idnits 2.17.1 draft-li-lsr-isis-area-proxy-01.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). == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: If the Inside Area supports Segment Routing and the selected TLV includes a Prefix Segment Identifier sub-TLV (3) [RFC8667], then the sub-TLV SHOULD be copied as well. The P-Flag SHOULD be set in the copy of the sub-TLV to indicate that penultimate hop popping SHOULD not be performed for this prefix. -- The document date (December 24, 2019) is 1578 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '1' on line 781 == Outdated reference: A later version (-18) exists of draft-ietf-lsr-dynamic-flooding-04 ** Downref: Normative reference to an Experimental draft: draft-ietf-lsr-dynamic-flooding (ref. 'I-D.ietf-lsr-dynamic-flooding') -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10589' ** Obsolete normative reference: RFC 3784 (Obsoleted by RFC 5305) Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 3 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: Standards Track Arista Networks 5 Expires: June 26, 2020 December 24, 2019 7 Area Proxy for IS-IS 8 draft-li-lsr-isis-area-proxy-01 10 Abstract 12 Link state routing protocols have hierarchical abstraction already 13 built into them. However, when lower levels are used for transit, 14 they must expose their internal topologies to each other, leading to 15 scale issues. 17 To avoid this, this document discusses extensions to the IS-IS 18 routing protocol that would allow level 1 areas to provide transit, 19 yet only inject an abstraction of the level 1 topology into level 2. 20 Each level 1 area is represented as a single level 2 node, thereby 21 enabling greater scale. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on June 26, 2020. 40 Copyright Notice 42 Copyright (c) 2019 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (https://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 58 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 59 2. Area Proxy . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 2.1. Segment Routing . . . . . . . . . . . . . . . . . . . . . 5 61 3. Inside Router Functions . . . . . . . . . . . . . . . . . . . 6 62 3.1. The Area Proxy Router Capability . . . . . . . . . . . . 6 63 3.2. Level 2 SPF Computation . . . . . . . . . . . . . . . . . 6 64 4. Area Leader Functions . . . . . . . . . . . . . . . . . . . . 7 65 4.1. Area Leader Election . . . . . . . . . . . . . . . . . . 7 66 4.2. Redundancy . . . . . . . . . . . . . . . . . . . . . . . 7 67 4.3. The Area Proxy TLV . . . . . . . . . . . . . . . . . . . 7 68 4.3.1. The Area Proxy System Id Sub-TLV . . . . . . . . . . 8 69 4.3.2. The Area Proxy Prefix SID Sub-TLV . . . . . . . . . . 9 70 4.3.2.1. Topology . . . . . . . . . . . . . . . . . . . . 10 71 4.3.2.2. Flags . . . . . . . . . . . . . . . . . . . . . . 10 72 4.3.2.3. The SID/Label Sub-Sub-TLV . . . . . . . . . . . . 11 73 4.4. Area Proxy LSP Generation . . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . . . 12 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 5. Inside Edge Router Functions . . . . . . . . . . . . . . . . 13 86 5.1. Generating L2 IIHs to Outside Routers . . . . . . . . . . 13 87 5.2. Filtering LSP information . . . . . . . . . . . . . . . . 14 88 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 89 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 90 8. Security Considerations . . . . . . . . . . . . . . . . . . . 15 91 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 92 9.1. Normative References . . . . . . . . . . . . . . . . . . 15 93 9.2. Informative References . . . . . . . . . . . . . . . . . 17 94 9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 17 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 97 1. Introduction 99 The IS-IS routing protocol IS-IS [ISO10589] currently supports a two- 100 level hierarchy of abstraction. The fundamental unit of abstraction 101 is the 'area', which is a (hopefully) connected set of systems 102 running IS-IS at the same level. Level 1, the lowest level, is 103 abstracted by routers that participate in both Level 1 and Level 2, 104 and they inject area information into Level 2. Level 2 systems 105 seeking to access Level 1, use this abstraction to compute the 106 shortest path to the Level 1 area. The full topology database of 107 Level 1 is not injected into Level 2, only a summary of the address 108 space contained within the area, so the scalability of the Level 2 109 Link State Database (LSDB) is protected. 