idnits 2.17.1 draft-shen-isis-spine-leaf-ext-07.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 date (October 16, 2018) is 2019 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) -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10589' == Outdated reference: A later version (-17) exists of draft-ietf-isis-reverse-metric-07 ** Obsolete normative reference: RFC 5306 (Obsoleted by RFC 8706) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Networking Working Group N. Shen 3 Internet-Draft L. Ginsberg 4 Intended status: Standards Track Cisco Systems 5 Expires: April 19, 2019 S. Thyamagundalu 6 October 16, 2018 8 IS-IS Routing for Spine-Leaf Topology 9 draft-shen-isis-spine-leaf-ext-07 11 Abstract 13 This document describes a mechanism for routers and switches in a 14 Spine-Leaf type topology to have non-reciprocal Intermediate System 15 to Intermediate System (IS-IS) routing relationships between the 16 leafs and spines. The leaf nodes do not need to have the topology 17 information of other nodes and exact prefixes in the network. This 18 extension also has application in the Internet of Things (IoT). 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on April 19, 2019. 37 Copyright Notice 39 Copyright (c) 2018 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 55 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 56 2. Motivations . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Spine-Leaf (SL) Extension . . . . . . . . . . . . . . . . . . 4 58 3.1. Topology Examples . . . . . . . . . . . . . . . . . . . . 4 59 3.2. Applicability Statement . . . . . . . . . . . . . . . . . 5 60 3.3. Spine-Leaf TLV . . . . . . . . . . . . . . . . . . . . . 6 61 3.3.1. Spine-Leaf Sub-TLVs . . . . . . . . . . . . . . . . . 7 62 3.3.1.1. Leaf-Set Sub-TLV . . . . . . . . . . . . . . . . 7 63 3.3.1.2. Info-Req Sub-TLV . . . . . . . . . . . . . . . . 8 64 3.3.2. Advertising IPv4/IPv6 Reachability . . . . . . . . . 8 65 3.3.3. Advertising Connection to RF-Leaf Node . . . . . . . 8 66 3.4. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 8 67 3.4.1. Pure CLOS Topology . . . . . . . . . . . . . . . . . 10 68 3.5. Implementation and Operation . . . . . . . . . . . . . . 11 69 3.5.1. CSNP PDU . . . . . . . . . . . . . . . . . . . . . . 11 70 3.5.2. Overload Bit . . . . . . . . . . . . . . . . . . . . 11 71 3.5.3. Spine Node Hostname . . . . . . . . . . . . . . . . . 11 72 3.5.4. IS-IS Reverse Metric . . . . . . . . . . . . . . . . 11 73 3.5.5. Spine-Leaf Traffic Engineering . . . . . . . . . . . 12 74 3.5.6. Other End-to-End Services . . . . . . . . . . . . . . 12 75 3.5.7. Address Family and Topology . . . . . . . . . . . . . 12 76 3.5.8. Migration . . . . . . . . . . . . . . . . . . . . . . 13 77 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 78 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 79 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 80 7. Document Change Log . . . . . . . . . . . . . . . . . . . . . 14 81 7.1. Changes to draft-shen-isis-spine-leaf-ext-05.txt . . . . 14 82 7.2. Changes to draft-shen-isis-spine-leaf-ext-04.txt . . . . 14 83 7.3. Changes to draft-shen-isis-spine-leaf-ext-03.txt . . . . 14 84 7.4. Changes to draft-shen-isis-spine-leaf-ext-02.txt . . . . 14 85 7.5. Changes to draft-shen-isis-spine-leaf-ext-01.txt . . . . 15 86 7.6. Changes to draft-shen-isis-spine-leaf-ext-00.txt . . . . 15 87 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 88 8.1. Normative References . . . . . . . . . . . . . . . . . . 15 89 8.2. Informative References . . . . . . . . . . . . . . . . . 16 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 92 1. Introduction 94 The IS-IS routing protocol defined by [ISO10589] has been widely 95 deployed in provider networks, data centers and enterprise campus 96 environments. In the data center and enterprise switching networks, 97 a Spine-Leaf topology is commonly used. This document describes a 98 mechanism where IS-IS routing can be optimized for a Spine-Leaf 99 topology. 