idnits 2.17.1 draft-ietf-lsr-isis-area-proxy-03.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 (August 5, 2020) is 1353 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- -- Looks like a reference, but probably isn't: '1' on line 843 == Outdated reference: A later version (-18) exists of draft-ietf-lsr-dynamic-flooding-07 == Outdated reference: A later version (-19) exists of draft-ietf-lsr-isis-srv6-extensions-08 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--).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: February 6, 2021 Arista Networks 6 G. Mishra 7 Verizon Inc. 8 August 5, 2020 10 Area Proxy for IS-IS 11 draft-ietf-lsr-isis-area-proxy-03 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 February 6, 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 4. Area Leader Functions . . . . . . . . . . . . . . . . . . . . 8 68 4.1. Area Leader Election . . . . . . . . . . . . . . . . . . 8 69 4.2. Redundancy . . . . . . . . . . . . . . . . . . . . . . . 8 70 4.3. Distributing Area Proxy Information . . . . . . . . . . . 8 71 4.3.1. The Area Proxy System Id Sub-TLV . . . . . . . . . . 8 72 4.3.2. The Area SID Sub-TLV . . . . . . . . . . . . . . . . 9 73 4.4. Proxy LSP Generation . . . . . . . . . . . . . . . . . . 10 74 4.4.1. The Protocols Supported TLV . . . . . . . . . . . . . 11 75 4.4.2. The Area Address TLV . . . . . . . . . . . . . . . . 11 76 4.4.3. The Dynamic Hostname TLV . . . . . . . . . . . . . . 11 77 4.4.4. The IS Neighbors TLV . . . . . . . . . . . . . . . . 11 78 4.4.5. The Extended IS Neighbors TLV . . . . . . . . . . . . 11 79 4.4.6. The MT Intermediate Systems TLV . . . . . . . . . . . 12 80 4.4.7. Reachability TLVs . . . . . . . . . . . . . . . . . . 12 81 4.4.8. The Router Capability TLV . . . . . . . . . . . . . . 13 82 4.4.9. The Multi-Topology TLV . . . . . . . . . . . . . . . 13 83 4.4.10. The SID/Label Binding and The Multi-Topology 84 SID/Label Binding SID TLV . . . . . . . . . . . . . . 13 85 4.4.11. The SRv6 Locator TLV . . . . . . . . . . . . . . . . 13 86 4.4.12. Traffic Engineering Information . . . . . . . . . . . 14 87 4.4.13. The Area SID . . . . . . . . . . . . . . . . . . . . 14 88 5. Inside Edge Router Functions . . . . . . . . . . . . . . . . 14 89 5.1. Generating L2 IIHs to Outside Routers . . . . . . . . . . 14 90 5.2. Filtering LSP information . . . . . . . . . . . . . . . . 15 91 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 92 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 93 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 94 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 95 9.1. Normative References . . . . . . . . . . . . . . . . . . 16 96 9.2. Informative References . . . . . . . . . . . . . . . . . 18 97 9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 18 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 100 1. Introduction 102 The IS-IS routing protocol IS-IS [ISO10589] currently supports a two- 103 level hierarchy of abstraction. The fundamental unit of abstraction 104 is the 'area', which is a (hopefully) connected set of systems 105 running IS-IS at the same level. Level 1, the lowest level, is 106 abstracted by routers that participate in both Level 1 and Level 2, 107 and they inject area information into Level 2. Level 2 systems 108 seeking to access Level 1, use this abstraction to compute the 109 shortest path to the Level 1 area. The full topology database of 110 Level 1 is not injected into Level 2, only a summary of the address 111 space contained within the area, so the scalability of the Level 2 112 Link State Database (LSDB) is protected. 114 This works well if the Level 1 area is tangential to the Level 2 115 area. This also works well if there are several routers in both 116 Level 1 and Level 2 and they are adjacent, so Level 2 traffic will 117 never need to transit Level 1 only routers. Level 1 will not contain 118 any Level 2 topology, and Level 2 will only contain area abstractions 119 for Level 1. 121 Unfortunately, this scheme does not work so well if the Level 1 only 122 area needs to provide transit for Level 2 traffic. For Level 2 123 shortest path first (SPF) computations to work correctly, the transit 124 topology must also appear in the Level 2 LSDB. This implies that all 125 routers that could provide transit, plus any links that might also 126 provide Level 2 transit must also become part of the Level 2 127 topology. If this is a relatively tiny portion of the Level 1 area, 128 this is not overly painful. 