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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 26, 2019 Red Hat 6 November 22, 2018 8 Split DNS Configuration for IKEv2 9 draft-ietf-ipsecme-split-dns-15 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 26, 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 . . . . . . . . . . . . . . . . . . . . . . 4 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, causing these requests to use the IPsec 104 connection. 106 The INTERNAL_DNSSEC_TA attribute type is used to convey a DNSSEC 107 trust anchor for such a domain. This is required if the external 108 view uses DNSSEC that would prove the internal view does not exist or 109 would expect a different DNSSEC key on the different versions 110 (internal and external) of the enterprise domain. 112 If an INTERNAL_DNS_DOMAIN is sent by the responder, the responder 113 MUST also include one or more INTERNAL_IP4_DNS or INTERNAL_IP6_DNS 114 attributes that contain the IPv4 or IPv6 address of the internal DNS 115 server. 117 For the purposes of this document, DNS resolution servers accessible 118 through an IPsec connection will be referred to as "internal DNS 119 servers", and other DNS servers will be referred to as "external DNS 120 servers". 122 Other tunnel-establishment protocols already support the assignment 123 of Split DNS domains. For example, there are proprietary extensions 124 to IKEv1 that allow a server to assign Split DNS domains to a client. 125 However, the IKEv2 standard does not include a method to configure 126 this option. This document defines a standard way to negotiate this 127 option for IKEv2. 129 1.1. Requirements Language 131 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 132 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 133 "OPTIONAL" in this document are to be interpreted as described in BCP 134 14 [RFC2119] [RFC8174] when, and only when, they appear in all 135 captials, as shown here. 137 2. Applicability 139 If the negotiated IPsec connection is not a split tunnel 140 configuration, the INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA 141 Configuration Payloads MUST be ignored. This prevents generic (non- 142 enterprise) VPN services from overriding the public DNS hierarchy, 143 which could lead to malicious overrides of DNS and DNSSEC. 145 Such configurations SHOULD instead use only the INTERNAL_IP4_DNS and 146 INTERNAL_IP6_DNS Configuration Payloads to ensure all of the user's 147 DNS traffic is send through the IPsec connection and does not leak 148 unencrypted onto the local network, as the local network is often 149 explicitely exempted from IPsec encryption. 151 For split tunnel configurations, an enterprise can require one or 152 more DNS domains to be resolved via internal DNS servers. This can 153 be a special domain, such as "corp.example.com" for an enterprise 154 that is publicly known to use "example.com". In this case, the 155 remote user needs to be informed what the internal-only domain names 156 are and what the IP addresses of the internal DNS servers are. An 157 enterprise can also run a different version of its public domain on 158 its internal network. In that case, the VPN client is instructed to 159 send DNS queries for the enterprise public domain (eg "example.com") 160 to the internal DNS servers. A configuration for this deployment 161 scenario is referred to as a Split DNS configuration. 