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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network T. Pauly 3 Internet-Draft Apple Inc. 4 Intended status: Standards Track P. Wouters 5 Expires: May 30, 2019 Red Hat 6 November 26, 2018 8 Split DNS Configuration for IKEv2 9 draft-ietf-ipsecme-split-dns-16 11 Abstract 13 This document defines two Configuration Payload Attribute Types 14 (INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA) for the Internet Key 15 Exchange Protocol Version 2 (IKEv2). These payloads add support for 16 private (internal-only) DNS domains. These domains are intended to 17 be resolved using non-public DNS servers that are only reachable 18 through the IPsec connection. DNS resolution for other domains 19 remains unchanged. These Configuration Payloads only apply to split 20 tunnel configurations. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on May 30, 2019. 39 Copyright Notice 41 Copyright (c) 2018 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 58 2. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Protocol Exchange . . . . . . . . . . . . . . . . . . . . . . 5 60 3.1. Configuration Request . . . . . . . . . . . . . . . . . . 5 61 3.2. Configuration Reply . . . . . . . . . . . . . . . . . . . 5 62 3.3. Mapping DNS Servers to Domains . . . . . . . . . . . . . 6 63 3.4. Example Exchanges . . . . . . . . . . . . . . . . . . . . 6 64 3.4.1. Simple Case . . . . . . . . . . . . . . . . . . . . . 6 65 3.4.2. Requesting Domains and DNSSEC trust anchors . . . . . 7 66 4. Payload Formats . . . . . . . . . . . . . . . . . . . . . . . 7 67 4.1. INTERNAL_DNS_DOMAIN Configuration Attribute Type Request 68 and Reply . . . . . . . . . . . . . . . . . . . . . . . . 8 69 4.2. INTERNAL_DNSSEC_TA Configuration Attribute . . . . . . . 8 70 5. INTERNAL_DNS_DOMAIN Usage Guidelines . . . . . . . . . . . . 10 71 6. INTERNAL_DNSSEC_TA Usage Guidelines . . . . . . . . . . . . . 11 72 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 73 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 74 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 75 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 76 9.2. Informative References . . . . . . . . . . . . . . . . . 15 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 79 1. Introduction 81 Split tunnel Virtual Private Network ("VPN") configurations only send 82 packets with a specific destination IP range, usually chosen from 83 [RFC1918], via the VPN. All other traffic is not sent via the VPN. 84 This allows an enterprise deployment to offer Remote Access VPN 85 services without needing to accept and forward all the non-enterprise 86 related network traffic generated by their remote users. Resources 87 within the enterprise can be accessed by the user via the VPN, while 88 all other traffic generated by the user is not send over the VPN. 90 These internal resources tend to only have internal-only DNS names 91 and require the use of special internal-only DNS servers to get 92 resolved. Split DNS [RFC2775] is a common configuration that is part 93 of split tunnel VPN configurations to support configuring Remote 94 Access users to use these special internal-only domain names. 96 The IKEv2 protocol [RFC7296] negotiates configuration parameters 97 using Configuration Payload Attribute Types. This document defines 98 two Configuration Payload Attribute Types that add support for 99 trusted Split DNS domains. 101 The INTERNAL_DNS_DOMAIN attribute type is used to convey that the 102 specified DNS domain MUST be resolved using the provided DNS 103 nameserver IP addresses as specified in the INTERNAL_IP4_DNS and 104 INTERNAL_IP6_DNS Configuration Payloads, causing these requests to 105 use the IPsec connection. 107 The INTERNAL_DNSSEC_TA attribute type is used to convey a DNSSEC 108 trust anchor for such a domain. This is required if the external 109 view uses DNSSEC that would prove the internal view does not exist or 110 would expect a different DNSSEC key on the different versions 111 (internal and external) of the enterprise domain. 113 If an INTERNAL_DNS_DOMAIN is sent by the responder, the responder 114 MUST also include one or more INTERNAL_IP4_DNS or INTERNAL_IP6_DNS 115 attributes that contain the IPv4 or IPv6 address of the internal DNS 116 server. 