idnits 2.17.1 draft-ietf-sidrops-aspa-verification-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (July 8, 2019) is 1747 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-10) exists of draft-ietf-grow-route-leak-detection-mitigation-00 == Outdated reference: A later version (-24) exists of draft-ietf-idr-bgp-open-policy-05 == Outdated reference: A later version (-17) exists of draft-ietf-sidrops-aspa-profile-00 == Outdated reference: A later version (-14) exists of draft-kumari-deprecate-as-set-confed-set-12 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Azimov 3 Internet-Draft Yandex 4 Intended status: Standards Track E. Bogomazov 5 Expires: January 9, 2020 Qrator Labs 6 K. Patel 7 Arrcus, Inc. 8 J. Snijders 9 NTT 10 July 8, 2019 12 Verification of AS_PATH Using the Resource Certificate Public Key 13 Infrastructure and Autonomous System Provider Authorization 14 draft-ietf-sidrops-aspa-verification-01 16 Abstract 18 This document defines the semantics of an Autonomous System Provider 19 Authorization object in the Resource Public Key Infrastructure to 20 verify the AS_PATH attribute of routes advertised in the Border 21 Gateway Protocol. 23 Requirements Language 25 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 26 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 27 "OPTIONAL" in this document are to be interpreted as described in BCP 28 14 [RFC2119] [RFC8174] when, and only when, they appear in all 29 capitals, as shown here. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on January 9, 2020. 48 Copyright Notice 50 Copyright (c) 2019 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (https://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 66 2. Anomaly Propagation . . . . . . . . . . . . . . . . . . . . . 3 67 3. Autonomous System Provider Authorization . . . . . . . . . . 4 68 4. Customer-Provider Verification Procedure . . . . . . . . . . 4 69 5. AS_PATH Verification . . . . . . . . . . . . . . . . . . . . 5 70 5.1. Upstream Paths . . . . . . . . . . . . . . . . . . . . . 5 71 5.2. Downstream Paths . . . . . . . . . . . . . . . . . . . . 6 72 5.3. Mitigation . . . . . . . . . . . . . . . . . . . . . . . 6 73 6. Disavowal of Provider Authorizaion . . . . . . . . . . . . . 7 74 7. Siblings (Complex Relations) . . . . . . . . . . . . . . . . 7 75 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 76 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 77 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 78 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 79 10.2. Informative References . . . . . . . . . . . . . . . . . 8 80 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 82 1. Introduction 84 The Border Gateway Protocol (BGP) was designed without mechanisms to 85 validate BGP attributes. Two consequences are BGP Hijacks and BGP 86 Route Leaks [RFC7908]. BGP extensions are able to partially solve 87 these problems. For example, ROA-based Origin Validation [RFC6483] 88 can be used to detect and filter accidental mis-originations, and 89 [I-D.ietf-grow-route-leak-detection-mitigation] can be used to detect 90 accidental route leaks. While these upgrades to BGP are quite 91 useful, they still rely on transitive BGP attributes, i.e. AS_PATH, 92 that can be manipulated by attackers. 94 BGPSec [RFC8205] was designed to solve the problem of AS_PATH 95 validation. Unfortunately, strict cryptographic validation brought 96 expensive computational overhead for BGP routers. BGPSec also proved 97 vulnerable to downgrade attacks that nullify the benefits of AS_PATH 98 signing. As a result, to abuse the AS_PATH or any other signed 99 transit attribute, an attacker merely needs to downgrade to 'old' 100 BGP-4. 102 An alternative approach was introduced with soBGP 103 [I-D.white-sobgp-architecture]. Instead of strong cryptographic 104 AS_PATH validation, it created an AS_PATH security function based on 105 a shared database of ASN adjacencies. While such an approach has 106 reasonable computational cost, the two side adjacencies don't provide 107 a way to automate anomaly detection without high adoption rate - an 108 attacker can easily create a one-way adjacency. SO-BGP transported 109 data about adjacencies in new additional BGP messages, which was 110 recursively complex thus significantly increasing adoption complexity 111 and risk. In addition, the general goal to verify all AS_PATHs was 112 not achievable given the indirect adjacencies at internet exchange 113 points. 