163 Split DNS configurations are often preferable to sending all DNS 164 queries to the enterprise. This allows the remote user to only send 165 DNS queries for the enterprise to the internal DNS servers. The 166 enterprise remains unaware of all non-enterprise (DNS) activitiy of 167 the user. It also allows the enterprise DNS servers to only be 168 configured for the enterprise DNS domains which removes the legal and 169 technical responsibility of the enterprise to resolve every DNS 170 domain potentially asked for by the remote user. 172 A client using these configuration payloads will be able to request 173 and receive Split DNS configurations using the INTERNAL_DNS_DOMAIN 174 and INTERNAL_DNSSEC_TA configuration attributes. These attributes 175 MUST be accompanied by one or more INTERNAL_IP4_DNS or 176 INTERNAL_IP6_DNS configuration attributes. The client device can 177 then use the internal DNS server(s) for any DNS queries within the 178 assigned domains. DNS queries for other domains MUST be sent to the 179 regular DNS service of the client. 181 3. Protocol Exchange 183 In order to negotiate which domains are considered internal to an 184 IKEv2 tunnel, initiators indicate support for Split DNS in their 185 CFG_REQUEST payloads, and responders assign internal domains (and 186 DNSSEC trust anchors) in their CFG_REPLY payloads. When Split DNS 187 has been negotiated, the existing DNS server configuration attributes 188 will be interpreted as internal DNS servers that can resolve 189 hostnames within the internal domains. 191 3.1. Configuration Request 193 To indicate support for Split DNS, an initiator includes one more 194 INTERNAL_DNS_DOMAIN attributes as defined in Section 4 as part of the 195 CFG_REQUEST payload. If an INTERNAL_DNS_DOMAIN attribute is included 196 in the CFG_REQUEST, the initiator MUST also include one or more 197 INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes in the CFG_REQUEST. 199 The INTERNAL_DNS_DOMAIN attribute sent by the initiator is usually 200 empty but MAY contain a suggested domain name. 202 The absence of INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST 203 payload indicates that the initiator does not support or is unwilling 204 to accept Split DNS configuration. 206 To indicate support for DNSSEC, an initiator includes one or more 207 INTERNAL_DNSSEC_TA attributes as defined in Section 4 as part of the 208 CFG_REQUEST payload. If an INTERNAL_DNSSEC_TA attribute is included 209 in the CFG_REQUEST, the initiator MUST also include one or more 210 INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST. If the initiator 211 includes an INTERNAL_DNSSEC_TA attribute, but does not inclue an 212 INTERNAL_DNS_DOMAIN attribute, the responder MAY still respond with 213 both INTERNAL_DNSSEC_TA and INTERNAL_DNS_DOMAIN attributes. 215 An initiator MAY convey its current DNSSEC trust anchors for the 216 domain specified in the INTERNAL_DNS_DOMAIN attribute. If it does 217 not wish to convey this information, it MUST use a length of 0. 219 The absence of INTERNAL_DNSSEC_TA attributes in the CFG_REQUEST 220 payload indicates that the initiator does not support or is unwilling 221 to accept DNSSEC trust anchor configuration. 223 3.2. Configuration Reply 225 Responders MAY send one or more INTERNAL_DNS_DOMAIN attributes in 226 their CFG_REPLY payload. If an INTERNAL_DNS_DOMAIN attribute is 227 included in the CFG_REPLY, the responder MUST also include one or 228 both of the INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes in the 229 CFG_REPLY. These DNS server configurations are necessary to define 230 which servers can receive queries for hostnames in internal domains. 231 If the CFG_REQUEST included an INTERNAL_DNS_DOMAIN attribute, but the 232 CFG_REPLY does not include an INTERNAL_DNS_DOMAIN attribute, the 233 initiator MUST behave as if Split DNS configurations are not 234 supported by the server, unless the initiator has been configured 235 with local polict to define a set of Split DNS domains to use by 236 default. 238 Each INTERNAL_DNS_DOMAIN represents a domain that the DNS servers 239 address listed in INTERNAL_IP4_DNS and INTERNAL_IP6_DNS can resolve. 241 If the CFG_REQUEST included INTERNAL_DNS_DOMAIN attributes with non- 242 zero lengths, the content MAY be ignored or be interpreted as a 243 suggestion by the responder. 