idnits 2.17.1 draft-ietf-lsr-isis-area-proxy-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords -- however, there's a paragraph with a matching beginning. Boilerplate error? (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (November 18, 2020) is 1252 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- -- Looks like a reference, but probably isn't: '1' on line 860 == Outdated reference: A later version (-18) exists of draft-ietf-lsr-dynamic-flooding-07 == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-11 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force T. Li 3 Internet-Draft S. Chen 4 Intended status: Experimental V. Ilangovan 5 Expires: May 22, 2021 Arista Networks 6 G. Mishra 7 Verizon Inc. 8 November 18, 2020 10 Area Proxy for IS-IS 11 draft-ietf-lsr-isis-area-proxy-05 13 Abstract 15 Link state routing protocols have hierarchical abstraction already 16 built into them. However, when lower levels are used for transit, 17 they must expose their internal topologies to each other, leading to 18 scale issues. 20 To avoid this, this document discusses extensions to the IS-IS 21 routing protocol that would allow level 1 areas to provide transit, 22 yet only inject an abstraction of the level 1 topology into level 2. 23 Each level 1 area is represented as a single level 2 node, thereby 24 enabling greater scale. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on May 22, 2021. 43 Copyright Notice 45 Copyright (c) 2020 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (https://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 61 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 62 2. Area Proxy . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 2.1. Segment Routing . . . . . . . . . . . . . . . . . . . . . 6 64 3. Inside Router Functions . . . . . . . . . . . . . . . . . . . 6 65 3.1. The Area Proxy TLV . . . . . . . . . . . . . . . . . . . 6 66 3.2. Level 2 SPF Computation . . . . . . . . . . . . . . . . . 7 67 3.3. Responsibilities with respect to the Proxy LSP . . . . . 8 68 4. Area Leader Functions . . . . . . . . . . . . . . . . . . . . 8 69 4.1. Area Leader Election . . . . . . . . . . . . . . . . . . 8 70 4.2. Redundancy . . . . . . . . . . . . . . . . . . . . . . . 8 71 4.3. Distributing Area Proxy Information . . . . . . . . . . . 8 72 4.3.1. The Area Proxy System Id Sub-TLV . . . . . . . . . . 8 73 4.3.2. The Area SID Sub-TLV . . . . . . . . . . . . . . . . 9 74 4.4. Proxy LSP Generation . . . . . . . . . . . . . . . . . . 11 75 4.4.1. The Protocols Supported TLV . . . . . . . . . . . . . 11 76 4.4.2. The Area Address TLV . . . . . . . . . . . . . . . . 11 77 4.4.3. The Dynamic Hostname TLV . . . . . . . . . . . . . . 11 78 4.4.4. The IS Neighbors TLV . . . . . . . . . . . . . . . . 11 79 4.4.5. The Extended IS Neighbors TLV . . . . . . . . . . . . 12 80 4.4.6. The MT Intermediate Systems TLV . . . . . . . . . . . 12 81 4.4.7. Reachability TLVs . . . . . . . . . . . . . . . . . . 12 82 4.4.8. The Router Capability TLV . . . . . . . . . . . . . . 13 83 4.4.9. The Multi-Topology TLV . . . . . . . . . . . . . . . 13 84 4.4.10. The SID/Label Binding and The Multi-Topology 85 SID/Label Binding SID TLV . . . . . . . . . . . . . . 14 86 4.4.11. The SRv6 Locator TLV . . . . . . . . . . . . . . . . 14 87 4.4.12. Traffic Engineering Information . . . . . . . . . . . 14 88 4.4.13. The Area SID . . . . . . . . . . . . . . . . . . . . 14 89 5. Inside Edge Router Functions . . . . . . . . . . . . . . . . 15 90 5.1. Generating L2 IIHs to Outside Routers . . . . . . . . . . 15 91 5.2. Filtering LSP information . . . . . . . . . . . . . . . . 15 92 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 93 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 94 8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 95 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 96 9.1. Normative References . . . . . . . . . . . . . . . . . . 17 97 9.2. Informative References . . . . . . . . . . . . . . . . . 18 98 9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 19 99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 101 1. Introduction 103 The IS-IS routing protocol IS-IS [ISO10589] currently supports a two- 104 level hierarchy of abstraction. The fundamental unit of abstraction 105 is the 'area', which is a (hopefully) connected set of systems 106 running IS-IS at the same level. Level 1, the lowest level, is 107 abstracted by routers that participate in both Level 1 and Level 2, 108 and they inject area information into Level 2. Level 2 systems 109 seeking to access Level 1, use this abstraction to compute the 110 shortest path to the Level 1 area. The full topology database of 111 Level 1 is not injected into Level 2, only a summary of the address 112 space contained within the area, so the scalability of the Level 2 113 Link State Database (LSDB) is protected. 