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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10589' ** Downref: Normative reference to an Informational RFC: RFC 5443 == Outdated reference: A later version (-07) exists of draft-shen-isis-spine-leaf-ext-03 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Networking Working Group N. Shen 3 Internet-Draft Cisco Systems 4 Intended status: Standards Track S. Amante 5 Expires: April 19, 2019 Apple, Inc. 6 M. Abrahamsson 7 T-Systems Nordic 8 October 16, 2018 10 IS-IS Routing with Reverse Metric 11 draft-ietf-isis-reverse-metric-14 13 Abstract 15 This document describes a mechanism to allow IS-IS routing to quickly 16 and accurately shift traffic away from either a point-to-point or 17 multi-access LAN interface during network maintenance or other 18 operational events. This is accomplished by signaling adjacent IS-IS 19 neighbors with a higher reverse metric, i.e., the metric towards the 20 signaling IS-IS router. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on April 19, 2019. 39 Copyright Notice 41 Copyright (c) 2018 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Node and Link Isolation . . . . . . . . . . . . . . . . . 2 58 1.2. Distributed Forwarding Planes . . . . . . . . . . . . . . 3 59 1.3. Spine-Leaf Applications . . . . . . . . . . . . . . . . . 3 60 1.4. LDP IGP Synchronization . . . . . . . . . . . . . . . . . 3 61 1.5. IS-IS Reverse Metric . . . . . . . . . . . . . . . . . . 3 62 1.6. Specification of Requirements . . . . . . . . . . . . . . 4 63 2. IS-IS Reverse Metric TLV . . . . . . . . . . . . . . . . . . 4 64 3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 6 65 3.1. Processing Changes to Default Metric . . . . . . . . . . 6 66 3.2. Multi-Topology IS-IS Support on Point-to-point links . . 7 67 3.3. Multi-Access LAN Procedures . . . . . . . . . . . . . . . 7 68 3.4. LDP/IGP Synchronization on LANs . . . . . . . . . . . . . 8 69 3.5. Operational Guidelines . . . . . . . . . . . . . . . . . 9 70 4. Security Considerations . . . . . . . . . . . . . . . . . . . 9 71 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 72 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 73 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 74 7.1. Normative References . . . . . . . . . . . . . . . . . . 10 75 7.2. Informative References . . . . . . . . . . . . . . . . . 11 76 Appendix A. Node Isolation Challenges . . . . . . . . . . . . . 12 77 Appendix B. Link Isolation Challenges . . . . . . . . . . . . . 13 78 Appendix C. Contributors' Addresses . . . . . . . . . . . . . . 14 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 81 1. Introduction 83 The IS-IS [ISO10589] routing protocol has been widely used in 84 Internet Service Provider IP/MPLS networks. Operational experience 85 with the protocol, combined with ever increasing requirements for 86 lossless operations have demonstrated some operational issues. This 87 document describes the issues and a mechanism for mitigating them. 89 1.1. Node and Link Isolation 91 IS-IS routing mechanism has the overload-bit, which can be used by 92 operators to perform disruptive maintenance on the router. But in 93 many operational maintenance cases, it is not necessary to divert all 94 the traffic away from this node. It is necessary to avoid only a 95 single link during the maintenance. More detailed descriptions of 96 the challenges can be found in Appendix A and Appendix B of this 97 document. 99 1.2. Distributed Forwarding Planes 101 In a distributed forwarding platform, different forwarding line-cards 102 may have interfaces and IS-IS connections to neighbor routers. If 103 one of the line-card's software resets, it may take some time for the 104 forwarding entries to be fully populated on the line-card, in 105 particular if the router is a PE (Provider Edge) router in ISP's MPLS 106 VPN. An IS-IS adjacency may be established with a neighbor router 107 long before the entire BGP VPN prefixes are downloaded to the 108 forwarding table. It is important to signal to the adjacent IS-IS 109 routers to raise metric values and not to use the corresponding IS-IS 110 adjacency inbound to this router if possible. Temporarily signaling 111 the 'Reverse Metric' over this link to discourage the traffic via the 112 corresponding line-card will help to reduce the traffic loss in the 113 network. In the meantime, the remote PE routers will select a 114 different set of PE routers for the BGP best path calculation or use 115 a different link towards the same PE router on which a line-card is 116 resetting. 