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If these are generic example addresses, they should be changed to use the 233.252.0.x range defined in RFC 5771 Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (January 2, 2018) is 2277 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-04) exists of draft-keyupate-idr-bgp-spf-03 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group X. Xu 3 Internet-Draft K. Bi 4 Intended status: Standards Track Huawei 5 Expires: July 6, 2018 J. Tantsura 6 Individual 7 January 2, 2018 9 BGP Neighbor Autodiscovery 10 draft-xu-idr-neighbor-autodiscovery-03 12 Abstract 14 BGP has been used as the underlay routing protocol in many hyper- 15 scale data centers. This document proposes a BGP neighbor 16 autodiscovery mechanism that greatly simplifies BGP deployments. 17 This mechanism is very useful for those hyper-scale data centers 18 where BGP is used as the underlay routing protocol. 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 55 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. BGP Hello Message Format . . . . . . . . . . . . . . . . . . 3 58 4. Hello Message Procedure . . . . . . . . . . . . . . . . . . . 5 59 5. HELLO Message Error Handling . . . . . . . . . . . . . . . . 6 60 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 61 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 62 7.1. BGP Hello Message . . . . . . . . . . . . . . . . . . . . 6 63 7.2. TLVs of BGP Hello Message . . . . . . . . . . . . . . . . 7 64 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 65 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 66 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 67 9.2. Informative References . . . . . . . . . . . . . . . . . 8 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 70 1. Introduction 72 BGP has been used as the underlay routing protocol instead of IGP in 73 many hyper-scale data centers [RFC7938]. Furthermore, there is an 74 ongoing effort to leverage BGP link-state distribution mechanism to 75 achieve BGP-SPF [I-D.keyupate-idr-bgp-spf]. However, BGP is not good 76 as an IGP from the perspective of deployment automation and 77 simplicity. For instance, the IP address and the Autonomous System 78 Number (ASN) of each and every BGP neighbor have to be manually 79 configured on BGP routers although these BGP peers are directly 80 connected. In addition, for those directly connected BGP routers, 81 it's usually not ideal to establish BGP sessions over their directly 82 connected interface addresses due to the following reasons: 1) it's 83 not convient to do trouble-shooting; 2) the BGP update volume is 84 unnecessarily increased when there are multiple physical links 85 between them and those links couldn't be configured as a Link 86 Aggregtion Group (LAG) due to whatever reason (e.g., diffferent link 87 type or speed). As a result, it's more common that loopback 88 interface addresses of those directly connected BGP peers are used 89 for BGP session establishment. To make those loopback addresses of 90 directly connected BGP peers reachable from one another, either 91 static routes have to be configured or some kind of IGP has to be 92 enabled. The former is not good from the automation perspective 93 while the latter is in conflict with the original intention of using 94 BGP as an IGP. 96 This draft specifies a BGP neighbor autodiscovery mechanism by 97 borrowing some ideas from the Label Distribution Protocol (LDP) 98 [RFC5036] . More specifically, directly connected BGP routers could 99 automatically discovery the loopback address and the ASN of one other 100 through the exchange of the to-be-defined BGP messages. The BGP 101 session establishment process as defined in [RFC4271] could be 102 triggered once directly connected BGP neighbors are discovered from 103 one another. Note that the BGP session should be established over 104 the discovered loopback address of the BGP neighbor. In addition, to 105 elimnate the need of configuring static routes or enabling IGP for 106 the loopback addresses, a certain type of routes towards the BGP 107 neighbor's loopback addresses are dynatically instantiated once the 108 BGP neighbor has been discovered. The administritive distance of 109 such type of routes MUST be smaller than their equivalents that are 110 learnt by the regular BGP update messages . Otherwise, circular 111 dependency would occur once these loopback addresses are advertised 112 via the regular BGP updates. 114 1.1. Requirements Language 116 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 117 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 118 document are to be interpreted as described in RFC 2119 [RFC2119]. 120 2. Terminology 122 This memo makes use of the terms defined in [RFC4271]. 