115 This works well if the Level 1 area is tangential to the Level 2 116 area. This also works well if there are several routers in both 117 Level 1 and Level 2 and they are adjacent, so Level 2 traffic will 118 never need to transit Level 1 only routers. Level 1 will not contain 119 any Level 2 topology, and Level 2 will only contain area abstractions 120 for Level 1. 122 Unfortunately, this scheme does not work so well if the Level 1 only 123 area needs to provide transit for Level 2 traffic. For Level 2 124 shortest path first (SPF) computations to work correctly, the transit 125 topology must also appear in the Level 2 LSDB. This implies that all 126 routers that could provide transit, plus any links that might also 127 provide Level 2 transit must also become part of the Level 2 128 topology. If this is a relatively tiny portion of the Level 1 area, 129 this is not overly painful. 131 However, with today's data center topologies, this is problematic. A 132 common application is to use a Layer 3 Leaf-Spine (L3LS) topology, 133 which is a folded 3-stage Clos [Clos] fabric. It can also be thought 134 of as a complete bipartite graph. In such a topology, the desire is 135 to use Level 1 to contain the routing dynamics of the entire L3LS 136 topology and then to use Level 2 for the remainder of the network. 137 Leaves in the L3LS topology are appropriate for connection outside of 138 the data center itself, so they would provide connectivity for Level 139 2. If there are multiple connections to Level 2 for redundancy, or 140 other areas, these too would also be made to the leaves in the 141 topology. This creates a difficulty because there are now multiple 142 Level 2 leaves in the topology, with connectivity between the leaves 143 provided by the spines. 145 Following the current rules of IS-IS, all spine routers would 146 necessarily be part of the Level 2 topology, plus all links between a 147 Level 2 leaf and the spines. In the limit, where all leaves need to 148 support Level 2, it implies that the entire L3LS topology becomes 149 part of Level 2. This is seriously problematic as it more than 150 doubles the LSDB held in the L3LS topology and eliminates any 151 benefits of the hierarchy. 153 This document discusses the handling of IP traffic. Supporting MPLS 154 based traffic is a subject for future work. 156 1.1. Requirements Language 158 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 159 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 160 document are to be interpreted as described in BCP 14 [1] [RFC2119] 161 [RFC8174] when, and only when, they appear in all capitals, as shown 162 here. 164 2. Area Proxy 166 To address this, we propose to completely abstract away the details 167 of the Level 1 area topology within Level 2, making the entire area 168 look like a single proxy system directly connected to all of the 169 area's Level 2 neighbors. By only providing an abstraction of the 170 topology, Level 2's requirement for connectivity can be satisfied 171 without the full overhead of the area's internal topology. It then 172 becomes the responsibility of the Level 1 area to ensure the 173 forwarding connectivity that's advertised. 175 For this discussion, we'll consider a single Level 1 IS-IS area to be 176 the Inside Area, and the remainder of the Level 2 area is the Outside 177 Area. All routers within the Inside Area speak Level 1 and Level 2 178 IS-IS on all of the links within the topology. We propose to 179 implement Area Proxy by having a Level 2 Proxy Link State Protocol 180 Data Unit (PDU, LSP) that represents the entire Inside Area. We will 181 refer to this as the Proxy LSP. This is the only LSP from the area 182 that will be flooded into the overall Level 2 LSDB. 184 There are four classes of routers that we need to be concerned with 185 in this discussion: 187 Inside Router A router within the Inside Area that runs Level 1 and 188 Level 2 IS-IS. A router is recognized as an Inside Router by the 189 existence of its LSP in the Level 1 LSDB. 191 Area Leader The Area Leader is an Inside Router that is elected to 192 represent the Level 1 area by injecting the Proxy LSP into the 193 Level 2 LSDB. There may be multiple candidates for Area Leader, 194 but only one is elected at a given time. Any Inside Router can be 195 Area Leader. 197 Inside Edge Router An Inside Edge Router is an Inside Area Router 198 that has at least one Level 2 interface outside of the Inside 199 Area. An interface on an Inside Edge Router that is connected to 200 an Outside Edge Router is an Area Proxy Boundary. 