118 For the purposes of this document, DNS resolution servers accessible 119 through an IPsec connection will be referred to as "internal DNS 120 servers", and other DNS servers will be referred to as "external DNS 121 servers". 123 Other tunnel-establishment protocols already support the assignment 124 of Split DNS domains. For example, there are proprietary extensions 125 to IKEv1 that allow a server to assign Split DNS domains to a client. 126 However, the IKEv2 standard does not include a method to configure 127 this option. This document defines a standard way to negotiate this 128 option for IKEv2. 130 1.1. Requirements Language 132 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 133 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 134 "OPTIONAL" in this document are to be interpreted as described in BCP 135 14 [RFC2119] [RFC8174] when, and only when, they appear in all 136 captials, as shown here. 138 2. Applicability 140 If the negotiated IPsec connection is not a split tunnel 141 configuration, the INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA 142 Configuration Payloads MUST be ignored. This prevents generic (non- 143 enterprise) VPN services from overriding the public DNS hierarchy, 144 which could lead to malicious overrides of DNS and DNSSEC. 146 Such configurations SHOULD instead use only the INTERNAL_IP4_DNS and 147 INTERNAL_IP6_DNS Configuration Payloads to ensure all of the user's 148 DNS traffic is send through the IPsec connection and does not leak 149 unencrypted onto the local network, as the local network is often 150 explicitely exempted from IPsec encryption. 152 For split tunnel configurations, an enterprise can require one or 153 more DNS domains to be resolved via internal DNS servers. This can 154 be a special domain, such as "corp.example.com" for an enterprise 155 that is publicly known to use "example.com". In this case, the 156 remote user needs to be informed what the internal-only domain names 157 are and what the IP addresses of the internal DNS servers are. An 158 enterprise can also run a different version of its public domain on 159 its internal network. In that case, the VPN client is instructed to 160 send DNS queries for the enterprise public domain (eg "example.com") 161 to the internal DNS servers. A configuration for this deployment 162 scenario is referred to as a Split DNS configuration. 164 Split DNS configurations are often preferable to sending all DNS 165 queries to the enterprise. This allows the remote user to only send 166 DNS queries for the enterprise to the internal DNS servers. The 167 enterprise remains unaware of all non-enterprise (DNS) activitiy of 168 the user. It also allows the enterprise DNS servers to only be 169 configured for the enterprise DNS domains which removes the legal and 170 technical responsibility of the enterprise to resolve every DNS 171 domain potentially asked for by the remote user. 173 A client using these configuration payloads will be able to request 174 and receive Split DNS configurations using the INTERNAL_DNS_DOMAIN 175 and INTERNAL_DNSSEC_TA configuration attributes. These attributes 176 MUST be accompanied by one or more INTERNAL_IP4_DNS or 177 INTERNAL_IP6_DNS configuration attributes. The client device can 178 then use the internal DNS server(s) for any DNS queries within the 179 assigned domains. DNS queries for other domains SHOULD be sent to 180 the regular DNS service of the client unless it prefers to use the 181 IPsec tunnel for all its DNS queries. For example, the client could 182 trust the IPsec provided DNS servers more than the locally provided 183 DNS servers especially in the case of connecting to unknown or 184 untrusted networks (eg coffee shops or hotel networks). Or the 185 client could prefer the IPsec based DNS servers because those provide 186 additional features over the local DNS servers. 188 3. Protocol Exchange 190 In order to negotiate which domains are considered internal to an 191 IKEv2 tunnel, initiators indicate support for Split DNS in their 192 CFG_REQUEST payloads, and responders assign internal domains (and 193 DNSSEC trust anchors) in their CFG_REPLY payloads. When Split DNS 194 has been negotiated, the existing DNS server configuration attributes 195 will be interpreted as internal DNS servers that can resolve 196 hostnames within the internal domains. 