130 However, with today's data center topologies, this is problematic. A 131 common application is to use a Layer 3 Leaf-Spine (L3LS) topology, 132 which is a folded 3-stage Clos [Clos] fabric. It can also be thought 133 of as a complete bipartite graph. In such a topology, the desire is 134 to use Level 1 to contain the routing dynamics of the entire L3LS 135 topology and then to use Level 2 for the remainder of the network. 136 Leaves in the L3LS topology are appropriate for connection outside of 137 the data center itself, so they would provide connectivity for Level 138 2. If there are multiple connections to Level 2 for redundancy, or 139 other areas, these too would also be made to the leaves in the 140 topology. This creates a difficulty because there are now multiple 141 Level 2 leaves in the topology, with connectivity between the leaves 142 provided by the spines. 144 Following the current rules of IS-IS, all spine routers would 145 necessarily be part of the Level 2 topology, plus all links between a 146 Level 2 leaf and the spines. In the limit, where all leaves need to 147 support Level 2, it implies that the entire L3LS topology becomes 148 part of Level 2. This is seriously problematic as it more than 149 doubles the LSDB held in the L3LS topology and eliminates any 150 benefits of the hierarchy. 152 This document discusses the handling of IP traffic. Supporting MPLS 153 based traffic is a subject for future work. 155 1.1. Requirements Language 157 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 158 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 159 document are to be interpreted as described in BCP 14 [1] [RFC2119] 160 [RFC8174] when, and only when, they appear in all capitals, as shown 161 here. 163 2. Area Proxy 165 To address this, we propose to completely abstract away the details 166 of the Level 1 area topology within Level 2, making the entire area 167 look like a single proxy system directly connected to all of the 168 area's Level 2 neighbors. By only providing an abstraction of the 169 topology, Level 2's requirement for connectivity can be satisfied 170 without the full overhead of the area's internal topology. It then 171 becomes the responsibility of the Level 1 area to ensure the 172 forwarding connectivity that's advertised. 174 For this discussion, we'll consider a single Level 1 IS-IS area to be 175 the Inside Area, and the remainder of the Level 2 area is the Outside 176 Area. All routers within the Inside Area speak Level 1 and Level 2 177 IS-IS on all of the links within the topology. We propose to 178 implement Area Proxy by having a Level 2 Proxy Link State Protocol 179 Data Unit (PDU, LSP) that represents the entire Inside Area. We will 180 refer to this as the Proxy LSP. This is the only LSP from the area 181 that will be flooded into the overall Level 2 LSDB. 183 There are four classes of routers that we need to be concerned with 184 in this discussion: 186 Inside Router A router within the Inside Area that runs Level 1 and 187 Level 2 IS-IS. A router is recognized as an Inside Router by the 188 existence of its LSP in the Level 1 LSDB. 190 Area Leader The Area Leader is an Inside Router that is elected to 191 represent the Level 1 area by injecting the Proxy LSP into the 192 Level 2 LSDB. There may be multiple candidates for Area Leader, 193 but only one is elected at a given time. 195 Inside Edge Router An Inside Edge Router is an Inside Area Router 196 that has at least one Level 2 interface outside of the Inside 197 Area. An interface on an Inside Edge Router that is connected to 198 an Outside Edge Router is an Area Proxy Boundary. 200 Outside Edge Router An Outside Edge Router is a Level 2 router that 201 is outside of the Inside Area that has an adjacency with an Inside 202 Edge Router. 204 Inside Area 206 +--------+ +--------+ 207 | Inside |-----------------| Inside | 208 | Router | | Edge | 209 +--------+ +------------| Router | 210 | / +--------+ 211 | / | 212 +--------+ / =============|====== 213 | Area |/ || | 214 | Leader | || +---------+ 215 +--------+ || | Outside | 216 || | Edge | 217 || | Router | 218 || +---------+ 220 Outside Area 222 An example of router classes 224 All Inside Edge Routers learn the Area Proxy System Identifier from 225 the Level 1 LSDB and use that as the system identifier in their Level 226 2 IS-IS Hello PDUs (IIHs) on all Outside interfaces. Outside Edge 227 Routers should then advertise an adjacency to the Area Proxy System 228 Identifier. This allows all Outside Routers to use the Proxy LSP in 229 their SPF computations without seeing the full topology of the Inside 230 Area. 232 Area Proxy functionality assumes that all circuits on Inside Routers 233 are either Level 1-2 circuits within the Inside Area, or Level 2 234 circuits between Outside Edge Routers and Inside Edge Routers. 