111 This works well if the Level 1 area is tangential to the Level 2 112 area. This also works well if there are several routers in both 113 Level 1 and Level 2 and they are adjacent, so Level 2 traffic will 114 never need to transit Level 1 only routers. Level 1 will not contain 115 any Level 2 topology, and Level 2 will only contain area abstractions 116 for Level 1. 118 Unfortunately, this scheme does not work so well if the Level 1 only 119 area needs to provide transit for Level 2 traffic. For Level 2 120 shortest path first (SPF) computations to work correctly, the transit 121 topology must also appear in the Level 2 LSDB. This implies that all 122 routers that could provide transit, plus any links that might also 123 provide Level 2 transit must also become part of the Level 2 124 topology. If this is a relatively tiny portion of the Level 1 area, 125 this is not overly painful. 127 However, with today's data center topologies, this is problematic. A 128 common application is to use a Layer 3 Leaf-Spine (L3LS) topology, 129 which is a folded 3-stage Clos [Clos] fabric. It can also be thought 130 of as a complete bipartite graph. In such a topology, the desire is 131 to use Level 1 to contain the routing dynamics of the entire L3LS 132 topology and then to use Level 2 for the remainder of the network. 133 Leaves in the L3LS topology are appropriate for connection outside of 134 the data center itself, so they would provide connectivity for Level 135 2. If there are multiple connections to Level 2 for redundancy, or 136 other areas, these too would also be made to the leaves in the 137 topology. This creates a difficulty because there are now multiple 138 Level 2 leaves in the topology, with connectivity between the leaves 139 provided by the spines. 141 Following the current rules of IS-IS, all spine routers would 142 necessarily be part of the Level 2 topology, plus all links between a 143 Level 2 leaf and the spines. In the limit, where all leaves need to 144 support Level 2, it implies that the entire L3LS topology becomes 145 part of Level 2. This is seriously problematic as it more than 146 doubles the LSDB held in the L3LS topology and eliminates any 147 benefits of the hierarchy. 149 This document discusses the handling of IP traffic. Supporting MPLS 150 based traffic is a subject for future work. 152 1.1. Requirements Language 154 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 155 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 156 document are to be interpreted as described in BCP 14 [1] [RFC2119] 157 [RFC8174] when, and only when, they appear in all capitals, as shown 158 here. 160 2. Area Proxy 162 To address this, we propose to completely abstract away the details 163 of the Level 1 area topology within Level 2, making the entire area 164 look like a single proxy system directly connected to all of the 165 area's Level 2 neighbors. By only providing an abstraction of the 166 topology, Level 2's requirement for connectivity can be satisfied 167 without the full overhead of the area's internal topology. It then 168 becomes the responsibility of the Level 1 area to ensure the 169 forwarding connectivity that's advertised. 