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Murphy 5 Expires: October 20, 2016 SPARTA, Inc., a Parsons Company 6 April 18, 2016 8 BGPSec Considerations for AS Migration 9 draft-ietf-sidr-as-migration-05 11 Abstract 13 This document discusses considerations and methods for supporting and 14 securing a common method for AS-Migration within the BGPSec protocol. 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at http://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on October 20, 2016. 33 Copyright Notice 35 Copyright (c) 2016 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (http://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 51 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 52 1.2. Documentation note . . . . . . . . . . . . . . . . . . . 3 53 2. General Scenario . . . . . . . . . . . . . . . . . . . . . . 3 54 3. RPKI Considerations . . . . . . . . . . . . . . . . . . . . . 3 55 3.1. Origin Validation . . . . . . . . . . . . . . . . . . . . 4 56 3.2. Path Validation . . . . . . . . . . . . . . . . . . . . . 5 57 3.2.1. Outbound announcements (PE-->CE) . . . . . . . . . . 5 58 3.2.2. Inbound announcements (CE-->PE) . . . . . . . . . . . 5 59 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6 60 5. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 6 61 5.1. Outbound (PE->CE) . . . . . . . . . . . . . . . . . . . . 8 62 5.2. Inbound (CE->PE) . . . . . . . . . . . . . . . . . . . . 8 63 5.3. Other considerations . . . . . . . . . . . . . . . . . . 8 64 5.4. Example . . . . . . . . . . . . . . . . . . . . . . . . . 9 65 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 66 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 67 8. Note for RFC Editor . . . . . . . . . . . . . . . . . . . . . 13 68 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 69 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 70 10.1. Normative References . . . . . . . . . . . . . . . . . . 13 71 10.2. Informative References . . . . . . . . . . . . . . . . . 14 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 74 1. Introduction 76 A method of managing a BGP Autonomous System Number (ASN) migration 77 is described in RFC7705 [RFC7705]. Since it concerns the handling of 78 AS_PATH attributes, it is necessary to ensure that the process and 79 features are properly supported in BGPSec 80 [I-D.ietf-sidr-bgpsec-protocol], because BGPSec is explicitly 81 designed to protect against changes in the BGP AS_PATH, whether by 82 choice, by misconfiguration, or by malicious intent. It is critical 83 that the BGPSec protocol framework is able to support this 84 operationally necessary tool without creating an unacceptable 85 security risk or exploit in the process. 87 1.1. Requirements Language 89 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 90 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 91 document are to be interpreted as described in RFC 2119 [RFC2119]. 93 1.2. Documentation note 95 This document uses Autonomous System Numbers (ASNs) from the range 96 reserved for documentation as described in RFC 5398 [RFC5398]. In 97 the examples used here, they are intended to represent Globally 98 Unique ASNs, not private ASNs as documented in RFC 1930 [RFC1930] 99 section 10. 101 2. General Scenario 103 This document assumes that the reader has read and understood the ASN 104 migration method discussed in RFC7705 [RFC7705] including its 105 examples (see section 2 of the referenced document), as they will be 106 heavily referenced here. The use case being discussed in the 107 referenced document is as follows: For whatever the reason, a 108 provider is in the process of merging two or more ASNs, where 109 eventually one subsumes the other(s). BGP AS Confederations RFC 5065 110 [RFC5065] is not enabled between the ASNs, but a mechanism is being 111 used to modify BGP's default behavior and allow the migrating 112 Provider Edge router (PE) to masquerade as the old ASN for the 113 Provider Edge to Customer Edge (PE-CE) eBGP session, or to manipulate 114 the AS_PATH, or both. While BGPSec [I-D.ietf-sidr-bgpsec-protocol] 115 does have a method to handle standard confederation implementations, 116 it is not applicable in this exact case. This migration requires a 117 slightly different solution in BGPSec than for a standard 118 confederation because unlike in a confederation, eBGP peers may not 119 be peering with the "correct" external ASN, and the forward-signed 120 updates are for a public ASN, rather than a private one, so there is 121 no expectation that the BGP speaker would strip the affected 122 signatures before propagating the route to its eBGP neighbors. 