236 Area Proxy Boundary multi-access circuits (i.e. Ethernets in LAN 237 mode) with multiple Inside Edge Routers on them are not supported. 238 The Inside Edge Router on any boundary LAN MUST NOT flood Inside 239 Router LSPs on this link. Boundary LANs SHOULD NOT be enabled for 240 Level 1. An Inside Edge Router may be elected the DIS for a Boundary 241 LAN. In this case using the Area Proxy System Id as the basis for 242 the LAN pseudonode identifier could create a collision, so the 243 Insider Edge Router SHOULD compose the pseudonode identifier using 244 its native system identifier. 246 2.1. Segment Routing 248 If the Inside Area supports Segment Routing [RFC8402], then all 249 Inside Nodes MUST advertise an SR Global Block (SRGB). The first 250 value of the SRGB advertised by all Inside Nodes MUST start at the 251 same value. The range advertised for the area will be the minimum of 252 all Inside Nodes. 254 To support Segment Routing, the Area Leader will take the global SID 255 information found in the L1 LSDB and convey that to L2 through the 256 Proxy LSP. Prefixes with SID assignments will be copied to the Proxy 257 LSP. Adjacency SIDs for Outside Edge Nodes will be copied to the 258 Proxy LSP. 260 To further extend Segment Routing, it would be helpful to have a 261 segment that refers to the entire Inside Area. This allows a path to 262 refer to an area and have any node within that area accept and 263 forward the packet. In effect, this becomes an anycast SID that is 264 accepted by all Inside Edge Nodes. The information about this SID is 265 distributed in the Area SID Sub-TLV, as part of the Area Leader's 266 Area Proxy TLV (Section 4.3.2). The Inside Edge Nodes MUST establish 267 forwarding based on this SID. The Area Leader SHALL also include the 268 Area SID in the Proxy LSP so that the remainder of L2 can use it for 269 path construction. (Section 4.4.13). 271 3. Inside Router Functions 273 All Inside Routers run Level 1-2 IS-IS and must be explicitly 274 instructed to enable the Area Proxy functionality. To signal their 275 readiness to participate in Area Proxy functionality, they will 276 advertise the Area Proxy TLV. 278 3.1. The Area Proxy TLV 280 The Area Proxy TLV serves multiple functions: 282 The presence of the Area Proxy TLV in a node's LSP indicates that 283 the node is enabled for Area Proxy. 285 An LSP containing the Area Proxy TLV is also an Inside Node. All 286 Inside Nodes, including pseudonodes, MUST advertise the Area Proxy 287 TLV. 289 It is a container for sub-TLVs with Area Proxy information. 291 A node advertises the Area Proxy TLV in its L2 LSP. The Area Proxy 292 TLV is not used in the Proxy LSP. The format of the Area Proxy TLV 293 is: 295 0 1 2 296 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 298 | TLV Type | TLV Length | Sub-TLVs ... 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 TLV Type: YYY 303 TLV Length: length of the sub-TLVs 305 3.2. Level 2 SPF Computation 307 When Outside Routers perform a Level 2 SPF computation, they will use 308 the Proxy LSP for computing a path transiting the Inside Area. 309 Because the topology has been abstracted away, the cost for 310 transiting the Inside Area will be zero. 312 When Inside Routers perform a Level 2 SPF computation, they MUST 313 ignore the Proxy LSP. Further, because these systems do see the 314 Inside Area topology, the link metrics internal to the area are 315 visible. This could lead to different and possibly inconsistent SPF 316 results, potentially leading to forwarding loops. 318 To prevent this, the Inside Routers MUST consider the metrics of 319 links outside of the Inside Area (inter-area metrics) separately from 320 the metrics of the Inside Area links (intra-area metrics). Intra- 321 area metrics MUST be treated as less than any inter-area metric. 