171 For this discussion, we'll consider a single Level 1 IS-IS area to be 172 the Inside Area, and the remainder of the Level 2 area is the Outside 173 Area. All routers within the Inside Area speak Level 1 and Level 2 174 IS-IS on all of the links within the topology. We propose to 175 implement Area Proxy by having a Level 2 Proxy Link State Protocol 176 Data Unit (PDU, LSP) that represents the entire Inside Area. This is 177 the only LSP from the area that will be flooded into the overall 178 Level 2 LSDB. 180 There are four classes of routers that we need to be concerned with 181 in this discussion: 183 Inside Router A router within the Inside Area that runs Level 1 and 184 Level 2 IS-IS. A router is recognized as an Inside Router by the 185 existence of its LSP in the Level 1 LSDB. 187 Area Leader The Area Leader is an Inside Router that is elected to 188 represent the Level 1 area by injecting the Proxy LSP into the 189 Level 2 LSDB. There may be multiple candidates for Area Leader, 190 but only one is elected at a given time. 192 Inside Edge Router An Inside Edge Router is an Inside Area Router 193 that has at least one Level 2 interface outside of the Inside 194 Area. An interface on an Inside Edge Router that is connected to 195 an Outside Edge Router is an Area Proxy Boundary. 197 Outside Edge Router An Outside Edge Router is a Level 2 router that 198 is outside of the Inside Area that has an adjacency with an Inside 199 Edge Router. 201 All Inside Edge Routers learn the Area Proxy System Identifier from 202 the Level 1 LSDB and use that as the system identifier in their Level 203 2 IS-IS Hello PDUs (IIHs) on all Outside interfaces. Outside Edge 204 Routers should then advertise an adjacency to the Area Proxy System 205 Identifier. This allows all Outside Routers to use the Proxy LSP in 206 their SPF computations without seeing the full topology of the Inside 207 Area. 209 Area Proxy functionality assumes that all circuits on Inside Routers 210 are either Level 1-2 circuits within the Inside Area, or Level 2 211 circuits between Outside Edge Routers and Inside Edge Routers. 213 Area Proxy Boundary multi-access circuits (i.e. Ethernets in LAN 214 mode) with multiple Inside Edge Routers and Outside Routers are not 215 recommended. The Inside Edge Routers MUST NOT flood Inside Router 216 LSPs on this link and thus the Boundary LAN does not provide 217 connectivity within the Inside Area. Boundary LANs SHOULD NOT be 218 enabled for Level 1. An Inside Edge Router may be elected the DIS 219 for a Boundary LAN. In this case using the Area Proxy System Id as 220 the basis for the LAN pseudonode identifier could create a collision, 221 so the Insider Edge Router SHOULD compose the pseudonode identifier 222 using its native system identifier. 224 2.1. Segment Routing 226 If the Inside Area supports Segment Routing [RFC8402], then all 227 Inside Nodes MUST advertise an SR Global Block (SRGB). The values of 228 the SRGB advertised by all Inside Nodes MUST be the same. 230 To support Segment Routing, the Area Leader will take the global SID 231 information found in the L1 LSDB and convey that to L2 through the 232 Proxy LSP. Prefixes with SID assignments will be copied to the Proxy 233 LSP. Adjacency SIDs for Outside Edge Nodes will be copied to the 234 Proxy LSP. 236 To further extend Segment Routing, it would be helpful to have a SID 237 that refers to the entire Inside Area. This allows a path to refer 238 to an area and have any node within that area accept and forward the 239 packet. In effect, this becomes an anycast SID that is accepted by 240 all Inside Edge Nodes. The information about this SID is distributed 241 in the Area Proxy Prefix SID Sub-TLV, as part of the Area Leader's L1 242 LSP. The Inside Edge Nodes MUST establish forwarding based on this 243 SID. The Area Leader SHALL also include the prefix and SID in the 244 Area Proxy LSP so that the remainder of L2 can use it for path 245 construction. 247 3. Inside Router Functions 249 All Inside Routers run Level 1-2 IS-IS and must be explicitly 250 instructed to enable the Area Proxy functionality. To signal their 251 readiness to participate in Area Proxy functionality, they will 252 advertise the Area Proxy Router Capability as part of its Level 1 253 Router Capability TLV. 255 3.1. The Area Proxy Router Capability 257 The Area Proxy Router Capability is a sub-TLV of the Router 258 Capability TLV [RFC7981] and has the following format: 260 0 1 261 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 263 | TLV Type | TLV Length | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 TLV Type: YYY 268 TLV Length: 0 270 A router advertising this TLV indicates that it is running Level 1-2 271 and is prepared to perform Area Proxy functions. 