198 3.1. Configuration Request 200 To indicate support for Split DNS, an initiator includes one more 201 INTERNAL_DNS_DOMAIN attributes as defined in Section 4 as part of the 202 CFG_REQUEST payload. If an INTERNAL_DNS_DOMAIN attribute is included 203 in the CFG_REQUEST, the initiator MUST also include one or more 204 INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes in the CFG_REQUEST. 206 The INTERNAL_DNS_DOMAIN attribute sent by the initiator is usually 207 empty but MAY contain a suggested domain name. 209 The absence of INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST 210 payload indicates that the initiator does not support or is unwilling 211 to accept Split DNS configuration. 213 To indicate support for DNSSEC, an initiator includes one or more 214 INTERNAL_DNSSEC_TA attributes as defined in Section 4 as part of the 215 CFG_REQUEST payload. If an INTERNAL_DNSSEC_TA attribute is included 216 in the CFG_REQUEST, the initiator MUST also include one or more 217 INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST. If the initiator 218 includes an INTERNAL_DNSSEC_TA attribute, but does not inclue an 219 INTERNAL_DNS_DOMAIN attribute, the responder MAY still respond with 220 both INTERNAL_DNSSEC_TA and INTERNAL_DNS_DOMAIN attributes. 222 An initiator MAY convey its current DNSSEC trust anchors for the 223 domain specified in the INTERNAL_DNS_DOMAIN attribute. If it does 224 not wish to convey this information, it MUST use a length of 0. 226 The absence of INTERNAL_DNSSEC_TA attributes in the CFG_REQUEST 227 payload indicates that the initiator does not support or is unwilling 228 to accept DNSSEC trust anchor configuration. 230 3.2. Configuration Reply 232 Responders MAY send one or more INTERNAL_DNS_DOMAIN attributes in 233 their CFG_REPLY payload. If an INTERNAL_DNS_DOMAIN attribute is 234 included in the CFG_REPLY, the responder MUST also include one or 235 both of the INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes in the 236 CFG_REPLY. These DNS server configurations are necessary to define 237 which servers can receive queries for hostnames in internal domains. 238 If the CFG_REQUEST included an INTERNAL_DNS_DOMAIN attribute, but the 239 CFG_REPLY does not include an INTERNAL_DNS_DOMAIN attribute, the 240 initiator MUST behave as if Split DNS configurations are not 241 supported by the server, unless the initiator has been configured 242 with local polict to define a set of Split DNS domains to use by 243 default. 245 Each INTERNAL_DNS_DOMAIN represents a domain that the DNS servers 246 address listed in INTERNAL_IP4_DNS and INTERNAL_IP6_DNS can resolve. 248 If the CFG_REQUEST included INTERNAL_DNS_DOMAIN attributes with non- 249 zero lengths, the content MAY be ignored or be interpreted as a 250 suggestion by the responder. 252 For each DNS domain specified in an INTERNAL_DNS_DOMAIN attribute, 253 one or more INTERNAL_DNSSEC_TA attributes MAY be included by the 254 responder. This attribute lists the corresponding internal DNSSEC 255 trust anchor information of a DS record (see [RFC4034]). The 256 INTERNAL_DNSSEC_TA attribute MUST immediately follow the 257 INTERNAL_DNS_DOMAIN attribute that it applies to. 259 3.3. Mapping DNS Servers to Domains 261 All DNS servers provided in the CFG_REPLY MUST support resolving 262 hostnames within all INTERNAL_DNS_DOMAIN domains. In other words, 263 the INTERNAL_DNS_DOMAIN attributes in a CFG_REPLY payload form a 264 single list of Split DNS domains that applies to the entire list of 265 INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes. 267 3.4. Example Exchanges 269 3.4.1. Simple Case 271 In this example exchange, the initiator requests INTERNAL_IP4_DNS and 272 INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST, but does not 273 specify any value for either. This indicates that it supports Split 274 DNS, but has no preference for which DNS requests will be routed 275 through the tunnel. 277 The responder replies with two DNS server addresses, and two internal 278 domains, "example.com" and "city.other.test". 280 Any subsequent DNS queries from the initiator for domains such as 281 "www.example.com" SHOULD use 198.51.100.2 or 198.51.100.4 to resolve. 283 CP(CFG_REQUEST) = 284 INTERNAL_IP4_ADDRESS() 285 INTERNAL_IP4_DNS() 286 INTERNAL_DNS_DOMAIN() 288 CP(CFG_REPLY) = 289 INTERNAL_IP4_ADDRESS(198.51.100.234) 290 INTERNAL_IP4_DNS(198.51.100.2) 291 INTERNAL_IP4_DNS(198.51.100.4) 292 INTERNAL_DNS_DOMAIN(example.com) 293 INTERNAL_DNS_DOMAIN(city.other.test) 295 3.4.2. Requesting Domains and DNSSEC trust anchors 297 In this example exchange, the initiator requests INTERNAL_IP4_DNS, 298 INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA attributes in the 299 CFG_REQUEST. 