322 Thus, if two paths have different total inter-area metrics, the path 323 with the lower inter-area metric would be preferred, regardless of 324 any intra-area metrics involved. However, if two paths have equal 325 inter-area metrics, then the intra-area metrics would be used to 326 compare the paths. 328 Point-to-Point links between two Inside Routers are considered to be 329 Inside Area links. LAN links which have a pseudonode LSP in the 330 Level 1 LSDB are considered to be Inside Area links. 332 4. Area Leader Functions 334 The Area Leader has several responsibilities. First, it MUST inject 335 the Area Proxy System Identifier into the Level 1 LSDB. Second, the 336 Area Leader MUST generate the Proxy LSP for the Inside Area. 338 4.1. Area Leader Election 340 The Area Leader is selected using the election mechanisms and TLVs 341 described in Dynamic Flooding for IS-IS 342 [I-D.ietf-lsr-dynamic-flooding]. 344 4.2. Redundancy 346 If the Area Leader fails, another candidate may become Area Leader 347 and MUST regenerate the Proxy LSP. The failure of the Area Leader is 348 not visible outside of the area and appears to simply be an update of 349 the Proxy LSP. 351 For consistency, all Area Leader candidates SHOULD be configured with 352 the same Proxy System Id, Proxy Hostname, and any other information 353 that may be inserted into the Proxy LSP. 355 4.3. Distributing Area Proxy Information 357 The Area Leader is responsible for distributing information about the 358 area to all Inside Nodes. In particular, the Area Leader distributes 359 the Proxy System Id and the Area SID. This is done using two sub- 360 TLVs of the Area Proxy TLV. 362 4.3.1. The Area Proxy System Id Sub-TLV 364 The Area Proxy System Id Sub-TLV MUST be used by the Area Leader to 365 distribute the Area Proxy System Id. This is an additional system 366 identifier that is used by Inside Nodes and an indication that Area 367 Proxy is active. The format of this sub-TLV is: 369 0 1 2 370 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 1 371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 372 | Type | Length | Proxy System ID | 373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 374 | Proxy System Identifier continued | 375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 377 Type: AAA 379 Length: length of a system ID (6) 380 Proxy System Identifier: the Area Proxy System Identifier. 382 The Area Leader MUST advertise the Area Proxy System Identifier Sub- 383 TLV when it observes that all Inside Routers are advertising the Area 384 Proxy TLV. Their advertisements indicate that they are individually 385 ready to perform Area Proxy functionality. The Area Leader then 386 advertises the Area Proxy System Identifier TLV to indicate that the 387 Inside Area MUST enable Area Proxy functionality. 389 Other candidates for Area Leader MAY also advertise the Area Proxy 390 System Identifier when they observe that all Inside Routers are 391 advertising the Area Proxy Router Capability. All candidates 392 advertising the Area Proxy System Identifier TLV MUST be advertising 393 the same system identifier. Multiple proxy system identifiers in a 394 single area is a misconfiguration and each unique occurrence SHOULD 395 be logged. 397 The Area Leader and other candidates for Area Leader MAY withdraw the 398 Area Proxy System Identifier when one or more Inside Routers are not 399 advertising the Area Proxy Router Capability. This will disable Area 400 Proxy functionality. However, before withdrawing the Area Proxy 401 System Identifier, an implementation SHOULD protect against 402 unnecessary churn from transients by delaying the withdrawal. The 403 amount of delay is implementation-dependent. 405 4.3.2. The Area SID Sub-TLV 407 The Area SID Sub-TLV allows the Area Leader to advertise a prefix and 408 SID that represents the entirety of the Inside Area to the Outside 409 Area. This sub-TLV is learned by all of the Inside Edge Nodes who 410 should consume this SID at forwarding time. The Area SID Sub-TLV has 411 the format: 413 0 1 2 414 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 1 415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 416 | Type | Length | Flags | 417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 418 | SID/Index/Label (variable) | 419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 420 | Prefix Length | Prefix (variable) | 421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 423 where: 425 Type: BBB 427 Length: variable (1 + SID length) 428 Flags: 1 octet. 