101 In a Spine-Leaf topology, normally a leaf node connects to a number 102 of spine nodes. Data traffic going from one leaf node to another 103 leaf node needs to pass through one of the spine nodes. Also, the 104 decision to choose one of the spine nodes is usually part of equal 105 cost multi-path (ECMP) load sharing. The spine nodes can be 106 considered as gateway devices to reach destinations on other leaf 107 nodes. In this type of topology, the spine nodes have to know the 108 topology and routing information of the entire network, but the leaf 109 nodes only need to know how to reach the gateway devices to which are 110 the spine nodes they are uplinked. 112 This document describes the IS-IS Spine-Leaf extension that allows 113 the spine nodes to have all the topology and routing information, 114 while keeping the leaf nodes free of topology information other than 115 the default gateway routing information. The leaf nodes do not even 116 need to run a Shortest Path First (SPF) calculation since they have 117 no topology information. 119 1.1. Requirements Language 121 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 122 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 123 document are to be interpreted as described in RFC 2119 [RFC2119]. 125 2. Motivations 127 o The leaf nodes in a Spine-Leaf topology do not require complete 128 topology and routing information of the entire domain since their 129 forwarding decision is to use ECMP with spine nodes as default 130 gateways 132 o The spine nodes in a Spine-Leaf topology are richly connected to 133 leaf nodes, which introduces significant flooding duplication if 134 they flood all Link State PDUs (LSPs) to all the leaf nodes. It 135 saves both spine and leaf nodes' CPU and link bandwidth resources 136 if flooding is blocked to leaf nodes. For small Top of the Rack 137 (ToR) leaf switches in data centers, it is meaningful to prevent 138 full topology routing information and massive database flooding 139 through those devices. 141 o When a spine node advertises a topology change, every leaf node 142 connected to it will flood the update to all the other spine 143 nodes, and those spine nodes will further flood them to all the 144 leaf nodes, causing a O(n^2) flooding storm which is largely 145 redundant. 147 o Similar to some of the overlay technologies which are popular in 148 data centers, the edge devices (leaf nodes) may not need to 149 contain all the routing and forwarding information on the device's 150 control and forwarding planes. "Conversational Learning" can be 151 utilized to get the specific routing and forwarding information in 152 the case of pure CLOS topology and in the events of link and node 153 down. 155 o Small devices and appliances of Internet of Things (IoT) can be 156 considered as leafs in the routing topology sense. They have CPU 157 and memory constrains in design, and those IoT devices do not have 158 to know the exact network topology and prefixes as long as there 159 are ways to reach the cloud servers or other devices. 161 3. Spine-Leaf (SL) Extension 163 3.1. Topology Examples 165 +--------+ +--------+ +--------+ 166 | | | | | | 167 | Spine1 +----+ Spine2 +- ......... -+ SpineN | 168 | | | | | | 169 +-+-+-+-++ ++-+-+-+-+ +-+-+-+-++ 170 +------+ | | | | | | | | | | | 171 | +-----|-|-|------+ | | | | | | | 172 | | +--|-|-|--------+-|-|-----------------+ | | | 173 | | | | | | +---+ | | | | | 174 | | | | | | | +--|-|-------------------+ | | 175 | | | | | | | | | | +------+ +----+ 176 | | | | | | | | | +--------------|----------+ | 177 | | | | | | | | +-------------+ | | | 178 | | | | | +----|--|----------------|--|--------+ | | 179 | | | | +------|--|--------------+ | | | | | 180 | | | +------+ | | | | | | | | 181 ++--+--++ +-+-+--++ ++-+--+-+ ++-+--+-+ 182 | Leaf1 | | Leaf2 | ........ | LeafX | | LeafY | 183 +-------+ +-------+ +-------+ +-------+ 185 Figure 1: A Spine-Leaf Topology 187 +---------+ +--------+ 188 | Spine1 | | Spine2 | 189 +-+-+-+-+-+ +-+-+-+-++ 190 | | | | | | | | 191 | | | +-----------------|-|-|-|-+ 192 | | +------------+ | | | | | 193 +--------+ +-+ | | | | | | 194 | +----------------------------+ | | | | 195 | | | +------------------+ | +----+ 196 | | | | | +-------+ | | 197 | | | | | | | | 198 +-+---+-+ +--+--+-+ +-+--+--+ +--+--+-+ 199 | Leaf1 | | Leaf2 | | Leaf3 | | Leaf4 | 200 +-------+ +-------+ +-------+ +-------+ 202 Figure 2: A CLOS Topology 204 3.2. Applicability Statement 206 This extension assumes the network is a Spine-Leaf topology, and it 207 should not be applied in an arbitrary network setup. The spine nodes 208 can be viewed as the aggregation layer of the network, and the leaf 209 nodes as the access layer of the network. The leaf nodes use a load 210 sharing algorithm with spine nodes as nexthops in routing and 211 forwarding. 213 This extension works when the spine nodes are inter-connected, and it 214 works with a pure CLOS or Fat Tree topology based network where the 215 spines are NOT horizontally interconnected. 217 Although the example diagram in Figure 1 shows a fully meshed Spine- 218 Leaf topology, this extension also works in the case where they are 219 partially meshed. For instance, leaf1 through leaf10 may be fully 220 meshed with spine1 through spine5 while leaf11 through leaf20 is 221 fully meshed with spine4 through spine8, and all the spines are 222 inter-connected in a redundant fashion. 224 This extension can also work in multi-level spine-leaf topology. The 225 lower level spine node can be a 'leaf' node to the upper level spine 226 node. A spine-leaf 'Tier' can be exchanged with IS-IS hello packets 227 to allow tier X to be connected with tier X+1 using this extension. 228 Normally tier-0 will be the TOR routers and switches if provisioned. 230 This extension also works with normal IS-IS routing in a topology 231 with more than two layers of spine and leaf. For instance, in 232 example diagrams Figure 1 and Figure 2, there can be another Core 233 layer of routers/switches on top of the aggregation layer. From an 234 IS-IS routing point of view, the Core nodes are not affected by this 235 extension and will have the complete topology and routing information 236 just like the spine nodes. To make the network even more scalable, 237 the Core layer can operate as a level-2 IS-IS sub-domain while the 238 Spine and Leaf layers operate as stays at the level-1 IS-IS domain. 240 This extension assumes the link between the spine and leaf nodes are 241 point-to-point, or point-to-point over LAN [RFC5309]. The links 242 connecting among the spine nodes or the links between the leaf nodes 243 can be any type. 245 3.3. Spine-Leaf TLV 247 This extension introduces a new TLV, the Spine-Leaf TLV, which may be 248 advertised in IS-IS Hello (IIH) PDUs, LSPs, or in Circuit Scoped Link 249 State PDUs (CS-LSP) [RFC7356]. It is used by both spine and leaf 250 nodes in this Spine-Leaf mechanism. 252 0 1 2 3 253 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 1 254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 | Type | Length | SL Flag | 256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 257 | .. Optional Sub-TLVs 258 +-+-+-+-+-+-+-+-+-.... 260 The fields of this TLV are defined as follows: 262 Type: 1 octet Suggested value 150 (to be assigned by IANA) 264 Length: 1 octet (2 + length of sub-TLVs). 266 SL Flags: 16 bits 268 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 270 | Tier | Reserved |T|R|L| 271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 273 Tier: A value from 0 to 15. It represents the spine-leaf 274 tier level. The value 15 is reserved to indicate the 275 tier level is unknown. This value is only valid when 276 the 'T' bit (see below) is set. If the 'T' bit is 277 clear, this value MUST be set to zero on transmission, 278 and it MUST be ignored on receipt. 280 L bit (0x01): Only leaf node sets this bit. If the L bit is 281 set in the SL flag, the node indicates it is in 'Leaf- 282 Mode'. 