118 1.3. Spine-Leaf Applications 120 In the IS-IS Spine-Leaf extension [I-D.shen-isis-spine-leaf-ext], the 121 leaf nodes will perform equal-cost or unequal-cost load sharing 122 towards all the spine nodes. In certain operational cases, for 123 instance, when one of the backbone links on a spine node is 124 congested, a spine node can push a higher metric towards the 125 connected leaf nodes to reduce the transit traffic through the 126 corresponding spine node or link. 128 1.4. LDP IGP Synchronization 130 In the [RFC5443], a mechanism is described to achieve LDP IGP 131 synchronization by using the maximum link metric value on the 132 interface. But in the case of a new IS-IS node joining the broadcast 133 network (LAN), it is not optimal to change all the nodes on the LAN 134 to the maximum link metric value, as described in [RFC6138]. In this 135 case, the Reverse Metric can be used to discourage both outbound and 136 inbound traffic without affecting the traffic of other IS-IS nodes on 137 the LAN. 139 1.5. IS-IS Reverse Metric 141 This document uses the routing protocol itself as the transport 142 mechanism to allow one IS-IS router to advertise a "reverse metric" 143 in an IS-IS Hello (IIH) PDU to an adjacent node on a point-to-point 144 or multi-access LAN link. This would allow the provisioning to be 145 performed only on a single node, setting a "reverse metric" on a link 146 and have traffic bidirectionally shift away from that link gracefully 147 to alternate, viable paths. 149 This Reverse Metric mechanism is used for both point-to-point and 150 multi-access LAN links. Unlike the point-to-point links, the IS-IS 151 protocol currently does not have a way to influence the traffic 152 towards a particular node on LAN links. This mechanism provides IS- 153 IS routing the capability of altering traffic in both directions on 154 either a point-to-point link or a multi-access link of an IS-IS node. 156 The metric value in the "reverse metric" TLV and the Traffic 157 Engineering metric in the sub-TLV being advertised is an offset or 158 relative metric to be added to the existing local link and Traffic 159 Engineering metric values of the receiver. 161 1.6. Specification of Requirements 163 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 164 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 165 "OPTIONAL" in this document are to be interpreted as described in BCP 166 14 [RFC2119] [RFC8174] when, and only when, they appear in all 167 capitals, as shown here. 169 2. IS-IS Reverse Metric TLV 171 The Reverse Metric TLV is a new TLV to be used inside IS-IS Hello 172 PDU. This TLV is used to support the IS-IS Reverse Metric mechanism 173 that allows a "reverse metric" to be send to the IS-IS neighbor. 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 | Flags | Metric 179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 180 Metric (Continue) | sub-TLV Len |Optional sub-TLV 181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 Figure 1: Reverse Metric TLV 185 The Value part of the Reverse Metric TLV is composed of a 3 octet 186 field containing an IS-IS Metric Value, a 1 octet field of Flags, and 187 a 1 octet Reverse Metric sub-TLV length field representing the length 188 of a variable number of sub-TLVs. If the "sub-TLV len" is non-zero, 189 then the Value field MUST also contain one or more sub-TLVs. 191 The Reverse Metric TLV MAY be present in any IS-IS Hello PDU. A 192 sender MUST only transmit a single Reverse Metric TLV in a IS-IS 193 Hello PDU. If a received IS-IS Hello PDU contains more than one 194 Reverse Metric TLV, an implementation MUST ignore all the Reverse 195 Metric TLVs. 197 TYPE: 16 198 LENGTH: variable (5 - 255 octets) 199 VALUE: 201 Flags (1 octet) 202 Metric (3 octets) 203 sub-TLV length (1 octet) 204 sub-TLV data (0 - 250 octets) 206 0 1 2 3 4 5 6 7 207 +-+-+-+-+-+-+-+-+ 208 | Reserved |U|W| 209 +-+-+-+-+-+-+-+-+ 