430 SID/Index/Label: as defined in [RFC8667] Section 2.1.1.1 432 Prefix Length: 1 octet 434 Prefix: 0-16 octets 436 The Flags octet is defined as follows: 438 0 1 2 3 4 5 6 7 439 +-+-+-+-+-+-+-+-+ 440 |F|V|L| | 441 +-+-+-+-+-+-+-+-+ 443 where: 445 F: Address-Family Flag. If unset, then this proxy SID is used 446 when forwarding IPv4-encapsulated traffic. If set, then this 447 proxy SID is used when forwarding IPv6-encapsulated traffic. 449 V: Value Flag. If set, then the proxy SID carries a value. 451 L: Local Flag. If set, then the value/index carried by the proxy 452 SID has local significance. 454 Other bits: MUST be zero when originated and ignored when 455 received. 457 4.4. Proxy LSP Generation 459 Each Inside Router generates a Level 2 LSP, and the Level 2 LSPs for 460 the Inside Edge Routers will include adjacencies to Outside Edge 461 Routers. Unlike normal Level 2 operations, these LSPs are not 462 advertised outside of the Inside Area and MUST be filtered by all 463 Inside Edge Routers to not be flooded to Outside Routers. Only the 464 Proxy LSP is injected into the overall Level 2 LSDB. 466 The Area Leader uses the Level 2 LSPs generated by the Inside Edge 467 Routers to generate the Proxy LSP. This LSP is originated using the 468 Area Proxy System Identifier. The Area Leader MAY also insert the 469 following additional TLVs into the Proxy LSP for additional 470 information for the Outside Area. LSPs generated by unreachable 471 nodes MUST NOT be considered. 473 4.4.1. The Protocols Supported TLV 475 The Area Leader SHOULD insert a Protocols Supported TLV (129) 476 [RFC1195] into the Proxy LSP. The values included in the TLV SHOULD 477 be the protocols supported by the Inside Area. 479 4.4.2. The Area Address TLV 481 The Area Leader SHOULD insert an Area Addresses TLV (1) [ISO10589] 482 into the Proxy LSP. 484 4.4.3. The Dynamic Hostname TLV 486 It is RECOMMENDED that the Area Leader insert the Dynamic Hostname 487 TLV (137) [RFC5301] into the Proxy LSP. The contents of the hostname 488 may be specified by configuration. The presence of the hostname 489 helps to simplify debugging the network. 491 4.4.4. The IS Neighbors TLV 493 The Area Leader MAY insert the IS Neighbors TLV (2) [ISO10589] into 494 the Proxy LSP for Outside Edge Routers. The Area Leader learns of 495 the Outside Edge Routers by examining the LSPs generated by the 496 Inside Edge Routers copying any IS Neighbors TLVs referring to 497 Outside Edge Routers into the Proxy LSP. Since the Outside Edge 498 Routers advertise an adjacency to the Area Proxy System Identifier, 499 this will result in a bi-directional adjacency. 501 An entry for a neighbor in both the IS Neighbors TLV and the Extended 502 IS Neighbors would be functionally redundant, so the Area Leader 503 SHOULD NOT do this. 505 4.4.5. The Extended IS Neighbors TLV 507 The Area Leader MAY insert the Extended IS Reachability TLV (22) 508 [RFC5305] into the Proxy LSP. The Area Leader SHOULD copy each 509 Extended IS Reachability TLV advertised by an Inside Edge Router 510 about an Outside Edge Router into the Proxy LSP. 512 If the Inside Area supports Segment Routing and Segment Routing 513 selects a SID where the L-Flag is unset, then the Area Lead SHOULD 514 include an Adjacency Segment Identifier sub-TLV (31) [RFC8667] using 515 the selected SID. 517 If the inside area supports SRv6, the Area Leader SHOULD copy the 518 "SRv6 End.X SID" and "SRv6 LAN End.X SID" sub-TLVs of the extended IS 519 reachability TLVs advertised by Inside Edge Routers about Outside 520 Edge Routers. 522 If the inside area supports Traffic Engineering (TE), the Area Leader 523 SHOULD copy TE related sub-TLVs [RFC5305] Section 3 to each Extended 524 IS Reachability TLV in the Proxy LSP. 526 4.4.6. The MT Intermediate Systems TLV 528 If the Inside Area supports Multi-Topology, then the Area Leader 529 SHOULD copy each Outside Edge Router advertisement that is advertised 530 by an Inside Edge Router in a MT Intermediate Systems TLV into the 531 Proxy LSP. 533 4.4.7. Reachability TLVs 535 The Area Leader SHOULD insert additional TLVs describing any routing 536 prefixes that should be advertised on behalf of the area. These 537 prefixes may be learned from the Level 1 LSDB, Level 2 LSDB, or 538 redistributed from another routing protocol. This applies to all of 539 various types of TLVs used for prefix advertisement: 541 