284 R bit (0x02): Only Spine node sets this bit. If the R bit is 285 set, the node indicates to the leaf neighbor that it 286 can be used as the default route gateway. 288 T bit (0x04): If set, the value in the "Tier" field (see 289 above) is valid. 291 Optional Sub-TLV: Not defined in this document, for future 292 extension 294 sub-TLVs MAY be included when the TLV is in a CS-LSP. 295 sub-TLVs MUST NOT be included when the TLV is in an IIH 297 3.3.1. Spine-Leaf Sub-TLVs 299 If the data center topology is a pure CLOS or Fat Tree, there are no 300 link connections among the spine nodes. If we also assume there is 301 not another Core layer on top of the aggregation layer, then the 302 traffic from one leaf node to another may have a problem if there is 303 a link outage between a spine node and a leaf node. For instance, in 304 the diagram of Figure 2, if Leaf1 sends data traffic to Leaf3 through 305 Spine1 node, and the Spine1-Leaf3 link is down, the data traffic will 306 be dropped on the Spine1 node. 308 To address this issue spine and leaf nodes may send/request specific 309 reachability information via the sub-TLVs defined below. 311 Two Spine-Leaf sub-TLVs are defined. The Leaf-Set sub-TLV and the 312 Info-Req sub-TLV. 314 3.3.1.1. Leaf-Set Sub-TLV 316 This sub-TLV is used by spine nodes to optionally advertise Leaf 317 neighbors to other Leaf nodes. The fields of this sub-TLV are 318 defined as follows: 320 Type: 1 octet Suggested value 1 (to be assigned by IANA) 322 Length: 1 octet MUST be a multiple of 6 octets. 324 Leaf-Set: A list of IS-IS System-ID of the leaf node neighbors of 325 this spine node. 327 3.3.1.2. Info-Req Sub-TLV 329 This sub-TLV is used by leaf nodes to request the advertisement of 330 more specific prefix information from a selected spine node. The 331 list of leaf nodes in this sub-TLV reflects the current set of leaf- 332 nodes for which not all spine node neighbors have indicated the 333 presence of connectivity in the Leaf-Set sub-TLV (See 334 Section 3.3.1.1). The fields of this sub-TLV are defined as follows: 336 Type: 1 octet Suggested value 2 (to be assigned by IANA) 338 Length: 1 octet. It MUST be a multiple of 6 octets. 340 Info-Req: List of IS-IS System-IDs of leaf nodes for which 341 connectivity information is being requested. 343 3.3.2. Advertising IPv4/IPv6 Reachability 345 In cases where connectivity between a leaf node and a spine node is 346 down, the leaf node MAY request reachability information from a spine 347 node as described in Section 3.3.1.2. The spine node utilizes TLVs 348 135 [RFC5305] and TLVs 236 [RFC5308] to advertise this information. 349 These TLVs MAY be included either in IIHs or CS-LSPs [RFC7356] sent 350 from the spine to the requesting leaf node. Sending such information 351 in IIHs has limited scale - all reachability information MUST fit 352 within a single IIH. It is therefore recommended that CS-LSPs be 353 used. 355 3.3.3. Advertising Connection to RF-Leaf Node 357 For links between Spine and Leaf Nodes on which the Spine Node has 358 set the R-bit and the Leaf node has set the L-bit in their respective 359 Spine-Leaf TLVs, spine nodes may advertise the link with a bit in the 360 "link-attribute" sub-TLV [RFC5029] to express this link is not used 361 for LSP flooding. This information can be used by nodes computing a 362 flooding topology e.g., [DYNAMIC-FLOODING], to exclude the RF-Leaf 363 nodes from the computed flooding topology. 365 3.4. Mechanism 367 Leaf nodes in a spine-leaf application using this extension are 368 provisioned with two attributes: 370 1)Tier level of 0. This indicates the node is a Leaf Node. The 371 value 0 is advertised in the Tier field of Spine-Leaf TLV defined 372 above. 