301 Any subsequent DNS queries from the initiator for domains such as 302 "www.example.com" or "city.other.test" would be DNSSEC validated 303 using the DNSSEC trust anchor received in the CFG_REPLY. 305 In this example, the initiator has no existing DNSSEC trust anchors 306 would the requested domain. the "example.com" dommain has DNSSEC 307 trust anchors that are returned, while the "other.test" domain has no 308 DNSSEC trust anchors. 310 CP(CFG_REQUEST) = 311 INTERNAL_IP4_ADDRESS() 312 INTERNAL_IP4_DNS() 313 INTERNAL_DNS_DOMAIN() 314 INTERNAL_DNSSEC_TA() 316 CP(CFG_REPLY) = 317 INTERNAL_IP4_ADDRESS(198.51.100.234) 318 INTERNAL_IP4_DNS(198.51.100.2) 319 INTERNAL_IP4_DNS(198.51.100.4) 320 INTERNAL_DNS_DOMAIN(example.com) 321 INTERNAL_DNSSEC_TA(43547,8,1,B6225AB2CC613E0DCA7962BDC2342EA4...) 322 INTERNAL_DNSSEC_TA(31406,8,2,F78CF3344F72137235098ECBBD08947C...) 323 INTERNAL_DNS_DOMAIN(city.other.test) 325 4. Payload Formats 327 All multi-octet fields representing integers are laid out in big 328 endian order (also known as "most significant byte first", or 329 "network byte order"). 331 4.1. INTERNAL_DNS_DOMAIN Configuration Attribute Type Request and Reply 333 1 2 3 334 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 1 335 +-+-----------------------------+-------------------------------+ 336 |R| Attribute Type | Length | 337 +-+-----------------------------+-------------------------------+ 338 | | 339 ~ Domain Name in DNS presentation format ~ 340 | | 341 +---------------------------------------------------------------+ 343 o Reserved (1 bit) - Defined in IKEv2 RFC [RFC7296]. 345 o Attribute Type (15 bits) set to value 25 for INTERNAL_DNS_DOMAIN. 347 o Length (2 octets) - Length of domain name. 349 o Domain Name (0 or more octets) - A Fully Qualified Domain Name 350 used for Split DNS rules, such as "example.com", in DNS 351 presentation format and using IDNA A-label [RFC5890] for 352 Internationalized Domain Names. Implementors need to be careful 353 that this value is not null-terminated. 355 4.2. INTERNAL_DNSSEC_TA Configuration Attribute 357 An INTERNAL_DNSSEC_TA Configuration Attribute can either be empty, or 358 it can contain one Trust Anchor by containing a non-zero Length with 359 a DNSKEY Key Tag, DNSKEY Algorithm, Digest Type and Digest Data 360 fields. 362 An empty INTERNAL_DNSSEC_TA CFG attribute: 364 1 2 3 365 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 1 366 +-+-----------------------------+-------------------------------+ 367 |R| Attribute Type | Length (set to 0) | 368 +-+-----------------------------+-------------------------------+ 370 o Reserved (1 bit) - Defined in IKEv2 RFC [RFC7296]. 372 o Attribute Type (15 bits) set to value 26 for INTERNAL_DNSSEC_TA. 374 o Length (2 octets) - Set to 0 for an empty attribute. 376 A non-empty INTERNAL_DNSSEC_TA CFG attribute: 378 1 2 3 379 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 1 380 +-+-----------------------------+-------------------------------+ 381 |R| Attribute Type | Length | 382 +-+-----------------------------+---------------+---------------+ 383 | DNSKEY Key Tag | DNSKEY Alg | Digest Type | 384 +-------------------------------+---------------+---------------+ 385 | | 386 ~ Digest Data ~ 387 | | 388 +---------------------------------------------------------------+ 390 o Reserved (1 bit) - Defined in IKEv2 RFC [RFC7296]. 392 o Attribute Type (15 bits) set to value 26 for INTERNAL_DNSSEC_TA. 394 o Length (2 octets) - Length of DNSSEC Trust Anchor data (4 octets 395 plus the length of the Digest Data). 397 o DNSKEY Key Tag value (2 octets) - Delegation Signer (DS) Key Tag 398 as specified in [RFC4034] Section 5.1. 400 o DNSKEY Algorithm (1 octet) - DNSKEY algorithm value from the IANA 401 DNS Security Algorithm Numbers Registry. 403 o Digest Type (1 octet) - DS algorithm value from the IANA 404 Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms 405 Registry. 407 o Digest Data (1 or more octets) - The DNSKEY digest as specified in 408 [RFC4034] Section 5.1 in presentation format. 