245 For each DNS domain specified in an INTERNAL_DNS_DOMAIN attribute, 246 one or more INTERNAL_DNSSEC_TA attributes MAY be included by the 247 responder. This attribute lists the corresponding internal DNSSEC 248 trust anchor in the DNS presentation format of a DS record as 249 specified in [RFC4034]. The INTERNAL_DNSSEC_TA attribute MUST 250 immediately follow the INTERNAL_DNS_DOMAIN attribute that it applies 251 to. 253 3.3. Mapping DNS Servers to Domains 255 All DNS servers provided in the CFG_REPLY MUST support resolving 256 hostnames within all INTERNAL_DNS_DOMAIN domains. In other words, 257 the INTERNAL_DNS_DOMAIN attributes in a CFG_REPLY payload form a 258 single list of Split DNS domains that applies to the entire list of 259 INTERNAL_IP4_DNS and INTERNAL_IP6_DNS attributes. 261 3.4. Example Exchanges 263 3.4.1. Simple Case 265 In this example exchange, the initiator requests INTERNAL_IP4_DNS and 266 INTERNAL_DNS_DOMAIN attributes in the CFG_REQUEST, but does not 267 specify any value for either. This indicates that it supports Split 268 DNS, but has no preference for which DNS requests will be routed 269 through the tunnel. 271 The responder replies with two DNS server addresses, and two internal 272 domains, "example.com" and "city.other.test". 274 Any subsequent DNS queries from the initiator for domains such as 275 "www.example.com" SHOULD use 198.51.100.2 or 198.51.100.4 to resolve. 277 CP(CFG_REQUEST) = 278 INTERNAL_IP4_ADDRESS() 279 INTERNAL_IP4_DNS() 280 INTERNAL_DNS_DOMAIN() 282 CP(CFG_REPLY) = 283 INTERNAL_IP4_ADDRESS(198.51.100.234) 284 INTERNAL_IP4_DNS(198.51.100.2) 285 INTERNAL_IP4_DNS(198.51.100.4) 286 INTERNAL_DNS_DOMAIN(example.com) 287 INTERNAL_DNS_DOMAIN(city.other.test) 289 3.4.2. Requesting Domains and DNSSEC trust anchors 291 In this example exchange, the initiator requests INTERNAL_IP4_DNS, 292 INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA attributes in the 293 CFG_REQUEST. 295 Any subsequent DNS queries from the initiator for domains such as 296 "www.example.com" or "city.other.test" would be DNSSEC validated 297 using the DNSSEC trust anchor received in the CFG_REPLY. 299 In this example, the initiator has no existing DNSSEC trust anchors 300 would the requested domain. the "example.com" dommain has DNSSEC 301 trust anchors that are returned, while the "other.test" domain has no 302 DNSSEC trust anchors. 304 CP(CFG_REQUEST) = 305 INTERNAL_IP4_ADDRESS() 306 INTERNAL_IP4_DNS() 307 INTERNAL_DNS_DOMAIN() 308 INTERNAL_DNSSEC_TA() 310 CP(CFG_REPLY) = 311 INTERNAL_IP4_ADDRESS(198.51.100.234) 312 INTERNAL_IP4_DNS(198.51.100.2) 313 INTERNAL_IP4_DNS(198.51.100.4) 314 INTERNAL_DNS_DOMAIN(example.com) 315 INTERNAL_DNSSEC_TA(43547,8,1,B6225AB2CC613E0DCA7962BDC2342EA4...) 316 INTERNAL_DNSSEC_TA(31406,8,2,F78CF3344F72137235098ECBBD08947C...) 317 INTERNAL_DNS_DOMAIN(city.other.test) 319 4. Payload Formats 321 All multi-octet fields representing integers are laid out in big 322 endian order (also known as "most significant byte first", or 323 "network byte order"). 325 4.1. INTERNAL_DNS_DOMAIN Configuration Attribute Type Request and Reply 327 1 2 3 328 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 1 329 +-+-----------------------------+-------------------------------+ 330 |R| Attribute Type | Length | 331 +-+-----------------------------+-------------------------------+ 332 | | 333 ~ Domain Name in DNS presentation format ~ 334 | | 335 +---------------------------------------------------------------+ 337 o Reserved (1 bit) - Defined in IKEv2 RFC [RFC7296]. 339 o Attribute Type (15 bits) set to value 25 for INTERNAL_DNS_DOMAIN. 341 o Length (2 octets) - Length of domain name. 343 o Domain Name (0 or more octets) - A Fully Qualified Domain Name 344 used for Split DNS rules, such as "example.com", in DNS 345 presentation format and optionally using IDNA [RFC5890] for 346 Internationalized Domain Names. Implementors need to be careful 347 that this value is not null-terminated. 