115 Instead of checking AS_PATH correctness, this document focuses on 116 solving real-world operational problems - automatic detection of 117 malicious hijacks and route leaks. To achieve this a new AS_PATH 118 verification procedure is defined which is able to automatically 119 detect invalid (malformed) AS_PATHs in announcements that are 120 received from customers and peers. This procedure uses a shared 121 signed database of customer-to-provider relationships using a new 122 RPKI object - Autonomous System Provider Authorization (ASPA). This 123 technique provides benefits for participants even during early and 124 incremental adoption. 126 2. Anomaly Propagation 128 Both route leaks and hijacks have similar effects on ISP operations - 129 they redirect traffic, resulting in increased latency, packet loss, 130 or possible MiTM attacks. But the level of risk depends 131 significantly on the propagation of the anomalies. For example, a 132 hijack that is propagated only to customers may concentrate traffic 133 in a particular ISP's customer cone; while if the anomaly is 134 propagated through peers, upstreams, or reaches Tier-1 networks, thus 135 distributing globally, traffic may be redirected at the level of 136 entire countries and/or global providers. 138 The ability to constrain propagation of BGP anomalies to upstreams 139 and peers, without requiring support from the source of the anomaly 140 (which is critical if source has malicious intent), should 141 significantly improve the security of inter-domain routing and solve 142 the majority of problems. 144 3. Autonomous System Provider Authorization 146 As described in [RFC6480], the RPKI is based on a hierarchy of 147 resource certificates that are aligned to the Internet Number 148 Resource allocation structure. Resource certificates are X.509 149 certificates that conform to the PKIX profile [RFC5280], and to the 150 extensions for IP addresses and AS identifiers [RFC3779]. A resource 151 certificate is a binding by an issuer of IP address blocks and 152 Autonomous System (AS) numbers to the subject of a certificate, 153 identified by the unique association of the subject's private key 154 with the public key contained in the resource certificate. The RPKI 155 is structured so that each current resource certificate matches a 156 current resource allocation or assignment. 158 ASPAs are digitally signed objects that bind a selected AFI Provider 159 AS number to a Customer AS number (in terms of BGP announcements not 160 business), and are signed by the holder of the Customer AS. An ASPA 161 attests that a Customer AS holder (CAS) has authorized a particular 162 Provider AS (PAS) to propagate the Customer's IPv4/IPv6 announcements 163 onward, e.g. to the Provider's upstream providers or peers. The ASPA 164 record profile is described in [I-D.ietf-sidrops-aspa-profile]. 166 4. Customer-Provider Verification Procedure 168 This section describes an abstract procedure that checks that pair of 169 ASNs (AS1, AS2) is included in the set of signed ASPAs. The 170 semantics of its usage is defined in next section. The procedure 171 takes (AS1, AS2, ROUTE_AFI) as input parameters and returns three 172 types of results: "valid", "invalid" and "unknown". 174 A relying party (RP) must have access to a local cache of the 175 complete set of cryptographically valid ASPAs when performing 176 customer-provider verification procedure. 178 1. Retrieve all cryptographically valid ASPAs in a selected AFI with 179 a customer value of AS1. This selection forms the set of 180 "candidate ASPAs." 182 2. If the set of candidate ASPAs is empty, then the procedure exits 183 with an outcome of "unknown." 185 3. If there is at least one candidate ASPA where the provider field 186 is AS2, then the procedure exits with an outcome of "valid." 188 4. Otherwise, the procedure exits with an outcome of "invalid." 190 Since an AS1 may have different set providers in different AFI, it 191 should also have different set of corresponding ASPAs. In this case, 192 the output of this procedure with input (AS1, AS2, ROUTE_AFI) may 193 have different output for different ROUTE_AFI values. 195 5. AS_PATH Verification 197 The AS_PATH attribute identifies the autonomous systems through which 198 an UPDATE message has passed. AS_PATH may contain two types of 199 components: ordered AS_SEQes and unordered AS_SETs, as defined in 200 [RFC4271]. 202 The value of each concatenated value of AS_SEQ components can be 203 described as set of pairs {(AS(I), prepend(I)), (AS(I-1), 204 prepend(I-1))...}. In this case, the sequence {AS(I), AS(I-1),...} 205 represents different ASNs, that packet should pass towards the 206 destination. 208 The bellow procedure is applicable only for 32-bit AS number 209 compatible BGP speakers. 