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Jalil 10 Verizon 11 February 12, 2017 13 OSPF Link Overload 14 draft-ietf-ospf-link-overload-03 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 August 16, 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. OSPFv3 Link Overload sub-TLV . . . . . . . . . . . . . . 5 79 5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 5 80 5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 6 81 5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 6 82 5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 7 83 5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 7 84 6. Backward compatibility . . . . . . . . . . . . . . . . . . . 7 85 7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 7 86 7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 7 87 7.2. Controller based Traffic Engineering Deployments . . . . 8 88 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 89 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 90 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 91 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 92 11.1. Normative References . . . . . . . . . . . . . . . . . . 10 93 11.2. Informative References . . . . . . . . . . . . . . . . . 10 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 96 1. Introduction 98 When a node is being prepared for a planned maintenance or upgrade, 99 [RFC6987] provides mechanisms to advertise the node being in an 100 overload state by setting all outgoing link costs to MAX-METRIC 101 (0xffff). These procedures are specific to the maintenance activity 102 on a node and cannot be used when a single link attached to the node, 103 requires maintenance. 105 In traffic-engineering deployments, LSPs need to be moved away from 106 the link without disrupting the services. It is useful to be able to 107 advertise the impending maintenance activity on the link and to have 108 LSP re-routing policies at the ingress to route the LSPs away from 109 the link. 111 Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned 112 by means of pseudo-wires or L2-circuits. When the devices in the 113 underlying network go for maintenance, it is useful to divert the 114 traffic away from the node before the maintenance is actually 115 scheduled. Since the nodes in the underlying network are not visible 116 to OSPF, the existing stub router mechanism described in [RFC6987] 117 cannot be used. Application specific to this use case is described 118 in Section 7.1 120 This document provides mechanisms to advertise link overload state in 121 the flexible encodings provided by OSPFv2 Prefix/Link Attribute 122 Advertisement( [RFC7684]) and OSPFv3 Extended LSA 123 ([I-D.ietf-ospf-ospfv3-lsa-extend]). Throughout this document, OSPF 124 is used when the text applies to both OSPFv2 and OSPFv3. OSPFv2 or 125 OSPFv3 is used when the text is specific to one version of the OSPF 126 protocol. 128 2. Motivation 130 The motivation of this document is to reduce manual intervention 131 during maintenance activities. The following objectives help to 132 accomplish this in a range of deployment scenarios. 134 1. Advertise impending maintenance activity so that the traffic from 135 both directions can be diverted away from the link. 137 2. Allow the solution to be backward compatible so that nodes that 138 do not understand the new advertisement do not cause routing 139 loops. 141 3. Advertise the maintenance activity to other nodes in the network 142 so that LSP ingress routers/controllers can learn the impending 143 maintenance activity and apply specific policies to re-route the 144 LSP for traffic-engineering based deployments. 146 4. Allow the link to be used as last resort link to prevent traffic 147 disruption when alternate paths are not available. 149 3. Flooding Scope 151 The link overload information can be flood in area scoped extended 152 link LSA [RFC7684] or link scoped RI LSA [RFC7770] or both based on 153 the need of the application. Section 7 describes applications 154 requiring area scope as well as link scope Link-overload information. 156 3.1. Area scope flooding 158 For OSPFv2, Link overload Sub-TLV is carried in the extended Link TLV 159 as defined in [RFC7684] . 161 3.2. Link scope flooding 163 The link local scope RI LSA MAY carry the link overload sub TLV as 164 defined in Section 4.The link local scope RI-LSA corresponds to the 165 link on which the LSA arrives and there is no need to explicitly 166 specify the remote ipv4 address.The remote ipv4 address field MAY be 167 zero when the link overload sub-TLV is carried in the link local RI 168 LSA. The link-overload sub-tlv MAY appear in any instance of the 169 link local RI-LSA. The Link overload sub-TLV is carried in the RI- 170 LSA for both OSPFv2 and OSPFv3. 172 4. Link overload sub-TLV 174 4.1. OSPFv2 Link overload sub-TLV 176 The Link Overload sub-TLV identifies the link being in overload 177 state. It is carried in extended Link TLV as defined in [RFC7684] or 178 link local scope RI LSA as defined in [RFC7770]. 180 0 1 2 3 181 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 1 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 | Type | Length | 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 | Remote IP address | 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 188 Figure 1: Link Overload sub-TLV for OSPFv2 190 Type : TBA (suggested value 4) 192 Length: 4 194 Value: Remote IPv4 address. The remote IP4 address is used to 195 identify the particular link that is in the overload state when there 196 are multiple parallel links between two nodes. 