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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'OPENFABRIC' is defined on line 729, but no explicit reference was found in the text -- 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 'ISO10589' == Outdated reference: A later version (-17) exists of draft-ietf-isis-reverse-metric-07 ** Obsolete normative reference: RFC 5306 (Obsoleted by RFC 8706) == Outdated reference: A later version (-07) exists of draft-white-openfabric-04 Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 2 comments (--).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: July 6, 2018 S. Thyamagundalu 6 January 2, 2018 8 IS-IS Routing for Spine-Leaf Topology 9 draft-shen-isis-spine-leaf-ext-05 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 https://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 July 6, 2018. 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 (https://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. Extension Encoding . . . . . . . . . . . . . . . . . . . 6 61 3.3.1. Spine-Leaf Sub-TLVs . . . . . . . . . . . . . . . . . 7 62 3.3.1.1. Leaf-Set Sub-TLV . . . . . . . . . . . . . . . . 8 63 3.3.1.2. Info-Req Sub-TLV . . . . . . . . . . . . . . . . 8 64 3.3.2. Advertising IPv4/IPv6 Reachability . . . . . . . . . 8 65 3.4. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 8 66 3.4.1. Pure CLOS Topology . . . . . . . . . . . . . . . . . 10 67 3.5. Implementation and Operation . . . . . . . . . . . . . . 11 68 3.5.1. CSNP PDU . . . . . . . . . . . . . . . . . . . . . . 11 69 3.5.2. Leaf to Leaf connection . . . . . . . . . . . . . . . 11 70 3.5.3. Overload Bit . . . . . . . . . . . . . . . . . . . . 11 71 3.5.4. Spine Node Hostname . . . . . . . . . . . . . . . . . 12 72 3.5.5. IS-IS Reverse Metric . . . . . . . . . . . . . . . . 12 73 3.5.6. Spine-Leaf Traffic Engineering . . . . . . . . . . . 12 74 3.5.7. Other End-to-End Services . . . . . . . . . . . . . . 12 75 3.5.8. Address Family and Topology . . . . . . . . . . . . . 13 76 3.5.9. 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 also supports the leaf nodes having local connections 241 to other leaf nodes, in the example diagram Figure 1 there is a 242 connection between 'Leaf1' node and 'Leaf2' node, and an external 243 host can be dual homed into both of the leaf nodes. 245 This extension assumes the link between the spine and leaf nodes are 246 point-to-point, or point-to-point over LAN [RFC5309]. The links 247 connecting among the spine nodes or the links between the leaf nodes 248 can be any type. 250 3.3. Extension Encoding 252 This extension introduces one new TLV which may be used in IS-IS 253 Hello (IIH) PDUs, LSPs, or in Circuit Scoped Link State PDUs (CS-LSP) 254 [RFC7356]. It is used by both spine and leaf nodes in this Spine- 255 Leaf mechanism. 257 0 1 2 3 258 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 1 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 | Type | Length | SL Flag | 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 262 | .. Optional Sub-TLVs 263 +-+-+-+-+-+-+-+-+-.... 265 The fields of this TLV are defined as follows: 267 Type: 1 octet Suggested value 150 (to be assigned by IANA) 269 Length: 1 octet (2 + length of sub-TLVs). 271 Flags 16 bits 273 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 275 | Tier | Reserved |T|B|R|L| 276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 Tier: A 4 bits value range from 0 to 15. It is used to 278 represent the spine-leaf tier level when the 'T' bit 279 is set. If the 'T' is cleared, this value MUST be set 280 to zero from the sender, and it MUST be ignored on the 281 receiver. The value 15 is reserved to indicate the 282 tier level is unknown or not configured. 284 L bit (0x01): Only leaf node sets this bit. If the L bit is 285 set in the SL flag, the node indicates it is in 'Leaf- 286 Mode'. 