124 3. BGP Hello Message Format 126 To automatically discover directly connected BGP neighbors, a BGP 127 router periodically sends BGP HELLO messages out those interfaces on 128 which BGP neighbor autodiscovery are enabled. The BGP HELLO message 129 is a new BGP message which has the same fixed-size BGP header as the 130 exiting BGP messages. However, the HELLO message MUST sent as UDP 131 packets addressed to the to-be-assigned BGP discovery port (179 is 132 the suggested port value) for the "all routers on this subnet" group 133 multicast address (i.e., 224.0.0.2 in the IPv4 case and FF02::2 in 134 the IPv6 case). The IP source address is set to the address of the 135 interface over which the message is sent out. 137 In addition to the fixed-size BGP header, the HELLO message contains 138 the following fields: 140 0 1 2 3 141 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 1 142 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 143 | Version | Hold Time | Message Length | 144 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 145 | AS number | 146 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 147 | TLVs | 148 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 149 Figure 1: BGP Hello Message 151 Version: This 1-octet unsigned integer indicates the protocol 152 version number of the message. The current BGP version number is 153 4. 155 Hold Time: Hello hold timer in seconds. Hello Hold Time specifies 156 the time the sending BGP peer will maintain its record of Hellos 157 from the receiving BGP peer without receipt of another Hello. A 158 pair of BGP peers negotiates the hold times they use for Hellos 159 from each other. Each proposes a hold time. The hold time used 160 is the minimum of the hold times proposed in their Hellos. A 161 value of 0 means use the default 15 seconds. 163 Message Length: This 2-octet unsigned integer specifies the length 164 in octects of the Connection Address TLV and other TLVs. 166 AS number: AS Number of the Hello message sender. 168 TLVs: This field contains Connection Address TLV and other TLVs. 170 The Accepted ASN List TLV format is shown as follows: 172 0 1 2 3 173 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 1 174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 175 | Type=TBD1 | Length | 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 | Accepted ASN List(variable) | 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 179 Figure 2: Accepted ASN List TLV 181 Type: TBD1 183 Length:Specifies the length of the Value field in octets. 185 Accepted ASN-List: This variable-length field contains one or more 186 accepted 4-octet ASNs. 188 The Connection Address TLV format is shown as follows: 190 0 1 2 3 191 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 1 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 193 | Type=TBD2 | Length | 194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 195 | Connection Address (4-octet or 16-octet) | 196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 197 Figure 3: Connection Address TLV 199 Type: TBD2 201 Length:Specifies the length of the Value field in octets. 203 Connection Address: This variable-length field indicates the IPv4 204 or IPv6 loopback address which is used for establishing BGP 205 sessions. 207 The Router ID TLV format is shown as follows: 209 0 1 2 3 210 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 1 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 | Type=TBD3 | Length | 213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 214 | Router ID (4-octet or 16-octet) | 215 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 216 Figure 4: Router ID TLV 218 Type: TBD3 220 Length:Specifies the length of the Value field in octets and it's 221 set to 4 for the IPv4-address-formatted BGP Router ID. 223 Router ID: This variable-length field indicates the BGP router ID 224 which could be used for performing the BGP-SPF algorithm as 225 described in [I-D.keyupate-idr-bgp-spf]. 227 4. Hello Message Procedure 229 A BGP peer receiving Hellos from another peer maintains a Hello 230 adjacency corresponding to the Hellos. The peer maintains a hold 231 timer with the Hello adjacency, which it restarts whenever it 232 receives a Hello that matches the Hello adjacency. If the hold timer 233 for a Hello adjacency expires the peer discards the Hello adjacency. 235 We recommend that the interval between Hello transmissions be at most 236 one third of the Hello hold time. 238 A BGP session with a peer has one or more Hello adjacencies. 