273 3.2. Level 2 SPF Computation 275 When Outside Routers perform a Level 2 SPF computation, they will use 276 the Area Proxy LSP for computing a path transiting the Inside Area. 277 Because the topology has been abstracted away, the cost for 278 transiting the Inside Area will be zero. 280 When Inside Routers perform a Level 2 SPF computation, they MUST 281 ignore the Area Proxy LSP. Further, because these systems do see the 282 Inside Area topology, the link metrics internal to the area are 283 visible. This could lead to different and possibly inconsistent SPF 284 results, potentially leading to forwarding loops. 286 To prevent this, the Inside Routers MUST consider the metrics of 287 links outside of the Inside Area (inter-area metrics) separately from 288 the metrics of the Inside Area links (intra-area metrics). Intra- 289 area metrics MUST be treated as less than any inter-area metric. 290 Thus, if two paths have different total inter-area metrics, the path 291 with the lower inter-area metric would be preferred, regardless of 292 any intra-area metrics involved. However, if two paths have equal 293 inter-area metrics, then the intra-area metrics would be used to 294 compare the paths. 296 Point-to-Point links between two Inside Routers are considered to be 297 Inside Area links. LAN links which have a pseudonode LSP in the 298 Level 1 LSDB are considered to be Inside Area links. 300 4. Area Leader Functions 302 The Area Leader has several responsibilities. First, it MUST inject 303 the Area Proxy System Identifier into the Level 1 LSDB. Second, the 304 Area Leader MUST generate the Proxy LSP for the Inside Area. 306 4.1. Area Leader Election 308 The Area Leader is selected using the election mechanisms and TLVs 309 described in Dynamic Flooding for IS-IS 310 [I-D.ietf-lsr-dynamic-flooding]. 312 4.2. Redundancy 314 If the Area Leader fails, another candidate may become Area Leader 315 and MUST regenerate the Area Proxy LSP. The failure of the Area 316 Leader is not visible outside of the area and appears to simply be an 317 update of the Area Proxy LSP. 319 For consistency, all Area Leader candidates SHOULD be configured with 320 the same Proxy System Id, Proxy Hostname, and any other information 321 that may be inserted into the Proxy LSP. 323 4.3. The Area Proxy TLV 325 The Area Proxy TLV is a container for sub-TLVs with Area Proxy 326 Information. This TLV is injected into the Area Leader's Level 1 327 LSP. 329 The format of the Area Proxy TLV is: 331 0 1 2 332 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 | TLV Type | TLV Length | Sub-TLVs ... 335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 336 TLV Type: XXX 338 TLV Length: length of the sub-TLVs 340 4.3.1. The Area Proxy System Id Sub-TLV 342 The Area Proxy System Id Sub-TLV MUST be used by the Area Leader to 343 distribute the Area Proxy System Id. This is an additional system 344 identifier that is used by Inside Nodes. The format of this sub-TLV 345 is: 347 0 1 2 348 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 1 349 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 350 | Type | Length | Proxy System ID | 351 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 352 | Proxy System Identifier continued | 353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 355 Type: AAA 357 Length: length of a system ID (6) 359 Proxy System Identifier: the Area Proxy System Identifier. 361 The Area Leader SHOULD advertise the Area Proxy System Identifier 362 Sub-TLV when it observes that all Inside Routers are advertising the 363 Area Proxy Router Capability. Their advertisements indicate that 364 they are individually ready to perform Area Proxy functionality. The 365 Area Leader then advertises the Area Proxy System Identifier TLV to 366 indicate that the Inside Area SHOULD enable Area Proxy functionality. 