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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-23) exists of draft-ietf-ospf-ospfv3-lsa-extend-10 ** Downref: Normative reference to an Informational RFC: RFC 6987 ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) Summary: 2 errors (**), 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 28, 2018 Arrcus Inc. 6 H. Gredler 7 Individual 8 M. Nanduri 9 ebay Corporation 10 L. Jalil 11 Verizon 12 January 24, 2018 14 OSPF Graceful Link shutdown 15 draft-ietf-ospf-link-overload-14 17 Abstract 19 When a link is being prepared to be taken out of service, the traffic 20 needs to be diverted from both ends of the link. Increasing the 21 metric to the highest value on one side of the link is not sufficient 22 to divert the traffic flowing in the other direction. 24 It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be 25 able to advertise a link as being in a graceful-shutdown state to 26 indicate impending maintenance activity on the link. This 27 information can be used by the network devices to re-route the 28 traffic effectively. 30 This document describes the protocol extensions to disseminate 31 graceful-link-shutdown information in OSPFv2 and OSPFv3. 33 Requirements Language 35 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 36 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 37 document are to be interpreted as described in RFC 2119 [RFC2119]. 39 Status of This Memo 41 This Internet-Draft is submitted in full conformance with the 42 provisions of BCP 78 and BCP 79. 44 Internet-Drafts are working documents of the Internet Engineering 45 Task Force (IETF). Note that other groups may also distribute 46 working documents as Internet-Drafts. The list of current Internet- 47 Drafts is at https://datatracker.ietf.org/drafts/current/. 49 Internet-Drafts are draft documents valid for a maximum of six months 50 and may be updated, replaced, or obsoleted by other documents at any 51 time. It is inappropriate to use Internet-Drafts as reference 52 material or to cite them other than as "work in progress." 54 This Internet-Draft will expire on July 28, 2018. 56 Copyright Notice 58 Copyright (c) 2018 IETF Trust and the persons identified as the 59 document authors. All rights reserved. 61 This document is subject to BCP 78 and the IETF Trust's Legal 62 Provisions Relating to IETF Documents 63 (https://trustee.ietf.org/license-info) in effect on the date of 64 publication of this document. Please review these documents 65 carefully, as they describe your rights and restrictions with respect 66 to this document. Code Components extracted from this document must 67 include Simplified BSD License text as described in Section 4.e of 68 the Trust Legal Provisions and are provided without warranty as 69 described in the Simplified BSD License. 71 Table of Contents 73 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 74 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4 75 3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4 76 4. Graceful-Link-Shutdown sub-TLV . . . . . . . . . . . . . . . 4 77 4.1. OSPFv2 graceful-link-shutdown sub-TLV . . . . . . . . . . 4 78 4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 5 79 4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 6 80 4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV . . . . . . . . . . 6 81 4.5. BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . . 7 82 4.6. Distinguishing parallel links . . . . . . . . . . . . . . 7 83 5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 8 84 5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 8 85 5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 9 86 5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 9 87 5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 10 88 5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 10 89 6. Maximum TE Metric . . . . . . . . . . . . . . . . . . . . . . 10 90 7. Backward compatibility . . . . . . . . . . . . . . . . . . . 10 91 8. Applications . . . . . . . . . . . . . . . . . . . . . . . . 11 92 8.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 11 93 8.2. Controller based Traffic Engineering Deployments . . . . 12 94 8.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 13 95 8.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 13 96 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 97 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 98 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 99 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 100 12.1. Normative References . . . . . . . . . . . . . . . . . . 14 101 12.2. Informative References . . . . . . . . . . . . . . . . . 15 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 104 1. Introduction 106 When a node is being prepared for a planned maintenance or upgrade, 107 [RFC6987] provides mechanisms to advertise the node being in a 108 graceful-shutdown state by setting all outgoing link costs to 109 MaxLinkMetric (0xffff). These procedures are specific to the 110 maintenance activity on a node and cannot be used when a single link 111 on the node requires maintenance. 