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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 R. Li 4 Intended status: Experimental Futurewei 5 Expires: August 25, 2021 Y. Yang 6 IBM 7 A. Kumar S N 8 RtBrick 9 Y. Fan 10 Casa Systems 11 N. So 13 V. Liu 15 M. Toy 16 Verizon 17 L. Liu 18 Fujitsu 19 K. Makhijani 20 Futurewei 21 February 21, 2021 23 IS-IS Topology-Transparent Zone 24 draft-ietf-lsr-isis-ttz-02.txt 26 Abstract 28 This document specifies a topology-transparent zone in an IS-IS area. 29 A zone is a subset (block/piece) of an area, which comprises a group 30 of routers and a number of circuits connecting them. It is 31 abstracted as a virtual entity such as a single virtual node or zone 32 edges mesh. Any router outside of the zone is not aware of the zone. 33 The information about the circuits and routers inside the zone is not 34 distributed to any router outside of the zone. 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at https://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on August 25, 2021. 53 Copyright Notice 55 Copyright (c) 2021 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (https://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 71 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 72 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 73 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5 74 3. Zone Abstraction . . . . . . . . . . . . . . . . . . . . . . 5 75 3.1. Node Abstraction Model . . . . . . . . . . . . . . . . . 5 76 3.2. Mesh Abstraction Model . . . . . . . . . . . . . . . . . 6 77 4. Topology-Transparent Zone . . . . . . . . . . . . . . . . . . 6 78 4.1. Zone as a Single Node . . . . . . . . . . . . . . . . . . 6 79 4.1.1. An Example of Zone as a Single Node . . . . . . . . . 7 80 4.1.2. Zone Leader Election . . . . . . . . . . . . . . . . 9 81 4.1.3. LS Generation for Zone as a Single Node . . . . . . . 10 82 4.1.4. Adjacency Establishment . . . . . . . . . . . . . . . 10 83 4.1.5. Computation of Routes . . . . . . . . . . . . . . . . 11 84 4.2. Extensions to Protocols . . . . . . . . . . . . . . . . . 12 85 4.2.1. Zone ID TLV . . . . . . . . . . . . . . . . . . . . . 12 86 4.3. Zone as Edges Full Mesh . . . . . . . . . . . . . . . . . 14 87 4.3.1. An Example of Zone as Edges Full Mesh . . . . . . . . 14 88 4.3.2. Updating LSPs for Zone as Edges Full Mesh . . . . . . 15 89 4.3.3. Computation of Routes . . . . . . . . . . . . . . . . 16 90 4.4. Advertisement of LSPs . . . . . . . . . . . . . . . . . . 16 91 4.4.1. Advertisement of LSPs within Zone . . . . . . . . . . 16 92 4.4.2. Advertisement of LSPs through Zone . . . . . . . . . 17 93 5. Seamless Migration . . . . . . . . . . . . . . . . . . . . . 17 94 5.1. Transfer Zone to a Single Node . . . . . . . . . . . . . 17 95 5.2. Roll Back from Zone as a Single Node . . . . . . . . . . 18 97 6. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 19 98 6.1. Configuring Zone . . . . . . . . . . . . . . . . . . . . 19 99 6.2. Transferring Zone to Node . . . . . . . . . . . . . . . . 20 100 6.3. Rolling back Node to Zone . . . . . . . . . . . . . . . . 20 101 7. Experiment Scope . . . . . . . . . . . . . . . . . . . . . . 21 102 8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 103 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 104 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22 105 11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 22 106 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 107 12.1. Normative References . . . . . . . . . . . . . . . . . . 22 108 12.2. Informative References . . . . . . . . . . . . . . . . . 24 109 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 111 1. Introduction 113 [ISO10589] and [RFC1195] describe two levels of areas in IS-IS, level 114 1 and level 2 areas. There are scalability issues in using areas as 115 the number of routers in a network becomes larger and larger. When 116 an IS-IS area becomes larger, its convergence on a network event such 117 as a link down will take a longer time. During the period of network 118 converging, more traffic that is transported through the network area 119 will get lost. 121 Through splitting the network into multiple level 1 areas connected 122 by level 2, we may extend the network further. However, dividing a 123 network from one area into multiple areas or from a number of 124 existing areas to even more areas can be a challenging and time 125 consuming task since it involves significant network architecture 126 changes. It needs a careful planning and many configurations on the 127 network. 129 These issues can be resolved by using topology-transparent zone 130 (TTZ), which abstracts a zone (i.e., a subset of an area) as a single 131 virtual node or zone edges' mesh with minimum efforts and minimum 132 service interruption. Note that a zone can be an entire area. 134 This document presents topology-transparent zone and specifies 135 extensions to IS-IS that support topology-transparent zone. 137 1.1. Requirements Language 139 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 140 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 141 document are to be interpreted as described in [RFC2119] [RFC8174] 142 when, and only when, they appear in all capitals, as shown here. 144 1.2. Terminology 146 Zone: A subset (block or piece) of an area. In a special case, a 147 zone is an entire area. 149 TTZ: Topology-Transparent Zone (TTZ) is a mechanism that abstracts a 150 zone as a single virtual node or zone edges' full mesh. The 151 virtual node appears connected to all the zone neighbors. 