202 Outside Edge Router An Outside Edge Router is a Level 2 router that 203 is outside of the Inside Area that has an adjacency with an Inside 204 Edge Router. 206 Inside Area 208 +--------+ +--------+ 209 | Inside |-----------------| Inside | 210 | Router | | Edge | 211 +--------+ +------------| Router | 212 | / +--------+ 213 | / | 214 +--------+ / =============|====== 215 | Area |/ || | 216 | Leader | || +---------+ 217 +--------+ || | Outside | 218 || | Edge | 219 || | Router | 220 || +---------+ 222 Outside Area 224 An example of router classes 226 All Inside Edge Routers learn the Area Proxy System Identifier from 227 the Area Proxy TLV advertised by the Area Leader and use that as the 228 system identifier in their Level 2 IS-IS Hello PDUs (IIHs) on all 229 Outside interfaces. Outside Edge Routers should then advertise an 230 adjacency to the Area Proxy System Identifier. This allows all 231 Outside Routers to use the Proxy LSP in their SPF computations 232 without seeing the full topology of the Inside Area. 234 Area Proxy functionality assumes that all circuits on Inside Routers 235 are either Level 1-2 circuits within the Inside Area, or Level 2 236 circuits between Outside Edge Routers and Inside Edge Routers. 238 Area Proxy Boundary multi-access circuits (i.e. Ethernets in LAN 239 mode) with multiple Inside Edge Routers on them are not supported. 241 The Inside Edge Router on any boundary LAN MUST NOT flood Inside 242 Router LSPs on this link. Boundary LANs SHOULD NOT be enabled for 243 Level 1. An Inside Edge Router may be elected the DIS for a Boundary 244 LAN. In this case using the Area Proxy System Id as the basis for 245 the LAN pseudonode identifier could create a collision, so the 246 Insider Edge Router SHOULD compose the pseudonode identifier using 247 its native system identifier. This choice of pseudonode identifier 248 may confuse neighbors with an extremely strict implementation, in 249 which case the Inside Edge Router may be configured with priority 0, 250 causing an Outside Router to be elected DIS. 252 2.1. Segment Routing 254 If the Inside Area supports Segment Routing [RFC8402], then all 255 Inside Nodes MUST advertise an SR Global Block (SRGB). The first 256 value of the SRGB advertised by all Inside Nodes MUST start at the 257 same value. The range advertised for the area will be the minimum of 258 all Inside Nodes. 260 To support Segment Routing, the Area Leader will take the global SID 261 information found in the L1 LSDB and convey that to L2 through the 262 Proxy LSP. Prefixes with SID assignments will be copied to the Proxy 263 LSP. Adjacency SIDs for Outside Edge Nodes will be copied to the 264 Proxy LSP. 266 To further extend Segment Routing, it would be helpful to have a 267 segment that refers to the entire Inside Area. This allows a path to 268 refer to an area and have any node within that area accept and 269 forward the packet. In effect, this becomes an anycast SID that is 270 accepted by all Inside Edge Nodes. The information about this SID is 271 distributed in the Area SID Sub-TLV, as part of the Area Leader's 272 Area Proxy TLV (Section 4.3.2). The Inside Edge Nodes MUST establish 273 forwarding based on this SID. The Area Leader SHALL also include the 274 Area SID in the Proxy LSP so that the remainder of L2 can use it for 275 path construction. (Section 4.4.13). 277 3. Inside Router Functions 279 All Inside Routers run Level 1-2 IS-IS and must be explicitly 280 instructed to enable the Area Proxy functionality. To signal their 281 readiness to participate in Area Proxy functionality, they will 282 advertise the Area Proxy TLV in their L2 LSP. 284 3.1. The Area Proxy TLV 286 The Area Proxy TLV serves multiple functions: 288 The presence of the Area Proxy TLV in a node's LSP indicates that 289 the node is enabled for Area Proxy. 291 An LSP containing the Area Proxy TLV is also an Inside Node. All 292 Inside Nodes, including pseudonodes, MUST advertise the Area Proxy 293 TLV. 295 It is a container for sub-TLVs with Area Proxy information. 297 A node advertises the Area Proxy TLV in fragment 0 of its L2 LSP. 298 Nodes MUST NOT advertise the Area Proxy TLV in a L1 LSP. Nodes MUST 299 ignore the Area Proxy TLV if it is found in a L1 LSP. The Area Proxy 300 TLV is not used in the Proxy LSP. The format of the Area Proxy TLV 301 is: 303 0 1 2 304 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | TLV Type | TLV Length | Sub-TLVs ... 