113 In traffic-engineering deployments, LSPs need to be diverted from the 114 link without disrupting the services. [RFC5817] describes 115 requirements and procedures for graceful shutdown of MPLS links. It 116 is useful to be able to advertise the impending maintenance activity 117 on the link and to have LSP re-routing policies at the ingress to 118 route the LSPs away from the link. 120 Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned 121 by means of pseudo-wires or L2-circuits. Prior to devices in the 122 underlying network going offline for maintenance, it is useful to 123 divert the traffic away from the node before the maintenance is 124 actually performed. Since the nodes in the underlying network are 125 not visible to OSPF, the existing stub router mechanism described in 126 [RFC6987] cannot be used. In a service provider's network, there may 127 be many CE-to-CE connections that run over a single PE. It is 128 cumbersome to change the metric on every CE-to-CE connection in both 129 directions. This document provides a mechanism to change metric in 130 other direction of the link and also use the link as a last-resort- 131 link if no alternate paths are available. An application specific to 132 this use case is described in detail in Section 8.1. 134 The procedures described in this draft may be used to divert the 135 traffic away from the link in other scenarios and is not restricted 136 to link-shutdown or link-replacement activity. 138 This document provides mechanisms to advertise graceful-link-shutdown 139 state in the flexible encodings provided by OSPFv2 Prefix/Link 140 Attribute Advertisement [RFC7684]. Throughout this document, OSPF is 141 used when the text applies to both OSPFv2 and OSPFv3. OSPFv2 or 142 OSPFv3 is used when the text is specific to one version of the OSPF 143 protocol. 145 2. Motivation 147 The motivation of this document is to reduce manual intervention 148 during maintenance activities. The following objectives help to 149 accomplish this in a range of deployment scenarios. 151 1. Advertise impending maintenance activity so that traffic from 152 both directions can be diverted away from the link. 154 2. Allow the solution to be backward compatible so that nodes that 155 do not understand the new advertisement do not cause routing 156 loops. 158 3. Advertise the maintenance activity to other nodes in the network 159 so that LSP ingress routers/controllers can learn about the 160 impending maintenance activity and apply specific policies to re- 161 route the LSPs for traffic-engineering based deployments. 163 4. Allow the link to be used as last resort link to prevent traffic 164 disruption when alternate paths are not available. 166 3. Flooding Scope 168 The graceful-link-shutdown information is flooded in area-scoped 169 Extended Link Opaque LSA [RFC7684] for OSPFv2 and E-Router-LSA for 170 OSPFv3 [I-D.ietf-ospf-ospfv3-lsa-extend]. The Graceful-Link-Shutdown 171 sub-TLV MAY be processed by the head-end nodes or the controller as 172 described in the Section 8. The procedures for processing the 173 Graceful-Link-Shutdown sub-TLV are described in Section 5. 175 4. Graceful-Link-Shutdown sub-TLV 177 4.1. OSPFv2 graceful-link-shutdown sub-TLV 179 The Graceful-Link-Shutdown sub-TLV identifies the link as being 180 gracefully shutdown. It is advertised in extended Link TLV of the 181 Extended Link Opaque LSA as defined in [RFC7684]. 183 0 1 2 3 184 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 1 185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 186 | Type | Length | 187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 Figure 1: Graceful-Link-Shutdown sub-TLV for OSPFv2 191 Type : TBA (suggested value 7) 193 Length: 0 195 4.2. Remote IPv4 Address Sub-TLV 197 This sub-TLV specifies the IPv4 address of remote endpoint on the 198 link. It is advertised in the Extended Link TLV as defined in 199 [RFC7684]. This sub-TLV is optional and MAY be advertised in area- 200 scoped Extended Link Opaque LSA to identify the link when there are 201 multiple parallel links between two nodes. 203 0 1 2 3 204 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 1 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 206 | Type | Length | 207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 208 | Remote IPv4 address | 209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 211 Figure 2: Remote IPv4 Address Sub-TLV 213 Type : TBA (suggested value 8) 215 Length: 4 217 Value: Remote IPv4 address. The remote IP4 address is used to 218 identify the particular link when there are multiple parallel links 219 between two nodes. 