 549 for maintenance, all links on the Hub can be set to graceful-link- 550 shutdown state and traffic gets divered from the spoke sites as well 551 without having to make configuration changes on the spokes. 553 8. Security Considerations 555 This document does not introduce any further security issues other 556 than those discussed in [RFC2328] and [RFC5340]. 558 9. IANA Considerations 560 This specification updates one OSPF registry: 562 OSPFv2 Extended Link TLV Sub-TLVs 564 i) Graceful-Link-Shutdown Sub-TLV - Suggested value 7 566 ii) Remote IPv4 Address Sub-TLV - Suggested value 8 568 iii) Local/Remote Interface ID Sub-TLV - Suggested Value 9 570 OSPFv3 Extended-LSA sub-TLV Registry 572 i) Graceful-Link-Shutdown sub-TLV - suggested value 7 574 BGP-LS Link NLRI Registry [RFC7752] 576 i)Graceful-Link-Shutdown TLV - Suggested 1101 578 10. Acknowledgements 580 Thanks to Chris Bowers for valuable inputs and edits to the document. 581 Thanks to Jeffrey Zhang, Acee Lindem and Ketan Talaulikar for inputs. 582 Thanks to Karsten Thomann for careful review and inputs on the 583 applications where graceful-link-shutdown is useful. 585 11. References 587 11.1. Normative References 589 [I-D.ietf-ospf-ospfv3-lsa-extend] 590 Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 591 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-10 592 (work in progress), May 2016. 594 [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast 595 and Point-to-Multipoint Interface Type", RFC 6845, 596 DOI 10.17487/RFC6845, January 2013, 597 . 599 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 600 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 601 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 602 2015, . 604 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 605 S. Ray, "North-Bound Distribution of Link-State and 606 Traffic Engineering (TE) Information Using BGP", RFC 7752, 607 DOI 10.17487/RFC7752, March 2016, 608 . 610 [RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part 611 Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016, 612 . 614 11.2. Informative References 616 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 617 Requirement Levels", BCP 14, RFC 2119, 618 DOI 10.17487/RFC2119, March 1997, 619 . 621 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 622 DOI 10.17487/RFC2328, April 1998, 623 . 625 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 626 Support of Generalized Multi-Protocol Label Switching 627 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 628 . 630 [RFC4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the 631 Provider/Customer Edge Protocol for BGP/MPLS IP Virtual 632 Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577, 633 June 2006, . 635 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 636 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 637 RFC 4915, DOI 10.17487/RFC4915, June 2007, 638 . 640 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 641 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 642 . 644 [RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton, 645 "Graceful Shutdown in MPLS and Generalized MPLS Traffic 646 Engineering Networks", RFC 5817, DOI 10.17487/RFC5817, 647 April 2010, . 649 [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. 650 McPherson, "OSPF Stub Router Advertisement", RFC 6987, 651 DOI 10.17487/RFC6987, September 2013, 652 . 654 Authors' Addresses 656 Shraddha Hegde 657 Juniper Networks, Inc. 658 Embassy Business Park 659 Bangalore, KA 560093 660 India 662 Email: shraddha@juniper.net 664 Pushpasis Sarkar 665 Individual 667 Email: pushpasis.ietf@gmail.com 669 Hannes Gredler 670 Individual 672 Email: hannes@gredler.at 673 Mohan Nanduri 674 ebay Corporation 675 2025 Hamilton Avenue 676 San Jose, CA 98052 677 US 679 Email: mnanduri@ebay.com 681 Luay Jalil 682 Verizon 684 Email: luay.jalil@verizon.com