211 5.1. Upstream Paths 213 When a route is received from a customer, literal peer or by RS at 214 IX, each pair (AS(I-1), AS(I)) MUST belong to customer-provider or 215 sibling relationship. If there are other types of relationships, it 216 means that the route was leaked or the AS_PATH attribute was 217 malformed. The goal of the described bellow procedure is to check 218 the correctness of this statement. 220 If a route from ROUTE_AFI address family is received from a customer, 221 peer ot RS-client, its AS_PATH MUST be verified as follows: 223 1. If the closest AS in the AS_PATH is not the receiver's neighbor 224 ASN then procedure halts with the outcome "invalid"; 226 2. If there is a pair (AS(I-1), AS(I)), and customer-provider 227 verification procedure (Section 4) with parameters (AS(I-1), 228 AS(I), ROUTE_AFI) returns "invalid" then the procedure also halts 229 with the outcome "invalid"; 231 3. If the AS_PATH has at least one AS_SET segment then procedure 232 halts with the outcome "unverifiable"; 234 4. Otherwise, the procedure halts with an outcome of "valid". 236 5.2. Downstream Paths 238 When route is received from provider or RS it may have both Upstream 239 and Downstream paths. The first pair (AS(I-1), AS(I)) that has 240 "invalid" outcome of customer-provider verification procedure 241 indicates the end of Upstream path. All subsequent reverse pairs 242 (AS(J), AS(J-1)) MUST belong to customer-provider or sibling 243 relationship, thus can be also verified with ASPA objects. If there 244 are other types of relationships, it means that the route was leaked. 246 Additional caution should be done while processing prefixes that are 247 received from transparent IXes since they don't add their ASN in the 248 ASPATH. 250 If a route from ROUTE_AFI address family is received from a customer 251 or RS, its AS_PATH MUST be verified as follows: 253 1. If route is received from provider and the closest AS in the 254 AS_PATH is not the receiver's neighbor ASN then procedure halts 255 with the outcome "invalid"; 257 2. If there are two pairs (AS(I-1), AS(I)), (AS(J-1), AS(J)) where J 258 > I, and customer-provider verification procedure (Section 4) 259 returns "invalid" for both (AS(I-1), AS(I), ROUTE_AFI) and 260 (AS(J), AS(J-1), ROUTE_AFI), then the procedure also halts with 261 the outcome "invalid"; 263 3. If the AS_PATH has at least one AS_SET segment then procedure 264 halts with the outcome "unverifiable"; 266 4. Otherwise, the procedure halts with an outcome of "valid". 268 5.3. Mitigation 270 If the output of the AS_PATH verification procedure is "invalid" the 271 route MUST be rejected. 273 If the output of the AS_PATH verification procedure is 'unverifiable' 274 it means that AS_PATH can't be fully checked. Such routes should be 275 treated with caution and SHOULD be processed the same way as 276 "invalid" routes. This policy goes with full correspondence to 277 [I-D.kumari-deprecate-as-set-confed-set]. 279 The above AS_PATH verification procedure is able to check routes 280 received from customers and peers. The ASPA mechanism combined with 281 BGP Roles [I-D.ietf-idr-bgp-open-policy] and ROA-based Origin 282 Validation [RFC6483] provide a fully automated solution to detect and 283 filter hijacks and route leaks, including malicious ones. 285 6. Disavowal of Provider Authorizaion 287 An ASPA is a positive attestation that an AS holder has authorized 288 its provider to redistribute received routes to the provider's 289 providers and peers. This does not preclude the provider AS from 290 redistribution to its other customers. By creating an ASPA where the 291 provider AS is 0, the customer indicates that no provider should 292 further announce its routes. Specifically, AS 0 is reserved to 293 identify provider-free networks, Internet exchange meshes, etc. 295 An ASPA with a provider AS of 0 is a statement by the customer AS 296 that the its routes should not be received by any relying party AS 297 from any of its customers or peers. 299 By convention, an ASPA with a provider AS of 0 should be the only 300 ASPA issued by a given AS holder; although this is not a strict 301 requirement. A provider 0 ASPA may coexist with ASPAs that have 302 different provider AS values; though in such cases, the presence or 303 absence of the provider AS 0 ASPA does not alter the AS_PATH 304 verification procedure. 306 7. Siblings (Complex Relations) 308 There are peering relationships which can not be described as 309 strictly simple peer-peer or customer-provider; e.g. when both 310 parties are intentionally sending prefixes received from each other 311 to their peers and/or upstreams. 313 In this case, two symmetric ASPAs records {(AS1, AS2), (AS2, AS1)} 314 must be created by AS1 and AS2 respectively. 