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 309 TLV Type: 20 311 TLV Length: length of the sub-TLVs 313 3.2. Level 2 SPF Computation 315 When Outside Routers perform a Level 2 SPF computation, they will use 316 the Proxy LSP for computing a path transiting the Inside Area. 317 Because the topology has been abstracted away, the cost for 318 transiting the Inside Area will be zero. 320 When Inside Routers perform a Level 2 SPF computation, they MUST 321 ignore the Proxy LSP. Further, because these systems do see the 322 Inside Area topology, the link metrics internal to the area are 323 visible. This could lead to different and possibly inconsistent SPF 324 results, potentially leading to forwarding loops. 326 To prevent this, the Inside Routers MUST consider the metrics of 327 links outside of the Inside Area (inter-area metrics) separately from 328 the metrics of the Inside Area links (intra-area metrics). Intra- 329 area metrics MUST be treated as less than any inter-area metric. 330 Thus, if two paths have different total inter-area metrics, the path 331 with the lower inter-area metric would be preferred, regardless of 332 any intra-area metrics involved. However, if two paths have equal 333 inter-area metrics, then the intra-area metrics would be used to 334 compare the paths. 336 Point-to-Point links between two Inside Routers are considered to be 337 Inside Area links. LAN links which have a pseudonode LSP in the 338 Level 1 LSDB are considered to be Inside Area links. 340 3.3. Responsibilities with respect to the Proxy LSP 342 The Area Leader will generate a Proxy LSP that will be flooded across 343 the Inside Area. Inside Routers MUST ignore the contents of the 344 Proxy LSP other than for flooding. The Proxy LSP uses the Area Proxy 345 System Identifier as its Source ID. 347 4. Area Leader Functions 349 The Area Leader has several responsibilities. First, it MUST inject 350 the Area Proxy System Identifier into the Level 2 LSDB. Second, the 351 Area Leader MUST generate the Proxy LSP for the Inside Area. 353 4.1. Area Leader Election 355 The Area Leader is selected using the election mechanisms and TLVs 356 described in Dynamic Flooding for IS-IS 357 [I-D.ietf-lsr-dynamic-flooding]. 359 4.2. Redundancy 361 If the Area Leader fails, another candidate may become Area Leader 362 and MUST regenerate the Proxy LSP. The failure of the Area Leader is 363 not visible outside of the area and appears to simply be an update of 364 the Proxy LSP. 366 For consistency, all Area Leader candidates SHOULD be configured with 367 the same Proxy System Id, Proxy Hostname, and any other information 368 that may be inserted into the Proxy LSP. 370 4.3. Distributing Area Proxy Information 372 The Area Leader is responsible for distributing information about the 373 area to all Inside Nodes. In particular, the Area Leader distributes 374 the Proxy System Id and the Area SID. This is done using two sub- 375 TLVs of the Area Proxy TLV. 377 4.3.1. The Area Proxy System Id Sub-TLV 379 The Area Proxy System Id Sub-TLV MUST be used by the Area Leader to 380 distribute the Area Proxy System Id. This is an additional system 381 identifier that is used by Inside Nodes and an indication that Area 382 Proxy is active. The format of this sub-TLV is: 384 0 1 2 385 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 1 386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 387 | Type | Length | Proxy System ID | 388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 389 | Proxy System Identifier continued | 390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 392 Type: 1 394 Length: length of a system ID (6) 396 Proxy System Identifier: the Area Proxy System Identifier. 398 The Area Leader MUST advertise the Area Proxy System Identifier Sub- 399 TLV when it observes that all Inside Routers are advertising the Area 400 Proxy TLV. Their advertisements indicate that they are individually 401 ready to perform Area Proxy functionality. The Area Leader then 402 advertises the Area Proxy System Identifier TLV to indicate that the 403 Inside Area MUST enable Area Proxy functionality. 405 Other candidates for Area Leader MAY also advertise the Area Proxy 406 System Identifier when they observe that all Inside Routers are 407 advertising the Area Proxy Router Capability. All candidates 408 advertising the Area Proxy System Identifier TLV MUST be advertising 409 the same system identifier. Multiple proxy system identifiers in a 410 single area is a misconfiguration and each unique occurrence SHOULD 411 be logged. 413 The Area Leader and other candidates for Area Leader MAY withdraw the 414 Area Proxy System Identifier when one or more Inside Routers are not 415 advertising the Area Proxy Router Capability. This will disable Area 416 Proxy functionality. However, before withdrawing the Area Proxy 417 System Identifier, an implementation SHOULD protect against 418 unnecessary churn from transients by delaying the withdrawal. The 419 amount of delay is implementation-dependent. 