124 In the following examples (section 5.4) (Section 5.4), AS64510 is 125 being subsumed by AS64500, and both ASNs represent a Service Provider 126 (SP) network (see Figures 1 & 2 in RFC7705 [RFC7705]). AS64496 and 127 64499 represent end customer networks. References to PE, CE, and P 128 routers mirror the diagrams and references in the above cited draft. 130 3. RPKI Considerations 132 The methods and implementation discussed in RFC7705 [RFC7705] are 133 widely used during network integrations resulting from mergers and 134 acquisitions, as well as network redesigns, and therefore it is 135 necessary to support this capability on any BGPSec-enabled routers/ 136 ASNs. What follows is a discussion of the potential issues to be 137 considered regarding how ASN-migration and BGPSec 138 [I-D.ietf-sidr-bgpsec-protocol] validation might interact. 140 One of the primary considerations for this document and migration is 141 that service providers (SPs) rarely stop after one 142 merger/acquisition/divestiture, and end up accumulating several 143 legacy ASNs over time. Since they are using methods to migrate that 144 do not require coordination with customers, they do not have a great 145 deal of control over the length of the transition period as they 146 might with something completely under their administrative control 147 (e.g. a key roll). This leaves many SPs with multiple legacy ASNs 148 which don't go away very quickly, if at all. As solutions were being 149 proposed for RPKI implementations to solve this transition case, 150 operational complexity and hardware scaling considerations associated 151 with maintaining multiple legacy ASN keys on routers throughout the 152 combined network have been carefully considered. While SPs who 153 choose to remain in this transition phase indefinitely invite added 154 risks because of the operational complexity and scaling 155 considerations associated with maintaining multiple legacy ASN keys 156 on routers throughout the combined network, saying "don't do this" is 157 of limited utility as a solution. As a result, this solution 158 attempts to minimize the additional complexity during the transition 159 period, on the assumption that it will likely be protracted. Note: 160 While this document primarily discusses service provider 161 considerations, it is not solely applicable to SPs, as enterprises 162 often migrate between ASNs using the same functionality. 164 3.1. Origin Validation 166 Route Origin Validation as defined by RFC 6480 [RFC6480] does not 167 need a unique solution to enable AS migration, as the existing 168 protocol and procedure allows for a solution. In the scenario 169 discussed, AS64510 is being replaced by AS64500. If there are any 170 existing routes originated by AS64510 on the router being moved into 171 the new ASN, this simply requires generating new ROAs for the routes 172 with the new ASN and treating them as new routes to be added to 173 AS64500. However, we also need to consider the situation where one 174 or more other PEs are still in AS64510, and are originating one or 175 more routes that may be distinct from any that the router under 176 migration is originating. PE1 (which is now a part of AS64500 and 177 instructed to use Replace Old AS as defined in RFC 7705 [RFC7705] to 178 remove AS64510 from the path) needs to be able to properly handle 179 routes originated from AS64510. If the route now shows up as 180 originating from AS64500, any downstream peers' validation check will 181 fail unless a ROA is *also* available for AS64500 as the origin ASN. 182 In addition to generating a ROA for 65400 for any prefixes originated 183 by the router being moved, it may be necessary to generate ROAs for 184 65400 for prefixes that are originating on routers still in 65410, 185 since the AS replacement function will change the origin AS in some 186 cases. This means that there will be multiple ROAs showing different 187 ASes authorized to orignate the same prefixes until all routers 188 originating prefixes from AS64510 are migrated to AS64500. Multiple 189 ROAs of this type are permissible per RFC 6480 [RFC6480] section 3.2, 190 and so managing origin validation during a migration like this is 191 merely applying the defined case where a set of prefixes are 192 originated from more than one ASN. Therefore, for each ROA that 193 authorizes the old ASN (e.g. AS64510) to originate a prefix, a new 194 ROA MUST also be created that authorizes the replacing ASN (e.g. 195 AS64500) to originate the same prefix. 