221 4.3. Local/Remote Interface ID Sub-TLV 223 This sub-TLV specifies local and remote interface identifiers. It is 224 advertised in the Extended Link TLV as defined in [RFC7684]. This 225 sub-TLV is optional and MAY be advertised in area-scoped Extended 226 Link Opaque LSA to identify the link when there are multiple parallel 227 unnumbered links between two nodes. The local interface-id is 228 generally readily available. One of the mechanisms to obtain remote 229 interface-id is described 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 9) 245 Length: 8 247 Value: 4 octets of Local Interface ID followed by 4 octets of Remote 248 interface ID. 250 4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV 252 The Graceful-Link-Shutdown sub-TLV is carried in the Router-Link TLV 253 as defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The 254 Router-Link TLV contains the neighbour interface-id and can uniquely 255 identify the link on the remote node. 257 0 1 2 3 258 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 1 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 | Type | Length | 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 263 Figure 4: Graceful-Link-Shutdown sub-TLV for OSPFv3 265 Type : TBA (Suggested value 7) 267 Length: 0 269 4.5. BGP-LS Graceful-Link-Shutdown TLV 271 BGP-LS as defined in [RFC7752] is a mechanism to distribute network 272 information to external entities using BGP routing protocol. 273 Graceful-link-shutdown is an imporatant link information that the 274 external entities can use for various use cases as defined in 275 Section 8. BGP Link NLRI is used to carry the link information. A 276 new TLV called Graceful-Link-Shutdown is defined to describe the link 277 attribute corresponding to graceful-link-shutdown state. The TLV 278 format is as described in [RFC7752] sec 3.1. There is no value field 279 and length field is set to zero for this TLV. 281 4.6. Distinguishing parallel links 283 ++++++++++I.w I.y +++++++++ 284 |Router A|------------------|Router B | 285 | |------------------| | 286 ++++++++++I.x I.z++++++++++ 288 Figure 5: Parallel Linkls 290 Consider two routers A and B connected with two parallel point-to- 291 point interfaces. I.w and I.x represent the Interface address on 292 Router A's side and I.y and I.z represent Interface addresses on 293 Router B's side. The extended link opaque LSA as described in 294 [RFC7684] describes links using link-type, Link-ID and Link-data. 295 For ex. Link with address I.w is described as below on Router A. 297 Link-type = Point-to-point 299 Link-ID: Router-ID B 301 Link-Data = I.w 303 A third node (controller or head-end) in the network cannot 304 distinguish the Interface on router B which is connected to this 305 particular Interface with the above information. Interface with 306 address I.y or I.z could be chosen due to this ambiguity. In such 307 cases Remote-IPv4 Address sub-TLV should be originated and added to 308 the extended link-TLV. The use cases as described in Section 8 309 require controller or head-end nodes to interpret the graceful-link- 310 shutdown information and hence the need for the RemoteIPv4 address 311 sub-TLV. I.y is carried in the extended-link-TLV which unambiguously 312 identifies the interface on the remote side. OSPFv3 Router-link-TLV 313 as described in [I-D.ietf-ospf-ospfv3-lsa-extend] contains Interface 314 ID and neighbor's Interface-ID which can uniquely identify connecting 315 interface on the remote side and hence OSPFv3 does not require 316 seperate Remote-IPv6 address to be advertised along with OSPFv3- 317 Graceful-Link-Shutdown sub-TLV. 319 5. Elements of procedure 321 As defined in [RFC7684] every link on the node will have a separate 322 Extended Link Opaque LSA. The node that has the link to be taken out 323 of service MUST advertise the Graceful-Link-Shutdown sub-TLV in the 324 Extended Link TLV of the Extended Link Opaque LSA as defined in 325 [RFC7684] for OSPFv2 and Router-Link TLV of E-Router-LSA for OSPFv3. 326 The Graceful-Link-Shutdown sub-TLV indicates that the link identified 327 by the sub-TLV is subjected to maintenance. The Graceful-Link- 328 Shutdown information is advertised as a property of the link and is 329 flooded across the area. This information can be used by ingress 330 routers or controllers to take special actions. An application 331 specific to this use case is described in Section 8.2. 333 The precise action taken by the remote node at the other end of the 334 link identified for graceful-shutdown depends on the link type. 336 5.1. Point-to-point links 338 The node that has the link to be taken out of service MUST set metric 339 of the link to MaxLinkMetric (0xffff) and re-originate its router- 340 LSA. MAX-TE-METRIC (0xfffffffe). The TE metric SHOULD be set to 341 MAX-TE-METRIC (0xfffffffe) and the node SHOULD re-originate the 342 corresponding TE Link Opaque LSAs. When a Graceful-Link-Shutdown 343 sub-TLV is received for a point-to-point link, the remote node MUST 344 identify the local link which corresponds to the graceful-shutdown 345 link and set the metric to MaxLinkMetric (0xffff) and the remote node 346 MUST re-originate its router-LSA with the changed metric. The TE 347 metric SHOULD be set to MAX-TE-METRIC (0xfffffffe) and the TE opaque 348 LSA for the link SHOULD be re-originated with new value. 