368 Other candidates for Area Leader MAY also advertise the Area Proxy 369 System Identifier when they observe that all Inside Routers are 370 advertising the Area Proxy Router Capability. All candidates 371 advertising the Area Proxy System Identifier TLV MUST be advertising 372 the same system identifier. Multiple proxy system identifiers in a 373 single area is a misconfiguration and each unique occurrence SHOULD 374 be logged. 376 The Area Leader and other candidates for Area Leader MAY withdraw the 377 Area Proxy System Identifier when one or more Inside Routers are not 378 advertising the Area Proxy Router Capability. This will disable Area 379 Proxy functionality. However, before withdrawing the Area Proxy 380 System Identifier, an implementation SHOULD protect against 381 unnecessary churn from transients by delaying the withdrawal. The 382 amount of delay is implementation-dependent. 384 4.3.2. The Area Proxy Prefix SID Sub-TLV 386 The Area Proxy Prefix SID Sub-TLV allows the Area Leader to advertise 387 a SID that represents the entirety of the Inside Area to all of the 388 nodes in the area. This prefix and SID SHOULD also advertised in the 389 Proxy Node LSP using a normal Prefix-SID sub-TLV within an 390 appropriate reachability TLV. The Area Proxy Prefix SID Sub-TLV has 391 the format: 393 0 1 2 394 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 1 395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 396 | Type | Length | Topology | 397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 398 | Flags | Reserved | Range | 399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 400 | Prefix Length | Prefix (variable) // 401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 402 | Sub-Sub-TLVs (variable) | 403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 405 where: 407 Type: BBB 409 Length: variable (7 + Prefix Length + sub-TLV length) 411 Topology: 2 octets, see below. 413 Flags: 1 octet, see below. 415 Reserved: Reserved bits. MUST be zero on transmission, ignored on 416 reception. 418 Range: 2 octets. This field is not used and MUST be set to 1 for 419 compatibility with [RFC8667]. 421 Prefix Length: 1 octet, the length of the prefix in bits. Only 422 the most significant octets of the prefix are encoded. 424 Prefix: The prefix being advertised. If the Prefix Length is not 425 a multiple of 8, then any trailing bits are set to zero. 427 Sub-Sub-TLVs: variable length, see below. 429 4.3.2.1. Topology 431 Topology is defined as: 433 0 1 434 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 436 | Resvd | MT ID | 437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 439 where: 441 Resvd: Reserved bits. MUST be zero on transmission and ignored on 442 reception. 444 MT ID: MT ID is a 12-bit field containing the ID of the topology 445 being announced. [RFC5120] 447 4.3.2.2. Flags 449 The Flags octet is defined as follows: 451 0 1 2 3 4 5 6 7 452 +-+-+-+-+-+-+-+-+ 453 |F|M|S|D|A| | 454 +-+-+-+-+-+-+-+-+ 456 where: 458 F: Address-Family Flag. If unset, then the prefix carries an IPv4 459 prefix. If set, then the prefix carries an IPv6 prefix. 461 M: Not used. MUST be zero when originated and ignored when 462 received. Retained for compatibility with [RFC8667]. 464 S: Not used. MUST be zero when originated and ignored when 465 received. Retained for compatibility with [RFC8667]. 467 D: Not used. MUST be zero when originated and ignored when 468 received. Retained for compatibility with [RFC8667]. 470 A: Not used. MUST be zero when originated and ignored when 471 received. Retained for compatibility with [RFC8667]. 473 Other bits: MUST be zero when originated and ignored when 474 received. 476 4.3.2.3. The SID/Label Sub-Sub-TLV 478 The SID/Label Sub-Sub-TLV is defined in Section 2.3 of [RFC8667]. 