IP Internal Reachability Information TLV (128) [RFC1195] 543 IP External Reachability Information TLV (130) [RFC1195] 545 Extended IP Reachability TLV (135) [RFC5305] 547 IPv6 Reachability TLV (236) [RFC5308] 549 Multi-Topology Reachable IPv4 Prefixes TLV (235) [RFC5120] 551 Multi-Topology Reachable IPv6 Prefixes TLV (237) [RFC5120] 553 For TLVs in the Level 1 LSDB, for a given TLV type and prefix, the 554 Area Leader SHOULD select the TLV with the lowest metric and copy 555 that TLV into the Proxy LSP. 557 When examining the Level 2 LSDB for this function, the Area Leader 558 SHOULD only consider TLVs advertised by Inside Routers. Further, for 559 prefixes that represent Boundary links, the Area Leader SHOULD copy 560 all TLVs that have unique sub-TLV contents. 562 If the Inside Area supports Segment Routing and the selected TLV 563 includes a Prefix Segment Identifier sub-TLV (3) [RFC8667], then the 564 sub-TLV SHOULD be copied as well. The P-Flag SHOULD be set in the 565 copy of the sub-TLV to indicate that penultimate hop popping SHOULD 566 NOT be performed for this prefix. The E-Flag SHOULD be reset in the 567 copy of the sub-TLV to indicate that an explicit NULL is not 568 required. The R-Flag SHOULD simply be copied. 570 4.4.8. The Router Capability TLV 572 The Area Leader MAY insert the Router Capability TLV (242) [RFC7981] 573 into the Proxy LSP. If Segment Routing is supported by the inside 574 area, as indicated by the presence of an SRGB being advertised by all 575 Inside Nodes, then the Area Leader SHOULD advertise an SR- 576 Capabilities sub-TLV (2) [RFC8667] with an SRGB. The first value of 577 the SRGB is the same value as the first value advertised by all 578 Inside Nodes. The range advertised for the area will be the minimum 579 of all ranges advertised by Inside Nodes. The Area Leader SHOULD use 580 its own Router Id in the Router Capability TLV. 582 If SRv6 Capability sub-TLV [RFC7981] is advertised by all Inside 583 Routers, the Area Leader should insert an SRv6 Capability sub-TLV in 584 the Router Capability TLV. Each flag in the SRv6 Capability sub-TLV 585 should be set if the flag is set by all Inside Routers. 587 If the Node Maximum SID Depth (MSD) sub-TLV [RFC8491] is advertised 588 by all Inside Routers, the Area Leader should advertise common MSD 589 types and the smallest supported MSD values for each type. 591 4.4.9. The Multi-Topology TLV 593 If the Inside Area supports multi-topology, then the Area Leader 594 SHOULD insert the Multi-Topology TLV (229) [RFC5120], including the 595 topologies supported by the Inside Nodes. 597 If any Inside Node is advertising the 'O' (Overload) bit for a given 598 topology, then the Area Leader MUST advertise the 'O' bit for that 599 topology. If any Inside Node is advertising the 'A' (Attach) bit for 600 a given topology, then the Area Leader MUST advertise the 'A' bit for 601 that topology. 603 4.4.10. The SID/Label Binding and The Multi-Topology SID/Label Binding 604 SID TLV 606 If an Inside Node advertises the SID/Label Binding or Multi-Topology 607 SID/Label Binding SID TLV [RFC8667], then the Area Leader MAY copy 608 the TLV to the Proxy LSP. 610 4.4.11. The SRv6 Locator TLV 612 If the inside area supports SRv6, the Area Leader SHOULD copy all 613 SRv6 locator TLVs [I-D.ietf-lsr-isis-srv6-extensions] advertised by 614 Inside Routers to the Proxy LSP. 616 4.4.12. Traffic Engineering Information 618 If the inside area supports TE, the Area Leader SHOULD advertise a TE 619 Router ID TLV (134) [RFC5305] in the Proxy LSP. It SHOULD copy the 620 Shared Risk Link Group (SRLS) TLVs (138) [RFC5307] advertised by 621 Inside Edge Routers about links to Outside Edge Routers. 623 If the inside area supports IPv6 TE, the Area Leader SHOULD advertise 624 an IPv6 TE Router ID TLV (140) [RFC6119] in the Proxy LSP. It SHOULD 625 also copy the IPv6 SRLG TLVs (139) [RFC6119] advertised by Inside 626 Edge Routers about links to Outside Edge Routers. 628 4.4.13. The Area SID 630 When SR is enabled, it may be useful to advertise an Area SID which 631 will direct traffic to any of the Inside Edge Routers. The 632 information for the Area SID is distributed to all Inside Edge 633 Routers using the Area SID sub-TLV (Section 4.3.2) by the Area 634 Leader. 