288 R bit (0x02): Only Spine node sets this bit. If the R bit is 289 set, the node indicates to the leaf neighbor that it 290 can be used as the default route gateway. 292 B bit (0x04): Only leaf node sets this bit on Leaf-Leaf link, 293 in additional to the 'L' bit setting. If the B bit is 294 set, the node indicates to its leaf neighbor that it 295 can be used as the backup default route gateway. 297 T bit (0x08): If set, the value in the 'Tier' field represents 298 the spine-leaf tier level in the topology. 300 Optional Sub-TLV: Not defined in this document, for future 301 extension 303 sub-TLVs MAY be included when the TLV is in a CS-LSP. 304 sub-TLVs MUST NOT be included when the TLV is in an IIH 306 3.3.1. Spine-Leaf Sub-TLVs 308 If the data center topology is a pure CLOS or Fat Tree, there are no 309 link connections among the spine nodes. If we also assume there is 310 not another Core layer on top of the aggregation layer, then the 311 traffic from one leaf node to another may have a problem if there is 312 a link outage between a spine node and a leaf node. For instance, in 313 the diagram of Figure 2, if Leaf1 sends data traffic to Leaf3 through 314 Spine1 node, and the Spine1-Leaf3 link is down, the data traffic will 315 be dropped on the Spine1 node. 317 To address this issue spine and leaf nodes may send/request specific 318 reachability information via the sub-TLVs defined below. 320 Two Spine-Leaf sub-TLVs are defined. The Leaf-Set sub-TLV and the 321 Info-Req sub-TLV. 323 3.3.1.1. Leaf-Set Sub-TLV 325 This sub-TLV is used by spine nodes to optionally advertise Leaf 326 neighbors to other Leaf nodes. The fields of this sub-TLV are 327 defined as follows: 329 Type: 1 octet Suggested value 1 (to be assigned by IANA) 331 Length: 1 octet MUST be a multiple of 6 octets. 333 Leaf-Set: A list of IS-IS System-ID of the leaf node neighbors of 334 this spine node. 336 3.3.1.2. Info-Req Sub-TLV 338 This sub-TLV is used by leaf nodes to request more specific prefix 339 information from a selected spine node, upon detecting one of the 340 spine node has lost the connection to a leaf node. The fields of 341 this sub-TLV are defined as follows: 343 Type: 1 octet Suggested value 2 (to be assigned by IANA) 345 Length: 1 octet. It MUST be a multiple of 6 octets. 347 Info-Req: List of IS-IS System-IDs of leaf nodes for which 348 connectivity information is being requested. 350 3.3.2. Advertising IPv4/IPv6 Reachability 352 In cases where connectivity between a leaf node and a spine node is 353 down, the leaf node MAY request reachability information from a spine 354 node as described in Section 3.3.1.2. The spine node utilizes TLVs 355 135 [RFC5305] and TLVs 236 [RFC5308] to advertise this information. 356 These TLVs MAY be included either in IIHs or CS-LSPs sent from the 357 spine to the requesting leaf node. Sending such information in IIHs 358 has limited scale - all reachability information MUST fit within a 359 single IIH. It is therefore recommended that CS-LSPs be used. 361 3.4. Mechanism 363 Leaf nodes in a spine-leaf application using this extension are 364 provisioned with two attributes: 366 1)Tier level of 0. This indicates the node is a Leaf Node. The 367 value 0 is advertised in the Tier field of Spine-Leaf TLV defined 368 above. 370 2)Flooding reduction enabled/disabled. If flooding reduction is 371 enabled the L-bit is set to one in the Spine-Leaf TLV defined above 373 A spine node does not need explicit configuration. Spine nodes can 374 dynamically discover their tier level by computing the number of hops 375 to a leaf node. Until a spine node determines its tier level it MUST 376 advertise level 15 (unknown tier level) in the Spine-Leaf TLV defined 377 above. 