350 The Extended link opaque LSAs and the Extended link TLV are not 351 scoped for multi-topology [RFC4915]. In multi-topology deployments 352 [RFC4915], the Graceful-Link-Shutdown sub-TLV advertised in an 353 Extended Link opaque LSA corresponds to all the topologies which 354 include the link. The receiver node SHOULD change the metric in the 355 reverse direction for all the topologies which include the remote 356 link and re-originate the router-LSA as defined in [RFC4915]. 358 When the originator of the Graceful-Link-Shutdown sub-TLV purges the 359 Extended Link Opaque LSA or re-originates it without the Graceful- 360 Link-Shutdown sub-TLV, the remote node must re-originate the 361 appropriate LSAs with the metric and TE metric values set to their 362 original values. 364 5.2. Broadcast/NBMA links 366 Broadcast or NBMA networks in OSPF are represented by a star topology 367 where the Designated Router (DR) is the central point to which all 368 other routers on the broadcast or NBMA network logically connect. As 369 a result, routers on the broadcast or NBMA network advertise only 370 their adjacency to the DR. Routers that do not act as DR do not form 371 or advertise adjacencies with each other. For the Broadcast links, 372 the MaxLinkMetric on the remote link cannot be changed since all the 373 neighbors are on same link. Setting the link cost to MaxLinkMetric 374 would impact paths going via all neighbors. 376 The node that has the link to be taken out of service MUST set metric 377 of the link to MaxLinkMetric (0xffff) and re-originate the Router- 378 LSA. The TE metric SHOULD be set to MAX-TE-METRIC( 0xfffffffe) and 379 the node SHOULD re-originate the corresponding TE Link Opaque LSAs. 380 For a broadcast link, the two part metric as described in [RFC8042] 381 is used. The node originating the Graceful-Link-Shutdown sub-TLV 382 MUST set the metric in the Network-to-Router Metric sub-TLV to 383 MaxLinkMetric (0xffff) for OSPFv2 and OSPFv3 and re-originate the 384 corresponding LSAs. The nodes that receive the two-part metric 385 should follow the procedures described in [RFC8042]. The backward 386 compatibility procedures described in [RFC8042] should be followed to 387 ensure loop free routing. 389 5.3. Point-to-multipoint links 391 Operation for the point-to-multipoint links is similar to the point- 392 to-point links. When a Graceful-Link-Shutdown sub-TLV is received 393 for a point-to-multipoint link the remote node MUST identify the 394 neighbour which corresponds to the graceful-shutdown link and set the 395 metric to MaxLinkMetric (0xffff). The remote node MUST re-originate 396 the router-LSA with the changed metric for the correponding neighbor. 398 5.4. Unnumbered interfaces 400 Unnumbered interface do not have a unique IP address and borrow their 401 address from other interfaces. [RFC2328] describes procedures to 402 handle unnumbered interfaces in the context of the router-LSA. We 403 apply a similar procedure to the Extended Link TLV advertising the 404 Graceful-Link-Shutdown sub-TLV in order to handle unnumbered 405 interfaces. The link-data field in the Extended Link TLV includes 406 the Local interface-id instead of the IP address. The Local/Remote 407 Interface ID sub-TLV MUST be advertised when there are multiple 408 parallel unnumbered interfaces between two nodes. One of the 409 mechanisms to obtain the interface-id of the remote side are defined 410 in [RFC4203]. 412 5.5. Hybrid Broadcast and P2MP interfaces 414 Hybrid Broadcast and P2MP interfaces represent a broadcast network 415 modeled as P2MP interfaces. [RFC6845] describes procedures to handle 416 these interfaces. Operation for the Hybrid interfaces is similar to 417 the P2MP interfaces. When a Graceful-Link-Shutdown sub-TLV is 418 received for a hybrid link, the remote node MUST identify the 419 neighbor which corresponds to the graceful-shutdown link and set the 420 metric to MaxLinkMetric (0xffff). All the remote nodes connected to 421 originator MUST re-originate the router-LSA with the changed metric 422 for the neighbor. 424 6. Maximum TE Metric 426 MAX-TE-METRIC is a new fixed architectural value introduced in this 427 document. 429 The metric value indicates that a link with this metric should be 430 used as a last-resort link to carry the traffic. It is defined to be 431 of value 0xfffffffe. 433 7. Backward compatibility 435 The mechanisms described in the document are fully backward 436 compatible. It is required that the node adverting the Graceful- 437 Link-Shutdown sub-TLV as well as the node at the remote end of the 438 graceful-shutdown link support the extensions described herein for 439 the traffic to diverted from the graceful-shutdown link. If the 440 remote node doesn't support the capability, it will still use the 441 graceful-shutdown link but there are no other adverse effects. In 442 the case of broadcast links using two-part metrics, the backward 443 compatibility procedures as described in [RFC8042] are applicable. 