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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force H. Chen 3 Internet-Draft A. Retana 4 Intended status: Experimental R. Li 5 Expires: March 21, 2020 Futurewei 6 A. Kumar S N 7 RtBrick 8 N. So 9 V. Liu 11 M. Toy 12 Verizon 13 L. Liu 14 Fijitsu 15 September 18, 2019 17 IS-IS Topology-Transparent Zone 18 draft-chen-isis-ttz-06.txt 20 Abstract 22 This document presents a topology-transparent zone in a domain. A 23 zone comprises a group of routers and a number of circuits connecting 24 them. Any router outside of the zone is not aware of the zone. The 25 information about the circuits and routers inside the zone is not 26 distributed to any router outside of the zone. Any link state change 27 such as a circuit down inside the zone is not seen by any router 28 outside of the zone. 30 Status of this Memo 32 This Internet-Draft is submitted to IETF in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on March 21, 2020. 47 Copyright Notice 48 Copyright (c) 2019 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Conventions Used in This Document . . . . . . . . . . . . . . 4 65 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 4. Topology-Transparent Zone . . . . . . . . . . . . . . . . . . 4 67 4.1. Overview of Topology-Transparent Zone . . . . . . . . . . 4 68 4.2. An Example of TTZ . . . . . . . . . . . . . . . . . . . . 5 69 5. Extensions to IS-IS Protocols . . . . . . . . . . . . . . . . 6 70 5.1. TTZ TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6 71 6. Updating LSPs for TTZ . . . . . . . . . . . . . . . . . . . . 9 72 6.1. Updating LSP for a TTZ Internal Router . . . . . . . . . . 9 73 6.2. Updating LSP for a TTZ Edge Router . . . . . . . . . . . . 9 74 7. Establishing Adjacencies . . . . . . . . . . . . . . . . . . . 10 75 7.1. Discover TTZ Neighbor over Normal Adjacency . . . . . . . 10 76 7.2. Establishing TTZ Adjacencies . . . . . . . . . . . . . . . 10 77 7.3. Adjacency between TTZ Edge and Router outside . . . . . . 10 78 8. Distribution of LSPs . . . . . . . . . . . . . . . . . . . . . 11 79 8.1. Distribution of LSPs within TTZ . . . . . . . . . . . . . 11 80 8.2. Distribution of LSPs through TTZ . . . . . . . . . . . . . 11 81 9. Computation of Routing Table . . . . . . . . . . . . . . . . . 12 82 10. Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 12 83 10.1. Configuring TTZ . . . . . . . . . . . . . . . . . . . . . 12 84 10.2. Smooth Migration to TTZ . . . . . . . . . . . . . . . . . 13 85 10.3. Adding a Router into TTZ . . . . . . . . . . . . . . . . . 14 86 11. Security Considerations . . . . . . . . . . . . . . . . . . . 14 87 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 88 13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 15 89 14. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 15 90 15. Normative References . . . . . . . . . . . . . . . . . . . . . 15 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 93 1. Introduction 95 ISO/IEC 10589 describes IS-IS areas or levels in an Autonomous System 96 (AS). Each level 1 area has a number of level 1 and level 2 routers 97 connected to the level 2 area. Each level 1 and level 2 router may 98 summarize the topology of its attached level 1 areas to the level 2 99 area or vice versa. 101 The number of routers in a network becomes larger and larger as the 102 Internet traffic keeps growing. Through splitting the network into 103 multiple areas, we can extend the network further. However, there 104 are a number of issues when a network is split further into more 105 areas. 107 At first, dividing a network from one area into multiple areas or 108 from a number of existing areas to even more areas is a very 109 challenging and time consuming task since it is involved in 110 significant network architecture changes. 112 Secondly, the services carried by the network may be interrupted 113 while the network is being split from one area into multiple areas or 114 from a number of existing areas into even more areas. 