211 Figure 2: Flags 213 The Metric field contains a 24-bit unsigned integer. This value is a 214 metric offset that a neighbor SHOULD add to the existing, configured 215 Default Metric for the IS-IS link [ISO10589]. Refer to "Elements of 216 Procedure", in Section 3 for details on how an IS-IS router should 217 process the Metric field in a Reverse Metric TLV. 219 The Metric field, in the Reverse Metric TLV, is a "reverse offset 220 metric" that will either be in the range of 0 - 63 when a "narrow" 221 IS-IS metric is used (IS Neighbors TLV, Pseudonode LSP) [RFC1195] or 222 in the range of 0 - (2^24 - 2) when a "wide" Traffic Engineering 223 metric value is used, (Extended IS Reachability TLV) [RFC5305] 224 [RFC5817]. 226 There are currently only two Flag bits defined. 228 W bit (0x01): The "Whole LAN" bit is only used in the context of 229 multi-access LANs. When a Reverse Metric TLV is transmitted from a 230 node to the Designated Intermediate System (DIS), if the "Whole LAN" 231 bit is set (1), then a DIS SHOULD add the received Metric value in 232 the Reverse Metric TLV to each node's existing Default Metric in the 233 Pseudonode LSP. If the "Whole LAN" bit is not set (0), then a DIS 234 SHOULD add the received Metric value in the Reverse Metric TLV to the 235 existing "default metric" in the Pseudonode LSP for the single node 236 from whom the Reverse Metric TLV was received. Please refer to 237 "Multi-Access LAN Procedures", in Section 3.3, for additional 238 details. The W bit MUST be clear when a Reverse Metric TLV is 239 transmitted in an IIH PDU on a point-to-point link, and MUST be 240 ignored when received on a point-to-point link. 242 U bit (0x02): The "Unreachable" bit specifies that the metric 243 calculated by addition of the reverse metric value to the "default 244 metric" is limited to (2^24-1). This "U" bit applies to both the 245 default metric in the Extended IS Reachability TLV and the Traffic 246 Engineering Default Metric sub-TLV of the link. This is only 247 relevant to the IS-IS "wide" metric mode. 249 The Reserved bits of Flags field MUST be set to zero and MUST be 250 ignored when received. 252 The Reverse Metric TLV MAY include sub-TLVs when an IS-IS router 253 wishes to signal additional information to its neighbor. In this 254 document, the Reverse Metric Traffic Engineering Metric sub-TLV, with 255 Type 18, is defined. This Traffic Engineering Metric contains a 256 24-bit unsigned integer. This sub-TLV is optional, if it appears 257 more than once then the entire Reverse Metric TLV MUST be ignored. 258 Upon receiving this Traffic Engineering METRIC sub-TLV in a Reverse 259 Metric TLV, a node SHOULD add the received Traffic Engineering Metric 260 offset value to its existing, configured Traffic Engineering Default 261 Metric within its Extended IS Reachability TLV. The use of other 262 sub-TLVs is outside the scope of this document. The "sub-TLV Len" 263 value MUST be set to zero when an IS-IS router does not have Traffic 264 Engineering sub-TLVs that it wishes to send to its IS-IS neighbor. 266 3. Elements of Procedure 268 3.1. Processing Changes to Default Metric 270 It is important to use the same IS-IS metric type on both ends of the 271 link and in the entire IS-IS area or level. On the receiving side of 272 the 'reverse-metric' TLV, the accumulated value of configured metric 273 and the reverse-metric needs to be limited to 63 in "narrow" metric 274 mode and to (2^24 - 2) in "wide" metric mode. This applies to both 275 the Default Metric of Extended IS Reachability TLV and the Traffic 276 Engineering Default Metric sub-TLV in LSP or Pseudonode LSP for the 277 "wide" metric mode case. If the "U" bit is present in the flags, the 278 accumulated metric value is to be limited to (2^24 - 1) for both the 279 normal link metric and Traffic Engineering metric in IS-IS "wide" 280 metric mode. 282 If an IS-IS router is configured to originate a Traffic Engineering 283 Default Metric sub-TLV for a link, but receives a Reverse Metric TLV 284 from its neighbor that does not contain a Traffic Engineering Default 285 Metric sub-TLV, then the IS-IS router MUST NOT change the value of 286 its Traffic Engineering Default Metric sub-TLV for that link. 288 