379 When a spine node receives an IIH which includes the Spine-Leaf TLV 380 with Tier level 0 and 'L' bit set, it labels the point-to-point 381 interface and adjacency to be a 'Reduced Flooding Leaf-Peer (RF- 382 Leaf)'. IIHs sent by a spine node on a link to an RF-Leaf include 383 the Spine-Leaf TLV with the 'R' bit set in the flags field. The 'R' 384 bit indicates to the RF-Leaf neighbor that the spine node can be used 385 as a default routing nexthop. 387 There is no change to the IS-IS adjacency bring-up mechanism for 388 Spine-Leaf peers. 390 A spine node blocks LSP flooding to RF-Leaf adjacencies, except for 391 the LSP PDUs in which the IS-IS System-ID matches the System-ID of 392 the RF-Leaf neighbor. This exception is needed since when the leaf 393 node reboots, the spine node needs to forward to the leaf node non- 394 purged LSPs from the RF-Leaf's previous incarnation. 396 Leaf nodes will perform IS-IS LSP flooding as normal over all of its 397 IS-IS adjacencies, but in the case of RF-Leafs only self-originated 398 LSPs will exist in its LSP database. 400 Spine nodes will receive all the LSP PDUs in the network, including 401 all the spine nodes and leaf nodes. It will perform Shortest Path 402 First (SPF) as a normal IS-IS node does. There is no change to the 403 route calculation and forwarding on the spine nodes. 405 RF-Leaf nodes do not have any LSP in the network except for its own. 406 Therefore there is no need to perform SPF calculation on the RF-Leaf 407 node. It only needs to download the default route with the nexthops 408 of those Spine Neighbors which have the 'R' bit set in the Spine-Leaf 409 TLV in IIH PDUs. IS-IS can perform equal cost or unequal cost load 410 sharing while using the spine nodes as nexthops. The aggregated 411 metric of the outbound interface and the 'Reverse Metric' 412 [REVERSE-METRIC] can be used for this purpose. 414 3.4.1. Pure CLOS Topology 416 In a data center where the topology is pure CLOS or Fat Tree, there 417 is no interconnection among the spine nodes, and there is not another 418 Core layer above the aggregation layer with reachability to the leaf 419 nodes. When flooding reduction to RF-Leafs is in use, if the link 420 between a spine and a leaf goes down, there is then a possibility of 421 black holing the data traffic in the network. 423 As in the diagram Figure 2, if the link Spine1-Leaf3 goes down, there 424 needs to be a way for Leaf1, Leaf2 and Leaf4 to avoid the Spine1 if 425 the destination of data traffic is to Leaf3 node. 427 In the above example, the Spine1 and Spine2 are provisioned to 428 advertise the Leaf-Set sub-TLV of the Spine-Leaf TLV. Originally 429 both Spines will advertise Leaf1 through Leaf4 as their Leaf-Set. 430 When the Spine1-Leaf3 link is down, Spine1 will only have Leaf1, 431 Leaf2 and Leaf4 in its Leaf-Set. This allows the other leaf nodes to 432 know that Spine1 has lost connectivity to the leaf node of Leaf3. 434 Each RF-Leaf node can select another spine node to request for some 435 prefix information associated with the lost leaf node. In this 436 diagram of Figure 2, there are only two spine nodes (Spine-Leaf 437 topology can have more than two spine nodes in general). Each RF- 438 Leaf node can independently select a spine node for the leaf 439 information. The RF-Leaf nodes will include the Info-Req sub-TLV in 440 the Spine-Leaf TLV in hellos sent to the selected spine node, Spine2 441 in this case. 443 The spine node, upon receiving the request from one or more leaf 444 nodes, will find the IPv6/IPv4 prefixes advertised by the leaf nodes 445 listed in the Info-Req sub-TLV. The spine node will use the 446 mechanism defined in Section 3.3.2 to advertise these prefixes to the 447 RF-Leaf node. For instance, it will include the IPv4 loopback prefix 448 of leaf3 based on the policy configured or administrative tag 449 attached to the prefixes. When the leaf nodes receive the more 450 specific prefixes, they will install the advertised prefixes towards 451 the other spine nodes (Spine2 in this example). 