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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR and SIDR K. Sriram, Ed. 3 Internet-Draft USA NIST 4 Intended status: Standards Track A. Azimov, Ed. 5 Expires: January 28, 2021 Yandex 6 July 27, 2020 8 Methods for Detection and Mitigation of BGP Route Leaks 9 draft-ietf-grow-route-leak-detection-mitigation-03 11 Abstract 13 Problem definition for route leaks and enumeration of types of route 14 leaks are provided in RFC 7908. This document describes a new well- 15 known Large Community that provides a way for route-leak prevention, 16 detection, and mitigation. The configuration process for this 17 Community can be automated with the methodology for setting BGP roles 18 that is described in ietf-idr-bgp-open-policy draft. 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 January 28, 2021. 37 Copyright Notice 39 Copyright (c) 2020 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 2. Peering Relationships . . . . . . . . . . . . . . . . . . . . 3 56 3. Community vs Attribute . . . . . . . . . . . . . . . . . . . 3 57 4. Down Only Community . . . . . . . . . . . . . . . . . . . . . 4 58 4.1. Route-Leak Mitigation . . . . . . . . . . . . . . . . . . 5 59 4.2. Only Marking . . . . . . . . . . . . . . . . . . . . . . 6 60 5. Implementation Considerations . . . . . . . . . . . . . . . . 7 61 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 62 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 63 8. Informative References . . . . . . . . . . . . . . . . . . . 7 64 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8 65 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 8 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 68 1. Introduction 70 RFC 7908 [RFC7908] provides a definition of the route-leak problem 71 and enumerates several types of route leaks. For this document, the 72 definition that is applied is that a route leak occurs when a route 73 received from a transit provider or a lateral peer is forwarded 74 (against commonly used policy) to another transit provider or a 75 lateral peer. The commonly used policy is that a route received from 76 a transit provider or a lateral peer MAY be forwarded only to 77 customers. 79 This document describes a solution for prevention, detection and 80 mitigation route leaks which is based on conveying route-leak 81 detection information in a transitive well-known BGP Large Community. 82 The configuration process for the Large Community MUST be defined 83 according to peering relations between ISPs. This process can be 84 automated with the methodology for setting BGP roles that is 85 described in [I-D.ietf-idr-bgp-open-policy]. 87 The techniques described in this document can be incrementally 88 deployed. If a pair of ISPs and/or Internet Exchanges (IXes) deploy 89 the proposed techniques, then they would detect and mitigate any 90 route leaks that occur in an AS path between them even when other 91 ASes in the path are not upgraded. 93 2. Peering Relationships 95 As described in [I-D.ietf-idr-bgp-open-policy] there are several 96 common peering relations between eBGP neighbors: 98 o Provider - sender is a transit provider of the neighbor; 100 o Customer - sender is a customer of the neighbor; 102 o Route Server (RS) - sender is route server at an internet exchange 103 (IX) 105 o RS-client - sender is client of an RS at an IX 107 o Peer - sender and neighbor are lateral (non-transit) peers; 109 If a route is received from a provider, peer or RS-client, it MUST 110 follow the 'down only' rule, i.e., it MAY be advertised only to 111 customers. If a route is sent to a customer, peer or RS-client, it 112 also MUST follow the 'down only' rule at each subsequent AS in the AS 113 path. 115 A standardized transitive route-leak detection signal is needed that 116 will prevent Autonomous Systems (ASes) from leaking and also inform a 117 remote ISP (or AS) in the AS path that a received route violates 118 'down only' policy. This signal would facilitate a way to stop the 119 propagation of leaked prefixes. 121 To improve reliability and cover for non-participating preceding 122 neighbor, the signal should be set on both receiver and sender sides. 124 3. Community vs Attribute 126 This section presents a brief discussion of the advantages and 127 disadvantages of communities and BGP path attributes for the purpose 128 of route-leak detection. 130 A transitive path attribute is a native way to implement the route- 131 leak detection signal. Based on the way BGP protocol works, the use 132 of a transitive attribute makes it more certain that the route-leak 133 detection signal would pass unaltered through non-participating 134 (i.e., not upgraded) BGP routers. The main disadvantage of this 135 approach is that the deployment of a new BGP attribute requires a 136 software upgrade in router OS which may delay wide adoption for 137 years. 139 On the other hand, BGP Communities do not require a router OS update. 