3.2. Multi-Topology IS-IS Support on Point-to-point links 290 The Reverse Metric TLV is applicable to Multi-Topology IS-IS (M-ISIS) 291 [RFC5120]. On point-to-point links, if an IS-IS router is configured 292 for M-ISIS, it MUST send only a single Reverse Metric TLV in IIH PDUs 293 toward its neighbor(s) on the designated link. When an M-ISIS router 294 receives a Reverse Metric TLV, it MUST add the received Metric value 295 to its Default Metric in all Extended IS Reachability TLVs for all 296 topologies. If an M-ISIS router receives a Reverse Metric TLV with a 297 Traffic Engineering Default Metric sub-TLV, then the M-ISIS router 298 MUST add the received Traffic Engineering Default Metric value to 299 each of its Default Metric sub-TLVs in all of its MT Intermediate 300 Systems TLVs. If an M-ISIS router is configured to advertise Traffic 301 Engineering Default Metric sub-TLVs for one or more topologies, but 302 does not receive a Traffic Engineering Default Metric sub-TLV in a 303 Reverse Metric TLV, then the M-ISIS router MUST NOT change the value 304 in each of the Traffic Engineering Default Metric sub-TLVs for all 305 topologies. 307 3.3. Multi-Access LAN Procedures 309 On a Multi-Access LAN, only the DIS SHOULD act upon information 310 contained in a received Reverse Metric TLV. All non-DIS nodes MUST 311 silently ignore a received Reverse Metric TLV. The decision process 312 of the routers on the LAN MUST follow the procedure in section 313 7.2.8.2 of [ISO10589], and use the "Two-way connectivity check" 314 during the topology and route calculation. 316 The Reverse Metric Traffic Engineering sub-TLV also applies to the 317 DIS. If a DIS is configured to apply Traffic Engineering over a link 318 and it receives metric sub-TLV in a Reverse Metric TLV, it should 319 update the Traffic Engineering Default Metric sub-TLV value of the 320 corresponding Extended IS Reachability TLV or insert a new one if not 321 present. 323 In the case of multi-access LANs, the "W" Flags bit is used to signal 324 from a non-DIS to the DIS whether to change the metric and, 325 optionally Traffic Engineering parameters for all nodes in the 326 Pseudonode LSP or solely the node on the LAN originating the Reverse 327 Metric TLV. 329 A non-DIS node, e.g., Router B, attached to a multi-access LAN will 330 send the DIS a Reverse Metric TLV with the W bit clear when Router B 331 wishes the DIS to add the Metric value to the Default Metric 332 contained in the Pseudonode LSP specific to just Router B. Other 333 non-DIS nodes, e.g., Routers C and D, may simultaneously send a 334 Reverse Metric TLV with the W bit clear to request the DIS to add 335 their own Metric value to their Default Metric contained in the 336 Pseudonode LSP. 338 As long as at least one IS-IS node on the LAN sending the signal to 339 DIS with the W bit set, the DIS would add the metric value in the 340 Reverse Metric TLV to all neighbor adjacencies in the Pseudonode LSP, 341 regardless if some of the nodes on the LAN advertise the Reverse 342 Metric TLV without the W bit set. The DIS MUST use the reverse 343 metric of the highest source MAC address Non-DIS advertising the 344 Reverse Metric TLV with the W bit set. 346 Local provisioning on the DIS to adjust the Default Metric(s) is 347 another way to insert Reverse Metric in the Pseudonode LSP towards an 348 IS-IS node on a LAN. In the case where Reverse Metric TLV is also 349 used in the IS-IS Hello PDU of the node, the local provisioning MUST 350 take precedence over received Reverse Metric TLVs. For instance, 351 local policy on the DIS may be provisioned to ignore the W bit 352 signaling on a LAN. 354 Multi-Topology IS-IS [RFC5120] specifies there is no change to 355 construction of the Pseudonode LSP, regardless of the Multi-Topology 356 capabilities of a multi-access LAN. If any MT capable node on the 357 LAN advertises the Reverse Metric TLV to the DIS, the DIS should 358 update, as appropriate, the Default Metric contained in the 359 Pseudonode LSP. If the DIS updates the Default Metric in and floods 360 a new Pseudonode LSP, those default metric values will be applied to 361 all topologies during Multi-Topology SPF calculations. 