453 For instance in the data center overlay scenario, when any IP 454 destination or MAC destination uses the leaf3's loopback as the 455 tunnel nexthop, the overlay tunnel from leaf nodes will only select 456 Spine2 as the gateway to reach leaf3 as long as the Spine1-Leaf3 link 457 is still down. 459 This negative routing is only relevant between tier 0 and tier 1 460 spine-leaf levels in a multi-level spine-leaf topology when the 461 reduced flooding extension is in use. Nodes in tiers 1 or greater 462 have the full topology information. 464 3.5. Implementation and Operation 466 3.5.1. CSNP PDU 468 In Spine-Leaf extension, Complete Sequence Number PDU (CSNP) does not 469 need to be transmitted over the Spine-Leaf link to an RF-Leaf. Some 470 IS-IS implementations send periodic CSNPs after the initial adjacency 471 bring-up over a point-to-point interface. There is no need for this 472 optimization here since the RF-Leaf does not need to receive any 473 other LSPs from the network, and the only LSPs transmitted across the 474 Spine-Leaf link is the leaf node LSP. 476 Also in the graceful restart case[RFC5306], for the same reason, 477 there is no need to send the CSNPs over the Spine-Leaf interface to 478 an RF-Leaf. Spine nodes only need to set the SRMflag on the LSPs 479 belonging to the RF-Leaf. 481 3.5.2. Leaf to Leaf connection 483 Leaf to leaf node links are useful in host redundancy cases in 484 switching networks, and normally there is no flooding extensions are 485 required in this case. Each leaf node will set tier level = 0 in the 486 Spine-Leaf TLV included in hellos to leaf neighbors. LSP will be 487 exchanged over this link. In the example diagram Figure 1, the Leaf1 488 will get Leaf2's LSP and Leaf2 will get Leaf1's LSP. They will 489 install more specific routes towards each other using this local 490 Leaf-Leaf link. SPF will be performed in this case just like when 491 the entire network only involves with those two IS-IS nodes. This 492 does not affect the normal Spine-Leaf mechanism they perform toward 493 the spine nodes. 495 Besides the local leaf-to-leaf traffic, the leaf node can serve as a 496 backup gateway for its leaf neighbor. It needs to remove the 497 'Overload-Bit' setting in its LSP, and it sets both the 'L' bit and 498 the 'B' bit in the SL-flag with a high 'Reverse Metric' value. 500 3.5.3. Overload Bit 502 The leaf node SHOULD set the 'overload' bit on its LSP PDU, since if 503 the spine nodes were to forward traffic not meant for the local node, 504 the leaf node does not have the topology information to prevent a 505 routing/forwarding loop. 507 3.5.4. Spine Node Hostname 509 This extension creates a non-reciprocal relationship between the 510 spine node and leaf node. The spine node will receive leaf's LSP and 511 will know the leaf's hostname, but the leaf does not have spine's 512 LSP. This extension allows the Dynamic Hostname TLV [RFC5301] to be 513 optionally included in spine's IIH PDU when sending to a 'Leaf-Peer'. 514 This is useful in troubleshooting cases. 516 3.5.5. IS-IS Reverse Metric 518 This metric is part of the aggregated metric for leaf's default route 519 installation with load sharing among the spine nodes. When a spine 520 node is in 'overload' condition, it should use the IS-IS Reverse 521 Metric TLV in IIH [REVERSE-METRIC] to set this metric to maximum to 522 discourage the leaf using it as part of the loadsharing. 524 In some cases, certain spine nodes may have less bandwidth in link 525 provisioning or in real-time condition, and it can use this metric to 526 signal to the leaf nodes dynamically. 528 In other cases, such as when the spine node loses a link to a 529 particular leaf node, although it can redirect the traffic to other 530 spine nodes to reach that destination leaf node, but it MAY want to 531 increase this metric value if the inter-spine connection becomes over 532 utilized, or the latency becomes an issue. 