421 4.3.2. The Area SID Sub-TLV 423 The Area SID Sub-TLV allows the Area Leader to advertise a prefix and 424 SID that represents the entirety of the Inside Area to the Outside 425 Area. This sub-TLV is learned by all of the Inside Edge Nodes who 426 should consume this SID at forwarding time. The Area SID Sub-TLV has 427 the format: 429 0 1 2 430 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 1 431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 432 | Type | Length | Flags | 433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 434 | SID/Index/Label (variable) | 435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 436 | Prefix Length | Prefix (variable) | 437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 439 where: 441 Type: 2 443 Length: variable (1 + SID length) 445 Flags: 1 octet. 447 SID/Index/Label: as defined in [RFC8667] Section 2.1.1.1 449 Prefix Length: 1 octet 451 Prefix: 0-16 octets 453 The Flags octet is defined as follows: 455 0 1 2 3 4 5 6 7 456 +-+-+-+-+-+-+-+-+ 457 |F|V|L| | 458 +-+-+-+-+-+-+-+-+ 460 where: 462 F: Address-Family Flag. If unset, then this proxy SID is used 463 when forwarding IPv4-encapsulated traffic. If set, then this 464 proxy SID is used when forwarding IPv6-encapsulated traffic. 466 V: Value Flag. If set, then the proxy SID carries a value. 468 L: Local Flag. If set, then the value/index carried by the proxy 469 SID has local significance. 471 Other bits: MUST be zero when originated and ignored when 472 received. 474 4.4. Proxy LSP Generation 476 Each Inside Router generates a Level 2 LSP, and the Level 2 LSPs for 477 the Inside Edge Routers will include adjacencies to Outside Edge 478 Routers. Unlike normal Level 2 operations, these LSPs are not 479 advertised outside of the Inside Area and MUST be filtered by all 480 Inside Edge Routers to not be flooded to Outside Routers. Only the 481 Proxy LSP is injected into the overall Level 2 LSDB. 483 The Area Leader uses the Level 2 LSPs generated by the Inside Edge 484 Routers to generate the Proxy LSP. This LSP is originated using the 485 Area Proxy System Identifier. The Area Leader MAY also insert the 486 following additional TLVs into the Proxy LSP for additional 487 information for the Outside Area. LSPs generated by unreachable 488 nodes MUST NOT be considered. 490 4.4.1. The Protocols Supported TLV 492 The Area Leader SHOULD insert a Protocols Supported TLV (129) 493 [RFC1195] into the Proxy LSP. The values included in the TLV SHOULD 494 be the protocols supported by the Inside Area. 496 4.4.2. The Area Address TLV 498 The Area Leader SHOULD insert an Area Addresses TLV (1) [ISO10589] 499 into the Proxy LSP. 501 4.4.3. The Dynamic Hostname TLV 503 It is RECOMMENDED that the Area Leader insert the Dynamic Hostname 504 TLV (137) [RFC5301] into the Proxy LSP. The contents of the hostname 505 may be specified by configuration. The presence of the hostname 506 helps to simplify debugging the network. 508 4.4.4. The IS Neighbors TLV 510 The Area Leader MAY insert the IS Neighbors TLV (2) [ISO10589] into 511 the Proxy LSP for Outside Edge Routers. The Area Leader learns of 512 the Outside Edge Routers by examining the LSPs generated by the 513 Inside Edge Routers copying any IS Neighbors TLVs referring to 514 Outside Edge Routers into the Proxy LSP. Since the Outside Edge 515 Routers advertise an adjacency to the Area Proxy System Identifier, 516 this will result in a bi-directional adjacency. 518 An entry for a neighbor in both the IS Neighbors TLV and the Extended 519 IS Neighbors would be functionally redundant, so the Area Leader 520 SHOULD NOT do this. 522 4.4.5. The Extended IS Neighbors TLV 524 The Area Leader MAY insert the Extended IS Reachability TLV (22) 525 [RFC5305] into the Proxy LSP. The Area Leader SHOULD copy each 526 Extended IS Reachability TLV advertised by an Inside Edge Router 527 about an Outside Edge Router into the Proxy LSP. 529 If the Inside Area supports Segment Routing and Segment Routing 530 selects a SID where the L-Flag is unset, then the Area Lead SHOULD 531 include an Adjacency Segment Identifier sub-TLV (31) [RFC8667] using 532 the selected SID. 534 If the inside area supports SRv6, the Area Leader SHOULD copy the 535 "SRv6 End.X SID" and "SRv6 LAN End.X SID" sub-TLVs of the extended IS 536 reachability TLVs advertised by Inside Edge Routers about Outside 537 Edge Routers. 