116 Furthermore, it is complex for a Multi-Protocol Label Switching 117 (MPLS) Traffic Engineering (TE) Label Switching Path (LSP) crossing 118 multiple areas to be setup. In one option, a TE path crossing 119 multiple areas is computed by using collaborating Path Computation 120 Elements (PCEs) [RFC5441] through the PCE Communication Protocol 121 (PCEP)[RFC5440], which is not easy to configure by operators since 122 the manual configuration of the sequence of domains is required. 123 Although this issue can be addressed by using the Hierarchical PCE, 124 this solution may further increase the complexity of network design. 125 Especially, the current PCE standard method may not guarantee that 126 the path found is optimal. 128 This document presents a topology-transparent zone in a domain or an 129 area and describes extensions to IS-IS for supporting the topology- 130 transparent zone, which is scalable and resolves the issues above. 132 A topology-transparent zone comprises a group of routers and a number 133 of circuits connecting these routers. Any router outside of the zone 134 is not aware of the zone. The information about the circuits and 135 routers inside the zone is not distributed to any router outside of 136 the zone. Any link state change such as a circuit down inside the 137 zone is not seen by any router outside of the zone. 139 2. Conventions Used in This Document 141 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 142 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 143 document are to be interpreted as described in RFC 2119. 145 3. Requirements 147 Topology-Transparent Zone (TTZ) may be deployed for resolving some 148 critical issues such as scalability in existing networks and future 149 networks. The requirements for TTZ are listed as follows: 151 o TTZ MUST be backward compatible. When a TTZ is deployed on a set 152 of routers in a network, the routers outside of the TTZ in the 153 network do not need to know or support TTZ. 155 o TTZ MUST support at least one more levels of network hierarchies, 156 in addition to the hierarchies supported by existing routing 157 protocols. 159 o Users SHOULD be able to easily set up an end to end service 160 crossing TTZs. 162 o The configuration for a TTZ in a network SHOULD be minimum. 164 o The changes on the existing protocols for supporting TTZ SHOULD be 165 minimum. 167 4. Topology-Transparent Zone 169 4.1. Overview of Topology-Transparent Zone 171 A Topology-Transparent Zone (TTZ) is identified by an Identifier 172 (ID), and it includes a group of routers and a number of circuits 173 connecting the routers. A TTZ is in an IS-IS domain (area). 175 The ID of a TTZ or TTZ ID is a number that is unique for identifying 176 an entity such as a node in an IS-IS domain (area). It is not zero 177 in general. 179 In addition to having the functions of an IS-IS level or area, an 180 IS-IS TTZ makes some improvements on an IS-IS level or area, which 181 include: 183 o An IS-IS TTZ is virtualized as the TTZ edge routers connected. 185 o An IS-IS TTZ receives the link state information about the 186 topology outside of the TTZ, stores the information in the TTZ and 187 floods the information through the TTZ to the routers outside of 188 TTZ. 190 4.2. An Example of TTZ 192 The figure below illustrates an example of a routing domain 193 containing a TTZ: TTZ 600. 195 TTZ 600 196 \ 197 \ ^~^~^~^~^~^~^~^~^~^~^~^~ 198 ( ) 199 ===[R15]========(==[R61]------------[R63]==)======[R29]=== 200 || ( | \ / | ) || 201 || ( | \ / | ) || 202 || ( | \ / | ) || 203 || ( | ___\ / | ) || 204 || ( | / [R71] | ) || 205 || ( | [R73] / \ | ) || 206 || ( | / \ | ) || 207 || ( | / \ | ) || 208 || ( | / \ | ) || 209 ===[R17]========(==[R65]------------[R67]==)======[R31]=== 210 \\ (// \\) // 211 || //v~v~v~v~v~v~v~v~v~v~v~\\ || 212 || // \\ || 213 || // \\ || 214 \\ // \\ // 215 ======[R23]==============================[R25]===== 216 // \\ 217 // \\ 219 Figure 1: An Example of TTZ 221 The routing domain comprises routers R15, R17, R23, R25, R29 and R31. 