374 2)Flooding reduction enabled/disabled. If flooding reduction is 375 enabled the L-bit is set to one in the Spine-Leaf TLV defined above 377 A spine node does not need explicit configuration. Spine nodes can 378 dynamically discover their tier level by computing the number of hops 379 to a leaf node. Until a spine node determines its tier level it MUST 380 advertise level 15 (unknown tier level) in the Spine-Leaf TLV defined 381 above. Each tier level can also be statically provisioned on the 382 node. 384 When a spine node receives an IIH which includes the Spine-Leaf TLV 385 with Tier level 0 and 'L' bit set, it labels the point-to-point 386 interface and adjacency to be a 'Reduced Flooding Leaf-Peer (RF- 387 Leaf)'. IIHs sent by a spine node on a link to an RF-Leaf include 388 the Spine-Leaf TLV with the 'R' bit set in the flags field. The 'R' 389 bit indicates to the RF-Leaf neighbor that the spine node can be used 390 as a default routing nexthop. 392 There is no change to the IS-IS adjacency bring-up mechanism for 393 Spine-Leaf peers. 395 A spine node blocks LSP flooding to RF-Leaf adjacencies, except for 396 the LSP PDUs in which the IS-IS System-ID matches the System-ID of 397 the RF-Leaf neighbor. This exception is needed since when the leaf 398 node reboots, the spine node needs to forward to the leaf node non- 399 purged LSPs from the RF-Leaf's previous incarnation. 401 Leaf nodes will perform IS-IS LSP flooding as normal over all of its 402 IS-IS adjacencies, but in the case of RF-Leafs only self-originated 403 LSPs will exist in its LSP database. 405 Spine nodes will receive all the LSP PDUs in the network, including 406 all the spine nodes and leaf nodes. It will perform Shortest Path 407 First (SPF) as a normal IS-IS node does. There is no change to the 408 route calculation and forwarding on the spine nodes. 410 The LSPs of a node only floods north bound towards the upper layer 411 spine nodes. The default route is generated with loadsharing also 412 towards the upper layer spine nodes. 414 RF-Leaf nodes do not have any LSP in the network except for its own. 415 Therefore there is no need to perform SPF calculation on the RF-Leaf 416 node. It only needs to download the default route with the nexthops 417 of those Spine Neighbors which have the 'R' bit set in the Spine-Leaf 418 TLV in IIH PDUs. IS-IS can perform equal cost or unequal cost load 419 sharing while using the spine nodes as nexthops. The aggregated 420 metric of the outbound interface and the 'Reverse Metric' 421 [REVERSE-METRIC] can be used for this purpose. 423 3.4.1. Pure CLOS Topology 425 In a data center where the topology is pure CLOS or Fat Tree, there 426 is no interconnection among the spine nodes, and there is not another 427 Core layer above the aggregation layer with reachability to the leaf 428 nodes. When flooding reduction to RF-Leafs is in use, if the link 429 between a spine and a leaf goes down, there is then a possibility of 430 black holing the data traffic in the network. 432 As in the diagram Figure 2, if the link Spine1-Leaf3 goes down, there 433 needs to be a way for Leaf1, Leaf2 and Leaf4 to avoid the Spine1 if 434 the destination of data traffic is to Leaf3 node. 436 In the above example, the Spine1 and Spine2 are provisioned to 437 advertise the Leaf-Set sub-TLV of the Spine-Leaf TLV. Originally 438 both Spines will advertise Leaf1 through Leaf4 as their Leaf-Set. 439 When the Spine1-Leaf3 link is down, Spine1 will only have Leaf1, 440 Leaf2 and Leaf4 in its Leaf-Set. This allows the other leaf nodes to 441 know that Spine1 has lost connectivity to the leaf node of Leaf3. 443 Each RF-Leaf node can select another spine node to request for some 444 prefix information associated with the lost leaf node. In this 445 diagram of Figure 2, there are only two spine nodes (Spine-Leaf 446 topology can have more than two spine nodes in general). Each RF- 447 Leaf node can independently select a spine node for the leaf 448 information. The RF-Leaf nodes will include the Info-Req sub-TLV in 449 the Spine-Leaf TLV in hellos sent to the selected spine node, Spine2 450 in this case. 452 The spine node, upon receiving the request from one or more leaf 453 nodes, will find the IPv6/IPv4 prefixes advertised by the leaf nodes 454 listed in the Info-Req sub-TLV. The spine node will use the 455 mechanism defined in Section 3.3.2 to advertise these prefixes to the 456 RF-Leaf node. For instance, it will include the IPv4 loopback prefix 457 of leaf3 based on the policy configured or administrative tag 458 attached to the prefixes. When the leaf nodes receive the more 459 specific prefixes, they will install the advertised prefixes towards 460 the other spine nodes (Spine2 in this example). 