349 4.2. INTERNAL_DNSSEC_TA Configuration Attribute 351 An INTERNAL_DNSSEC_TA Configuration Attribute can either be empty, or 352 it can contain one Trust Anchor by containing a non-zero Length with 353 a DNSKEY Key Tag, DNSKEY Algorithm, Digest Type and Digest Data 354 fields. 356 An empty INTERNAL_DNSSEC_TA CFG attribute: 358 1 2 3 359 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 1 360 +-+-----------------------------+-------------------------------+ 361 |R| Attribute Type | Length (set to 0) | 362 +-+-----------------------------+-------------------------------+ 364 o Reserved (1 bit) - Defined in IKEv2 RFC [RFC7296]. 366 o Attribute Type (15 bits) set to value 26 for INTERNAL_DNSSEC_TA. 368 o Length (2 octets) - Set to 0 for an empty attribute. 370 A non-empty INTERNAL_DNSSEC_TA CFG attribute: 372 1 2 3 373 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 1 374 +-+-----------------------------+-------------------------------+ 375 |R| Attribute Type | Length | 376 +-+-----------------------------+---------------+---------------+ 377 | DNSKEY Key Tag | DNSKEY Alg | Digest Type | 378 +-------------------------------+---------------+---------------+ 379 | | 380 ~ Digest Data ~ 381 | | 382 +---------------------------------------------------------------+ 384 o Reserved (1 bit) - Defined in IKEv2 RFC [RFC7296]. 386 o Attribute Type (15 bits) set to value 26 for INTERNAL_DNSSEC_TA. 388 o Length (2 octets) - Length of DNSSEC Trust Anchor data (4 octets 389 plus the length of the Digest Data). 391 o DNSKEY Key Tag value (2 octets) - Delegation Signer (DS) Key Tag 392 as specified in [RFC4034] Section 5.1. 394 o DNSKEY Algorithm (1 octet) - DNSKEY algorithm value from the IANA 395 DNS Security Algorithm Numbers Registry. 397 o Digest Type (1 octet) - DS algorithm value from the IANA 398 Delegation Signer (DS) Resource Record (RR) Type Digest Algorithms 399 Registry. 401 o Digest Data (1 or more octets) - The DNSKEY digest as specified in 402 [RFC4034] Section 5.1 in presentation format. 404 Each INTERNAL_DNSSEC_TA attribute in the CFG_REPLY payload MUST 405 immediately follow a corresponding INTERNAL_DNS_DOMAIN attribute. As 406 the INTERNAL_DNSSEC_TA format itself does not contain the domain 407 name, it relies on the preceding INTERNAL_DNS_DOMAIN to provide the 408 domain for which it specifies the trust anchor. Any 409 INTERNAL_DNSSEC_TA attribute that is not immediately preceded by an 410 INTERNAL_DNS_DOMAIN or another INTERNAL_DNSSEC_TA attribute applying 411 to the same domain name MUST be ignored and treated as a protocol 412 error. 414 5. INTERNAL_DNS_DOMAIN Usage Guidelines 416 If a CFG_REPLY payload contains no INTERNAL_DNS_DOMAIN attributes, 417 the client MAY use the provided INTERNAL_IP4_DNS or INTERNAL_IP6_DNS 418 servers as the default DNS server(s) for all queries. 420 If a client is configured by local policy to only accept a limited 421 number of INTERNAL_DNS_DOMAIN values, the client MUST ignore any 422 other INTERNAL_DNS_DOMAIN values. 424 For each INTERNAL_DNS_DOMAIN entry in a CFG_REPLY payload that is not 425 prohibited by local policy, the client MUST use the provided 426 INTERNAL_IP4_DNS or INTERNAL_IP6_DNS DNS servers as the only 427 resolvers for the listed domains and its sub-domains and it MUST NOT 428 attempt to resolve the provided DNS domains using its external DNS 429 servers. Other domain names SHOULD be resolved using some other 430 external DNS resolver(s), configured independently from IKE. Queries 431 for these other domains MAY be sent to the internal DNS resolver(s) 432 listed in that CFG_REPLY message, but have no guarantee of being 433 answered. For example, if the INTERNAL_DNS_DOMAIN attribute 434 specifies "example.test", then "example.test", "www.example.test" and 435 "mail.eng.example.test" MUST be resolved using the internal DNS 436 resolver(s), but "otherexample.test" and "ple.test" MUST NOT be 437 resolved using the internal resolver and MUST use the system's 438 external DNS resolver(s). 