222 It also contains TTZ 600, which comprises routers R61, R63, R65, R67, 223 R71 and R73, and the circuits connecting them. 225 There are two types of routers in a TTZ: TTZ internal routers and TTZ 226 edge routers. A TTZ internal router is a router inside the TTZ and 227 its adjacent routers are inside the TTZ. A TTZ edge router is a 228 router inside the TTZ and has at least one adjacent router that is 229 outside of the TTZ. 231 The TTZ in the figure above comprises four TTZ edge routers R61, R63, 232 R65 and R67. Each TTZ edge router is connected to at least one 233 router outside of the TTZ. For instance, router R61 is a TTZ edge 234 router since it is connected to router R15, which is outside of the 235 TTZ. 237 In addition, the TTZ comprises two TTZ internal routers R71 and R73. 238 A TTZ internal router is not connected to any router outside of the 239 TTZ. For instance, router R71 is a TTZ internal router since it is 240 not connected to any router outside of the TTZ. It is just connected 241 to routers R61, R63, R65, R67 and R73 inside the TTZ. 243 A TTZ MUST hide the information inside the TTZ from the outside. It 244 MUST NOT directly distribute any internal information about the TTZ 245 to a router outside of the TTZ. 247 For instance, the TTZ in the figure above MUST NOT send the 248 information about TTZ internal router R71 to any router outside of 249 the TTZ in the routing domain; it MUST NOT send the information about 250 the circuit between TTZ router R61 and R65 to any router outside of 251 the TTZ. 253 In order to create a TTZ, we MUST configure the same TTZ ID on the 254 edge routers and identify the TTZ internal circuits on them. In 255 addition, we SHOULD configure the TTZ ID on every TTZ internal router 256 which indicates that every circuit of the router is a TTZ internal 257 circuit. 259 From a router outside of the TTZ, a TTZ is seen as a group of routers 260 fully connected. For instance, router R15 in the figure above, which 261 is outside of TTZ 600, sees TTZ 600 as a group of TTZ edge routers: 262 R61, R63, R65 and R67. These four TTZ edge routers are fully 263 connected. 265 In addition, a router outside of the TTZ sees TTZ edge routers having 266 normal connections to the routers outside of the TTZ. For example, 267 router R15 sees four TTZ edge routers R61, R63, R65 and R67, which 268 have the normal connections to R15, R29, R17 and R23, R25 and R31 269 respectively. 271 5. Extensions to IS-IS Protocols 273 5.1. TTZ TLV 275 A new TLV, which is called TTZ TLV, may be added into a link state 276 PDU(LSP) or a Hello PDU for a TTZ node. It has the following format. 278 TTZ TLV Length in Byte 279 +----------------------+ 280 | Type = TBD | 1 281 +----------------------+ 282 | Length | 1 283 +----------------------+ 284 | Flags | 2 285 +----------------------+ 286 | TTZ ID | 4 287 +----------------------+ 288 | Sub-TLVs | Length of Sub-TLVs 289 +----------------------+ 291 Figure 2: TTZ TLV 293 A TTZ TLV has 1 byte of Type, 1 byte of Length of the value field of 294 the TLV, which is followed by 2 bytes of Flags and 4 bytes of TTZ ID. 295 A TTZ TLV in an LSP may contains a number of sub TLVs and have Flags 296 defined as follows. 298 0 1 299 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 |E|T|M|N|R| 0 | 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 E = 1: Edge router of TTZ 304 T = 1: Distributing TTZ Topology Information for Migration 305 M = 1: Migrating to TTZ 306 N = 1: Distributing Normal Topology Information for Rollback 307 R = 1: Rolling back from TTZ 309 When a router in a TTZ receives a CLI command triggering TTZ 310 information distribution for migration, it updates its LSP by adding 311 a TTZ TLV with T set to 1. When a router in a TTZ receives a CLI 312 command activating migration to TTZ, it sets M to 1 in the TTZ TLV in 313 its LSP. 315 Two new sub-TLVs are defined, which may be added into a TTZ TLV in an 316 LSP. One is TTZ IS Neighbor sub-TLV, or TTZ ISN sub-TLV for short. 317 The other is TTZ ES Neighbor sub-TLV, or TTZ ESN sub-TLV for short. 318 A TTZ ISN sub-TLV contains the information about a number of TTZ IS 319 neighbors connected to a TTZ edge router. It has the format below. 