636 The Area Leader SHOULD advertise the Area SID information in the 637 Proxy LSP as a Node SID as defined in [RFC8667] Section 2.1. The 638 advertisement in the Proxy LSP informs the remainder of the network 639 that packets directed to the SID will be forwarded by one of the 640 Inside Edge Nodes and the Area SID will be consumed. 642 Other uses of the Area SID are outside the scope of this document. 643 Documents which define other use cases for the Area SID MUST specify 644 whether the SID value should be the same or different from that used 645 in support of Area Proxy. 647 5. Inside Edge Router Functions 649 The Inside Edge Router has two additional and important functions. 650 First, it MUST generate IIHs that appear to have come from the Area 651 Proxy System Identifier. Second, it MUST filter the L2 LSPs, Partial 652 Sequence Number PDUs (PSNPs), and Complete Sequence Number PDUs 653 (CSNPs) that are being advertised to Outside Routers. 655 5.1. Generating L2 IIHs to Outside Routers 657 The Inside Edge Router has one or more Level 2 interfaces to Outside 658 Routers. These may be identified by explicit configuration or by the 659 fact that they are not also Level 1 circuits. On these Level 2 660 interfaces, the Inside Edge Router MUST NOT send an IIH until it has 661 learned the Area Proxy System Id from the Area Leader. Then, once it 662 has learned the Area Proxy System Id, it MUST generate its IIHs on 663 the circuit using the Proxy System Id as the source of the IIH. 665 Using the Proxy System Id causes the Outside Router to advertise an 666 adjacency to the Proxy System Id, not to the Inside Edge Router, 667 which supports the proxy function. The normal system id of the 668 Inside Edge Router MUST NOT be used as it will cause unnecessary 669 adjacencies to form and subsequently flap. 671 5.2. Filtering LSP information 673 For the area proxy abstraction to be effective the L2 LSPs generated 674 by the Inside Routers MUST be restricted to the Inside Area. The 675 Inside Routers know which system ids are members of the Inside Area 676 based on the advertisement of the Area Proxy TLV. To prevent 677 unwanted LSP information from escaping the Inside Area, the Inside 678 Edge Router MUST perform filtering of LSP flooding, CSNPs, and PSNPs. 679 Specifically: 681 A Level 2 LSP with a source system identifier that is found in the 682 Level 1 LSDB MUST NOT be flooded to an Outside Router. 684 A Level 2 LSP that contains the Area Proxy TLV MUST NOT be flooded 685 to an Outside Router. 687 A Level 2 CSNP sent to an Outside Router MUST NOT contain any 688 information about an LSP with a system identifier found in the 689 Level 1 LSDB. If an Inside Edge Router filters a CSNP and there 690 is no remaining content, then the CSNP MUST NOT be sent. The 691 source address of the CSNP MUST be the Area Proxy System Id. 693 A Level 2 PSNP sent to an Outside Router MUST NOT contain any 694 information about an LSP with a system identifier found in the 695 Level 1 LSDB. If an Inside Edge Router filters a PSNP and there 696 is no remaining content, then the PSNP MUST NOT be sent. The 697 source address of the PSNP MUST be the Area Proxy System Id. 699 6. Acknowledgments 701 The authors would like to thank Bruno Decraene and Gunter Van De 702 Velde for their many helpful comments. The authors would also like 703 to thank a small group that wishes to remain anonymous for their 704 valuable contributions. 706 7. IANA Considerations 708 This memo requests that IANA allocate and assign one code point from 709 the IS-IS TLV Codepoints registry for the Area Proxy TLV (YYY). The 710 registry fields should be: IIH:n, LSP:y, SNP:n, Purge:n. 712 In association with this, this memo requests that IANA create a 713 registry for code points for the sub-TLVs of the Area Proxy TLV. 715 Name of the registry: Sub-TLVs for TLV YYY (Area Proxy TLV) 717 Required information for registrations: Temporary registrations 718 may be made under the Early IANA Allocation of Standards Track 719 Code Points policy. [RFC7120] Permanent registrations require the 720 publication of an RFC describing the usage of the code point. 722 Applicable registration policy: RFC Required and Expert Review. 