440 The initiator SHOULD allow the DNS domains listed in the 441 INTERNAL_DNS_DOMAIN attributes to resolve to special IP address 442 ranges, such as those of [RFC1918], even if the initiator host is 443 otherwise configured to block DNS answer containing these special IP 444 address ranges. 446 When an IKE SA is terminated, the DNS forwarding MUST be 447 unconfigured. This includes deleting the DNS forwarding rules; 448 flushing all cached data for DNS domains provided by the 449 INTERNAL_DNS_DOMAIN attribute, including negative cache entries; 450 removing any obtained DNSSEC trust anchors from the list of trust 451 anchors; and clearing the outstanding DNS request queue. 453 INTERNAL_DNS_DOMAIN attributes SHOULD only be used on split tunnel 454 configurations where only a subset of traffic is routed into a 455 private remote network using the IPsec connection. If all traffic is 456 routed over the IPsec connection, the existing global 457 INTERNAL_IP4_DNS and INTERNAL_IP6_DNS can be used without creating 458 specific DNS exemptions. 460 6. INTERNAL_DNSSEC_TA Usage Guidelines 462 DNS records can be used to publish specific records containing trust 463 anchors for applications. The most common record type is the TLSA 464 record specified in [RFC6698]. This DNS record type publishes which 465 CA certificate or EE certificate to expect for a certain host name. 466 These records are protected by DNSSEC and thus can be trusted by the 467 application. Whether to trust TLSA records instead of the 468 traditional WebPKI depends on the local policy of the client. By 469 accepting an INTERNAL_DNSSEC_TA trust anchor via IKE from the remote 470 IKE server, the IPsec client might be allowing the remote IKE server 471 to override the trusted certificates for TLS. Similar override 472 concerns apply to other public key or fingerprint based DNS records, 473 such as OPENPGPKEY, SMIMEA or IPSECKEY records. 475 Thus, installing an INTERNAL_DNSSEC_TA trust anchor can be seen as 476 the equivalent of installing an Enterprise Certificate Authority (CA) 477 certificate. It allows the remote IKE/IPsec server to modify DNS 478 answers including its DNSSEC cryptographic signatures by overriding 479 existing DNS information with trust anchor conveyed via IKE and 480 (temporarilly) installed on the IKE client. Of specific concern is 481 the overriding of [RFC6698] based TLSA records, which represent a 482 confirmation or override of an existing WebPKI TLS certificate. 483 Other DNS record types that convey cryptographic materials (public 484 keys or fingerprints) are OPENPGPKEY, SMIMEA, SSHP and IPSECKEY 485 records. 487 IKE clients willing to accept INTERNAL_DNSSEC_TA attributes MUST use 488 a whitelist of one or more domains that can be updated out of band. 489 IKE clients with an empty whitelist MUST NOT use any 490 INTERNAL_DNSSEC_TA attributes received over IKE. Such clients MAY 491 interpret receiving an INTERNAL_DNSSEC_TA attribute for a non- 492 whitelisted domain as an indication that their local configuration 493 may need to be updated out of band. 495 IKE clients should take care to only whitelist domains that apply to 496 internal or managed domains, rather than to generic Internet traffic. 497 The DNS root zone (".") MUST be ignored if it appears in a whitelist. 