410 Each INTERNAL_DNSSEC_TA attribute in the CFG_REPLY payload MUST 411 immediately follow a corresponding INTERNAL_DNS_DOMAIN attribute. As 412 the INTERNAL_DNSSEC_TA format itself does not contain the domain 413 name, it relies on the preceding INTERNAL_DNS_DOMAIN to provide the 414 domain for which it specifies the trust anchor. Any 415 INTERNAL_DNSSEC_TA attribute that is not immediately preceded by an 416 INTERNAL_DNS_DOMAIN or another INTERNAL_DNSSEC_TA attribute applying 417 to the same domain name MUST be ignored and treated as a protocol 418 error. 420 5. INTERNAL_DNS_DOMAIN Usage Guidelines 422 If a CFG_REPLY payload contains no INTERNAL_DNS_DOMAIN attributes, 423 the client MAY use the provided INTERNAL_IP4_DNS or INTERNAL_IP6_DNS 424 servers as the default DNS server(s) for all queries. 426 If a client is configured by local policy to only accept a limited 427 number of INTERNAL_DNS_DOMAIN values, the client MUST ignore any 428 other INTERNAL_DNS_DOMAIN values. 430 For each INTERNAL_DNS_DOMAIN entry in a CFG_REPLY payload that is not 431 prohibited by local policy, the client MUST use the provided 432 INTERNAL_IP4_DNS or INTERNAL_IP6_DNS DNS servers as the only 433 resolvers for the listed domains and its sub-domains and it MUST NOT 434 attempt to resolve the provided DNS domains using its external DNS 435 servers. Other domain names SHOULD be resolved using some other 436 external DNS resolver(s), configured independently from IKE. Queries 437 for these other domains MAY be sent to the internal DNS resolver(s) 438 listed in that CFG_REPLY message, but have no guarantee of being 439 answered. For example, if the INTERNAL_DNS_DOMAIN attribute 440 specifies "example.test", then "example.test", "www.example.test" and 441 "mail.eng.example.test" MUST be resolved using the internal DNS 442 resolver(s), but "otherexample.test" and "ple.test" MUST NOT be 443 resolved using the internal resolver and MUST use the system's 444 external DNS resolver(s). 446 The initiator SHOULD allow the DNS domains listed in the 447 INTERNAL_DNS_DOMAIN attributes to resolve to special IP address 448 ranges, such as those of [RFC1918], even if the initiator host is 449 otherwise configured to block DNS answer containing these special IP 450 address ranges. 452 When an IKE SA is terminated, the DNS forwarding MUST be 453 unconfigured. This includes deleting the DNS forwarding rules; 454 flushing all cached data for DNS domains provided by the 455 INTERNAL_DNS_DOMAIN attribute, including negative cache entries; 456 removing any obtained DNSSEC trust anchors from the list of trust 457 anchors; and clearing the outstanding DNS request queue. 459 INTERNAL_DNS_DOMAIN attributes SHOULD only be used on split tunnel 460 configurations where only a subset of traffic is routed into a 461 private remote network using the IPsec connection. If all traffic is 462 routed over the IPsec connection, the existing global 463 INTERNAL_IP4_DNS and INTERNAL_IP6_DNS can be used without creating 464 specific DNS exemptions. 466 6. INTERNAL_DNSSEC_TA Usage Guidelines 468 DNS records can be used to publish specific records containing trust 469 anchors for applications. The most common record type is the TLSA 470 record specified in [RFC6698]. This DNS record type publishes which 471 CA certificate or EE certificate to expect for a certain host name. 472 These records are protected by DNSSEC and thus can be trusted by the 473 application. Whether to trust TLSA records instead of the 474 traditional WebPKI depends on the local policy of the client. By 475 accepting an INTERNAL_DNSSEC_TA trust anchor via IKE from the remote 476 IKE server, the IPsec client might be allowing the remote IKE server 477 to override the trusted certificates for TLS. Similar override 478 concerns apply to other public key or fingerprint based DNS records, 479 such as OPENPGPKEY, SMIMEA or IPSECKEY records. 481 Thus, installing an INTERNAL_DNSSEC_TA trust anchor can be seen as 482 the equivalent of installing an Enterprise Certificate Authority (CA) 483 certificate. It allows the remote IKE/IPsec server to modify DNS 484 answers including its DNSSEC cryptographic signatures by overriding 485 existing DNS information with trust anchor conveyed via IKE and 486 (temporarilly) installed on the IKE client. Of specific concern is 487 the overriding of [RFC6698] based TLSA records, which represent a 488 confirmation or override of an existing WebPKI TLS certificate. 489 Other DNS record types that convey cryptographic materials (public 490 keys or fingerprints) are OPENPGPKEY, SMIMEA, SSHP and IPSECKEY 491 records. 