321 TTZ ISN sub-TLV Length in Byte 322 +----------------------+ 323 | Sub-Type = 1 | 1 324 +----------------------+ 325 | Length | n*(IDLength + 5) 326 +----------------------+ 327 | Default Metric(i) | 1 328 +----------------------+ 329 | Delay Metric(i) | 1 330 +----------------------+ 331 | Expense Metric(i) | 1 332 +----------------------+ 333 | Error Metric(i) | 1 334 +----------------------+ 335 | Neighbor ID(i) | IDLength + 1 336 +----------------------+ 338 Figure 3: TTZ ISN sub TLV 340 A TTZ ESN sub-TLV contains the information about a number of TTZ ES 341 neighbors connected to a TTZ edge router. It has the format below. 343 TTZ ESN sub-TLV Length in Byte 344 +----------------------+ 345 | Sub-Type = 2 | 1 346 +----------------------+ 347 | Length | 4 + n*IDLength 348 +----------------------+ 349 | Default Metric | 1 350 +----------------------+ 351 | Delay Metric | 1 352 +----------------------+ 353 | Expense Metric | 1 354 +----------------------+ 355 | Error Metric | 1 356 +----------------------+ 357 | Neighbor ID | IDLength 358 +----------------------+ 359 | . . . . . . | 360 +----------------------+ 361 | Neighbor ID | IDLength 362 +----------------------+ 364 Figure 4: TTZ ESN sub TLV 366 6. Updating LSPs for TTZ 368 6.1. Updating LSP for a TTZ Internal Router 370 A TTZ internal router adds a TTZ TLV into its LSP after it receives 371 an LSP containing a TTZ TLV with T = 1 or a CLI command triggering 372 TTZ information distribution for migration. The TLV has a TTZ ID set 373 to the ID of the TTZ and E bit in Flags set to 0 indicating TTZ 374 internal router. The router floods its LSP to its neighbors in the 375 TTZ. 377 When a router inside the TTZ receives a link state packet (LSP) 378 containing a TTZ TLV from a neighboring router in the TTZ, it stores 379 the link state and floods the link state to the other neighboring 380 routers in the TTZ. 382 6.2. Updating LSP for a TTZ Edge Router 384 For every edge router of a TTZ, it updates its LSP in three steps and 385 floods the LSP to all its neighbors. 387 At first, a TTZ edge router adds a TTZ TLV into its LSP after it 388 receives an LSP containing a TTZ TLV with T = 1 or a CLI command 389 triggering TTZ information distribution for migration. The TLV has a 390 TTZ ID set to the ID of the TTZ, E bit in Flags set to 1 indicating 391 TTZ edge router and a TTZ ISN sub TLV. The sub TLV contains the 392 information about the TTZ IS neighbors connected to the TTZ edge 393 router. In addition, the TLV may has a TTZ ESN sub TLV comprising 394 the information about the TTZ end systems connected to the TTZ edge 395 router. 397 Secondly, it adds each of the other TTZ edge routers as an IS 398 neighbor into the Intermediate System Neighbors TLV in the LSP after 399 it receives an LSP containing a TTZ TLV with M = 1 or a CLI command 400 activating migration to TTZ. The metric to the neighbor is the 401 metric of the shortest path to the edge router within the TTZ. 403 In addition, it adds a Prefix Neighbors TLV into its LSP. The TLV 404 contains a number of address prefixes in the TTZ to be reachable from 405 outside of the TTZ. 407 And then it removes the IS neighbors corresponding to the IS 408 neighbors in the TTZ TLV (i.e., in the TTZ ISN sub TLV) from 409 Intermediate System Neighbors TLV in the LSP, and the ES neighbors 410 corresponding to the ES neighbors in the TTZ TLV (i.e., in the TTZ 411 ESN sub TLV) from End System Neighbors TLV in the LSP. This SHOULD 412 be done after it receives the LSPs for virtualizing TTZ from the 413 other TTZ edges for a given time. 415 7. Establishing Adjacencies 417 7.1. Discover TTZ Neighbor over Normal Adjacency 419 For two routers A and B connected by a P2P circuit and having a 420 normal adjacency, they discover TTZ each other through including a 421 TTZ TLV containing a TTZ ID in their hello packets. If two ends of 422 the circuit have the same TTZ ID, A and B are TTZ neighbors; 423 otherwise, they are not TTZ neighbors, but normal neighbors. 425 For a number of routers connected through a broadcast circuit and 426 having normal adjacencies among them, they also discover TTZ each 427 other through including a TTZ TLV containing a TTZ ID in their hello 428 packets. The DIS for the circuit "forms" TTZ adjacency with each of 429 the other routers if all the routers attached to the circuit have the 430 same TTZ ID configured on the connections to the circuit and included 431 in their hello packets; otherwise, they are not TTZ neighbors, but 432 still normal neighbors. 