198 4.2. OSPFv3 Link Overload sub-TLV 200 The Link Overload sub-TLV is carried in the Router-Link TLV as 201 defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. or in 202 the link local scope OSPFV3 RI LSA as defined in [RFC7770]. The 203 Router-Link TLV contains the neighbour interface-id and can uniquely 204 identify the link on the remote node. 206 0 1 2 3 207 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 1 208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 | Type | Length | 210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 Figure 2: Link Overload sub-TLV for OSPFv3 214 Type : TBA (Suggested value 4) 216 Length: 0 218 5. Elements of procedure 220 The Link Overload sub-TLV indicates that the link identified in by 221 the sub-TLV is overloaded. The node that has the link to be taken 222 out of service SHOULD originate the Link Overload sub-TLV in the 223 Extended Link TLV in the Extended Link Opaque LSA as defined in 225 [RFC7684] for OSPFv2 or in the E-Router-LSA as defined in 226 [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The link-overload 227 information is carried as a property of the link and is flooded 228 across the area. This information can be used by ingress routers or 229 controllers to take special actions. Application specific to this 230 use case is described in Section 7.2. 232 The precise action taken by the remote node at the other end of the 233 link identified as overloaded depends on the link type. 235 5.1. Point-to-point links 237 The node that has the link to be taken out of service SHOULD set 238 metric of the link to MAX-METRIC (0xffff) and re- originate the 239 Router-LSA. The TE metric SHOULD be set to MAX-TE-METRIC-1 240 (0xfffffffe) and the node SHOULD re-originate the TE Link Opaque 241 LSAs. When a Link Overload sub-TLV is received for a point-to-point 242 link, the remote node SHOULD identify the local link which 243 corresponds to the overloaded link and set the metric to MAX-METRIC 244 (0xffff). The remote node MUST re-originate the router-LSA with the 245 changed metric and flood into the OSPF area. The TE metric SHOULD be 246 set to MAX-TE-METRIC-1 (0xfffffffe) and the TE opaque LSA for the 247 link MUST be re-originated with new value. 249 In multi-topology deployments [RFC4915], the Link overload Sub-TLV 250 carried in an Extended Link opaque LSA corresponds to all the 251 topologies the link belongs to. The receiver node SHOULD change the 252 metric in the reverse direction corresponding to all the topologies 253 to which the reverse link belongs. 255 When the originator of the Link Overload sub-TLV purges the Extended 256 Link Opaque LSA/E-Router-LSA or re-originates it without the Link 257 Overload sub-TLV, the remote node must re-originate the appropriate 258 LSAs with the metric and TE metric values set to their original 259 values. 261 5.2. Broadcast/NBMA links 263 Broadcast or NBMA networks in OSPF are represented by a star topology 264 where the Designated Router (DR) is the central point to which all 265 other routers on the broadcast or NBMA network connect logically. As 266 a result, routers on the broadcast or NBMA network advertise only 267 their adjacency to the DR. Routers that do not act as DR do not form 268 or advertise adjacencies with each other. For the Broadcast links, 269 the MAX-METRIC on the remote link cannot be changed since all the 270 neighbours are on same link. Setting the link cost to MAX-METRIC 271 would impact paths going via all neighbours. 273 The node that has the link to be taken out of service SHOULD set 274 metric of the link to MAX-METRIC (0xffff) and re-originate the 275 Router-LSA. The TE metric SHOULD be set to MAX-TE-METRIC- 276 1(0xfffffffe) and the node SHOULD re-originate the TE Link Opaque 277 LSAs. For a broadcast link, the two part metric as described in 278 [RFC8042] is used. The node originating the Link Overload sub-TLV 279 MUST set the metric in the Network-to-Router Metric sub-TLV to MAX- 280 METRIC 0xffff for OSPFv2 and OSPFv3 and re-originate the LSAs the TLV 281 is carried-in. The nodes that receive the two part metric should 282 follow the procedures described in [RFC8042]. The backward 283 compatibility procedures described in [RFC8042] should be followed to 284 ensure loop free routing. 286 5.3. Point-to-multipoint links 288 Operation for the point-to-multipoint links is similar to the point- 289 to-point links. When a Link Overload sub-TLV is received for a 290 point-to-multipoint link the remote node SHOULD identify the 291 neighbour which corresponds to the overloaded link and set the metric 292 to MAX-METRIC (0xffff). The remote node MUST re-originate the 293 Router-LSA with the changed metric and flood into the OSPF area. 295 5.4. Unnumbered interfaces 297 Unnumbered interface do not have a unique IP addresses and borrow 298 address from other interfaces. [RFC2328] describes procedures to 299 handle unnumbered interfaces. The link-data field in the Extended 300 Link TLV carries the interface-id instead of the IP address. The 301 Link Overload sub-TLV carries the remote interface-id in the Remote- 302 ip-address field if the interface is unnumbered. Procedures to 303 obtain interface-id of the remote side is defined in [RFC4203]. 305 6. Backward compatibility 307 The mechanism described in the document is fully backward 308 compatible.It is required that the originator of the Link Overload 309 sub-TLV as well as the node at the remote end of the link identified 310 as overloaded understand the extensions defined in this document. In 311 the case of broadcast links, the backward compatibility procedures as 312 described in [RFC8042] are applicable. . 