493 IKE clients willing to accept INTERNAL_DNSSEC_TA attributes MUST use 494 a whitelist of one or more domains that can be updated out of band. 495 IKE clients with an empty whitelist MUST NOT use any 496 INTERNAL_DNSSEC_TA attributes received over IKE. Such clients MAY 497 interpret receiving an INTERNAL_DNSSEC_TA attribute for a non- 498 whitelisted domain as an indication that their local configuration 499 may need to be updated out of band. 501 IKE clients should take care to only whitelist domains that apply to 502 internal or managed domains, rather than to generic Internet traffic. 503 The DNS root zone (".") MUST be ignored if it appears in a whitelist. 504 Other generic or public domains, such as top-level domains (TLDs), 505 similarly MUST be ignored if these appear in a whitelist unless the 506 entity actually is the operator of the TLD. To determine this, an 507 implementation MAY interactively ask the user when a VPN profile is 508 installed or activated to confirm this. Alternatively, it MAY 509 provide a special override keyword in its provisioning configuration 510 to ensure non-interactive agreement can be achieved only by the party 511 provisioning the VPN client, who presumbly is a trusted entity by the 512 end-user. Similarly, an entity might be using a special domain name, 513 such as ".internal", for its internal-only view and might wish to 514 force its provisioning system to accept such a domain in a Split DNS 515 configuration. 517 Any updates to this whitelist of domain names MUST happen via 518 explicit human interaction or by a trusted automated provision system 519 to prevent malicious invisible installation of trust anchors in case 520 of aIKE server compromise. 522 IKE clients SHOULD accept any INTERNAL_DNSSEC_TA updates for 523 subdomain names of the whitelisted domain names. For example, if 524 "example.net" is whitelisted, then INTERNAL_DNSSEC_TA received for 525 "antartica.example.net" SHOULD be accepted. 527 IKE clients MAY interpret an INTERNAL_DNSSEC_TA for domain that was 528 not preconfigured as an indication that it needs to update its IKE 529 configuration (out of band). The client MUST NOT use such a 530 INTERNAL_DNSSEC_TA to reconfigure its local DNS settings. 532 IKE clients MUST ignore any received INTERNAL_DNSSEC_TA requests for 533 a FDQN for which it did not receive and accept an INTERNAL_DNS_DOMAIN 534 Configuration Payload. 536 In most deployment scenario's, the IKE client has an expectation that 537 it is connecting, using a split-network setup, to a specific 538 organisation or enterprise. A recommended policy would be to only 539 accept INTERNAL_DNSSEC_TA directives from that organization's DNS 540 names. However, this might not be possible in all deployment 541 scenarios, such as one where the IKE server is handing out a number 542 of domains that are not within one parent domain. 544 7. Security Considerations 546 As stated in Section 2, if the negotiated IPsec connection is not a 547 split tunnel configuration, the INTERNAL_DNS_DOMAIN and 548 INTERNAL_DNSSEC_TA Configuration Payloads MUST be ignored. 549 Otherwise, generic VPN service providers could maliciously override 550 DNSSEC based trust anchors of public DNS domains. 552 An initiator MUST only accept INTERNAL_DNSSEC_TA's for which it has a 553 whitelist. It MAY treat a received INTERNAL_DNSSEC_TA for an non- 554 whitelisted domain as a signal to update the whitelist via a non-IKE 555 provisioning mechanism. See Section 6 for additional security 556 considerations for DNSSEC trust anchors. 558 The use of Split DNS configurations assigned by an IKEv2 responder is 559 predicated on the trust established during IKE SA authentication. 560 However, if IKEv2 is being negotiated with an anonymous or unknown 561 endpoint (such as for Opportunistic Security [RFC7435]), the 562 initiator MUST ignore Split DNS configurations assigned by the 563 responder. 