445 8. Applications 447 8.1. Pseudowire Services 449 Many service providers offer pseudo-wire services to customers using 450 L2 circuits. The IGP protocol that runs in the customer network 451 would also run over the pseudo-wire to create a seamless private 452 network for the customer. Service providers want to offer graceful- 453 shutdown functionality when the PE device is taken-out for 454 maintenance. The provider should guarantee that the PE is taken out 455 for maintenance only after the service is successfully diverted on an 456 alternate path. There can be large number of customers attached to a 457 PE node and the remote end-points for these pseudo-wires are spread 458 across the service provider's network. It is a tedious and error- 459 prone process to change the metric for all pseudo-wires in both 460 directions. The graceful-link-shutdown feature simplifies the 461 process by increasing the metric on the link in the reverse direction 462 as well so that traffic in both directions is diverted away from the 463 PE undergoing maintenance. The Graceful-Link-Shutdown feature allows 464 the link to be used as a last resort link so that traffic is not 465 disrupted when alternative paths are not available. 467 Private VLAN 468 ======================================= 469 | | 470 | | 471 | ------PE3---------------PE4------CE3 472 | / \ 473 | / \ 474 CE1---------PE1----------PE2---------CE2 475 | \ 476 | \ 477 | ------CE4 478 | | 479 | | 480 | | 481 ================================= 482 Private VLAN 484 Figure 6: Pseudowire Services 486 In the example shown in Figure 6, when the PE1 node is going out of 487 service for maintenance, service providers set the PE1 to graceful- 488 link-shutdown state. The PE1 going in to maintenance state triggers 489 all the CEs connected to the PE (CE1 in this case) to set their 490 pseudowire links passing via PE1 to graceful-link-shutdown state. 491 The mechanisms used to communicate between PE1 and CE1 is outside the 492 scope of this document. CE1 sets the graceful-link-shutdown state on 493 its private VLAN connecting CE3, CE2 and CE4 and changes the metric 494 to MaxLinkMetric and re-originates the corresponding LSA. The remote 495 end of the link at CE3, CE2, and CE4 also set the metric on the link 496 to MaxLinkMetric and the traffic from both directions gets diverted 497 away from the pseudowires. 499 8.2. Controller based Traffic Engineering Deployments 501 In controller-based deployments where the controller participates in 502 the IGP protocol, the controller can also receive the graceful-link- 503 shutdown information as a warning that link maintenance is imminent. 504 Using this information, the controller can find alternate paths for 505 traffic which uses the affected link. The controller can apply 506 various policies and re-route the LSPs away from the link undergoing 507 maintenance. If there are no alternate paths satisfying the traffic 508 engineering constraints, the controller might temporarily relax those 509 constraints and put the service on a different path. Increasing the 510 link metric alone does not specify the maintenance activity as the 511 metric could increase in events such as LDP-IGP synchronisation. An 512 explicit indication from the router using the graceful-link-shutdown 513 sub-TLV is needed to inform the Controller or head-end routers. 515 _____________ 516 | | 517 -------------| Controller |-------------- 518 | |____________ | | 519 | | 520 |--------- Primary Path ------------------| 521 PE1---------P1----------------P2---------PE2 522 | | 523 | | 524 |________P3________| 526 Alternate Path 528 Figure 7: Controller based Traffic Engineering 530 In the above example, PE1->PE2 LSP is set-up to satisfy a constraint 531 of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have 532 only 1 Gbps capacity and there is no alternate path satisfying the 533 bandwidth constraint of 10Gbps. When P1->P2 link is being prepared 534 for maintenance, the controller receives the graceful-link-shutdown 535 information, as there is no alternate path available which satisfies 536 the constraints, the controller chooses a path that is less optimal 537 and temporarily sets up an alternate path via P1->P3->P2. Once the 538 traffic is diverted, the P1->P2 link can be taken out of service for 539 maintenance/upgrade. 541 8.3. L3VPN Services and sham-links 543 Many service providers offer L3VPN services to customers and CE-PE 544 links run OSPF [RFC4577]. When PE is taken out of service for 545 maintenance, all the links on the PE can be set to graceful-link- 546 shutdown state which will gurantee that the traffic to/from dual- 547 homed CEs gets diverted. The interaction between OSPF and BGP is 548 outside the scope of this document. [RFC6987] based mechanism with 549 summaries and externals advertised with high metrics could also be 550 used to achieve the same functionality when implementations support 551 high metrics advertisement for summaries and externals. 