153 TTZ Virtual Entity: A single virtual node or zone edges' full mesh 154 to which a zone is transformed using TTZ. 156 A TTZ: A zone that is (to be) abstracted using TTZ. 158 Zone External Node: A node outside of a zone. 160 Zone Internal Node: A node within a zone without any connection to a 161 node outside of the zone. 163 Zone Edge/Border Node: A node that is part of a zone connecting to a 164 node outside of the zone. 166 Zone Node: A zone internal node or a zone edge/border node (i.e., a 167 node that is part of a zone). 169 Zone Link: A link connecting zone nodes (i.e., a link that is part 170 of a zone). 172 Zone Neighbor Node: A node outside of a zone that is a neighbor of 173 a zone edge/border node. 175 Zone Neighbor: A Zone Neighbor Node. 177 CLI: Command Line Interface. 179 LSP: A Link State Protocol Data Unit (PDU) in IS-IS. An LSP 180 contains link state information. In general, a router/node 181 originates multiple LSPs, distinguished by LSP fragment number, 182 to carry the link state information about it and the links 183 attached to it. 185 LS: Link State. In general, the LS for a node is all the LSPs that 186 the node originates. The LS for a zone is the set of LSPs that 187 all the nodes in the zone originate to carry the information 188 about them and the links attached to them inside the zone. 190 2. Requirements 192 Topology-Transparent Zone (TTZ) may be deployed to resolve some 193 critical issue of scalability in existing networks and future 194 networks. The requirements for TTZ are as follows: 196 o TTZ MUST be backward compatible. When a TTZ is deployed on a set 197 of routers in a network, the routers outside of the TTZ in the 198 network do not need to know or support TTZ. 200 o TTZ MUST support at least one more levels of network hierarchy, in 201 addition to the hierarchies supported by existing IS-IS. 203 o Transforming a zone (i.e., a block of network area) to a TTZ 204 virtual entity SHOULD be smooth with minimum service interruption. 205 A TTZ virtual entity is either a single virtual node or zone 206 edges' full mesh. 208 o Transforming (or say rolling back) a TTZ virtual entity back to 209 its zone (i.e., its original block of network area not using TTZ) 210 (refer to Section 5.2) SHOULD be smooth with minimum service 211 interruption. 213 o The configuration for a TTZ in a network SHOULD be minimal. 215 o The changes on the existing protocols to support TTZ SHOULD be 216 minimal. 218 3. Zone Abstraction 220 When abstracting a zone, a user may select one of two models: node 221 abstraction model and mesh abstraction model. 223 3.1. Node Abstraction Model 225 In node abstraction model (or node model for short), a zone is 226 abstracted as a single virtual node. The virtual node represents the 227 entire zone. It appears connected to all the zone neighbors and is 228 in the same area as those neighbors. 230 Deploying node model may cause changes on some routes since the block 231 of an area (zone) becomes a single virtual node. Some of the routes 232 that are optimal before the abstraction may be changed to be 233 suboptimal after the abstraction (refer to Section 4.1.5). 235 The advantage of node model is that it provides a higher degree of 236 abstraction rate than the mesh model. It is more scalable. 238 3.2. Mesh Abstraction Model 240 In mesh abstraction model (or mesh model for short), a zone is 241 abstracted as its edges' full mesh, there is a full mesh of 242 connections among the edges and each edge is also connected to its 243 neighbors outside of the zone. 245 The advantage of mesh model is that it keeps the routes unchanged. 246 After a zone is abstracted as the full mesh of the edges of the zone, 247 every route is still optimal (refer to Section 4.3.3). 249 The disadvantage of mesh model is that it does not scale when the 250 number of edge nodes of a zone is large. 252 4. Topology-Transparent Zone 254 A Topology-Transparent Zone (TTZ) comprises an Identifier (ID) and a 255 subset (piece/block) of an area such as a Level 2 area in IS-IS. It 256 is abstracted as a single virtual node or its edges' full mesh. TTZ 257 and zone as well as node and router will be used interchangeably 258 below. 260 A zone MUST be within a single area. In addition, all the nodes in a 261 zone MUST reside within a common level. There are three cases. All 262 the nodes in a zone are L1 nodes except for some of edge nodes of the 263 zone may be L1/L2 nodes. All the nodes in a zone are L2 nodes except 264 for some of edge nodes of the zone may be L1/L2 nodes. All the nodes 265 in a zone are L1/L2 nodes. 267 4.1. Zone as a Single Node 269 After a zone is abstracted as a single virtual node having a virtual 270 node ID, every node outside of the zone sees a number of links 271 connected to this single node. Each of these links connects to a 272 zone neighbor. The link states inside the zone are not advertised to 273 any node outside of the zone. The virtual node ID may be derived 274 from the zone ID. The value of the zone ID is transferred to four 275 bytes of an IPv4 address, and then to 12 digitals of the IPv4 address 276 in dotted form. The node ID of 6 bytes is from these 12 digitals, 2 277 digitals for 1 byte. 279 The sections below describe the behaviors of zone nodes when/after a 280 zone is abstracted to a single virtual node. They are summarized as 281 follows. 283 o Zone leader originates the LS (i.e., a set of LSPs) for the 284 virtual node (refer to Section 4.1.3). 286 o Zone nodes re-advertise the LS originated by the zone leader 287 (refer to Section 4.1.3 and Section 4.1.4). 289 o Zone edge/border node forms adjacencies with zone neighbor nodes 290 using the identity of the virtual node not its own identity (refer 291 to Section 4.1.4). 