140 The potential disadvantage of using a Community for the route-leak 141 detection signal is that it is more likely to be dropped somewhere 142 along the way in the AS path. Currently, the use of BGP Communities 143 is somewhat overloaded. BGP Communities are already used for 144 numerous applications: different types of route marking, route policy 145 control, blackholing, etc. It is observed that some ASes seem to 146 purposefully or accidentally remove transitive communities on 147 receipt, sometimes well-known ones. Perhaps this issue may be 148 mitigated with strong policy guidance related to the handling of 149 Communities. 151 Due to frequently occurring regional and global disruptions in 152 Internet connectivity, it is critical to move forward with a solution 153 that is viable in the near term. That solution would be route-leak 154 detection using BGP Community. 156 Large Communities have much higher capacity, and therefore they are 157 likely to be less overloaded. Hence, Large Community is proposed to 158 be used for route-leak detection. This document suggests reserving 159 class for the purpose of transitive well-known Large 160 Communities that MUST NOT be stripped on ingress or egress. 162 While it is not a part of this document, the route-leak detection 163 signal described here can also be carried in a transitive BGP Path 164 Attribute, and similar prevention and mitigation techniques as 165 described here would apply (see [I-D.ietf-idr-bgp-open-policy]). 167 4. Down Only Community 169 This section specifies the semantics of route-leak detection 170 Community and its usage. This Community is given the specific name 171 Down Only (DO) Community. The DO Community is carried in a BGP Large 172 Community with a format as shown in Figure 1. 174 0 1 2 3 175 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 1 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 | TBD1 (class for transitive well-known Large Communities) | 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 179 | TBD2 (subclass for DO) | 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 | ASN | 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 184 Figure 1: Format of the DO Community using a Large Community 185 [RFC8092]. 187 The authors studied different options for route-leak mitigation. The 188 main options considered are (1) drop detected route leaks and (2) 189 deprioritize detected route leaks. It can be demonstrated that the 190 loose mode that uses deprioritization is not safe. Traffic 191 Engineering (TE) techniques which limit prefix visibility are quite 192 common. It may happen that a more specific TE prefix is sent only to 193 downstream ASes or to IX(es)/selected peers, and a control Community 194 is used to restrict its propagation. If such a more specific prefix 195 is leaked, deprioritization will not stop such a route leak from 196 propagating. In addition, propagation of leaked prefixes based on 197 deprioritization may result in priority loops leading to BGP wedgies 198 [RFC4264] or even persistent route oscillations. 200 So, the only truly safe way to implement route-leak mitigation is to 201 drop detected route leaks. The ingress and egress policies 202 corresponding to 'drop detected route leaks' is described in 203 Section 4.1. This policy SHOULD be used as a default behavior. 205 Nevertheless, early adopters might want to deploy only the signaling 206 and perhaps use it only for diagnostics before applying any route- 207 leak mitigation policy. They are also encouraged to use slightly 208 limited marking, which is described in Section 4.2. 210 4.1. Route-Leak Mitigation 212 This section describes the eBGP ingress and egress policies that MUST 213 be used to perform route-leak prevention, detection and mitigation 214 using the DO Community. 216 The ingress policy MUST use the following procedure: 218 1. If a route with DO Community set (i.e., DO is attached) is 219 received from a Customer or RS-client, then it is a route leak 220 and MUST be rejected. The procedure halts. 222 2. If a route with DO Community set is received from Peer (non- 223 transit) and DO value is not equal to the sending neighbor's ASN, 224 then it is a route leak and MUST be rejected. The procedure 225 halts. 227 3. If a route is received from a Provider, Peer or RS, then the DO 228 Community MUST be added with a value equal to the sending 229 neighbor's ASN. 231 The egress policy MUST use the following procedure: 233 1. A route with DO Community set MUST NOT be sent to Providers, 234 Peers, and RS. 236 2. If a route is sent to a Customer or Peer, then the DO Community 237 MUST be added with a value equal to the ASN of the sender. 239 The above procedures comprehensively provide route-leak prevention, 240 detection and mitigation. Policy consisting of these procedures 241 SHOULD be used as a default behavior. 243 4.2. Only Marking 245 This section describes eBGP ingress and egress marking policies that 246 MUST be used if an AS is not performing route-leak mitigation (i.e., 247 dropping detected route leaks) as described in Section 4.1, but wants 248 to use only marking with DO Community. The slightly limited DO 249 marking (compared to that in Section 4.1) described below guarantees 250 that this DO marking will not limit the leak detection opportunities 251 for subsequent ASes in the AS path. 253 The ingress policy MUST use the following procedure: 255 1. If a route with DO Community set is received from a Customer or 256 RS-client, then it is a route leak. The procedure halts. 