363 3.4. LDP/IGP Synchronization on LANs 365 As described in [RFC6138] when a new IS-IS node joins a broadcast 366 network, it is unnecessary and sometimes even harmful for all IS-IS 367 nodes on the LAN to advertise maximum link metric. [RFC6138] 368 proposes a solution to have the new node not advertise its adjacency 369 towards the pseudo-node when it is not in a "cut-edge" position. 371 With the introduction of Reverse Metric in this document, a simpler 372 alternative solution to the above mentioned problem can be used. The 373 Reverse Metric allows the new node on the LAN to advertise its 374 inbound metric value to be the maximum and this puts the link of this 375 new node in the last resort position without impacting the other IS- 376 IS nodes on the same LAN. 378 Specifically, when IS-IS adjacencies are being established by the new 379 node on the LAN, besides setting the maximum link metric value (2^24 380 - 2) on the interface of the LAN for LDP IGP synchronization as 381 described in [RFC5443], it SHOULD advertise the maximum metric offset 382 value in the Reverse Metric TLV in its IIH PDU sent on the LAN. It 383 SHOULD continue this advertisement until it completes all the LDP 384 label binding exchanges with all the neighbors over this LAN, either 385 by receiving the LDP End-of-LIB [RFC5919] for all the sessions or by 386 exceeding the provisioned timeout value for the node LDP/IGP 387 synchronization. 389 3.5. Operational Guidelines 391 For the use case in Section 1.1, a router SHOULD limit the duration 392 of advertising a Reverse Metric TLV towards a neighbor only for the 393 period of operational window. 395 The use of Reverse Metric does not alter IS-IS metric parameters 396 stored in a router's persistent provisioning database. 398 Routers that receive a Reverse Metric TLV MAY send a syslog message 399 or SNMP trap, in order to assist in rapidly identifying the node in 400 the network that is advertising an IS-IS metric or Traffic 401 Engineering parameters different from that which is configured 402 locally on the device. 404 When the link Traffic Engineering metric is raised to (2^24 - 1) 405 [RFC5817], either due to the reverse-metric mechanism or by explicit 406 user configuration, this SHOULD immediately trigger the CSPF re- 407 calculation to move the Traffic Engineering traffic away from that 408 link. It is RECOMMENDED also that the CSPF does the immediate CSPF 409 re-calculation when the Traffic Engineering metric is raised to (2^24 410 - 2) to be the last resort link. 412 It is RECOMMENDED that implementations provide a capability to 413 disable any changes by Reverse Metric mechanism through neighbor's 414 Hello PDUs. It can be to a node's individual interface Default 415 Metric or Traffic Engineering parameters based upon receiving a 416 properly formatted Reverse Metric TLVs. 418 If an implementation enables this mechanism by default, it is 419 RECOMMENDED that it be disabled by the operators when not explicitly 420 using it. 422 4. Security Considerations 424 Security concerns for IS-IS are addressed in [ISO10589], [RFC5304], 425 [RFC5310], and with various deployment and operational security 426 considerations in [RFC7645]. The enhancement in this document makes 427 it possible for one IS-IS router to manipulate the IS-IS Default 428 Metric and, optionally, Traffic Engineering parameters of adjacent 429 IS-IS neighbors. Although IS-IS routers within a single Autonomous 430 System nearly always are under the control of a single administrative 431 authority, it is highly RECOMMENDED that operators configure 432 authentication of IS-IS PDUs to mitigate use of the Reverse Metric 433 TLV as a potential attack vector. 435 5. IANA Considerations 437 IANA has allocated IS-IS TLV Codepoints of 16 for the Reverse Metric 438 TLV. This new TLV has the following attributes: IIH = y, LSP = n, 439 SNP = n, Purge = n. 441 This document also introduces a new registry for sub-TLVs of the 442 Reverse Metric TLV. The registration policy is Expert Review as 443 defined in [RFC8126]. This registry is part of the "IS-IS TLV 444 Codepoints" registry. The name of the registry is "Sub-TLVs for 445 Reverse Metric TLV". The defined values are: 447 0: Reserved 448 1-17: Unassigned 449 18: Traffic Engineering Metric sub-TLV, as specified in this 450 document (Section 2) 451 19-255: Unassigned 453 6. Acknowledgments 455 The authors would like to thank Mike Shand, Dave Katz, Guan Deng, 456 Ilya Varlashkin, Jay Chen, Les Ginsberg, Peter Ashwood-Smith, Uma 457 Chunduri, Alexander Okonnikov, Jonathan Harrison, Dave Ward, Himanshu 458 Shah, Wes George, Danny McPherson, Ed Crabbe, Russ White, Robert 459 Razsuk, Tom Petch and Acee Lindem for their comments and 460 contributions. 