293 o Zone edge/border node re-advertises the LS for the virtual node as 294 it originates the LS (refer to Section 4.1.4). 296 o Zone edge/border node purges its existing LSP and originates a new 297 LSP containing its zone links after receiving the LS for the 298 virtual node (refer to Section 4.1.4). 300 o Zone edge/border nodes do not advertise the LSPs originated by 301 zone nodes to its zone neighbors (refer to Section 4.1.4 and 302 Section 4.4.1). 304 o Zone edge/border nodes continue to operate IS-IS as normal to 305 advertise the LSPs received from its zone neighbors (refer to 306 Section 4.1.4 and Section 4.4.2). 308 o Zone internal nodes continue to operate IS-IS as normal to 309 advertise the LSPs received from its neighbors (refer to 310 Section 4.4.1). 312 o Zone nodes compute routes from the topology without the virtual 313 node (refer to Section 4.1.5). 315 4.1.1. An Example of Zone as a Single Node 317 The figure below shows an example of an area containing a TTZ: TTZ 318 600. 320 TTZ 600 321 \ 322 \ ^~^~^~^~^~^~^~^~^~^~^~^~ 323 ( ) 324 ===[R15]========(==[R61]------------[R63]==)======[R29]=== 325 ||\ ( | \ / | ) || 326 || \ ( | \ / | ) || 327 || \___ ( | \ / | ) || 328 || \ ( | ___\ / | ) || 329 || \ ( | / [R71] | ) || 330 || \( | [R73] / \ | ) || 331 || (\ | / \ | ) || 332 || ( \ | / \ | ) || 333 || ( \| / \ | ) || 334 ===[R17]========(==[R65]------------[R67]==)======[R31]=== 335 \\ (// \\) // 336 || //v~v~v~v~v~v~v~v~v~v~v~\\ || 337 || // \\ || 338 || // \\ || 339 \\ // \\ // 340 ======[R23]==============================[R25]===== 341 // \\ 342 // \\ 344 Figure 1: An Example of TTZ 600 346 The area comprises routers R15, R17, R23, R25, R29 and R31. It also 347 contains TTZ 600, which comprises routers R61, R63, R65, R67, R71 and 348 R73, and the circuits connecting them. 350 There are two types of routers in a TTZ: TTZ internal routers and TTZ 351 edge/border routers. A TTZ internal router is a router inside the 352 TTZ and its adjacent routers are inside the TTZ. A TTZ edge/border 353 router is a router inside the TTZ and has at least one adjacent 354 router that is outside of the TTZ. 356 The TTZ in the figure above comprises four TTZ edge/border routers 357 R61, R63, R65 and R67. Each TTZ edge/border router is connected to 358 at least one router outside of the TTZ. For instance, router R61 is 359 a TTZ edge/border router since it is connected to router R15, which 360 is outside of the TTZ. 362 In addition, the TTZ comprises two TTZ internal routers R71 and R73. 363 A TTZ internal router is not connected to any router outside of the 364 TTZ. For instance, router R71 is a TTZ internal router since it is 365 not connected to any router outside of the TTZ. It is just connected 366 to routers R61, R63, R65, R67 and R73 inside the TTZ. 368 A TTZ MUST hide the information inside the TTZ from the outside. It 369 MUST NOT directly distribute any internal information about the TTZ 370 to a router outside of the TTZ. 372 From a router outside of the TTZ, a TTZ is seen as a single node 373 (refer to the Figure below). For instance, router R15, which is 374 outside of TTZ 600, sees TTZ 600 as a single node Rz, which has 375 normal connections to R15, R29, R17 and R23, R25 and R31. 377 TTZ 600 378 \ 379 \ ^~^~^~^~^~^~^~^~^~^~^~^~ 380 ( ) 381 ===[R15]========( )======[R29]=== 382 ||\ ( ) || 383 || \ ( ) || 384 || \ ( ) || 385 || \ ( ) || 386 || \ ( Rz ) || 387 || \ ( ) || 388 || \ ( ) || 389 || \ ( ) || 390 || \( ) || 391 ===[R17]========( )======[R31]=== 392 \\ ( ) // 393 || //v~v~v~v~v~v~v~v~v~v~v~\\ || 394 || // \\ || 395 || // \\ || 396 \\ // \\ // 397 ======[R23]==============================[R25]===== 398 // \\ 399 // \\ 401 Figure 2: TTZ 600 as Single Node Rz 403 4.1.2. Zone Leader Election 405 A node in a zone is elected as a leader for the zone, which is the 406 node with the highest priority (and the highest node ID when there 407 are more than one nodes having the same highest priority) in the 408 zone. The leader election mechanism described in 409 [I-D.ietf-lsr-dynamic-flooding] is used to elect the leader for the 410 zone. 412 4.1.3. LS Generation for Zone as a Single Node 414 The leader for the zone originates the LS (i.e., set of LSPs) for the 415 zone as a single virtual node and sends it to its neighbors. Each of 416 the nodes in the zone re-advertises the LS to all its neighbors 417 except for the one from which the LS is received. 419 This LS comprises all the adjacencies between the virtual node and 420 the zone neighbors. The System ID of each LSP ID is the ID of the 421 virtual node for the zone. The Source ID or Advertising Node/Router 422 ID is the ID of the virtual node. 424 In addition, this LS may contain the IP prefixes such as the loopback 425 IP addresses inside the zone to be accessed by zone external nodes 426 (i.e., nodes outside of the zone). These IP prefixes are included in 427 the IP internal reachability TLV. 429 When the existing zone leader fails, a new zone leader is elected. 430 The new leader originates the LSPs for the virtual node based on the 431 LSPs received from the failed leader. It retains the System ID of 432 each LSP ID and the live adjacencies between the virtual node and the 433 zone neighbors. 435 4.1.4. Adjacency Establishment 437 A zone edge node X, acting as a proxy for the single virtual node for 438 the zone, forms a new adjacency between the virtual node and a node Y 439 that is outside of the zone and in node X's area. There are two 440 cases. One case is that there is an existing adjacency between X and 441 Y; the other is that no adjacency exists between X and Y. 443 4.1.4.1. New Adjacency with Existing One 445 At first, zone edge node X acting as a proxy for the virtual node 446 creates a new adjacency between the virtual node for the zone and 447 node Y in a normal way. It sends Hellos and other packets containing 448 the virtual node ID as Source ID to node Y. Node Y establishes an 449 adjacency with the virtual node in the normal way. 451 Then, after receiving the LS for the virtual node originated by the 452 zone leader, node X does a number of things as follows. 