462 For instance in the data center overlay scenario, when any IP 463 destination or MAC destination uses the leaf3's loopback as the 464 tunnel nexthop, the overlay tunnel from leaf nodes will only select 465 Spine2 as the gateway to reach leaf3 as long as the Spine1-Leaf3 link 466 is still down. 468 In cases where multiple links or nodes fail at the same time, the RF- 469 leaf node may need to send the Info-Req to multiple upper layer spine 470 nodes in order to obtain reachability information for all the 471 partially connected nodes. 473 This negative routing is more useful between tier 0 and tier 1 spine- 474 leaf levels in a multi-level spine-leaf topology when the reduced 475 flooding extension is in use. Nodes in tiers 1 or greater may have 476 much richer topology information and alternative paths. 478 3.5. Implementation and Operation 480 3.5.1. CSNP PDU 482 In Spine-Leaf extension, Complete Sequence Number PDU (CSNP) does not 483 need to be transmitted over the Spine-Leaf link to an RF-Leaf. Some 484 IS-IS implementations send periodic CSNPs after the initial adjacency 485 bring-up over a point-to-point interface. There is no need for this 486 optimization here since the RF-Leaf does not need to receive any 487 other LSPs from the network, and the only LSPs transmitted across the 488 Spine-Leaf link is the leaf node LSP. 490 Also in the graceful restart case[RFC5306], for the same reason, 491 there is no need to send the CSNPs over the Spine-Leaf interface to 492 an RF-Leaf. Spine nodes only need to set the SRMflag on the LSPs 493 belonging to the RF-Leaf. 495 3.5.2. Overload Bit 497 The leaf node SHOULD set the 'overload' bit on its LSP PDU, since if 498 the spine nodes were to forward traffic not meant for the local node, 499 the leaf node does not have the topology information to prevent a 500 routing/forwarding loop. 502 3.5.3. Spine Node Hostname 504 This extension creates a non-reciprocal relationship between the 505 spine node and leaf node. The spine node will receive leaf's LSP and 506 will know the leaf's hostname, but the leaf does not have spine's 507 LSP. This extension allows the Dynamic Hostname TLV [RFC5301] to be 508 optionally included in spine's IIH PDU when sending to a 'Leaf-Peer'. 509 This is useful in troubleshooting cases. 511 3.5.4. IS-IS Reverse Metric 513 This metric is part of the aggregated metric for leaf's default route 514 installation with load sharing among the spine nodes. When a spine 515 node is in 'overload' condition, it should use the IS-IS Reverse 516 Metric TLV in IIH [REVERSE-METRIC] to set this metric to maximum to 517 discourage the leaf using it as part of the loadsharing. 519 In some cases, certain spine nodes may have less bandwidth in link 520 provisioning or in real-time condition, and it can use this metric to 521 signal to the leaf nodes dynamically. 523 In other cases, such as when the spine node loses a link to a 524 particular leaf node, although it can redirect the traffic to other 525 spine nodes to reach that destination leaf node, but it MAY want to 526 increase this metric value if the inter-spine connection becomes over 527 utilized, or the latency becomes an issue. 529 In the leaf-leaf link as a backup gateway use case, the 'Reverse 530 Metric' SHOULD always be set to very high value. 532 3.5.5. Spine-Leaf Traffic Engineering 534 Besides using the IS-IS Reverse Metric by the spine nodes to affect 535 the traffic pattern for leaf default gateway towards multiple spine 536 nodes, the IPv6/IPv4 Info-Advertise sub-TLVs can be selectively used 537 by traffic engineering controllers to move data traffic around the 538 data center fabric to alleviate congestion and to reduce the latency 539 of a certain class of traffic pairs. By injecting more specific leaf 540 node prefixes, it will allow the spine nodes to attract more traffic 541 on some underutilized links. 