480 4.4. Area Proxy LSP Generation 482 Each Inside Router generates a Level 2 LSP, and the Level 2 LSPs for 483 the Inside Edge Routers will include adjacencies to Outside Edge 484 Routers. Unlike normal Level 2 operations, these LSPs are not 485 advertised outside of the Inside Area and MUST be filtered by all 486 Inside Edge Routers to not be flooded to Outside Routers. Only the 487 Area Proxy LSP is injected into the overall Level 2 LSDB. 489 The Area Leader uses the Level 2 LSPs generated by the Inside Edge 490 Routers to generate the Area Proxy LSP. This LSP is originated using 491 the Area Proxy System Identifier. The Area Leader MAY also insert 492 the following additional TLVs into the Area Proxy LSP for additional 493 information for the Outside Area. 495 4.4.1. The Protocols Supported TLV 497 The Area Leader SHOULD insert a Protocols Supported TLV (129) 498 [RFC1195] into the Area Proxy LSP. The values included in the TLV 499 SHOULD be the protocols supported by the Inside Area. 501 4.4.2. The Area Address TLV 503 The Area Leader SHOULD insert an Area Addresses TLV (1) [ISO10589] 504 into the Area Proxy LSP. 506 4.4.3. The Dynamic Hostname TLV 508 It is RECOMMENDED that the Area Leader insert the Dynamic Hostname 509 TLV (137) [RFC5301] into the Area Proxy LSP. The contents of the 510 hostname may be specified by configuration. The presence of the 511 hostname helps to simplify debugging the network. 513 4.4.4. The IS Neighbors TLV 515 The Area Leader MAY insert the IS Neighbors TLV (2) [ISO10589] into 516 the Area Proxy LSP once for each Outside Edge Router. The Area 517 Leader learns of the Outside Edge Routers by examining the LSPs 518 generated by the Inside Edge Routers and using the lowest metric for 519 each Outside Edge Router. Since the Outside Edge Routers also 520 advertise an adjacency to the Area Proxy System Identifier, this will 521 result in a bi-directional adjacency. 523 An entry for a neighbor in both the IS Neighbors TLV and the Extended 524 IS Neighbors would be functionally redundant, so the Area Leader 525 SHOULD NOT do this. 527 4.4.5. The Extended IS Neighbors TLV 529 The Area Leader MAY insert the Extended IS Reachability TLV (22) 530 [RFC3784] into the Area Proxy LSP. The Area Leader SHOULD copy the 531 lowest metric advertisement of each Outside Edge Router in an 532 Extended IS Reachability TLV into the Proxy LSP. 534 If the Inside Area supports Segment Routing and Segment Routing 535 selects a SID where the L-Flag is unset, then the Area Lead SHOULD 536 include an Adjacency Segment Identifier sub-TLV (31) [RFC8667] using 537 the selected SID. 539 4.4.6. The MT Intermediate Systems TLV 541 If the Inside Area supports Multi-Topology, then the Area Leader 542 SHOULD copy each Outside Edge Router advertisement that is advertised 543 by an Inside Edge Router in a MT Intermediate Systems TLV into the 544 Proxy LSP. 546 4.4.7. Reachability TLVs 548 The Area Leader SHOULD insert additional TLVs describing any routing 549 prefixes that should be advertised on behalf of the area. These 550 prefixes may be learned from the Level 1 LSDB, Level 2 LSDB, or 551 redistributed from another routing protocol. This applies to all of 552 various types of TLVs used for prefix advertisement: 554 IP Internal Reachability Information TLV (128) [RFC1195] 556 IP External Reachability Information TLV (130) [RFC1195] 558 Extended IP Reachability TLV (135) [RFC5305] 560 IPv6 Reachability TLV (236) [RFC5308] 562 Multi-Topology Reachable IPv4 Prefixes TLV (235) [RFC5120] 564 Multi-Topology Reachable IPv6 Prefixes TLV (237) [RFC5120] 566 For TLVs in the Level 1 LSDB, for a given TLV type and prefix, the 567 Area Leader SHOULD select the TLV with the lowest metric and copy 568 that TLV into the Area Proxy LSP. 570 When examining the Level 2 LSDB for this function, the Area Leader 571 SHOULD only consider TLVs advertised by Inside Routers. Further, for 572 prefixes that represent Boundary links, the Area Leader SHOULD copy 573 all TLVs that have unique sub-TLV contents. 575 If the Inside Area supports Segment Routing and the selected TLV 576 includes a Prefix Segment Identifier sub-TLV (3) [RFC8667], then the 577 sub-TLV SHOULD be copied as well. The P-Flag SHOULD be set in the 578 copy of the sub-TLV to indicate that penultimate hop popping SHOULD 579 not be performed for this prefix. 