197 3.2. Path Validation 199 BGPSec Path Validation requires that each router in the AS Path 200 cryptographically sign its update to assert that "Every AS on the 201 path of ASes listed in the update message has explicitly authorized 202 the advertisement of the route to the subsequent AS in the path." 203 (see intro of [I-D.ietf-sidr-bgpsec-protocol]) Since the referenced 204 AS migration technique is explicitly modifying the AS_PATH between 205 two eBGP peers who are not coordinating with one another (are not in 206 the same administrative domain), no level of trust can be assumed, 207 and therefore it may be difficult to identify legitimate manipulation 208 of the AS_PATH for migration activities when compared to manipulation 209 due to misconfiguration or malicious intent. 211 3.2.1. Outbound announcements (PE-->CE) 213 When PE1 is moved from AS64510 to AS64500, it will be provisioned 214 with the appropriate keys for AS64500 to allow it to forward-sign 215 routes using AS64500. However, there is currently no guidance in the 216 BGPSec protocol specification [I-D.ietf-sidr-bgpsec-protocol] on 217 whether or not the forward-signed ASN value is required to match the 218 configured remote AS to validate properly. That is, if CE1's BGP 219 session is configured as "remote as 64510", the presence of "local as 220 64510" on PE1 will ensure that there is no ASN mismatch on the BGP 221 session itself, but if CE1 receives updates from its remote neighbor 222 (PE1) forward-signed from AS64500, there is no guidance as to whether 223 the BGPSec validator on CE1 still considers those valid by default. 224 RFC4271 [RFC4271] section 6.3 mentions this match between the ASN of 225 the peer and the AS_PATH data, but it is listed as an optional 226 validation, rather than a requirement. Assuming that this mismatch 227 will be allowed by vendor implementations and using it as a means to 228 solve this migration case is likely to be problematic. 230 3.2.2. Inbound announcements (CE-->PE) 232 Inbound is more complicated, because the CE doesn't know that PE1 has 233 changed ASNs, so it is forward-signing all of its routes with 234 AS64510, not AS64500. The BGPSec speaker cannot manipulate previous 235 signatures, and therefore cannot manipulate the previous AS Path 236 without causing a mismatch that will invalidate the route. If the 237 updates are simply left intact, the ISP would still need to publish 238 and maintain valid and active public-keys for AS 64510 if it is to 239 appear in the BGPSec_Path_Signature in order that receivers can 240 validate the BGPSEC_Path_Signature arrived intact/whole. However, if 241 the updates are left intact, this will cause the AS Path length to be 242 increased, which is undesirable as discussed in RFC7705 [RFC7705]. 244 4. Requirements 246 In order to be deployable, any solution to the described problem 247 needs to consider the following requirements, listed in no particular 248 order: 250 o BGPSec MUST support AS Migration for both inbound and outbound 251 route announcements (see Section 3.2.1 and 3.2.2) without reducing 252 BGPSec's protections for route path 254 o MUST NOT require any reconfiguration on the remote eBGP neighbor 255 (CE) 257 o SHOULD NOT require global (i.e. network-wide) configuration 258 changes to support migration. The goal is to limit required 259 configuration changes to the devices (PEs) being migrated. 