434 7.2. Establishing TTZ Adjacencies 436 When a router (say A) is connected via a P2P circuit to another 437 router (say B) and there is not any adjacency between them over the 438 circuit, a user configures TTZ on two ends of the circuit to form a 439 TTZ adjacency. 441 Routers A and B include a TTZ TLV containing a TTZ ID in their hello 442 packets. If two routers have the same TTZ IDs in their hellos, an 443 adjacency between these two routers is to be formed; otherwise, no 444 adjacency is formed. 446 For a number of routers connected through a broadcast circuit and 447 having no adjacency among them, they start to form TTZ adjacencies 448 after TTZ is configured on the circuit and a TTZ TLV with a TTZ ID is 449 included in their hello packets. The DIS for the circuit forms TTZ 450 adjacency with each of the other routers if all the routers attached 451 to the circuit have the same TTZ ID configured on the connections to 452 the circuit and included in the hello packets; otherwise, the DIS 453 does not form any adjacency with any router attached to the circuit. 455 7.3. Adjacency between TTZ Edge and Router outside 457 For an edge router in a TTZ, in addition to establishing adjacencies 458 with other routers in the TTZ that have connections with the edge 459 router, it forms an adjacency with any router outside of the TTZ that 460 has a connection with the edge router. 462 When the edge router synchronizes its link state database with the 463 router outside of the TTZ, it sends the router outside of the TTZ the 464 information about all the LSPs except for the LSPs belong to the TTZ 465 that are hidden from any router outside of the TTZ. 467 At the end of the link state database synchronization, the edge 468 router originates its own LSP and sends this LSP to the router 469 outside of the TTZ. This LSP contains two groups of circuits. 471 The first group of circuits are the circuits connecting to the 472 routers outside of the TTZ from this TTZ edge router. The second 473 group of circuits are the "virtual" circuits connecting to the other 474 TTZ edge routers from this TTZ edge router. 476 From the point of view of the router outside of the TTZ, it sees the 477 other end as a normal router and forms the adjacency in the same way 478 as a normal router. It is not aware of anything about its 479 neighboring TTZ. From the LSPs related to the TTZ edge router in the 480 other end, it knows that the TTZ edge router is connected to each of 481 the other TTZ edge routers and some routers outside of the TTZ. 483 8. Distribution of LSPs 485 LSPs can be divided into two classes according to their 486 distributions. One class of LSPs is distributed within a TTZ. The 487 other is distributed through a TTZ. 489 8.1. Distribution of LSPs within TTZ 491 Any LSP generated for a TTZ internal router in a TTZ is distributed 492 within the TTZ. It will not be distributed to any router outside of 493 the TTZ. 495 Any pseudo node LSP generated for a broadcast network inside a TTZ, 496 is distributed within the TTZ. It will not be distributed to any 497 router outside of the TTZ. 499 8.2. Distribution of LSPs through TTZ 501 Any LSP about a link state outside of a TTZ received by an edge 502 router of the TTZ is distributed through the TTZ; and any LSP about a 503 link state for the TTZ generated by a TTZ edge router is distributed 504 through the TTZ. 506 For example, when an edge router of a TTZ receives an LSP for a link 507 state outside of the TTZ from a router outside of the TTZ, it floods 508 it to its neighboring routers both inside the TTZ and outside of the 509 TTZ. This LSP may be any LSP such as a router LSP that is 510 distributed in a domain. 