498 Other generic or public domains, such as top-level domains (TLDs), 499 similarly MUST be ignored if these appear in a whitelist unless the 500 entity actually is the operator of the TLD. To determine this, an 501 implementation MAY interactively ask the user when a VPN profile is 502 installed or activated to confirm this. Alternatively, it MAY 503 provide a special override keyword in its provisioning configuration 504 to ensure non-interactive agreement can be achieved only by the party 505 provisioning the VPN client, who presumbly is a trusted entity by the 506 end-user. Similarly, an entity might be using a special domain name, 507 such as ".internal", for its internal-only view and might wish to 508 force its provisioning system to accept such a domain in a Split DNS 509 configuration. 511 Any updates to this whitelist of domain names MUST happen via 512 explicit human interaction or by a trusted automated provision system 513 to prevent malicious invisible installation of trust anchors in case 514 of aIKE server compromise. 516 IKE clients SHOULD accept any INTERNAL_DNSSEC_TA updates for 517 subdomain names of the whitelisted domain names. For example, if 518 "example.net" is whitelisted, then INTERNAL_DNSSEC_TA received for 519 "antartica.example.net" SHOULD be accepted. 521 IKE clients MAY interpret an INTERNAL_DNSSEC_TA for domain that was 522 not preconfigured as an indication that it needs to update its IKE 523 configuration (out of band). The client MUST NOT use such a 524 INTERNAL_DNSSEC_TA to reconfigure its local DNS settings. 526 IKE clients MUST ignore any received INTERNAL_DNSSEC_TA requests for 527 a FDQN for which it did not receive and accept an INTERNAL_DNS_DOMAIN 528 Configuration Payload. 530 In most deployment scenario's, the IKE client has an expectation that 531 it is connecting, using a split-network setup, to a specific 532 organisation or enterprise. A recommended policy would be to only 533 accept INTERNAL_DNSSEC_TA directives from that organization's DNS 534 names. However, this might not be possible in all deployment 535 scenarios, such as one where the IKE server is handing out a number 536 of domains that are not within one parent domain. 538 7. Security Considerations 540 As stated in Section 2, if the negotiated IPsec connection is not a 541 split tunnel configuration, the INTERNAL_DNS_DOMAIN and 542 INTERNAL_DNSSEC_TA Configuration Payloads MUST be ignored. 543 Otherwise, generic VPN service providers could maliciously override 544 DNSSEC based trust anchors of public DNS domains. 546 An initiator MUST only accept INTERNAL_DNSSEC_TA's for which it has a 547 whitelist. It MAY treat a received INTERNAL_DNSSEC_TA for an non- 548 whitelisted domain as a signal to update the whitelist via a non-IKE 549 provisioning mechanism. See Section 6 for additional security 550 considerations for DNSSEC trust anchors. 552 The use of Split DNS configurations assigned by an IKEv2 responder is 553 predicated on the trust established during IKE SA authentication. 554 However, if IKEv2 is being negotiated with an anonymous or unknown 555 endpoint (such as for Opportunistic Security [RFC7435]), the 556 initiator MUST ignore Split DNS configurations assigned by the 557 responder. 559 If a host connected to an authenticated IKE peer is connecting to 560 another IKE peer that attempts to claim the same domain via the 561 INTERNAL_DNS_DOMAIN attribute, the IKE connection SHOULD only process 562 the DNS information if the two connections are part of the same 563 logical entity. Otherwise, the client SHOULD refuse the DNS 564 information and potentially warn the end-user. For example, if a VPN 565 profile for "Example Corporation" is installed that provides two 566 IPsec connections, one covering 192.168.100.0/24 and one covering 567 10.13.14.0/24 it could be that both connections negotiate the same 568 INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA values. Since these are 569 part of the same remote organisation (or provisioning profile), the 570 Configuration Payloads can be used. However, if a user installs two 571 VPN profiles from two different unrelated independent entities, both 572 of these could be configured to use the same domain, for example 573 ".internal". These two connections MUST NOT be allowed to be active 574 at the same time. 576 If the initiator is using DNSSEC validation for a domain in its 577 public DNS view, and it requests and receives an INTERNAL_DNS_DOMAIN 578 attribute without an INTERNAL_DNSSEC_TA, it will need to reconfigure 579 its DNS resolver to allow for an insecure delegation. It SHOULD NOT 580 accept insecure delegations for domains that are DNSSEC signed in the 581 public DNS view, for which it has not explicitly requested such 582 deletation by specifying the domain specifically using a 583 INTERNAL_DNS_DOMAIN(domain) request. 