261 o MUST NOT lengthen AS Path during migration 263 o MUST operate within existing trust boundaries e.g. can't expect 264 remote side to accept pCount=0 (see Section 4.2 of 265 [I-D.ietf-sidr-bgpsec-protocol]) from untrusted/non-confed 266 neighbor 268 5. Solution 270 As noted in [I-D.ietf-sidr-bgpsec-protocol], section 4.2, BGPSec 271 already has a solution for hiding ASNs where increasing the AS Path 272 length is undesirable. So a simple solution would be to retain the 273 keys for AS64510 on PE1, and forward-sign towards CE1 with AS64510 274 and pCount=0. However, this would mean passing a pCount=0 between 275 two ASNs that are in different administrative and trust domains such 276 that it could represent a significant attack vector to manipulate 277 BGPSec-signed paths. The expectation for legitimate instances of 278 pCount=0 (to make a route-server that is not part of the transit path 279 invisible) is that there is some sort of existing trust relationship 280 between the operators of the route-server and the downstream peers 281 such that the peers could be explicitly configured by policy to 282 accept pCount=0 announcements only on the sessions where they are 283 expected. For the same reason that things like "Local AS" [RFC7705] 284 are used for ASN migration without end customer coordination, it is 285 unrealistic to assume any sort of coordination between the SP and the 286 administrators of CE1 to ensure that they will by policy accept 287 pCount=0 signatures during the transition period, and therefore this 288 is not a workable solution. 290 A better solution presents itself when considering how to handle 291 routes coming from the CE toward the PE, where the routes are 292 forward-signed to AS64510, but will eventually need to show AS64500 293 in the outbound route announcement. Because both AS64500 and AS64510 294 are in the same administrative domain, a signature from AS64510 295 forward-signed to AS64500 with pCount=0 would be acceptable as it 296 would be within the appropriate trust boundary so that each BGP 297 speaker could be explicitly configured to accept pCount=0 where 298 appropriate between the two ASNs. At the very simplest, this could 299 potentially be used at the eBGP boundary between the two ASNs during 300 migration. Since the AS_PATH manipulation described above usually 301 happens at the PE router on a per-session basis, and does not happen 302 network-wide simultaneously, it is not generally appropriate to apply 303 this AS hiding technique across all routes exchanged between the two 304 ASNs, as it may result in routing loops and other undesirable 305 behavior. Therefore the most appropriate place to implement this is 306 on the local PE that still has eBGP sessions with peers expecting to 307 peer with AS64510 (using the transition mechanisms detailed in 308 RFC7705 [RFC7705]). Since that PE has been moved to AS64500, it is 309 not possible for it to forward-sign AS64510 with pCount=0 without 310 some minor changes to the BGPSec implementation to address this use 311 case. 313 AS migration is using AS_PATH and remote AS manipulation to act as if 314 a PE under migration exists simultaneously in both ASNs even though 315 it is only configured with one global ASN. This document proposes 316 applying a similar technique to the BGPSec signatures generated for 317 routing updates processed through this migration machinery. Each 318 routing update that is received from or destined to an eBGP neighbor 319 that is still using the old ASN (64510) will be signed twice, once 320 with the ASN to be hidden and once with the ASN that will remain 321 visible. In essence, we are treating the update as if the PE had an 322 internal BGP hop and the update was passed across an eBGP session 323 between AS64500 and AS64510, configured to use and accept pCount=0, 324 while eliminating the processing and storage overhead of creating an 325 actual eBGP session between the two ASNs within the PE router. This 326 will result in a properly secured AS Path in the affected route 327 updates, because the PE router will be provisioned with valid keys 328 for both AS64500 and AS64510. An important distinction here is that 329 while AS migration under standard BGP4 is manipulating the AS_PATH 330 attribute, BGPSec uses an attribute called the Secure_Path (see 331 Section 3.1 of [I-D.ietf-sidr-bgpsec-protocol]), and BGPSec capable 332 neighbors do not exchange AS_PATH information in their route 333 announcements. However, a BGPSec neighbor peering with a non-BGPSec- 334 capable neighbor will use the information found in Secure_Path to 335 reconstruct a standard AS_PATH for updates sent to that neighbor. 