454 It terminates the existing adjacency between node X and node Y. It 455 stops sending Hellos for the adjacency to node Y. Without receiving 456 Hellos from node X for a given time such as hold-timer interval, node 457 Y removes the adjacency to node X. Even though this adjacency 458 terminates, node X keeps the link to node Y in its LSP. 460 It stops advertising or readvertising the LSPs that are originated by 461 the zone nodes to node Y (also refer to Section 4.4.1). 463 It purges its current LSP and originates a new LSP containing its 464 zone links. The new LSP does not contain the information about the 465 adjacencies to the zone neighbors. It advertises the new LSP to its 466 neighbors in the zone (also refer to Section 4.4.1). It does not 467 advertise the new LSP to its zone neighbors. 469 It re-advertises the LS to all its neighbors except for the one from 470 which the LS is received. It re-advertises the LS to node Y as it 471 originates the LS. 473 It re-advertises the LSP received from zone neighbor Y to its other 474 neighbors, including the nodes in the zone, which re-advertise the 475 LSP (received from Y outside of the zone) as normal IS-IS protocol 476 operations (also refer to Section 4.4.2). 478 In the case where node Y is not in node X's area, is in the backbone 479 and connected to node X, node X, acting as a proxy for the virtual 480 node, creates a new adjacency between the virtual node and node Y in 481 a normal way and sends the LS for the virtual node to node Y if the 482 zone includes all the nodes in its area. 484 4.1.4.2. New Adjacency without Existing One 486 Every IS-IS protocol packet, such as Hello, that zone edge node X 487 originates and sends node Y, uses the virtual node ID as Source ID. 489 When node X synchronizes its link state database (LSDB) with node Y, 490 it sends Y all the link state information except for the link state 491 belonging to the zone that is hidden from the nodes outside of the 492 zone. 494 At the end of the LSDB synchronization, the LS for the zone as a 495 single virtual node is originated by the zone leader and distributed 496 to node Y. This LS contains the adjacencies between the virtual node 497 and all the zone neighbors, including this newly formed zone neighbor 498 Y. 500 Then node X has the same behaviors as those described above except 501 for terminating the existing adjacency and purging its existing LSP. 503 4.1.5. Computation of Routes 505 After a zone is transferred/migrated to a single virtual node, every 506 zone node computes the routes (i.e., shortest paths to the 507 destinations) using the graph consisting of the zone topology, the 508 connections between each zone edge and its zone neighbor, and the 509 topology outside of the zone without the virtual node. The metric of 510 a link outside of the zone is one order of magnitude larger than the 511 metric of a link inside the zone. 513 Every node outside the zone computes the routes using the topology 514 outside of the zone with the virtual node. The node does not have 515 the topology inside the zone. The metric of every link outside of 516 the zone is not changed. 518 4.2. Extensions to Protocols 520 This document defines a new TLV for use in IS-IS as follows. 522 o Zone ID TLV: containing a zone ID, a flags field and optional sub- 523 TLVs. 525 4.2.1. Zone ID TLV 527 The format of IS-IS Zone ID TLV is illustrated below. It MUST be 528 added into an LSP for a zone node. 530 0 1 2 3 531 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 1 532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 533 | Type (TBD1) | Length | Zone ID | 534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 535 | Zone ID (Continue) | 536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 537 | RESV |E| OP | Sub TLVs | 538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 539 ~ ~ 540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 542 Figure 3: IS-IS Zone ID TLV 544 Type (1 byte): TBD1. 546 Length (1 byte): Its value is variable with a minimum of 8. A value 547 larger than 8 means that sub-TLVs are present. If length is less 548 than 8, the TLV MUST be ignored. 550 Zone ID (6 bytes): It is the identifier (ID) of a zone. 552 Flags field (16 bits): one flag bit E, OP of 3 bits, and a reserved 553 subfield are as follows: 555 RESV: Reserved. MUST be send as zero and ignored on receipt. 556 E = 1: Indicating a node is a zone edge node 557 E = 0: Indicating a node is a zone internal node 559 When a Zone ID is configured on a zone node (refer to Section 6.1), 560 the node updates its LSP by adding an IS-IS Zone ID TLV with the Zone 561 ID. If it is a zone internal node, the TLV has its flag E = 0; 562 otherwise (i.e., it is a zone edge node) the TLV has its flag E = 1 563 and includes a Zone ISN Sub TLV containing the zone links configured. 564 Every link of a zone internal node is a zone link. 566 OP Value Meaning (Operation) 567 0x001 (T): Advertising Zone Topology Information for Migration 568 0x010 (M): Migrating Zone to a Virtual Entity such as Virtual Node 569 0x011 (N): Advertising Normal Topology Information for Rollback 570 0x100 (R): Rolling Back from the Virtual Entity 572 The value of OP indicates one of the four operations above. When any 573 of the other values is received, the TLV MUST be ignored. 