543 3.5.6. Other End-to-End Services 545 Losing the topology information will have an impact on some of the 546 end-to-end network services, for instance, MPLS TE or end-to-end 547 segment routing. Some other mechanisms such as those described in 548 PCE [RFC4655] based solution may be used. In this Spine-Leaf 549 extension, the role of the leaf node is not too much different from 550 the multi-level IS-IS routing while the level-1 IS-IS nodes only have 551 the default route information towards the node which has the Attach 552 Bit (ATT) set, and the level-2 backbone does not have any topology 553 information of the level-1 areas. The exact mechanism to enable 554 certain end-to-end network services in Spine-Leaf network is outside 555 the scope of this document. 557 3.5.7. Address Family and Topology 559 IPv6 Address families[RFC5308], Multi-Topology (MT)[RFC5120] and 560 Multi-Instance (MI)[RFC8202] information is carried over the IIH PDU. 561 Since the goal is to simplify the operation of IS-IS network, for the 562 simplicity of this extension, the Spine-Leaf mechanism is applied the 563 same way to all the address families, MTs and MIs. 565 3.5.8. Migration 567 For this extension to be deployed in existing networks, a simple 568 migration scheme is needed. To support any leaf node in the network, 569 all the involved spine nodes have to be upgraded first. So the first 570 step is to migrate all the involved spine nodes to support this 571 extension, then the leaf nodes can be enabled with 'Leaf-Mode' one by 572 one. No flag day is needed for the extension migration. 574 4. IANA Considerations 576 A new TLV codepoint is defined in this document and needs to be 577 assigned by IANA from the "IS-IS TLV Codepoints" registry. It is 578 referred to as the Spine-Leaf TLV and the suggested value is 150. 579 This TLV is only to be optionally inserted either in the IIH PDU or 580 in the Circuit Flooding Scoped LSP PDU. IANA is also requested to 581 maintain the SL-flag bit values in this TLV, and 0x01, 0x02 and 0x04 582 bits are defined in this document. 584 Value Name IIH LSP SNP Purge CS-LSP 585 ----- --------------------- --- --- --- ----- ------- 586 150 Spine-Leaf y y n n y 588 This extension also proposes to have the Dynamic Hostname TLV, 589 already assigned as code 137, to be allowed in IIH PDU. 591 Value Name IIH LSP SNP Purge 592 ----- --------------------- --- --- --- ----- 593 137 Dynamic Name y y n y 595 Two new sub-TLVs are defined in this document and needs to be added 596 assigned by IANA from the "IS-IS TLV Codepoints". They are referred 597 to in this document as the Leaf-Set sub-TLV and the Info-Req sub-TLV. 598 It is suggested to have the values 1 and 2 respectively. 600 This document also requests that IANA allocate from the registry of 601 link-attribute bit values for sub-TLV 19 of TLV 22 (Extended IS 602 reachability TLV). This new bit is referred to as the "Connect to 603 RF-Leaf Node" bit. 605 Value Name Reference 606 ----- ----- ---------- 607 0x3 Connect to RF-Leaf Node This document 609 5. Security Considerations 611 Security concerns for IS-IS are addressed in [ISO10589], [RFC5304], 612 [RFC5310], and [RFC7602]. This extension does not raise additional 613 security issues. 615 6. Acknowledgments 617 The authors would like to thank Tony Przygienda for his discussion 618 and contributions. The authors also would like to thank Acee Lindem, 619 Russ White and Christian Hopps for their review and comments of this 620 document. 622 7. Document Change Log 624 7.1. Changes to draft-shen-isis-spine-leaf-ext-05.txt 626 o Submitted January 2018. 628 o Just a refresh. 630 7.2. Changes to draft-shen-isis-spine-leaf-ext-04.txt 632 o Submitted June 2017. 