585 Deployments that configure INTERNAL_DNS_DOMAIN domains should pay 586 close attention to their use of indirect reference RRtypes in their 587 internal-only domain names. Examples of such RRtypes are NS, CNAME, 588 DNAME, MX or SRV records. For example, if the MX record for 589 "internal.example.com" points to "mx.internal.example.net", then both 590 "internal.example.com" and "internal.example.net" should be sent 591 using an INTERNAL_DNS_DOMAIN Configuration Payload. 593 IKE clients MAY want to require whitelisted domains for Top Level 594 Domains (TLDs) and Second Level Domains (SLDs) to further prevent 595 malicious DNS redirections for well known domains. This prevents 596 users from unknowingly giving DNS queries to third parties. This is 597 even more important if those well known domains are not deploying 598 DNSSEC, as the VPN service provider could then even modify the DNS 599 answers without detection. 601 The content of INTERNAL_DNS_DOMAIN and INTERNAL_DNSSEC_TA may be 602 passed to another (DNS) program for processing. As with any network 603 input, the content SHOULD be considered untrusted and handled 604 accordingly. 606 8. IANA Considerations 608 This document defines two new IKEv2 Configuration Payload Attribute 609 Types, which are allocated from the "IKEv2 Configuration Payload 610 Attribute Types" namespace. 612 Multi- 613 Value Attribute Type Valued Length Reference 614 ------ ------------------- ------ ---------- --------------- 615 25 INTERNAL_DNS_DOMAIN YES 0 or more [this document] 616 26 INTERNAL_DNSSEC_TA YES 0 or more [this document] 618 Figure 1 620 9. References 622 9.1. Normative References 624 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 625 and E. Lear, "Address Allocation for Private Internets", 626 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 627 . 629 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 630 Requirement Levels", BCP 14, RFC 2119, 631 DOI 10.17487/RFC2119, March 1997, . 634 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 635 Rose, "Resource Records for the DNS Security Extensions", 636 RFC 4034, DOI 10.17487/RFC4034, March 2005, 637 . 639 [RFC5890] Klensin, J., "Internationalized Domain Names for 640 Applications (IDNA): Definitions and Document Framework", 641 RFC 5890, DOI 10.17487/RFC5890, August 2010, 642 . 644 [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication 645 of Named Entities (DANE) Transport Layer Security (TLS) 646 Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August 647 2012, . 649 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 650 Kivinen, "Internet Key Exchange Protocol Version 2 651 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 652 2014, . 654 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 655 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 656 May 2017, . 658 9.2. Informative References 660 [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, 661 DOI 10.17487/RFC2775, February 2000, . 664 [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection 665 Most of the Time", RFC 7435, DOI 10.17487/RFC7435, 666 December 2014, . 668 Authors' Addresses 670 Tommy Pauly 671 Apple Inc. 672 One Apple Park Way 673 Cupertino, California 95014 674 US 676 Email: tpauly@apple.com 678 Paul Wouters 679 Red Hat 681 Email: pwouters@redhat.com