575 The first two values of OP (i.e., OP = 0x001 and OP = 0x010) are used 576 for transforming a zone to a TTZ virtual entity (refer to 577 Section 5.1). The last two values (i.e., OP = 0x011 and OP = 0x100) 578 are used for transforming (or say rolling back) the TTZ virtual 579 entity back to the zone (refer to Section 5.2). 581 Two new sub-TLVs are defined, which may be added to an IS-IS Zone ID 582 TLV. One is the Zone IS Neighbor sub-TLV, or Zone ISN sub-TLV for 583 short. The other is the Zone ES Neighbor sub-TLV, or Zone ESN sub- 584 TLV for short. A Zone ISN sub-TLV contains the information about a 585 number of IS neighbors in the zone connected to a zone edge node. It 586 has the format below. 588 0 1 2 3 589 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 1 590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 | Type (1) | Length | Neighbor ID(i) | 592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 593 | | 594 + +-----------------------------------------------+ 595 | | Metric (i) | 596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 597 ~ ~ 598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 600 Figure 4: Zone ISN Sub TLV 602 A Zone ISN Sub TLV has 1 byte of Type, 1 byte of Length of 603 n*(IDLength + 3), which is followed by n tuples of Neighbor ID and 604 Metric. 606 A Zone ESN sub-TLV contains the information about a number of ES 607 neighbors in the zone connected to a zone edge node. It has the 608 format below. 610 0 1 2 3 611 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 1 612 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 613 | Type (2) | Length | Neighbor ID(i) | 614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 615 | | 616 + +-----------------------------------------------+ 617 | | Metric (i) | 618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 619 ~ ~ 620 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 622 Figure 5: Zone ESN Sub TLV 624 After a zone ID is configured on a zone internal node (refer to 625 Section 6.1), the zone internal node includes a Zone ID TLV with the 626 zone ID and E = 0 in its LSP. The TLV indicates that the node 627 originates the TLV is a zone internal node and all its links are zone 628 links. 630 After a zone ID is configured on every zone link of a zone edge/ 631 border node (refer to Section 6.1), the zone edge/border node 632 includes a Zone ID TLV with the zone ID, E = 1, Zone ISN Sub TLV and 633 Zone ESN Sub TLV in its LSP. The TLV indicates that the node 634 originates the TLV is a zone edge/border node and all the links in 635 the Sub TLVs are zone links. 637 After all the zone nodes in a zone include their Zone ID TLVs in 638 their LSPs, the zone is determined from the point of view of LSDB. 640 4.3. Zone as Edges Full Mesh 642 4.3.1. An Example of Zone as Edges Full Mesh 644 The figure below illustrates an area from the point of view on a 645 router outside of TTZ 600 after TTZ 600 is created and abstracted as 646 its edges full mesh from Figure 1. 648 TTZ 600 649 \ 650 \ ^~^~^~^~^~^~^~^~^~^~^ 651 ( ) 652 ===[R15]========(==[R61]=========[R63]==)======[R29]=== 653 ||\ ( || \\ // || ) || 654 || \ ( || \\ // || ) || 655 || \ ( || \\ // || ) || 656 || \____ ( || \\// || ) || 657 || \( || //\ || ) || 658 || \ || // \\ || ) || 659 || (\ || // \\ || ) || 660 || ( \ || // \\ || ) || 661 || ( \|| // \\ || ) || 662 ===[R17]========(==[R65]=========[R67]==)=======[R31]=== 663 \\ (// \\) // 664 || //v~v~v~v~v~v~v~v~v~v\\ || 665 || // \\ || 666 || // \\ || 667 \\ // \\ // 668 ======[R23]============================[R25]===== 669 // \\ 670 // \\ 672 Figure 6: TTZ 600 as Edges Full Mesh 674 From a router outside of the TTZ, a TTZ is seen as the TTZ edge 675 routers connected each other. For instance, router R15 sees that 676 R61, R63, R65 and R67 are connected each other. The cost from one 677 edge router to another edge router is the cost of the shortest path 678 between these two routers. 680 The adjacencies between each of the TTZ's edge routers and its 681 neighbors outside the TTZ are not changed. A router outside of the 682 TTZ sees TTZ edge routers having their normal original connections to 683 the routers outside of the TTZ. For example, router R15 sees that 684 R61, R63, R65 and R67 have their normal original connections to R15, 685 R29, R17 and R23, R25 and R31 respectively. 687 4.3.2. Updating LSPs for Zone as Edges Full Mesh 689 For every zone edge node, it updates its LSP in three steps and 690 floods the LSP to all its neighbors. 692 At first, it adds each of the other zone edge nodes as an IS neighbor 693 into the Intermediate System Neighbors TLV in its LSP after it 694 receives an LSP containing an IS-IS Zone ID TLV with OP = M or a 695 command activating migration zone to a TTZ virtual entity. The 696 metric to the neighbor is the metric of the shortest path to the edge 697 node within the zone. 699 In addition, it adds an IP internal reachability TLV into its LSP. 700 The TLV contains a number of IP prefixes in the zone to be reachable 701 from outside of the zone. 703 And then it removes the IS neighbors corresponding to the IS 704 neighbors in the Zone ID TLV (i.e., in the Zone ISN sub TLV) from 705 Intermediate System Neighbors TLV in its LSP, and the ES neighbors 706 corresponding to the ES neighbors in the Zone ID TLV (i.e., in the 707 Zone ESN sub TLV) from End System Neighbors TLV in the LSP. This 708 SHOULD be done after it receives the LSPs for virtualizing zone from 709 the other zone edges for a given time. 711 4.3.3. Computation of Routes 713 After a zone is transferred/migrated to the zone edges' full mesh, 714 every zone node computes the routes (i.e., shortest paths to the 715 destinations) using the graph consisting of the zone topology and the 716 topology outside of the zone without the full mesh. Every node 717 outside the zone computes the routes using the topology outside of 718 the zone with the full mesh. The metric of every link inside and 719 outside of the zone is not changed. 