539 If the inside area supports Traffic Engineering (TE), the Area Leader 540 SHOULD copy TE related sub-TLVs [RFC5305] Section 3 to each Extended 541 IS Reachability TLV in the Proxy LSP. 543 4.4.6. The MT Intermediate Systems TLV 545 If the Inside Area supports Multi-Topology, then the Area Leader 546 SHOULD copy each Outside Edge Router advertisement that is advertised 547 by an Inside Edge Router in a MT Intermediate Systems TLV into the 548 Proxy LSP. 550 4.4.7. Reachability TLVs 552 The Area Leader SHOULD insert additional TLVs describing any routing 553 prefixes that should be advertised on behalf of the area. These 554 prefixes may be learned from the Level 1 LSDB, Level 2 LSDB, or 555 redistributed from another routing protocol. This applies to all of 556 various types of TLVs used for prefix advertisement: 558 IP Internal Reachability Information TLV (128) [RFC1195] 560 IP External Reachability Information TLV (130) [RFC1195] 562 Extended IP Reachability TLV (135) [RFC5305] 564 IPv6 Reachability TLV (236) [RFC5308] 566 Multi-Topology Reachable IPv4 Prefixes TLV (235) [RFC5120] 568 Multi-Topology Reachable IPv6 Prefixes TLV (237) [RFC5120] 570 For TLVs in the Level 1 LSDB, for a given TLV type and prefix, the 571 Area Leader SHOULD select the TLV with the lowest metric and copy 572 that TLV into the Proxy LSP. 574 When examining the Level 2 LSDB for this function, the Area Leader 575 SHOULD only consider TLVs advertised by Inside Routers. Further, for 576 prefixes that represent Boundary links, the Area Leader SHOULD copy 577 all TLVs that have unique sub-TLV contents. 579 If the Inside Area supports Segment Routing and the selected TLV 580 includes a Prefix Segment Identifier sub-TLV (3) [RFC8667], then the 581 sub-TLV SHOULD be copied as well. The P-Flag SHOULD be set in the 582 copy of the sub-TLV to indicate that penultimate hop popping SHOULD 583 NOT be performed for this prefix. The E-Flag SHOULD be reset in the 584 copy of the sub-TLV to indicate that an explicit NULL is not 585 required. The R-Flag SHOULD simply be copied. 587 4.4.8. The Router Capability TLV 589 The Area Leader MAY insert the Router Capability TLV (242) [RFC7981] 590 into the Proxy LSP. If Segment Routing is supported by the inside 591 area, as indicated by the presence of an SRGB being advertised by all 592 Inside Nodes, then the Area Leader SHOULD advertise an SR- 593 Capabilities sub-TLV (2) [RFC8667] with an SRGB. The first value of 594 the SRGB is the same value as the first value advertised by all 595 Inside Nodes. The range advertised for the area will be the minimum 596 of all ranges advertised by Inside Nodes. The Area Leader SHOULD use 597 its own Router Id in the Router Capability TLV. 599 If SRv6 Capability sub-TLV [RFC7981] is advertised by all Inside 600 Routers, the Area Leader should insert an SRv6 Capability sub-TLV in 601 the Router Capability TLV. Each flag in the SRv6 Capability sub-TLV 602 should be set if the flag is set by all Inside Routers. 604 If the Node Maximum SID Depth (MSD) sub-TLV [RFC8491] is advertised 605 by all Inside Routers, the Area Leader should advertise common MSD 606 types and the smallest supported MSD values for each type. 608 4.4.9. The Multi-Topology TLV 610 If the Inside Area supports multi-topology, then the Area Leader 611 SHOULD insert the Multi-Topology TLV (229) [RFC5120], including the 612 topologies supported by the Inside Nodes. 614 If any Inside Node is advertising the 'O' (Overload) bit for a given 615 topology, then the Area Leader MUST advertise the 'O' bit for that 616 topology. If any Inside Node is advertising the 'A' (Attach) bit for 617 a given topology, then the Area Leader MUST advertise the 'A' bit for 618 that topology. 620 4.4.10. The SID/Label Binding and The Multi-Topology SID/Label Binding 621 SID TLV 623 If an Inside Node advertises the SID/Label Binding or Multi-Topology 624 SID/Label Binding SID TLV [RFC8667], then the Area Leader MAY copy 625 the TLV to the Proxy LSP. 627 4.4.11. The SRv6 Locator TLV 629 If the inside area supports SRv6, the Area Leader SHOULD copy all 630 SRv6 locator TLVs [I-D.ietf-lsr-isis-srv6-extensions] advertised by 631 Inside Routers to the Proxy LSP. 633 4.4.12. Traffic Engineering Information 635 If the inside area supports TE, the Area Leader SHOULD advertise a TE 636 Router ID TLV (134) [RFC5305] in the Proxy LSP. It SHOULD copy the 637 Shared Risk Link Group (SRLS) TLVs (138) [RFC5307] advertised by 638 Inside Edge Routers about links to Outside Edge Routers. 640 If the inside area supports IPv6 TE, the Area Leader SHOULD advertise 641 an IPv6 TE Router ID TLV (140) [RFC6119] in the Proxy LSP. It SHOULD 642 also copy the IPv6 SRLG TLVs (139) [RFC6119] advertised by Inside 643 Edge Routers about links to Outside Edge Routers. 