336 Unlike in Secure_Path where the ASN to be hidden is still present, 337 but ignored when considering AS Path (due to pCount=0), when 338 reconstructing an AS_PATH for a non-BGPSec neighbor, the pCount=0 339 ASNs will not appear in the AS_PATH at all (see section 4.4 of the 340 above-referenced draft). This document is not changing existing 341 AS_PATH reconstruction behavior, merely highlighting it for clarity. 343 The procedure to support AS Migration in BGPSec is slightly different 344 depending on whether the PE under migration is receiving the routes 345 from one of its eBGP peers ("inbound" as in section 3.2.2) or 346 destined toward the eBGP peers ("outbound" as in section 3.2.1). 348 5.1. Outbound (PE->CE) 350 When a PE router receives an update destined for an eBGP neighbor 351 that is locally configured with AS-migration mechanisms as discussed 352 in RFC7705 [RFC7705], it MUST generate a valid BGPSec signature as 353 defined in [I-D.ietf-sidr-bgpsec-protocol] for _both_ configured 354 ASNs. It MUST generate a signature from the new (global) ASN forward 355 signing to the old (local) ASN with pCount=0, and then it MUST 356 generate a forward signature from the old (local) ASN to the target 357 eBGP ASN with pCount=1 as normal. 359 5.2. Inbound (CE->PE) 361 When a PE router receives an update from an eBGP neighbor that is 362 locally configured with AS-migration mechanisms (i.e. the opposite 363 direction of the previous route flow), it MUST generate a signature 364 from the old (local) ASN forward signing to the new (global) ASN with 365 pCount=0. It is not necessary to generate the second signature from 366 the new (global) ASN because the Autonomous System Border Router 367 (ASBR) will generate that when it forward signs towards its eBGP 368 peers as defined in normal BGPSec operation. Note that a signature 369 is not normally added when a routing update is sent across an iBGP 370 session. The requirement to sign updates in iBGP represents a change 371 to the normal behavior for this specific AS-migration implementation 372 only. 374 5.3. Other considerations 376 In this case, the PE is adding BGPSec attributes to routes received 377 from or destined to an iBGP neighbor, and using pCount=0 to mask 378 them. While this is not prohibited by BGPSec 379 [I-D.ietf-sidr-bgpsec-protocol], BGPSec-capable routers that receive 380 updates from BGPSec-enabled iBGP neighbors MUST accept updates with 381 new (properly-formed) BGPSec attributes, including the presence of 382 pCount=0 on a previous signature, or they will interfere with this 383 implementation. In similar fashion, any BGPSec-capable route- 384 reflectors in the path of these updates MUST reflect them 385 transparently to their BGPSec-capable clients. 387 In order to secure this set of signatures, the PE router MUST be 388 provisioned with valid keys for _both_ configured ASNs (old and new), 389 and the key for the old ASN MUST be kept valid until all eBGP 390 sessions are migrated to the new ASN. Downstream neighbors will see 391 this as a valid BGPSec path, as they will simply trust that their 392 upstream neighbor accepted pCount=0 because it was explicitly 393 configured to do so based on a trust relationship and business 394 relationship between the upstream and its neighbor (the old and new 395 ASNs). 397 Additionally, section 4 of RFC7705 [RFC7705] discusses methods in 398 which AS migrations can be completed for iBGP peers such that a 399 session between two routers will be treated as iBGP even if the 400 neighbor ASN is not the same ASN on each peer's global configuration. 401 As far as BGPSec is concerned, this requires the same procedure as 402 when the routers migrating are applying AS migration mechanisms to 403 eBGP peers, but the router functioning as the "ASBR" between old and 404 new ASN is different. In eBGP, the router being migrated has direct 405 eBGP sessions to the old ASN and signs from old ASN to new with 406 pCount=0 before passing the update along to additional routers in its 407 global (new) ASN. In iBGP, the router being migrated is receiving 408 updates (that may have originated either from eBGP neighbors or other 409 iBGP neighbors) from its downstream neighbors in the old ASN, and 410 MUST sign those updates from old ASN to new with pCount=0 before 411 sending them on to other peers. 413 5.4. Example 415 The following example will illustrate the method being used above. 416 As with previous examples, PE1 is the router being migrated, AS64510 417 is the old ASN, which is being subsumed by AS64500, the ASN to be 418 permanently retained. 