721 4.4. Advertisement of LSPs 723 LSPs can be divided into a couple of classes according to their 724 Advertisements. The first class of LSPs is advertised within a zone. 725 The second is advertised through a zone. 727 4.4.1. Advertisement of LSPs within Zone 729 Any LSP about a link state in a zone is advertised only within the 730 zone. It is not advertised to any router outside of the zone. For 731 example, a LSP generated for a zone internal node is advertised only 732 within the zone. 734 Any LSP generated for a broadcast network in a zone is advertised 735 only within the zone. It is not advertised outside of the zone. 737 After migrating to a zone as a single virtual node or edges' full 738 mesh, every zone edge MUST NOT advertise any LSP belonging to the 739 zone or any information in a LSP belonging to the zone to any node 740 outside of the zone. The zone edge determines whether an LSP is 741 about a zone internal link state by checking if the originating node 742 of the LSP is a zone internal node. 744 For any LSP originated by a node within the zone, every zone edge 745 node MUST NOT advertise it to any node outside of the zone. 747 4.4.2. Advertisement of LSPs through Zone 749 Any LSP about a link state outside of a zone received by a zone edge 750 is advertised using the zone as transit. For example, when a zone 751 edge node receives an LSP from a node outside of the zone, it floods 752 the LSP to its neighbors both inside and outside of the zone. 754 The nodes in the zone continue to flood the LSP. When another zone 755 edge receives the LSP, it floods the LSP to its neighbors both inside 756 and outside of the zone. 758 5. Seamless Migration 760 This section presents the seamless migration between a zone and its 761 single virtual node. 763 5.1. Transfer Zone to a Single Node 765 Transferring a zone to a single virtual node smoothly takes a few 766 steps or stages. 768 At first, a user configures the zone on every node of the zone (refer 769 to Section 6.1). Every zone node updates its LSP by including a Zone 770 ID TLV. For a zone edge node, the TLV has the Zone ID configured, 771 its flag E = 1 and a Zone ISN Sub TLV containing the zone links 772 configured. For a zone internal node, the TLV has the Zone ID 773 configured and its flag E = 0. 775 Second, after finishing the configuration of the zone, a user may 776 issue a command, such as a CLI command, on a zone node, such as the 777 zone leader, to trigger transferring the zone to the single virtual 778 node. When the node receives the command, it updates its LSP by 779 setting OP = T in its Zone ID TLV, which is distributed to every zone 780 node. After receiving the Zone ID TLV with OP = T, every zone edge 781 node, acting as a proxy of the virtual node, establishes a new 782 adjacency between the virtual node and each of its zone neighbor 783 nodes. 785 The command may be replaced by the determination made by a zone node, 786 such as the zone leader. After determining that the configuration of 787 the zone is finished for a given time such as 10 seconds, it updates 788 its LSP by setting OP = T in its Zone ID TLV. The configuration is 789 complete if every zone link configured is bidirectional. For every 790 zone internal node configured with the Zone ID, there is an LSP 791 containing its Zone ID TLV with E = 0 in the LSDB, which indicates 792 that each link from the node (one direction) is a zone link. For 793 every zone edge node, each of its zone links configured from the edge 794 node (one direction) is included in its LSP containing its Zone ID 795 TLV with E = 1 and Zone ISN Sub TLV in the LSDB. 797 Third, after receiving the updated LSPs from all the zone neighbor 798 nodes, the zone leader checks if all the new adjacencies between the 799 virtual node and the zone neighbor nodes have been established. If 800 so, it originates an LS for the virtual node and updates its LSP 801 (i.e., the LSP for itself zone leader) by setting OP = M in its Zone 802 ID TLV, which is distributed to every zone node. 804 After receiving the LS for the virtual node or the Zone ID TLV with 805 OP = M, every zone node migrates to zone as virtual node. Every zone 806 edge node does not send any LS inside the zone to any zone neighbors. 807 It advertises its LSP without any zone links to the nodes outside of 808 the zone or purges its LSP outside of the zone, terminates its 809 adjacency to each of its zone neighbors, but contains the adjacency 810 in its LSP that is distributed within the zone. Every zone node 811 computes the routes according to Section 4.1.5. 813 5.2. Roll Back from Zone as a Single Node 815 After abstracting a zone to a single virtual node, we may want to 816 roll back the node to the zone smoothly in some cases. The process 817 of rolling back has a few steps or stages. 819 At first, a user issues a command, such as a CLI command, on a zone 820 node, such as the zone leader, to start (or prepare) for roll back. 821 When receiving the command, the node triggers the preparation for 822 roll back through updating its LSP by setting OP = N in its Zone ID 823 TLV, which will be distributed to every node in the zone. After 824 receiving the Zone ID TLV with OP = N, every zone edge node 825 establishes a normal adjacency between the edge node and each of its 826 zone neighbor nodes, and advertises the link state of the zone over 827 the adjacency if it crosses the adjacency, but holds off its LSP 828 containing the normal adjacency. 