565 If a host connected to an authenticated IKE peer is connecting to 566 another IKE peer that attempts to claim the same domain via the 567 INTERNAL_DNS_DOMAIN attribute, the IKE connection SHOULD only process 568 the DNS information if the two connections are part of the same 569 logical entity. Otherwise, the client SHOULD refuse the DNS 570 information and potentially warn the end-user. For example, if a VPN 571 profile for "Example Corporation" is installed that provides two 572 IPsec connections, one covering 192.168.100.0/24 and one covering 573 10.13.14.0/24 it could be that both connections negotiate the same 574 INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA values. Since these are 575 part of the same remote organisation (or provisioning profile), the 576 Configuration Payloads can be used. However, if a user installs two 577 VPN profiles from two different unrelated independent entities, both 578 of these could be configured to use the same domain, for example 579 ".internal". These two connections MUST NOT be allowed to be active 580 at the same time. 582 If the initiator is using DNSSEC validation for a domain in its 583 public DNS view, and it requests and receives an INTERNAL_DNS_DOMAIN 584 attribute without an INTERNAL_DNSSEC_TA, it will need to reconfigure 585 its DNS resolver to allow for an insecure delegation. It SHOULD NOT 586 accept insecure delegations for domains that are DNSSEC signed in the 587 public DNS view, for which it has not explicitly requested such 588 deletation by specifying the domain specifically using a 589 INTERNAL_DNS_DOMAIN(domain) request. 591 Deployments that configure INTERNAL_DNS_DOMAIN domains should pay 592 close attention to their use of indirect reference RRtypes in their 593 internal-only domain names. Examples of such RRtypes are NS, CNAME, 594 DNAME, MX or SRV records. For example, if the MX record for 595 "internal.example.com" points to "mx.internal.example.net", then both 596 "internal.example.com" and "internal.example.net" should be sent 597 using an INTERNAL_DNS_DOMAIN Configuration Payload. 599 IKE clients MAY want to require whitelisted domains for Top Level 600 Domains (TLDs) and Second Level Domains (SLDs) to further prevent 601 malicious DNS redirections for well known domains. This prevents 602 users from unknowingly giving DNS queries to third parties. This is 603 even more important if those well known domains are not deploying 604 DNSSEC, as the VPN service provider could then even modify the DNS 605 answers without detection. 607 The content of INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA may be 608 passed to another (DNS) program for processing. As with any network 609 input, the content SHOULD be considered untrusted and handled 610 accordingly. 612 8. IANA Considerations 614 This document defines two new IKEv2 Configuration Payload Attribute 615 Types, which are allocated from the "IKEv2 Configuration Payload 616 Attribute Types" namespace. 618 Multi- 619 Value Attribute Type Valued Length Reference 620 ------ ------------------- ------ ---------- --------------- 621 25 INTERNAL_DNS_DOMAIN YES 0 or more [this document] 622 26 INTERNAL_DNSSEC_TA YES 0 or more [this document] 624 Figure 1 626 9. References 628 9.1. Normative References 630 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 631 and E. Lear, "Address Allocation for Private Internets", 632 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 633 . 635 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 636 Requirement Levels", BCP 14, RFC 2119, 637 DOI 10.17487/RFC2119, March 1997, . 640 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 641 Rose, "Resource Records for the DNS Security Extensions", 642 RFC 4034, DOI 10.17487/RFC4034, March 2005, 643 . 645 [RFC5890] Klensin, J., "Internationalized Domain Names for 646 Applications (IDNA): Definitions and Document Framework", 647 RFC 5890, DOI 10.17487/RFC5890, August 2010, 648 . 650 [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication 651 of Named Entities (DANE) Transport Layer Security (TLS) 652 Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August 653 2012, . 655 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 656 Kivinen, "Internet Key Exchange Protocol Version 2 657 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 658 2014, . 660 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 661 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 662 May 2017, . 664 9.2. Informative References 666 [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, 667 DOI 10.17487/RFC2775, February 2000, . 670 [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection 671 Most of the Time", RFC 7435, DOI 10.17487/RFC7435, 672 December 2014, . 674 Authors' Addresses 676 Tommy Pauly 677 Apple Inc. 678 One Apple Park Way 679 Cupertino, California 95014 680 US 682 Email: tpauly@apple.com 684 Paul Wouters 685 Red Hat 687 Email: pwouters@redhat.com