534 In the leaf-leaf link as a backup gateway use case, the 'Reverse 535 Metric' SHOULD always be set to very high value. 537 3.5.6. Spine-Leaf Traffic Engineering 539 Besides using the IS-IS Reverse Metric by the spine nodes to affect 540 the traffic pattern for leaf default gateway towards multiple spine 541 nodes, the IPv6/IPv4 Info-Advertise sub-TLVs can be selectively used 542 by traffic engineering controllers to move data traffic around the 543 data center fabric to alleviate congestion and to reduce the latency 544 of a certain class of traffic pairs. By injecting more specific leaf 545 node prefixes, it will allow the spine nodes to attract more traffic 546 on some underutilized links. 548 3.5.7. Other End-to-End Services 550 Losing the topology information will have an impact on some of the 551 end-to-end network services, for instance, MPLS TE or end-to-end 552 segment routing. Some other mechanisms such as those described in 553 PCE [RFC4655] based solution may be used. In this Spine-Leaf 554 extension, the role of the leaf node is not too much different from 555 the multi-level IS-IS routing while the level-1 IS-IS nodes only have 556 the default route information towards the node which has the Attach 557 Bit (ATT) set, and the level-2 backbone does not have any topology 558 information of the level-1 areas. The exact mechanism to enable 559 certain end-to-end network services in Spine-Leaf network is outside 560 the scope of this document. 562 3.5.8. Address Family and Topology 564 IPv6 Address families[RFC5308], Multi-Topology (MT)[RFC5120] and 565 Multi-Instance (MI)[RFC8202] information is carried over the IIH PDU. 566 Since the goal is to simplify the operation of IS-IS network, for the 567 simplicity of this extension, the Spine-Leaf mechanism is applied the 568 same way to all the address families, MTs and MIs. 570 3.5.9. Migration 572 For this extension to be deployed in existing networks, a simple 573 migration scheme is needed. To support any leaf node in the network, 574 all the involved spine nodes have to be upgraded first. So the first 575 step is to migrate all the involved spine nodes to support this 576 extension, then the leaf nodes can be enabled with 'Leaf-Mode' one by 577 one. No flag day is needed for the extension migration. 579 4. IANA Considerations 581 A new TLV codepoint is defined in this document and needs to be 582 assigned by IANA from the "IS-IS TLV Codepoints" registry. It is 583 referred to as the Spine-Leaf TLV and the suggested value is 150. 584 This TLV is only to be optionally inserted either in the IIH PDU or 585 in the Circuit Flooding Scoped LSP PDU. IANA is also requested to 586 maintain the SL-flag bit values in this TLV, and 0x01, 0x02 and 0x04 587 bits are defined in this document. 589 Value Name IIH LSP SNP Purge CS-LSP 590 ----- --------------------- --- --- --- ----- ------- 591 150 Spine-Leaf y y n n y 593 This extension also proposes to have the Dynamic Hostname TLV, 594 already assigned as code 137, to be allowed in IIH PDU. 596 Value Name IIH LSP SNP Purge 597 ----- --------------------- --- --- --- ----- 598 137 Dynamic Name y y n y 600 Two new sub-TLVs are defined in this document and needs to be added 601 assigned by IANA from the "IS-IS TLV Codepoints". They are referred 602 to in this document as the Leaf-Set sub-TLV and the Info-Req sub-TLV. 603 It is suggested to have the values 1 and 2 respectively. 605 5. Security Considerations 607 Security concerns for IS-IS are addressed in [ISO10589], [RFC5304], 608 [RFC5310], and [RFC7602]. This extension does not raise additional 609 security issues. 611 6. Acknowledgments 613 TBD. 615 7. Document Change Log 617 7.1. Changes to draft-shen-isis-spine-leaf-ext-05.txt 619 o Submitted January 2018. 621 o Just a refresh. 623 7.2. Changes to draft-shen-isis-spine-leaf-ext-04.txt 625 o Submitted June 2017. 