258 2. If a route with DO Community set is received from a Peer and DO 259 value is not equal to the sending neighbor's ASN, then it is a 260 route leak. The procedure halts. 262 3. If a route is received from a Provider, Peer or RS, then the DO 263 Community MUST be added with value equal to the sending 264 neighbor's ASN. 266 The egress policy MUST use the following procedure: 268 1. If a route is sent to a Customer or RS-client, then the DO 269 Community MUST be added with value equal to the ASN of the 270 sender. 272 2. If DO Community is not set and the route is sent to a Peer, then 273 the DO Community MUST be added with value equal to the ASN of the 274 sender. 276 These above procedures specify setting DO signal in a way that can be 277 used to evaluate the potential impact of route-leak mitigation policy 278 before deploying strict dropping of detected route leaks. 280 5. Implementation Considerations 282 It was observed that the majority of BGP implementations do not 283 support negative match for communities like a:b:!c. Considering that 284 it is suggested to replace the second rule from ingress policy with 285 the following: 287 If a route with DO Community set is received from a Peer and DO value 288 is equal to the sending neighbor's ASN, then it is a valid route, 289 otherwise it is a route leak. The procedure halts. 291 This rule is based on a weaker assumption that a peer that is doing 292 marking is also doing filtering (dropping detected leaks). That is 293 why networks that do not follow the route-leak mitigation policy in 294 Section 4.1 MUST carefully follow marking rules described in 295 Section 4.2. 297 6. IANA Considerations 299 The draft suggests to reserve a Global Administrator ID for 300 transitive well-known Large Community registry. IANA is requested to 301 register a subclass for DO Community in this registry. 303 7. Security Considerations 305 In specific circumstances in a state of partial adoption, route-leak 306 mitigation mechanism can result in Denial of Service (DoS) for the 307 victim prefix. Such a scenario may happen only for a prefix that has 308 a single path from the originator to a Tier-1 ISP and only when the 309 prefix is not covered with a less specific prefix with multiple paths 310 to the Tier-1 ISP. If, in such unreliable topology, route leak is 311 injected somewhere inside this single path, then it may be rejected 312 by upper layer providers in the path, thus limiting prefix 313 visibility. While such anomaly is unlikely to happen, such an issue 314 should be easy to debug, since it directly affects the sequence of 315 originator's providers. 317 With the use of BGP Community, there is often a concern that the 318 Community propagates beyond its intended perimeter and causes harm 319 [streibelt]. However, that concern does not apply to the DO 320 Community because it is a transitive Community that must propagate as 321 far as the update goes. 323 8. Informative References 325 [I-D.ietf-idr-bgp-open-policy] 326 Azimov, A., Bogomazov, E., Bush, R., Patel, K., and K. 327 Sriram, "Route Leak Prevention using Roles in Update and 328 Open messages", draft-ietf-idr-bgp-open-policy-13 (work in 329 progress), July 2020. 331 [RFC4264] Griffin, T. and G. Huston, "BGP Wedgies", RFC 4264, 332 DOI 10.17487/RFC4264, November 2005, 333 . 335 [RFC7908] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E., 336 and B. Dickson, "Problem Definition and Classification of 337 BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June 338 2016, . 340 [RFC8092] Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas, 341 I., and N. Hilliard, "BGP Large Communities Attribute", 342 RFC 8092, DOI 10.17487/RFC8092, February 2017, 343 . 345 [streibelt] 346 Streibelt et al., F., "BGP Communities: Even more Worms in 347 the Routing Can", ACM IMC, October 2018, 348 . 350 Acknowledgements 352 The authors wish to thank John Scudder, Susan Hares, Ruediger Volk, 353 Jeffrey Haas, Mat Ford, Greg Skinner for their review and comments. 355 Contributors 357 The following people made significant contributions to this document 358 and should be considered co-authors: 360 Brian Dickson 361 Independent 362 Email: brian.peter.dickson@gmail.com 364 Doug Montgomery 365 USA National Institute of Standards and Technology 366 Email: dougm@nist.gov 368 Keyur Patel 369 Arrcus 370 Email: keyur@arrcus.com 372 Andrei Robachevsky 373 Internet Society 374 Email: robachevsky@isoc.org 376 Eugene Bogomazov 377 Qrator Labs 378 Email: eb@qrator.net 380 Randy Bush 381 Internet Initiative Japan 382 Email: randy@psg.com 384 Authors' Addresses 386 Kotikalapudi Sriram (editor) 387 USA National Institute of Standards and Technology 388 100 Bureau Drive 389 Gaithersburg, MD 20899 390 United States of America 392 Email: ksriram@nist.gov 394 Alexander Azimov (editor) 395 Yandex 396 Ulitsa Lva Tolstogo 16 397 Moscow 119021 398 Russia 400 Email: a.e.azimov@gmail.com