462 This document was produced using Marshall Rose's xml2rfc tool. 464 7. References 466 7.1. Normative References 468 [ISO10589] 469 ISO, "Intermediate system to Intermediate system routeing 470 information exchange protocol for use in conjunction with 471 the Protocol for providing the Connectionless-mode Network 472 Service (ISO 8473)", ISO/IEC 10589:2002. 474 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 475 dual environments", RFC 1195, DOI 10.17487/RFC1195, 476 December 1990, . 478 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 479 Requirement Levels", BCP 14, RFC 2119, 480 DOI 10.17487/RFC2119, March 1997, . 483 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 484 Topology (MT) Routing in Intermediate System to 485 Intermediate Systems (IS-ISs)", RFC 5120, 486 DOI 10.17487/RFC5120, February 2008, . 489 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 490 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 491 2008, . 493 [RFC5443] Jork, M., Atlas, A., and L. Fang, "LDP IGP 494 Synchronization", RFC 5443, DOI 10.17487/RFC5443, March 495 2009, . 497 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 498 Writing an IANA Considerations Section in RFCs", BCP 26, 499 RFC 8126, DOI 10.17487/RFC8126, June 2017, 500 . 502 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 503 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 504 May 2017, . 506 7.2. Informative References 508 [I-D.shen-isis-spine-leaf-ext] 509 Shen, N., Ginsberg, L., and S. Thyamagundalu, "IS-IS 510 Routing for Spine-Leaf Topology", draft-shen-isis-spine- 511 leaf-ext-03 (work in progress), March 2017. 513 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 514 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 515 2008, . 517 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 518 and M. Fanto, "IS-IS Generic Cryptographic 519 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 520 2009, . 522 [RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton, 523 "Graceful Shutdown in MPLS and Generalized MPLS Traffic 524 Engineering Networks", RFC 5817, DOI 10.17487/RFC5817, 525 April 2010, . 527 [RFC5919] Asati, R., Mohapatra, P., Chen, E., and B. Thomas, 528 "Signaling LDP Label Advertisement Completion", RFC 5919, 529 DOI 10.17487/RFC5919, August 2010, . 532 [RFC6138] Kini, S., Ed. and W. Lu, Ed., "LDP IGP Synchronization for 533 Broadcast Networks", RFC 6138, DOI 10.17487/RFC6138, 534 February 2011, . 536 [RFC7645] Chunduri, U., Tian, A., and W. Lu, "The Keying and 537 Authentication for Routing Protocol (KARP) IS-IS Security 538 Analysis", RFC 7645, DOI 10.17487/RFC7645, September 2015, 539 . 541 Appendix A. Node Isolation Challenges 543 On rare occasions, it is necessary for an operator to perform 544 disruptive network maintenance on an entire IS-IS router node, i.e., 545 major software upgrades, power/cooling augments, etc. In these 546 cases, an operator will set the IS-IS Overload Bit (OL-bit) within 547 the Link State Protocol Data Units (LSPs) of the IS-IS router about 548 to undergo maintenance. The IS-IS router immediately floods its 549 updated LSPs to all IS-IS routers in the IS-IS domain. Upon receipt 550 of the updated LSPs, all IS-IS routers recalculate their Shortest 551 Path First (SPF) tree excluding IS-IS routers whose LSPs have the OL- 552 bit set. This effectively removes the IS-IS router about to undergo 553 maintenance from the topology, thus preventing it from receiving any 554 transit traffic during the maintenance period. 556 After the maintenance activity has completed, the operator resets the 557 IS-IS Overload Bit within the LSPs of the original IS-IS router 558 causing it to flood updated IS-IS LSPs throughout the IS-IS domain. 