316 8. Security Considerations 318 The proposed mechanism is compatible only with BGP implementations 319 that can process 32-bit ASNs in the ASPATH. This limitation should 320 not have a real effect on operations - such legacy BGP routers a rare 321 and it's highly unlikely that they do support integration with RPKI. 323 ASPA issuers should be aware of the verification implication in 324 issuing an ASPA - an ASPA implicitly invalidates all routes passed to 325 upstream providers other than the provider ASs listed in the 326 collection of ASPAs. It is the Customer AS's duty to maintain a 327 correct set of ASPAs. 329 While the ASPA is capable to detect both mistake and malicious 330 activity for routes received from customers, RS-clients or peers, it 331 provides only detection of mistakes for routes that are received from 332 upstream providers and RS(s). 334 Since upstream provider becomes a trusted point, it will be able to 335 send hijacked prefixes of its customers or send hijacked prefixes 336 with malformed AS_PATHs back. While it may happen in theory, it's 337 doesn't seem to be a real scenario: normally customer and provider 338 have a signed agreement and such policy violation should have legal 339 consequences or customer can just drop relation with such provider 340 and remove corresponding ASPA record. 342 9. Acknowledgments 344 The authors wish to thank authors of [RFC6483] since its text was 345 used as an example while writing this document. The also authors 346 wish to thank Iljitsch van Beijnum for giving a hint about Downstream 347 paths. 349 10. References 351 10.1. Normative References 353 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 354 Requirement Levels", BCP 14, RFC 2119, 355 DOI 10.17487/RFC2119, March 1997, 356 . 358 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 359 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 360 May 2017, . 362 10.2. Informative References 364 [I-D.ietf-grow-route-leak-detection-mitigation] 365 Sriram, K. and A. Azimov, "Methods for Detection and 366 Mitigation of BGP Route Leaks", draft-ietf-grow-route- 367 leak-detection-mitigation-00 (work in progress), April 368 2019. 370 [I-D.ietf-idr-bgp-open-policy] 371 Azimov, A., Bogomazov, E., Bush, R., Patel, K., and K. 372 Sriram, "Route Leak Prevention using Roles in Update and 373 Open messages", draft-ietf-idr-bgp-open-policy-05 (work in 374 progress), February 2019. 376 [I-D.ietf-sidrops-aspa-profile] 377 Azimov, A., Uskov, E., Bush, R., Patel, K., Snijders, J., 378 and R. Housley, "A Profile for Autonomous System Provider 379 Authorization", draft-ietf-sidrops-aspa-profile-00 (work 380 in progress), May 2019. 382 [I-D.kumari-deprecate-as-set-confed-set] 383 Kumari, W. and K. Sriram, "Deprecation of AS_SET and 384 AS_CONFED_SET in BGP", draft-kumari-deprecate-as-set- 385 confed-set-12 (work in progress), July 2018. 387 [I-D.white-sobgp-architecture] 388 White, R., "Architecture and Deployment Considerations for 389 Secure Origin BGP (soBGP)", draft-white-sobgp- 390 architecture-02 (work in progress), June 2006. 392 [RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP 393 Addresses and AS Identifiers", RFC 3779, 394 DOI 10.17487/RFC3779, June 2004, 395 . 397 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 398 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 399 DOI 10.17487/RFC4271, January 2006, 400 . 402 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 403 Housley, R., and W. Polk, "Internet X.509 Public Key 404 Infrastructure Certificate and Certificate Revocation List 405 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 406 . 408 [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support 409 Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480, 410 February 2012, . 412 [RFC6483] Huston, G. and G. Michaelson, "Validation of Route 413 Origination Using the Resource Certificate Public Key 414 Infrastructure (PKI) and Route Origin Authorizations 415 (ROAs)", RFC 6483, DOI 10.17487/RFC6483, February 2012, 416 . 418 [RFC7908] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E., 419 and B. Dickson, "Problem Definition and Classification of 420 BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June 421 2016, . 423 [RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol 424 Specification", RFC 8205, DOI 10.17487/RFC8205, September 425 2017, . 427 Authors' Addresses 429 Alexander Azimov 430 Yandex 432 Email: a.e.azimov@gmail.com 434 Eugene Bogomazov 435 Qrator Labs 437 Email: eb@qrator.net 439 Keyur Patel 440 Arrcus, Inc. 442 Email: keyur@arrcus.com 444 Job Snijders 445 NTT Communications 446 Theodorus Majofskistraat 100 447 Amsterdam 1065 SZ 448 The Netherlands 450 Email: job@ntt.net