627 o Added the Tier level information to handle the multi-level spine- 628 leaf topology using this extension. 630 7.3. Changes to draft-shen-isis-spine-leaf-ext-03.txt 632 o Submitted March 2017. 634 o Added the Spine-Leaf sub-TLVs to handle the case of data center 635 pure CLOS topology and mechanism. 637 o Added the Spine-Leaf TLV and sub-TLVs can be optionally inserted 638 in either IIH PDU or CS-LSP PDU. 640 o Allow use of prefix Reachability TLVs 135 and 236 in IIHs/CS-LSPs 641 sent from spine to leaf. 643 7.4. Changes to draft-shen-isis-spine-leaf-ext-02.txt 645 o Submitted October 2016. 647 o Removed the 'Default Route Metric' field in the Spine-Leaf TLV and 648 changed to using the IS-IS Reverse Metric in IIH. 650 7.5. Changes to draft-shen-isis-spine-leaf-ext-01.txt 652 o Submitted April 2016. 654 o No change. Refresh the draft version. 656 7.6. Changes to draft-shen-isis-spine-leaf-ext-00.txt 658 o Initial version of the draft is published in November 2015. 660 8. References 662 8.1. Normative References 664 [ISO10589] 665 ISO "International Organization for Standardization", 666 "Intermediate system to Intermediate system intra-domain 667 routeing information exchange protocol for use in 668 conjunction with the protocol for providing the 669 connectionless-mode Network Service (ISO 8473), ISO/IEC 670 10589:2002, Second Edition.", Nov 2002. 672 [REVERSE-METRIC] 673 Shen, N., Amante, S., and M. Abrahamsson, "IS-IS Routing 674 with Reverse Metric", draft-ietf-isis-reverse-metric-07 675 (work in progress), 2017. 677 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 678 Requirement Levels", BCP 14, RFC 2119, 679 DOI 10.17487/RFC2119, March 1997, 680 . 682 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 683 Topology (MT) Routing in Intermediate System to 684 Intermediate Systems (IS-ISs)", RFC 5120, 685 DOI 10.17487/RFC5120, February 2008, 686 . 688 [RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange 689 Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301, 690 October 2008, . 692 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 693 Authentication", RFC 5304, DOI 10.17487/RFC5304, October 694 2008, . 696 [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic 697 Engineering", RFC 5305, DOI 10.17487/RFC5305, October 698 2008, . 700 [RFC5306] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS", 701 RFC 5306, DOI 10.17487/RFC5306, October 2008, 702 . 704 [RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, 705 DOI 10.17487/RFC5308, October 2008, 706 . 708 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 709 and M. Fanto, "IS-IS Generic Cryptographic 710 Authentication", RFC 5310, DOI 10.17487/RFC5310, February 711 2009, . 713 [RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding 714 Scope Link State PDUs (LSPs)", RFC 7356, 715 DOI 10.17487/RFC7356, September 2014, 716 . 718 [RFC7602] Chunduri, U., Lu, W., Tian, A., and N. Shen, "IS-IS 719 Extended Sequence Number TLV", RFC 7602, 720 DOI 10.17487/RFC7602, July 2015, 721 . 723 [RFC8202] Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS 724 Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June 725 2017, . 727 8.2. Informative References 729 [OPENFABRIC] 730 White, R. and S. Zandi, "Openfabric", draft-white- 731 openfabric-04 (work in progress), October 2017. 733 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 734 Element (PCE)-Based Architecture", RFC 4655, 735 DOI 10.17487/RFC4655, August 2006, 736 . 738 [RFC5309] Shen, N., Ed. and A. Zinin, Ed., "Point-to-Point Operation 739 over LAN in Link State Routing Protocols", RFC 5309, 740 DOI 10.17487/RFC5309, October 2008, 741 . 743 Authors' Addresses 745 Naiming Shen 746 Cisco Systems 747 560 McCarthy Blvd. 748 Milpitas, CA 95035 749 US 751 Email: naiming@cisco.com 753 Les Ginsberg 754 Cisco Systems 755 821 Alder Drive 756 Milpitas, CA 95035 757 US 759 Email: ginsberg@cisco.com 761 Sanjay Thyamagundalu 763 Email: tsanjay@gmail.com