559 All IS-IS routers recalculate their SPF tree and now include the 560 original IS-IS router in their topology calculations, allowing it to 561 be used for transit traffic again. 563 Isolating an entire IS-IS router from the topology can be especially 564 disruptive due to the displacement of a large volume of traffic 565 through an entire IS-IS router to other, sub-optimal paths, (e.g., 566 those with significantly larger delay). Thus, in the majority of 567 network maintenance scenarios, where only a single link or LAN needs 568 to be augmented to increase its physical capacity or is experiencing 569 an intermittent failure, it is much more common and desirable to 570 gracefully remove just the targeted link or LAN from service, 571 temporarily, so that the least amount of user-data traffic is 572 affected during the link-specific network maintenance. 574 Appendix B. Link Isolation Challenges 576 Before network maintenance events are performed on individual 577 physical links or LANs, operators substantially increase the IS-IS 578 metric simultaneously on both devices attached to the same link or 579 LAN. In doing so, the devices generate new Link State Protocol Data 580 Units (LSPs) that are flooded throughout the network and cause all 581 routers to gradually shift traffic onto alternate paths with very 582 little or no disruption to in-flight communications by applications 583 or end-users. When performed successfully, this allows the operator 584 to confidently perform disruptive augmentation, fault diagnosis or 585 repairs on a link without disturbing ongoing communications in the 586 network. 588 There are a number of challenges with the above solution. First, it 589 is quite common to have routers with several hundred interfaces and 590 individual interfaces that are from several hundred Gigabits/second 591 to Terabits/second of traffic. Thus, it is imperative that operators 592 accurately identify the same point-to-point link on two, separate 593 devices in order to increase (and, afterward, decrease) the IS-IS 594 metric appropriately. Second, the aforementioned solution is very 595 time consuming and even more error-prone to perform when it's 596 necessary to temporarily remove a multi-access LAN from the network 597 topology. Specifically, the operator needs to configure ALL devices 598 that have interfaces attached to the multi-access LAN with an 599 appropriately high IS-IS metric, (and then decrease the IS-IS metric 600 to its original value afterward). Finally, with respect to multi- 601 access LANs, there is currently no method to bidirectionally isolate 602 only a single node's interface on the LAN when performing more fine- 603 grained diagnosis and repairs to the multi-access LAN. 605 In theory, use of a Network Management System (NMS) could improve the 606 accuracy of identifying the appropriate subset of routers attached to 607 either a point-to-point link or a multi-access LAN as well as 608 signaling from the NMS to those devices, using a network management 609 protocol to adjust the IS-IS metrics on the pertinent set of 610 interfaces. The reality is that NMSs are, to a very large extent, 611 not used within Service Provider's networks for a variety of reasons. 612 In particular, NMSs do not interoperate very well across different 613 vendors or even separate platform families within the same vendor. 615 The risks of misidentifying one side of a point-to-point link or one 616 or more interfaces attached to a multi-access LAN and subsequently 617 increasing its IS-IS metric and potentially increased latency, jitter 618 or packet loss. This is unacceptable given the necessary performance 619 requirements for a variety of reasons including the customer 620 perception for near lossless operations and the associated demanding 621 Service Level Agreement's (SLAs) for all network services. 623 Appendix C. Contributors' Addresses 625 Tony Li 627 Email: tony.li@tony.li 629 Authors' Addresses 631 Naiming Shen 632 Cisco Systems 633 560 McCarthy Blvd. 634 Milpitas, CA 95035 635 USA 637 Email: naiming@cisco.com 639 Shane Amante 640 Apple, Inc. 641 1 Infinite Loop 642 Cupertino, CA 95014 643 USA 645 Email: samante@apple.com 647 Mikael Abrahamsson 648 T-Systems Nordic 649 Kistagangen 26 650 Stockholm 651 SE 653 Email: Mikael.Abrahamsson@t-systems.se