645 4.4.13. The Area SID 647 When SR is enabled, it may be useful to advertise an Area SID which 648 will direct traffic to any of the Inside Edge Routers. The 649 information for the Area SID is distributed to all Inside Edge 650 Routers using the Area SID sub-TLV (Section 4.3.2) by the Area 651 Leader. 653 The Area Leader SHOULD advertise the Area SID information in the 654 Proxy LSP as a Node SID as defined in [RFC8667] Section 2.1. The 655 advertisement in the Proxy LSP informs the Outside Area that packets 656 directed to the SID will be forwarded to one of the Inside Edge Nodes 657 and the Area SID will be consumed. 659 Other uses of the Area SID and area SID prefix are outside the scope 660 of this document. Documents which define other use cases for the 661 Area SID MUST specify whether the SID value should be the same or 662 different from that used in support of Area Proxy. 664 5. Inside Edge Router Functions 666 The Inside Edge Router has two additional and important functions. 667 First, it MUST generate IIHs that appear to have come from the Area 668 Proxy System Identifier. Second, it MUST filter the L2 LSPs, Partial 669 Sequence Number PDUs (PSNPs), and Complete Sequence Number PDUs 670 (CSNPs) that are being advertised to Outside Routers. 672 5.1. Generating L2 IIHs to Outside Routers 674 The Inside Edge Router has one or more Level 2 interfaces to Outside 675 Routers. These may be identified by explicit configuration or by the 676 fact that they are not also Level 1 circuits. On these Level 2 677 interfaces, the Inside Edge Router MUST NOT send an IIH until it has 678 learned the Area Proxy System Id from the Area Leader. Then, once it 679 has learned the Area Proxy System Id, it MUST generate its IIHs on 680 the circuit using the Proxy System Id as the source of the IIH. 682 Using the Proxy System Id causes the Outside Router to advertise an 683 adjacency to the Proxy System Id, not to the Inside Edge Router, 684 which supports the proxy function. The normal system id of the 685 Inside Edge Router MUST NOT be used as it will cause unnecessary 686 adjacencies to form and subsequently flap. 688 5.2. Filtering LSP information 690 For the area proxy abstraction to be effective the L2 LSPs generated 691 by the Inside Routers MUST be restricted to the Inside Area. The 692 Inside Routers know which system ids are members of the Inside Area 693 based on the advertisement of the Area Proxy TLV. To prevent 694 unwanted LSP information from escaping the Inside Area, the Inside 695 Edge Router MUST perform filtering of LSP flooding, CSNPs, and PSNPs. 696 Specifically: 698 A Level 2 LSP with a source system identifier that is found in the 699 Level 1 LSDB MUST NOT be flooded to an Outside Router. 701 A Level 2 LSP that contains the Area Proxy TLV MUST NOT be flooded 702 to an Outside Router. 704 A Level 2 CSNP sent to an Outside Router MUST NOT contain any 705 information about an LSP with a system identifier found in the 706 Level 1 LSDB. If an Inside Edge Router filters a CSNP and there 707 is no remaining content, then the CSNP MUST NOT be sent. The 708 source address of the CSNP MUST be the Area Proxy System Id. 710 A Level 2 PSNP sent to an Outside Router MUST NOT contain any 711 information about an LSP with a system identifier found in the 712 Level 1 LSDB. If an Inside Edge Router filters a PSNP and there 713 is no remaining content, then the PSNP MUST NOT be sent. The 714 source address of the PSNP MUST be the Area Proxy System Id. 716 6. Acknowledgments 718 The authors would like to thank Bruno Decraene and Gunter Van De 719 Velde for their many helpful comments. The authors would also like 720 to thank a small group that wishes to remain anonymous for their 721 valuable contributions. 723 7. IANA Considerations 725 This memo requests that IANA allocate and assign code point 20 from 726 the IS-IS TLV Codepoints registry for the Area Proxy TLV. The 727 registry fields should be: IIH:n, LSP:y, SNP:n, Purge:n. 729 In association with this, this memo requests that IANA create a 730 registry for code points for the sub-TLVs of the Area Proxy TLV. 732 Name of the registry: Sub-TLVs for TLV 20 (Area Proxy TLV) 734 Required information for registrations: Temporary registrations 735 may be made under the Early IANA Allocation of Standards Track 736 Code Points policy. [RFC7120] Permanent registrations require the 737 publication of an RFC describing the usage of the code point. 739 Applicable registration policy: RFC Required and Expert Review. 