581 4.4.8. The Router Capability TLV 583 The Area Leader MAY insert the Router Capability TLV (242) [RFC7981] 584 into the Area Proxy LSP. If Segment Routing is supported by the 585 inside area, as indicated by the presence of an SRGB being advertised 586 by all Inside Nodes, then the Area Leader SHOULD advertise an SR- 587 Capabilities sub-TLV (2) [RFC8667] with an SRGB identical to that 588 advertised by all Inside Routers. 590 4.4.9. The Multi-Topology TLV 592 If the Inside Area supports multi-topology, then the Area Leader 593 SHOULD insert the Multi-Topology TLV (229) [RFC5120], including the 594 topologies supported by the Inside Area. 596 4.4.10. The SID/Label Binding and The Multi-Topology SID/Label Binding 597 SID TLV 599 If an Inside Node advertises the SID/Label Binding or Multi-Topology 600 SID/Label Binding SID TLV [RFC8667], then the Area Leader MAY copy 601 the TLV to the Area Proxy LSP. 603 5. Inside Edge Router Functions 605 The Inside Edge Router has two additional and important functions. 606 First, it MUST generate IIHs that appear to have come from the Area 607 Proxy System Identifier. Second, it MUST filter the L2 LSPs, Partial 608 Sequence Number PDUs (PSNPs), and Complete Sequence Number PDUs 609 (CSNPs) that are being advertised to Outside Routers. 611 5.1. Generating L2 IIHs to Outside Routers 613 The Inside Edge Router has one or more Level 2 interfaces to Outside 614 Routers. These may be identified by explicit configuration or by the 615 fact that they are not also Level 1 circuits. On these Level 2 616 interfaces, the Inside Edge Router MUST NOT send an IIH until it has 617 learned the Area Proxy System Id from the Area Leader. Then, once it 618 has learned the Area Proxy System Id, it MUST generate its IIHs on 619 the circuit using the Proxy System Id as the source of the IIH. 621 Using the Proxy System Id causes the Outside Router to advertise an 622 adjacency to the Proxy System Id, not to the Inside Edge Router, 623 which supports the proxy function. The normal system id of the 624 Inside Edge Router MUST NOT be used as it will cause unnecessary 625 adjacencies to form and subsequently flap. 627 5.2. Filtering LSP information 629 For the proxy abstraction to be effective the L2 LSPs generated by 630 the Inside Routers MUST be restricted to the Inside Area. The Inside 631 Routers know which system ids are members of the Inside Area based on 632 the Level 1 LSDB. To prevent unwanted LSP information from escaping 633 the Inside Area, the Inside Edge Router MUST perform filtering of LSP 634 flooding, CSNPs, and PSNPs. Specifically: 636 A Level 2 LSP with a source system identifier that is found in the 637 Level 1 LSDB MUST never be flooded to an Outside Router. 639 A Level 2 CSNP sent to an Outside Router MUST NOT contain any 640 information about an LSP with a system identifier found in the 641 Level 1 LSDB. If an Inside Edge Router filters a CSNP and there 642 is no remaining content, then the CSNP MUST NOT be sent. The 643 source address of the CSNP MUST be the Area Proxy System Id. 645 A Level 2 PSNP sent to an Outside Router MUST NOT contain any 646 information about an LSP with a system identifier found in the 647 Level 1 LSDB. If an Inside Edge Router filters a PSNP and there 648 is no remaining content, then the PSNP MUST NOT be sent. The 649 source address of the PSNP MUST be the Area Proxy System Id. 651 6. Acknowledgments 653 The authors would like to thank Bruno Decraene, Vivek Ilangovan, and 654 Gunter Van De Velde for their many helpful comments. The authors 655 would also like to thank a small group that wishes to remain 656 anonymous for their valuable contributions. 658 7. IANA Considerations 660 This memo requests that IANA allocate and assign one code point from 661 the IS-IS TLV Codepoints registry for the Area Proxy TLV (XXX). In 662 association with this, this memo requests that IANA create a registry 663 for code points for the sub-TLVs of the Area Proxy TLV. 665 Name of the registry: Sub-TLVs for TLV XXX (Area Proxy TLV) 666 Required information for registrations: Temporary registrations 667 may be made under the Early IANA Allocation of Standards Track 668 Code Points policy. [RFC7120] Permanent registrations require the 669 publication of an RFC describing the usage of the code point. 