512 The routers in the TTZ continue to flood the LSP. When another edge 513 router of the TTZ receives the LSP, it floods the LSP to its 514 neighboring routers both outside of the TTZ and inside the TTZ. 516 9. Computation of Routing Table 518 The computation of the routing table on a router outside of a TTZ is 519 the same as that described in ISO/SEC 10589. On a router in a TTZ, 520 the computation of the routing table has the same procedure flow as 521 that described in ISO/SEC 10589, with one exception. A router in a 522 TTZ MUST ignore the circuits in the router LSPs generated by the edge 523 routers of the TTZ for virtualizing the TTZ. 525 The routing table on a router inside the TTZ is computed through 526 using the link state database (LSDB) containing the LSPs for the 527 topology of the TTZ and the LSPs for the topology outside of the TTZ. 528 That is that the shortest path to every destination both inside the 529 TTZ and outside of the TTZ is computed over all the circuits 530 including the circuits inside the TTZ and the circuits outside of the 531 TTZ. 533 10. Operations 535 10.1. Configuring TTZ 537 This section proposes some options for configuring a TTZ. 539 1. Configuring TTZ on Every Circuit in TTZ 541 If every circuit in a TTZ is configured with a same TTZ ID as a TTZ 542 circuit, the TTZ is determined. A router with some TTZ circuits and 543 some normal circuits is a TTZ edge router. A router with only TTZ 544 circuits is a TTZ internal router. 546 2. Configuring TTZ on Every Router in TTZ 548 We may configure a same TTZ ID on every router in the TTZ, and on 549 every edge router's circuits connecting to the routers in the TTZ. 551 A router configured with the TTZ ID on some of its circuits is a TTZ 552 edge router. A router configured with the TTZ ID only is a TTZ 553 internal router. All the circuits on a TTZ internal router are TTZ 554 circuits. This option is simpler than the above one. 556 10.2. Smooth Migration to TTZ 558 For a group of routers and a number of circuits connecting the 559 routers in an area, making them transfer to work as a TTZ without any 560 service interruption may take a few of steps. 562 At first, users configure the TTZ feature on every router in the TTZ. 563 In this stage, a router does not update its LSPs. It will discover 564 its TTZ neighbors. 566 Secondly, after configuring the TTZ, users issue a CLI command on one 567 router in the TTZ, which triggers every router in the TTZ to 568 distribute TTZ information among the routers in the TTZ. When the 569 router receives the command, it updates its LSP by adding a TTZ TLV, 570 and distributes the LSP to its TTZ neighbors. The LSP has T = 1 in 571 Flags in the TTZ TLV (indicating TTZ information generation and 572 distribution for migration). When a router in the TTZ receives the 573 LSP with T = 1, it updates its LSP by adding a TTZ TLV. In this 574 stage, every router in the TTZ has dual roles. One is to function as 575 a normal router. The other is to generate and distribute TTZ 576 information. 578 Thirdly, users may check whether every router in the TTZ is ready for 579 transferring to work as a TTZ router. A router in the TTZ is ready 580 after it has received all the necessary information from all the 581 routers in the TTZ. This information may be displayed on a router 582 through a CLI command. 584 And then users activate the TTZ through using a CLI command such as 585 migrate to TTZ on one router in the TTZ. The router transfers to 586 work as a TTZ router, updates its LSP with M = 1 in the TTZ TLV 587 (indicating Migrating to TTZ) after it receives the command. 589 After a router in the TTZ receives the LSP with M = 1, it also 590 transfers to work as a TTZ router. Thus, activating the TTZ on one 591 TTZ router makes every router in the TTZ transfer to work as a TTZ 592 router, which computes routes through using the TTZ topology and the 593 topology outside of the TTZ. 595 For an edge router of the TTZ, transferring to work as a TTZ router 596 comprises updating its LSP to virtualize the TTZ by adding each of 597 the other TTZ edge routers as an IS neighbor and flooding this LSP to 598 all its direct neighboring routers. And then, the TTZ edge router 599 removes the IS neighbors corresponding to the IS neighbors in the TTZ 600 TLV (i.e., in the TTZ ISN sub TLV) from Intermediate System Neighbors 601 TLV in the LSP 603 10.3. Adding a Router into TTZ 605 When a non TTZ router (say R1) is connected via a P2P circuit to a 606 TTZ router (say T1) working as TTZ and there is a normal adjacency 607 between them over the circuit, a user can configure TTZ on two ends 608 of the circuit to add R1 into the TTZ to which T1 belongs. They 609 discover TTZ each other in the same way as described in section 7.1. 