64505 is another external peer, used to 419 demonstrate what the announcements will look like to a third party 420 peer that is not part of the migration. Some additional notation is 421 used to delineate the details of each signature as follows: 423 The origin BGPSEC signature attribute takes the form: sig(, Origin ASN, pCount, NLRI Prefix) key 426 Intermediate BGPSEC signature attributes take the form: sig(, Signer ASN, pCount, ) key 428 Equivalent AS_PATH refers to what the AS_PATH would look like if it 429 was reconstructed to be sent to a non-BGPSec peer, while Secure_Path 430 shows the AS Path as represented between BGPSec peers. 432 Note: The representation of signature attribute generation is being 433 simplified here somewhat for the sake of brevity; the actual details 434 of the signing process are as described Sections 4.1 and 4.2 in 435 [I-D.ietf-sidr-bgpsec-protocol]. For example, what is covered by the 436 signature also includes Flags, Algorithm Suite ID, NLRI length, etc. 437 Also, the key is not carried in the update, instead the SKI is 438 carried. 440 Before Merger 442 64505 443 | 444 ISP B ISP A 445 CE-1 <--- PE-1 <------------------- PE-2 <--- CE-2 446 64496 Old_ASN: 64510 Old_ASN: 64500 64499 448 CE-2 to PE-2: sig(<64500>, O=64499, pCount=1, N)K_64499-CE2 [sig1] 449 Equivalent AS_PATH=(64499) 450 Secure_Path=(64499) 451 length=sum(pCount)=1 453 PE-2 to 64505: sig(<64505>, 64500, pCount=1, )K_64500-PE2 [sig2] 454 sig(<64500>, 64499, pCount=1, N)K_64499-CE2 [sig1] 455 Equivalent AS_PATH=(64500,64499) 456 Secure_Path=(64500,64499) 457 length=sum(pCount)=2 459 PE-2 to PE-1: sig(<64510>, 64500, pCount=1, )K_64500-PE2 [sig3] 460 sig(<64500>, 64499, pCount=1, N)K_64499-CE2 [sig1] 461 Equivalent AS_PATH=(64500,64499) 462 Secure_Path=(64500,64499) 463 length=sum(pCount)=2 465 PE-1 to CE-1: sig(<64496>, 64510, pCount=1, )K_64510-PE1 [sig4] 466 sig(<64510>, 64500, pCount=1, )K_64500-PE2 [sig3] 467 sig(<64500>, 64499, pCount=1, N)K_64499-CE2 [sig1] 468 Equivalent AS_PATH= (64510,64500,64499) 469 Secure_Path=(64510,64500,64499) 470 length=sum(pCount)=3 472 Migrating, route flow outbound PE-1 to CE-1 474 64505 475 | 476 ISP A' ISP A' 477 CE-1 <--- PE-1 <------------------- PE-2 <--- CE-2 478 64496 Old_ASN: 64510 Old_ASN: 64500 64499 479 New_ASN: 64500 New_ASN: 64500 481 CE-2 to PE-2: sig(<64500>, 64499, pCount=1, N)K_64499-CE2 [sig11] 482 Equivalent AS_PATH=(64499) 483 Secure_Path=(64499) 484 length=sum(pCount)=1 486 PE-2 to 64505: sig(<64505>, 64500, pCount=1, )K_64500-PE2 [sig12] 487 sig(<64500>, 64499, pCount=1, N)K_64499-CE2 [sig11] 488 Equivalent AS_PATH=(64500,64499) 489 Secure_Path=(64500,64499) 490 length=sum(pCount)=2 492 PE-2 to PE-1: sig(<64500>, 64499, pCount=1, N)K_64499-CE2 [sig11] 493 Equivalent AS_PATH=(64499) 494 Secure_Path=(64499) 495 length=sum(pCount)=1 496 #PE-2 sends to PE-1 (in iBGP) the exact same update 497 #as received from AS64499. 499 PE-1 to CE-1: sig(<64496>, 64510, pCount=1, )K_64510-PE1 [sig14] 500 sig(<64510>, 64500, pCount=0, )K_64500-PE2 [sig13] 501 sig(<64500>, 64499, pCount=1, N)K_64499-CE2 [sig11] 502 Equivalent AS_PATH=(64510,64499) 503 Secure_Path=(64510, 64500(pCount=0),64499) 504 length=sum(pCount)=2 (length is NOT 3) 505 #PE1 adds [sig13] acting as AS64500 506 #PE1 accepts [sig13] with pCount=0 acting as AS64510, 507 #as it would if it received sig13 from an eBGP peer 508 Migrating, route flow inbound CE-1 to PE-1 510 64505 511 | 512 ISP A' ISP A' 513 CE-1 ---> PE-1 -------------------> PE-2 ---> CE-2 514 64496 Old_ASN: 64510 Old_ASN: 64500 64499 515 New_ASN: 64500 New_ASN: 64500 517 CE-1 to PE-1: sig(<64510>, 64496, pCount=1, N)K_64496-CE1 [sig21] 518 Equivalent AS_PATH=(64496) 519 Secure_Path=(64496) 520 length=sum(pCount)=1 522 PE-1 to PE-2: sig(<64500>, 64510, pCount=0, )K_64510-PE1 [sig22] 523 sig(<64510>, 64496, pCount=1, N)K_64496-CE1 [sig21] 524 Equivalent AS_PATH=(64496) 525 Secure_Path=(64510 (pCount=0),64496) 526 length=sum(pCount)=1 (length is NOT 2) 527 #PE1 adds [sig22] acting as AS64510 528 #PE1 accepts [sig22] with pCount=0 acting as AS64500, 529 #as it would if it received sig22 from an eBGP peer 531 PE-2 to 64505: sig(<64505>, 64500, pCount=1, )K_64500-PE2 [sig23] 532 sig(<64500>, 64510, pCount=0, )K_64510-PE1 [sig22] 533 sig(<64510>, 64496, pCount=1, N)K_64496-CE1 [sig21] 534 Equivalent AS_PATH=(64500,64496) 535 Secure_Path=(64500,64510 (pCount=0), 64496) 536 length=sum(pCount)=2 (length is NOT 3) 538 PE-2 to CE-2: sig(<64499>, 64500, pCount=1, )K_64500-PE2 [sig24] 539 sig(<64500>, 64510, pCount=0, )K_64510-PE1 [sig22] 540 sig(<64510>, 64496, pCount=1, N)K_64496-CE1 [sig21] 541 Equivalent AS_PATH=(64500,64496) 542 Secure_Path=(64500, 64510 (pCount=0), 64496) 543 length=sum(pCount)=2 (length is NOT 3) 545 6. Acknowledgements 547 Thanks to Kotikalapudi Sriram, Shane Amante, Warren Kumari, Terry 548 Manderson, Keyur Patel, Alia Atlas, and Alvaro Retana for their 549 review comments. 