314 7. Applications 316 7.1. Pseudowire Services 317 ---------PE3----------------PE4---------- 318 | | 319 | | 320 CE1---------PE1----------------PE2---------CE2 321 | | 322 | | 323 ----------------------------------------- 324 Private VLAN 326 Figure 3: Pseudowire Services 328 Many service providers offer pseudo-wire services to customers using 329 L2 circuits. The IGP protocol that runs in the customer network 330 would also run over the pseudo-wire to create seamless private 331 network for the customer. Service providers want to offer overload 332 kind of functionality when the PE device is taken-out for 333 maintenance. The provider should guarantee that the PE is taken out 334 for maintenance only after the service is successfully diverted on an 335 alternate path. There can be large number of customers attached to a 336 PE node and the remote end-points for these pseudo-wires are spread 337 across the service provider's network. It is a tedious and error- 338 prone process to change the metric for all pseudo-wires in both 339 directions.The link overload feature simplifies the process by 340 increasing the metric on the link in the reverse direction as well so 341 that traffic in both directions is diverted away from the PE 342 undergoing maintenance. The link-overload feature allows the link to 343 be used as a last resort link so that traffic is not disrupted when 344 alternative paths are not available. 346 7.2. Controller based Traffic Engineering Deployments 348 _____________ 349 | | 350 -------------| Controller |-------------- 351 | |____________ | | 352 | | 353 |--------- Primary Path ------------------| 354 PE1---------P1----------------P2---------PE2 355 | | 356 | | 357 |________P3________| 359 Alternate Path 361 Figure 4: Controller based Traffic Engineering 363 In controller-based deployments where the controller participates in 364 the IGP protocol, the controller can also receive the link-overload 365 information as a warning that link maintenance is imminent. Using 366 this information, the controller can find alternate paths for traffic 367 which use the affected link. The controller can apply various 368 policies and re-route the LSPs away from the link undergoing 369 maintenance. If there are no alternate paths satisfying the traffic 370 engineering constraints, the controller might temporarily relax those 371 constraints and put the service on a different path. 373 In the above example, PE1->PE2 LSP is set-up which satisfies a 374 constraint of 10 GB bandwidth on each link.The links P1->P3 and 375 P3->P2 have only 1 GB capacity. and there is no alternate path 376 satisfying the bandwidth constraint of 10GB. When P1->P2 link is 377 being prepared for maintenance, the controller receives the link- 378 overload information, as there is no alternate path available which 379 satisfies the constraints, controller chooses a path that is less 380 optimal and sets up an alternate path via P1->P3->P2 temporarily. 381 Once the traffic is diverted, P1->P2 link can be taken out for 382 maintenance/upgrade. 384 8. Security Considerations 386 This document does not introduce any further security issues other 387 than those discussed in [RFC2328] and [RFC5340]. 389 9. IANA Considerations 391 This specification updates one OSPF registry: 393 OSPF Extended Link TLVs Registry 395 i) TBD - Link Overload sub TLV 397 OSPFV3 Router Link TLV Registry 399 i) TBD - Link Overload sub TLV 401 10. Acknowledgements 403 Thanks to Chris Bowers for valuable inputs and edits to the document. 404 Thanks to Jeffrey Zhang and Acee Lindem for inputs. 406 11. References 407 11.1. Normative References 409 [I-D.ietf-ospf-ospfv3-lsa-extend] 410 Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 411 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-06 412 (work in progress), February 2015. 414 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 415 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 416 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 417 2015, . 419 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 420 S. Shaffer, "Extensions to OSPF for Advertising Optional 421 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 422 February 2016, . 424 [RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part 425 Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016, 426 . 428 11.2. Informative References 430 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 431 Requirement Levels", BCP 14, RFC 2119, 432 DOI 10.17487/RFC2119, March 1997, 433 . 435 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 436 DOI 10.17487/RFC2328, April 1998, 437 . 439 [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in 440 Support of Generalized Multi-Protocol Label Switching 441 (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, 442 . 444 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 445 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 446 RFC 4915, DOI 10.17487/RFC4915, June 2007, 447 . 449 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 450 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 451 . 453 [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. 454 McPherson, "OSPF Stub Router Advertisement", RFC 6987, 455 DOI 10.17487/RFC6987, September 2013, 456 . 458 Authors' Addresses 460 Shraddha Hegde 461 Juniper Networks, Inc. 462 Embassy Business Park 463 Bangalore, KA 560093 464 India 466 Email: shraddha@juniper.net 468 Pushpasis Sarkar 469 Individual 471 Email: pushpasis.ietf@gmail.com 473 Hannes Gredler 474 Individual 476 Email: hannes@gredler.at 478 Mohan Nanduri 479 Microsoft Corporation 480 One Microsoft Way 481 Redmond, WA 98052 482 US 484 Email: mnanduri@microsoft.com 486 Luay Jalil 487 Verizon 489 Email: luay.jalil@verizon.com