611 When a number of non TTZ routers are connected via a broadcast 612 circuit to a TTZ router (say T1) working as TTZ and there are normal 613 adjacencies among them, a user configures TTZ on the connection to 614 the circuit on every router to add the non TTZ routers into the TTZ 615 to which T1 belongs. The DIS for the circuit "forms" TTZ adjacency 616 with each of the other routers if all the routers have the same TTZ 617 ID configured on the connections to the circuit. 619 When a router (say R1) is connected via a P2P circuit to a TTZ router 620 (say T1) and there is not any adjacency between them over the 621 circuit, a user can configure TTZ on two ends of the circuit to add 622 R1 into the TTZ to which T1 belongs. R1 and T1 will form an 623 adjacency in the same way as described in section 7.2. 625 When a router (say R1) is connected via a broadcast circuit to a 626 group of TTZ routers on the circuit and there is not any adjacency 627 between R1 and any over the circuit, a user can configure TTZ on the 628 connection to the circuit on R1 to add R1 into the TTZ to which the 629 TTZ routers belong. R1 starts to form an adjacency with the DIS for 630 the circuit after the configuration. 632 11. Security Considerations 634 The mechanism described in this document does not raise any new 635 security issues for the IS-IS protocols. 637 12. IANA Considerations 639 This document requires the allocation for a new TLV and a couple of 640 new sub TLVs in the new TLV. IANA is requested to assign a new Type 641 (value 150 is suggested) for new TLV TTZ as follows: 643 +========+========+=======+=======+=======+=======+ 644 | Type | Name | IIH | LSP | SNP | Purge | 645 +========+========+=======+=======+=======+=======+ 646 | 150 | TTZ | Y | Y | N | N | 647 +========+========+=======+=======+=======+=======+ 649 This document defines two new Sub-TLVs in TLV 150. The values below 650 are suggested for them subject to assignment by IANA or Expert 651 review. 653 +========+==================================+ 654 | Type | Name and Description | 655 +========+==================================+ 656 | 1 | TTZ ISN, TTZ IS Neighbors | 657 +--------+----------------------------------+ 658 | 2 | TTZ ESN, TTZ ES Neighbors | 659 +========+==================================+ 661 13. Contributors 663 Veerendranatha Reddy Vallem 664 Huawei Technologies 665 Bangalore 666 India 667 Email: veerendranatharv@huawei.com 669 William McCall 670 cisco Systems, Inc. 671 Bellevue, WA 672 USA 673 wimccall@cisco.com 675 14. Acknowledgement 677 The author would like to thank Acee Lindem, Abhay Roy, Dean Cheng, 678 Wenhu Lu, Russ White, Tony Przygienda, Bingzhang Zhao, and Lin Han 679 for their valuable comments. 681 15. Normative References 683 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 684 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 685 RFC2119, March 1997, 686 . 688 [RFC7142] Shand, M. and L. Ginsberg, "Reclassification of RFC 1142 689 to Historic", RFC 7142, DOI 10.17487/RFC7142, 690 February 2014, . 692 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 693 dual environments", RFC 1195, DOI 10.17487/RFC1195, 694 December 1990, . 696 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 697 Engineering", RFC 5305, DOI 10.17487/RFC5305, 698 October 2008, . 700 [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link 701 Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, 702 September 2007, . 704 Authors' Addresses 706 Huaimo Chen 707 Futurewei 708 Boston, MA 709 USA 711 Email: huaimo.chen@futurewei.com 713 Alvaro Retana 714 Futurewei 715 Raleigh, NC 716 USA 718 Email: alvaro.retana@futurewei.com 720 Richard Li 721 Futurewei 722 2330 Central expressway 723 Santa Clara, CA 724 USA 726 Email: richard.li@futurewei.com 728 Anil Kumar S N 729 RtBrick 730 Bangalore 731 India 733 Email: anil.ietf@gmail.com 734 Ning So 735 Plano, TX 75082 736 USA 738 Email: ningso01@gmail.com 740 Vic Liu 741 USA 743 Email: liu.cmri@gmail.com 745 Mehmet Toy 746 Verizon 747 USA 749 Email: mehmet.toy@verizon.com 751 Lei Liu 752 Fijitsu 753 USA 755 Email: liulei.kddi@gmail.com