634 o Added the Tier level information to handle the multi-level spine- 635 leaf topology using this extension. 637 7.3. Changes to draft-shen-isis-spine-leaf-ext-03.txt 639 o Submitted March 2017. 641 o Added the Spine-Leaf sub-TLVs to handle the case of data center 642 pure CLOS topology and mechanism. 644 o Added the Spine-Leaf TLV and sub-TLVs can be optionally inserted 645 in either IIH PDU or CS-LSP PDU. 647 o Allow use of prefix Reachability TLVs 135 and 236 in IIHs/CS-LSPs 648 sent from spine to leaf. 650 7.4. Changes to draft-shen-isis-spine-leaf-ext-02.txt 652 o Submitted October 2016. 654 o Removed the 'Default Route Metric' field in the Spine-Leaf TLV and 655 changed to using the IS-IS Reverse Metric in IIH. 657 7.5. Changes to draft-shen-isis-spine-leaf-ext-01.txt 659 o Submitted April 2016. 661 o No change. Refresh the draft version. 663 7.6. Changes to draft-shen-isis-spine-leaf-ext-00.txt 665 o Initial version of the draft is published in November 2015. 667 8. References 669 8.1. Normative References 671 [ISO10589] 672 ISO "International Organization for Standardization", 673 "Intermediate system to Intermediate system intra-domain 674 routeing information exchange protocol for use in 675 conjunction with the protocol for providing the 676 connectionless-mode Network Service (ISO 8473), ISO/IEC 677 10589:2002, Second Edition.", Nov 2002. 679 [REVERSE-METRIC] 680 Shen, N., Amante, S., and M. Abrahamsson, "IS-IS Routing 681 with Reverse Metric", draft-ietf-isis-reverse-metric-07 682 (work in progress), 2017. 684 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 685 Requirement Levels", BCP 14, RFC 2119, 686 DOI 10.17487/RFC2119, March 1997, . 689 [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link 690 Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, 691 September 2007, . 693 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 694 Topology (MT) Routing in Intermediate System to 695 Intermediate Systems (IS-ISs)", RFC 5120, 696 DOI 10.17487/RFC5120, February 2008, . 699 [RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange 700 Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301, 701 October 2008, . 703 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 704 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 705 2008, . 707 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 708 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 709 2008, . 711 [RFC5306] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS", 712 RFC 5306, DOI 10.17487/RFC5306, October 2008, 713 . 715 [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, 716 DOI 10.17487/RFC5308, October 2008, . 719 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 720 and M. Fanto, "IS-IS Generic Cryptographic 721 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 722 2009, . 724 [RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding 725 Scope Link State PDUs (LSPs)", RFC 7356, 726 DOI 10.17487/RFC7356, September 2014, . 729 [RFC7602] Chunduri, U., Lu, W., Tian, A., and N. Shen, "IS-IS 730 Extended Sequence Number TLV", RFC 7602, 731 DOI 10.17487/RFC7602, July 2015, . 734 [RFC8202] Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS 735 Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June 736 2017, . 738 8.2. Informative References 740 [DYNAMIC-FLOODING] 741 Li, T., "Dynamic Flooding on Dense Graphs", draft-li- 742 dynamic-flooding (work in progress), 2018. 744 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 745 Element (PCE)-Based Architecture", RFC 4655, 746 DOI 10.17487/RFC4655, August 2006, . 749 [RFC5309] Shen, N., Ed. and A. Zinin, Ed., "Point-to-Point Operation 750 over LAN in Link State Routing Protocols", RFC 5309, 751 DOI 10.17487/RFC5309, October 2008, . 754 Authors' Addresses 756 Naiming Shen 757 Cisco Systems 758 560 McCarthy Blvd. 759 Milpitas, CA 95035 760 US 762 Email: naiming@cisco.com 764 Les Ginsberg 765 Cisco Systems 766 821 Alder Drive 767 Milpitas, CA 95035 768 US 770 Email: ginsberg@cisco.com 772 Sanjay Thyamagundalu 774 Email: tsanjay@gmail.com