551 Additionally, the solution presented in this document is an amalgam 552 of several SIDR interim meeting discussions plus a discussion at 553 IETF85, collected and articulated thanks to Sandy Murphy. 555 7. IANA Considerations 557 This memo includes no request to IANA. 559 8. Note for RFC Editor 561 This section can be removed prior to publication. 563 RFC Editor - this document updates draft-ietf-sidr-bgpsec-protocol, 564 but the normal Updates= metadata method cannot be used until an RFC 565 number is assigned to the document being updated. Please ensure that 566 the metadata is corrected when the bgpsec-protocol document has been 567 assigned an RFC number. 569 9. Security Considerations 571 RFC7705 [RFC7705] discusses a process by which one ASN is migrated 572 into and subsumed by another. Because this process involves 573 manipulating the AS_Path in a BGP route to make it deviate from the 574 actual path that it took through the network, this migration process 575 is attempting to do exactly what BGPSec is working to prevent. 576 BGPSec MUST be able to manage this legitimate use of AS_Path 577 manipulation without generating a vulnerability in the RPKI route 578 security infrastructure, and this document was written to define the 579 method by which the protocol can meet this need. 581 The solution discussed above is considered to be reasonably secure 582 from exploitation by a malicious actor because it requires both 583 signatures to be secured as if they were forward-signed between two 584 eBGP neighbors. This requires any router using this solution to be 585 provisioned with valid keys for both the migrated and subsumed ASN so 586 that it can generate valid signatures for each of the two ASNs it is 587 adding to the path. If the AS's keys are compromised, or zero-length 588 keys are permitted, this does potentially enable an AS_PATH 589 shortening attack, but this is not fundamentally altering the 590 existing security risks for BGPSec. 592 10. References 594 10.1. Normative References 596 [I-D.ietf-sidr-bgpsec-protocol] 597 Lepinski, M. and K. Sriram, "BGPsec Protocol 598 Specification", draft-ietf-sidr-bgpsec-protocol-15 (work 599 in progress), March 2016. 601 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 602 Requirement Levels", BCP 14, RFC 2119, 603 DOI 10.17487/RFC2119, March 1997, 604 . 606 [RFC7705] George, W. and S. Amante, "Autonomous System Migration 607 Mechanisms and Their Effects on the BGP AS_PATH 608 Attribute", RFC 7705, DOI 10.17487/RFC7705, November 2015, 609 . 611 10.2. Informative References 613 [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, 614 selection, and registration of an Autonomous System (AS)", 615 BCP 6, RFC 1930, DOI 10.17487/RFC1930, March 1996, 616 . 618 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 619 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 620 DOI 10.17487/RFC4271, January 2006, 621 . 623 [RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous 624 System Confederations for BGP", RFC 5065, 625 DOI 10.17487/RFC5065, August 2007, 626 . 628 [RFC5398] Huston, G., "Autonomous System (AS) Number Reservation for 629 Documentation Use", RFC 5398, DOI 10.17487/RFC5398, 630 December 2008, . 632 [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support 633 Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480, 634 February 2012, . 636 Authors' Addresses 638 Wesley George 639 Time Warner Cable 640 13820 Sunrise Valley Drive 641 Herndon, VA 20171 642 US 644 Phone: +1 703-561-2540 645 Email: wesley.george@twcable.com 646 Sandy Murphy 647 SPARTA, Inc., a Parsons Company 648 7110 Samuel Morse Drive 649 Columbia, MD 21046 650 US 652 Phone: +1 443-430-8000 653 Email: sandy@tislabs.com