240 A BGP session has multiple Hello adjacencies when a pair of BGP peers 241 is connected by multiple links that have the same connection address 242 (e.g., multiple PPP links between a pair of routers). In this 243 situation, the Hellos a BGP peer sends on each such link carry the 244 same Connection Address. In addition, to elimnate the need of 245 configuring static routes or enabling IGP for advertising the 246 loopback addresses, a certain type of routes towards the BGP 247 neighbor's loopback addresses (e.g., carried in the Connection 248 Address TLV) could be dymatically created once the BGP neighbor has 249 been discovered. The administritive distance of such type of routes 250 MUST be smaller than their equivalents which are learnt via the 251 normal BGP update messages. Otherwise, circular dependency problem 252 would occur once these loopback addresses are advertised via the 253 normal BGP update messages as well. 255 BGP uses the regular receipt of BGP Hellos to indicate a peer's 256 intent to keep BGP session identified by the Hello. A BGP peer 257 maintains a hold timer with each Hello adjacency that it restarts 258 when it receives a Hello that matches the adjacency. If the timer 259 expires without receipt of a matching Hello from the peer, BGP 260 concludes that the peer no longer wishes to keep BGP session for that 261 link or that the peer has failed. The BGP peer then deletes the 262 Hello adjacency. When the last Hello adjacency for an BGP session is 263 deleted, the BGP peer terminates the BGP session by sending a 264 Notification message and closing the transport connection. 266 5. HELLO Message Error Handling 268 TBD 270 6. Acknowledgements 272 The authors would like to thank Enke Chen and Nikos Triantafillis for 273 their valuable comments and suggestions on this document. 275 7. IANA Considerations 277 7.1. BGP Hello Message 279 This document requests IANA to allocate a new UDP port for BGP Hello 280 message. 282 Value TLV Name Reference 283 ----- ------------------------------------ ------------- 284 Service Name: BGP-HELLO 285 Transport Protocol(s): UDP 286 Assignee: IESG 287 Contact: IETF Chair . 288 Description: BGP Hello Message. 289 Reference: This document -- draft-xu-idr-neighbor-autodiscovery. 290 Port Number: TBD1 (179 is the suggested value) -- To be assigned by IANA. 292 7.2. TLVs of BGP Hello Message 294 This document requests IANA to create a new registry "TLVs of BGP 295 Hello Message" with the following registration procedure: 297 Registry Name: TLVs of BGP Hello Message. 299 Value TLV Name Reference 300 ------- ------------------------------------------ ------------- 301 0 Reserved This document 302 1 Accepted ASN List This document 303 2 Connection Address This document 304 3 Router ID This document 305 4-65500 Unassigned 306 65501-65534 Experimental This document 307 65535 Reserved This document 309 8. Security Considerations 311 For security purposes, BGP speakers usually only accept TCP 312 connection attempts to port 179 from the specified BGP peers or those 313 within the configured address range. With the BGP auto-discovery 314 mechanism, it's configurable to enable or disable sending/receiving 315 BGP hello messages on the per-interface basis and BGP hello messages 316 are only exchanged between physically connected peers that are 317 trustworthy. Therefore, the BGP auto-discovery mechanism doesn't 318 introduce additional security risks associated with BGP. 320 In addition, for the BGP sessions with the automatically discovered 321 peers via the BGP hello messages, the TTL of the TCP/BGP messages 322 (dest port=179) MUST be set to 255. Any received TCP/BGP message 323 with TTL being less than 254 MUST be dropped according to [RFC5082]. 325 9. References 326 9.1. Normative References 328 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 329 Requirement Levels", BCP 14, RFC 2119, 330 DOI 10.17487/RFC2119, March 1997, 331 . 333 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 334 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 335 DOI 10.17487/RFC4271, January 2006, 336 . 338 9.2. Informative References 340 [I-D.keyupate-idr-bgp-spf] 341 Patel, K., Lindem, A., Zandi, S., and G. Velde, "Shortest 342 Path Routing Extensions for BGP Protocol", draft-keyupate- 343 idr-bgp-spf-03 (work in progress), June 2017. 345 [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., 346 "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, 347 October 2007, . 349 [RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C. 350 Pignataro, "The Generalized TTL Security Mechanism 351 (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007, 352 . 354 [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of 355 BGP for Routing in Large-Scale Data Centers", RFC 7938, 356 DOI 10.17487/RFC7938, August 2016, 357 . 359 Authors' Addresses 361 Xiaohu Xu 362 Huawei 364 Email: xuxh.mail@gmail.com 366 Kunyang Bi 367 Huawei 369 Email: bikunyang@huawei.com 370 Jeff Tantsura 371 Individual 373 Email: jefftant.ietf@gmail.com