723 We propose the initial experts be Chris Hopps, Tony Li, and Sarah 724 Chen. 726 Size, format, and syntax of registry entries: Value (0-255), Name, 727 and Reference 729 Initial assignments and reservations: IANA is requested to assign 730 the following code points: 732 +-------+------------------------------+---------------+ 733 | Value | Name | Reference | 734 +-------+------------------------------+---------------+ 735 | AAA | Area Proxy System Identifier | This document | 736 | BBB | Area SID | This document | 737 +-------+------------------------------+---------------+ 739 8. Security Considerations 741 This document introduces no new security issues. Security of routing 742 within a domain is already addressed as part of the routing protocols 743 themselves. This document proposes no changes to those security 744 architectures. 746 9. References 748 9.1. Normative References 750 [I-D.ietf-lsr-dynamic-flooding] 751 Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda, 752 T., Cooper, D., Jalil, L., Dontula, S., and G. Mishra, 753 "Dynamic Flooding on Dense Graphs", draft-ietf-lsr- 754 dynamic-flooding-07 (work in progress), June 2020. 756 [I-D.ietf-lsr-isis-srv6-extensions] 757 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 758 Z. Hu, "IS-IS Extension to Support Segment Routing over 759 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08 760 (work in progress), April 2020. 762 [ISO10589] 763 International Organization for Standardization, 764 "Intermediate System to Intermediate System Intra-Domain 765 Routing Exchange Protocol for use in Conjunction with the 766 Protocol for Providing the Connectionless-mode Network 767 Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002. 769 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 770 dual environments", RFC 1195, DOI 10.17487/RFC1195, 771 December 1990, . 773 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 774 Requirement Levels", BCP 14, RFC 2119, 775 DOI 10.17487/RFC2119, March 1997, 776 . 778 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 779 Topology (MT) Routing in Intermediate System to 780 Intermediate Systems (IS-ISs)", RFC 5120, 781 DOI 10.17487/RFC5120, February 2008, 782 . 784 [RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange 785 Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301, 786 October 2008, . 788 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 789 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 790 2008, . 792 [RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions 793 in Support of Generalized Multi-Protocol Label Switching 794 (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008, 795 . 797 [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, 798 DOI 10.17487/RFC5308, October 2008, 799 . 801 [RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic 802 Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119, 803 February 2011, . 805 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 806 for Advertising Router Information", RFC 7981, 807 DOI 10.17487/RFC7981, October 2016, 808 . 810 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 811 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 812 May 2017, . 814 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 815 Decraene, B., Litkowski, S., and R. Shakir, "Segment 816 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 817 July 2018, . 819 [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 820 "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, 821 DOI 10.17487/RFC8491, November 2018, 822 . 824 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 825 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 826 Extensions for Segment Routing", RFC 8667, 827 DOI 10.17487/RFC8667, December 2019, 828 . 830 9.2. Informative References 832 [Clos] Clos, C., "A Study of Non-Blocking Switching Networks", 833 The Bell System Technical Journal Vol. 32(2), DOI 834 10.1002/j.1538-7305.1953.tb01433.x, March 1953, 835 . 837 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 838 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 839 2014, . 841 9.3. URIs 843 [1] https://tools.ietf.org/html/bcp14 845 Authors' Addresses 846 Tony Li 847 Arista Networks 848 5453 Great America Parkway 849 Santa Clara, California 95054 850 USA 852 Email: tony.li@tony.li 854 Sarah Chen 855 Arista Networks 856 5453 Great America Parkway 857 Santa Clara, California 95054 858 USA 860 Email: sarahchen@arista.com 862 Vivek Ilangovan 863 Arista Networks 864 5453 Great America Parkway 865 Santa Clara, California 95054 866 USA 868 Email: ilangovan@arista.com 870 Gyan S. Mishra 871 Verizon Inc. 873 13101 Columbia Pike 875 Silver Spring 876 , 878 MD 20904 880 United States of America 882 Phone: 883 301 502-1347 885 Email: 886 gyan.s.mishra@verizon.com