553 Another useful usecase is when ISPs provide sham-link services to 554 customers [RFC4577]. When PE goes out of service for maintenance, 555 all sham-links on the PE can be set to graceful-link-shutdown state 556 and traffic can be divered from both ends without having to touch the 557 configurations on the remote end of the sham-links. 559 8.4. Hub and spoke deployment 561 OSPF is largely deployed in Hub and Spoke deployments with a large 562 number of spokes connecting to the Hub. It is a general practice to 563 deploy multiple Hubs with all spokes connecting to these Hubs to 564 achieve redundancy. The [RFC6987] mechanism can be used to divert 565 the spoke-to-spoke traffic from the overloaded hub router. The 566 traffic that flows from spokes via the hub into an external network 567 may not be diverted in certain scenarios.When a Hub node goes down 568 for maintenance, all links on the Hub can be set to graceful-link- 569 shutdown state and traffic gets divered from the spoke sites as well 570 without having to make configuration changes on the spokes. 572 9. Security Considerations 574 This document does not introduce any further security issues other 575 than those discussed in [RFC2328] and [RFC5340]. 577 10. IANA Considerations 579 This specification updates one OSPF registry: 581 OSPFv2 Extended Link TLV Sub-TLVs 583 i) Graceful-Link-Shutdown Sub-TLV - Suggested value 7 585 ii) Remote IPv4 Address Sub-TLV - Suggested value 8 586 iii) Local/Remote Interface ID Sub-TLV - Suggested Value 9 588 OSPFv3 Extended-LSA sub-TLV Registry 590 i) Graceful-Link-Shutdown sub-TLV - suggested value 7 592 BGP-LS Link NLRI Registry [RFC7752] 594 i)Graceful-Link-Shutdown TLV - Suggested 1101 596 11. Acknowledgements 598 Thanks to Chris Bowers for valuable inputs and edits to the document. 599 Thanks to Jeffrey Zhang, Acee Lindem and Ketan Talaulikar for inputs. 600 Thanks to Karsten Thomann for careful review and inputs on the 601 applications where graceful-link-shutdown is useful. 603 12. References 605 12.1. Normative References 607 [I-D.ietf-ospf-ospfv3-lsa-extend] 608 Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 609 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-10 610 (work in progress), May 2016. 612 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 613 Requirement Levels", BCP 14, RFC 2119, 614 DOI 10.17487/RFC2119, March 1997, 615 . 617 [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast 618 and Point-to-Multipoint Interface Type", RFC 6845, 619 DOI 10.17487/RFC6845, January 2013, 620 . 622 [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. 623 McPherson, "OSPF Stub Router Advertisement", RFC 6987, 624 DOI 10.17487/RFC6987, September 2013, 625 . 627 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 628 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 629 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 630 2015, . 632 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 633 S. Ray, "North-Bound Distribution of Link-State and 634 Traffic Engineering (TE) Information Using BGP", RFC 7752, 635 DOI 10.17487/RFC7752, March 2016, 636 . 638 [RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part 639 Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016, 640 . 642 12.2. Informative References 644 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 645 DOI 10.17487/RFC2328, April 1998, 646 . 648 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 649 Support of Generalized Multi-Protocol Label Switching 650 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 651 . 653 [RFC4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the 654 Provider/Customer Edge Protocol for BGP/MPLS IP Virtual 655 Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577, 656 June 2006, . 658 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 659 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 660 RFC 4915, DOI 10.17487/RFC4915, June 2007, 661 . 663 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 664 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 665 . 667 [RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton, 668 "Graceful Shutdown in MPLS and Generalized MPLS Traffic 669 Engineering Networks", RFC 5817, DOI 10.17487/RFC5817, 670 April 2010, . 672 Authors' Addresses 673 Shraddha Hegde 674 Juniper Networks, Inc. 675 Embassy Business Park 676 Bangalore, KA 560093 677 India 679 Email: shraddha@juniper.net 681 Pushpasis Sarkar 682 Arrcus Inc. 684 Email: pushpasis.ietf@gmail.com 686 Hannes Gredler 687 Individual 689 Email: hannes@gredler.at 691 Mohan Nanduri 692 ebay Corporation 693 2025 Hamilton Avenue 694 San Jose, CA 98052 695 US 697 Email: mnanduri@ebay.com 699 Luay Jalil 700 Verizon 702 Email: luay.jalil@verizon.com