830 Second, a user may issue a command, such as a CLI command, on a zone 831 node, such as the zone leader, to roll back from the virtual node to 832 the zone if the following conditions are met. 834 Condition 1: All the normal adjacencies between every zone edge node 835 and each of its zone neighbor nodes have been established. 837 Condition 2: All the link state about the zone that is supposed to 838 be advertised outside of the zone has been advertised. 840 After receiving the command, the node updates its LSP by setting OP = 841 R in its Zone ID TLV, which is distributed to every zone node. After 842 receiving the Zone ID TLV with OP = R, 844 o every zone edge node, acting as a proxy of the virtual node, 845 terminates the adjacency between the virtual node and each of its 846 zone neighbor nodes and advertises its LSP containing the normal 847 adjacencies between it and each of its zone neighbor nodes; 849 o The zone leader purges the LS for the virtual node abstracted from 850 the zone; and 852 o Every zone node rolls back to normal. 854 The command may be replaced by the determination made by a zone node, 855 such as the zone leader. After determining that all the conditions 856 are met, it updates its LSP by setting OP = R in its Zone ID TLV, 857 which is distributed to every zone node. 859 Condition 1 is met if it has its LSDB containing the link from each 860 zone neighbor node to its zone edge node. That is that for every 861 link from a zone neighbor node to the virtual node in the LSDB, there 862 is a corresponding link from the zone neighbor to a zone edge node. 864 Condition 2 is met after Condition 1 has been met for a given time, 865 such as maximum LSP advertisement time (MaxLSPAdvTime) crossing a 866 network. We may assume that MaxLSPAdvTime is 5 seconds. 868 6. Operations 870 6.1. Configuring Zone 872 In general, a zone is a subset of an area and has a zone ID. It 873 consists of some zone internal nodes and zone edge nodes. To 874 configure it, a user configures this zone ID on every zone internal 875 node and on every zone link of each zone edge node. A zone ID MUST 876 be unique in an AS. It MUST NOT be any IP address in the AS from 877 which a system ID is transformed to and used. 879 When the configuration of the zone ID is not consistent across the 880 zone, some unexpected results will be generated. For example, when 881 two different zone IDs are configured for the zone, two virtual nodes 882 for two zones may be seen in the network. These are not expected. 883 Once the unexpected results are seen, the inconsistent configurations 884 MUST be fixed. 886 A node configured with the zone ID has all its links to be the zone 887 links. The zone internal nodes and all their links plus the zone 888 edge nodes and their zone links constitute the zone. 890 In a special case, a zone is an entire area and has a zone ID. All 891 the links in the area are the zone links of the zone. To configure 892 this zone, a user configures the zone ID on every zone node. 894 6.2. Transferring Zone to Node 896 Transferring a zone to a single virtual node smoothly may take a few 897 steps or stages. 899 At first, a user configures the zone on every node of the zone. 901 After finishing the configuration of the zone, the user may issue a 902 command, such as a CLI command, on a zone node, such as the zone 903 leader, to trigger transferring the zone to the node (refer to 904 Section 5.1). 906 If automatic transferring zone to node is enabled, the user does not 907 need to issue the command. A zone node, such as the zone leader, 908 will trigger transferring the zone to the node after determining that 909 the configuration of the zone has been finished. 911 Then, all the zone nodes, including the zone leader, zone edge nodes 912 and zone internal nodes, work together to make the zone to appear as 913 a single virtual node smoothly in a couple of steps. 915 6.3. Rolling back Node to Zone 917 After abstracting a zone to a single virtual node, we may want to 918 roll back the node to the zone smoothly in some cases. The process 919 of rolling back has a few steps or stages. 921 At first, a user issues a command, such as a CLI command, on a zone 922 node, such as the zone leader, to start (or prepare) for roll back. 923 When receiving the command, the node triggers the preparation for 924 roll back (refer to Section 5.2). 926 Second, a user may issue a command, such as a CLI command, on a zone 927 node, such as the zone leader, to roll back from the virtual node to 928 the zone if it is ready for roll back (refer to Section 5.2). 930 If automatic roll back Node to Zone is enabled, the user does not 931 need to issue the command. A zone node, such as the zone leader, 932 will trigger the roll back after determining that it is ready for 933 roll back. 935 7. Experiment Scope 937 The experiment on TTZ should focus on node model. The experiment on 938 TTZ mesh model in OSPF has been done. The experiment includes the 939 aspects as follows. 941 o Abstraction. A zone (i.e., a block of an area not using TTZ) is 942 abstracted as a single virtual node. The size of the LSDB for the 943 area is reduced. Every node outside of the zone will see the 944 virtual node and the other nodes outside of the zone after the 945 abstraction. It will not see any node in the zone including the 946 edge nodes of the zone. 948 o Separation. Any node that is not participating in a zone does not 949 need to know or support TTZ. 951 o Safety. When a zone is configured correctly, neither zone edge 952 node or zone internal node breaches after the zone is abstracted 953 as a single virtual node. 955 o Alarm on Misconfiguration. Some critical misconfigurations should 956 be detected and alarmed. 