740 We propose the initial experts be Chris Hopps, Tony Li, and Sarah 741 Chen. 743 Size, format, and syntax of registry entries: Value (0-255), Name, 744 and Reference 746 Initial assignments and reservations: IANA is requested to assign 747 the following code points: 749 +-------+------------------------------+---------------+ 750 | Value | Name | Reference | 751 +-------+------------------------------+---------------+ 752 | 1 | Area Proxy System Identifier | This document | 753 | 2 | Area SID | This document | 754 +-------+------------------------------+---------------+ 756 8. Security Considerations 758 This document introduces no new security issues. Security of routing 759 within a domain is already addressed as part of the routing protocols 760 themselves. This document proposes no changes to those security 761 architectures. 763 9. References 765 9.1. Normative References 767 [I-D.ietf-lsr-dynamic-flooding] 768 Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda, 769 T., Cooper, D., Jalil, L., Dontula, S., and G. Mishra, 770 "Dynamic Flooding on Dense Graphs", draft-ietf-lsr- 771 dynamic-flooding-07 (work in progress), June 2020. 773 [I-D.ietf-lsr-isis-srv6-extensions] 774 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 775 Z. Hu, "IS-IS Extension to Support Segment Routing over 776 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11 777 (work in progress), October 2020. 779 [ISO10589] 780 International Organization for Standardization, 781 "Intermediate System to Intermediate System Intra-Domain 782 Routing Exchange Protocol for use in Conjunction with the 783 Protocol for Providing the Connectionless-mode Network 784 Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002. 786 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 787 dual environments", RFC 1195, DOI 10.17487/RFC1195, 788 December 1990, . 790 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 791 Requirement Levels", BCP 14, RFC 2119, 792 DOI 10.17487/RFC2119, March 1997, 793 . 795 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 796 Topology (MT) Routing in Intermediate System to 797 Intermediate Systems (IS-ISs)", RFC 5120, 798 DOI 10.17487/RFC5120, February 2008, 799 . 801 [RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange 802 Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301, 803 October 2008, . 805 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 806 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 807 2008, . 809 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 810 in Support of Generalized Multi-Protocol Label Switching 811 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 812 . 814 [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, 815 DOI 10.17487/RFC5308, October 2008, 816 . 818 [RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic 819 Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119, 820 February 2011, . 822 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 823 for Advertising Router Information", RFC 7981, 824 DOI 10.17487/RFC7981, October 2016, 825 . 827 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 828 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 829 May 2017, . 831 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 832 Decraene, B., Litkowski, S., and R. Shakir, "Segment 833 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 834 July 2018, . 836 [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 837 "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, 838 DOI 10.17487/RFC8491, November 2018, 839 . 841 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 842 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 843 Extensions for Segment Routing", RFC 8667, 844 DOI 10.17487/RFC8667, December 2019, 845 . 847 9.2. Informative References 849 [Clos] Clos, C., "A Study of Non-Blocking Switching Networks", 850 The Bell System Technical Journal Vol. 32(2), DOI 851 10.1002/j.1538-7305.1953.tb01433.x, March 1953, 852 . 854 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 855 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 856 2014, . 858 9.3. URIs 860 [1] https://tools.ietf.org/html/bcp14 862 Authors' Addresses 864 Tony Li 865 Arista Networks 866 5453 Great America Parkway 867 Santa Clara, California 95054 868 USA 870 Email: tony.li@tony.li 872 Sarah Chen 873 Arista Networks 874 5453 Great America Parkway 875 Santa Clara, California 95054 876 USA 878 Email: sarahchen@arista.com 880 Vivek Ilangovan 881 Arista Networks 882 5453 Great America Parkway 883 Santa Clara, California 95054 884 USA 886 Email: ilangovan@arista.com 887 Gyan S. Mishra 888 Verizon Inc. 890 13101 Columbia Pike 892 Silver Spring 893 , 895 MD 20904 897 United States of America 899 Phone: 900 301 502-1347 902 Email: 903 gyan.s.mishra@verizon.com