671 Applicable registration policy: RFC Required and Expert Review. 672 We propose the initial experts be Chris Hopps, Tony Li, and Sarah 673 Chen. 675 Size, format, and syntax of registry entries: Value (0-255), Name, 676 and Reference 678 Initial assignments and reservations: IANA is requested to assign 679 the following code points: 681 +-------+------------------------------+---------------+ 682 | Value | Name | Reference | 683 +-------+------------------------------+---------------+ 684 | AAA | Area Proxy System Identifier | This document | 685 | BBB | Area Proxy Prefix SID | This document | 686 +-------+------------------------------+---------------+ 688 IANA is also requested to allocate and assign one code point from the 689 IS-IS Router Capability TLV sub-TLV registry for the Area Proxy 690 Capability (YYY). 692 8. Security Considerations 694 This document introduces no new security issues. Security of routing 695 within a domain is already addressed as part of the routing protocols 696 themselves. This document proposes no changes to those security 697 architectures. 699 9. References 701 9.1. Normative References 703 [I-D.ietf-lsr-dynamic-flooding] 704 Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda, 705 T., Cooper, D., Jalil, L., and S. Dontula, "Dynamic 706 Flooding on Dense Graphs", draft-ietf-lsr-dynamic- 707 flooding-04 (work in progress), November 2019. 709 [ISO10589] 710 International Organization for Standardization, 711 "Intermediate System to Intermediate System Intra-Domain 712 Routing Exchange Protocol for use in Conjunction with the 713 Protocol for Providing the Connectionless-mode Network 714 Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002. 716 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 717 dual environments", RFC 1195, DOI 10.17487/RFC1195, 718 December 1990, . 720 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 721 Requirement Levels", BCP 14, RFC 2119, 722 DOI 10.17487/RFC2119, March 1997, 723 . 725 [RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate 726 System (IS-IS) Extensions for Traffic Engineering (TE)", 727 RFC 3784, DOI 10.17487/RFC3784, June 2004, 728 . 730 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 731 Topology (MT) Routing in Intermediate System to 732 Intermediate Systems (IS-ISs)", RFC 5120, 733 DOI 10.17487/RFC5120, February 2008, 734 . 736 [RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange 737 Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301, 738 October 2008, . 740 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 741 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 742 2008, . 744 [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, 745 DOI 10.17487/RFC5308, October 2008, 746 . 748 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 749 for Advertising Router Information", RFC 7981, 750 DOI 10.17487/RFC7981, October 2016, 751 . 753 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 754 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 755 May 2017, . 757 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 758 Decraene, B., Litkowski, S., and R. Shakir, "Segment 759 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 760 July 2018, . 762 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 763 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 764 Extensions for Segment Routing", RFC 8667, 765 DOI 10.17487/RFC8667, December 2019, 766 . 768 9.2. Informative References 770 [Clos] Clos, C., "A Study of Non-Blocking Switching Networks", 771 The Bell System Technical Journal Vol. 32(2), DOI 772 10.1002/j.1538-7305.1953.tb01433.x, March 1953, 773 . 775 [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code 776 Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 777 2014, . 779 9.3. URIs 781 [1] https://tools.ietf.org/html/bcp14 783 Authors' Addresses 785 Tony Li 786 Arista Networks 787 5453 Great America Parkway 788 Santa Clara, California 95054 789 USA 791 Email: tony.li@tony.li 793 Sarah Chen 794 Arista Networks 795 5453 Great America Parkway 796 Santa Clara, California 95054 797 USA 799 Email: sarahchen@arista.com