958 8. Security Considerations 960 The mechanism described in this document does not raise any new 961 security issues for the IS-IS protocols. It is possible that an 962 attacker may become or act as a zone leader and inject bad LSPs for 963 the zone into the network, which disturbs the operations on the 964 network, especially the IS-IS protocols. Authentication methods 965 described in [RFC5304] and [RFC5310] SHOULD be used to prevent such 966 attack. 968 9. IANA Considerations 970 IANA is requested to make a new allocation in the "IS-IS TLV 971 Codepoint Registry" under the registry name "IS-IS TLV Codepoints" as 972 follows: 974 +==============+===================+=====================+ 975 | TLV Type | TLV Name | reference | 976 +==============+===================+=====================+ 977 | TBD1 | Zone ID | This document | 978 +--------------+-------------------+---------------------+ 979 Note that TBD1 is less than 255. 981 IANA is requested to create a new sub-registry "Sub-TLVs for TLV type 982 TBD1 (Zone ID TLV)" on the IANA IS-IS TLV Codepoints web page as 983 follows: 985 +==============+===================+=====================+ 986 | Type | Name | reference | 987 +==============+===================+=====================+ 988 | 0 | Reserved | 989 +--------------+-------------------+---------------------+ 990 | 1 | Zone ISN | This document | 991 +--------------+-------------------+---------------------+ 992 | 2 | Zone ESN | This document | 993 +--------------+-------------------+---------------------+ 994 | 3 - 255 | Unassigned | 995 +--------------+-------------------+---------------------+ 997 10. Contributors 999 Alvaro Retana 1000 Futurewei 1001 Raleigh, NC 1002 USA 1004 Email: alvaro.retana@futurewei.com 1006 11. Acknowledgement 1008 The authors would like to thank Acee Lindem, Adrian Farrel, Abhay 1009 Roy, Christian Hopps, Dean Cheng, Russ White, Tony Przygienda, Wenhu 1010 Lu, Lin Han, Donald Eastlake, Tony Li, Robert Raszuk, Padmadevi 1011 Pillay Esnault, and Yang Yu for their valuable comments on TTZ. 1013 12. References 1015 12.1. Normative References 1017 [I-D.ietf-lsr-dynamic-flooding] 1018 Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda, 1019 T., Cooper, D., Jalil, L., Dontula, S., and G. Mishra, 1020 "Dynamic Flooding on Dense Graphs", draft-ietf-lsr- 1021 dynamic-flooding-08 (work in progress), December 2020. 1023 [I-D.ietf-spring-segment-routing] 1024 Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., 1025 Litkowski, S., and R. Shakir, "Segment Routing 1026 Architecture", draft-ietf-spring-segment-routing-15 (work 1027 in progress), January 2018. 1029 [ISO10589] 1030 International Organization for Standardization, 1031 "Intermediate System to Intermediate System Intra-Domain 1032 Routing Exchange Protocol for use in Conjunction with the 1033 Protocol for Providing the Connectionless-mode Network 1034 Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002. 1036 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 1037 dual environments", RFC 1195, DOI 10.17487/RFC1195, 1038 December 1990, . 1040 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1041 Requirement Levels", BCP 14, RFC 2119, 1042 DOI 10.17487/RFC2119, March 1997, 1043 . 1045 [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link 1046 Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, 1047 September 2007, . 1049 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 1050 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 1051 2008, . 1053 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 1054 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 1055 2008, . 1057 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 1058 and M. Fanto, "IS-IS Generic Cryptographic 1059 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 1060 2009, . 1062 [RFC7142] Shand, M. and L. Ginsberg, "Reclassification of RFC 1142 1063 to Historic", RFC 7142, DOI 10.17487/RFC7142, February 1064 2014, . 1066 [RFC8099] Chen, H., Li, R., Retana, A., Yang, Y., and Z. Liu, "OSPF 1067 Topology-Transparent Zone", RFC 8099, 1068 DOI 10.17487/RFC8099, February 2017, 1069 . 1071 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1072 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1073 May 2017, . 1075 12.2. Informative References 1077 [Clos] Clos, C., "A Study of Non-Blocking Switching Networks", 1078 The Bell System Technical Journal Vol. 32(2), DOI 1079 10.1002/j.1538-7305.1953.tb01433.x, March 1953, 1080 . 1082 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 1083 in Support of Generalized Multi-Protocol Label Switching 1084 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 1085 . 1087 Authors' Addresses 1089 Huaimo Chen 1090 Futurewei 1091 Boston, MA 1092 USA 1094 Email: huaimo.chen@futurewei.com 1096 Richard Li 1097 Futurewei 1098 2330 Central expressway 1099 Santa Clara, CA 1100 USA 1102 Email: richard.li@futurewei.com 1104 Yi Yang 1105 IBM 1106 Cary, NC 1107 United States of America 1109 Email: yyietf@gmail.com 1111 Anil Kumar S N 1112 RtBrick 1113 Bangalore 1114 India 1116 Email: anil.ietf@gmail.com 1117 Yanhe Fan 1118 Casa Systems 1119 USA 1121 Email: yfan@casa-systems.com 1123 Ning So 1124 Plano, TX 75082 1125 USA 1127 Email: ningso01@gmail.com 1129 Vic Liu 1130 USA 1132 Email: liu.cmri@gmail.com 1134 Mehmet Toy 1135 Verizon 1136 USA 1138 Email: mehmet.toy@verizon.com 1140 Lei Liu 1141 Fujitsu 1142 USA 1144 Email: liulei.kddi@gmail.com 1146 Kiran Makhijani 1147 Futurewei 1148 USA 1150 Email: kiranm@futurewei.com