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Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 3736 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 6106 (Obsoleted by RFC 8106) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Jeong 3 Internet-Draft Sungkyunkwan University 4 Obsoletes: 6106 (if approved) S. Park 5 Intended status: Standards Track Samsung Electronics 6 Expires: December 16, 2016 L. Beloeil 7 France Telecom R&D 8 S. Madanapalli 9 iRam Technologies 10 June 14, 2016 12 IPv6 Router Advertisement Options for DNS Configuration 13 draft-ietf-6man-rdnss-rfc6106bis-14 15 Abstract 17 This document specifies IPv6 Router Advertisement (RA) options 18 (called DNS RA options) to allow IPv6 routers to advertise a list of 19 DNS recursive server addresses and a DNS Search List to IPv6 hosts. 21 This document obsoletes RFC 6106 and allows a higher default value of 22 the lifetime of the DNS RA options to avoid the frequent expiry of 23 the options on links with a relatively high rate of packet loss. 25 Status of This Memo 27 This Internet-Draft is submitted to IETF in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF), its areas, and its working groups. Note that 32 other groups may also distribute working documents as Internet- 33 Drafts. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 The list of current Internet-Drafts can be accessed at 41 http://www.ietf.org/ietf/1id-abstracts.txt. 43 The list of Internet-Draft Shadow Directories can be accessed at 44 http://www.ietf.org/shadow.html. 46 This Internet-Draft will expire on December 16, 2016. 48 Copyright Notice 49 Copyright (c) 2016 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.1. Applicability Statements . . . . . . . . . . . . . . . . . 3 66 1.2. Coexistence of RA Options and DHCP Options for DNS 67 Configuration . . . . . . . . . . . . . . . . . . . . . . 4 68 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 69 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 71 5. Neighbor Discovery Extension . . . . . . . . . . . . . . . . . 5 72 5.1. Recursive DNS Server Option . . . . . . . . . . . . . . . 5 73 5.2. DNS Search List Option . . . . . . . . . . . . . . . . . . 7 74 5.3. Procedure of DNS Configuration . . . . . . . . . . . . . . 8 75 5.3.1. Procedure in IPv6 Hosts . . . . . . . . . . . . . . . 8 76 5.3.2. Warnings for DNS Options Configuration . . . . . . . . 9 77 6. Implementation Considerations . . . . . . . . . . . . . . . . 9 78 6.1. DNS Repository Management . . . . . . . . . . . . . . . . 10 79 6.2. Synchronization between DNS Server List and Resolver 80 Repository . . . . . . . . . . . . . . . . . . . . . . . . 10 81 6.3. Synchronization between DNS Search List and Resolver 82 Repository . . . . . . . . . . . . . . . . . . . . . . . . 11 83 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 84 7.1. Security Threats . . . . . . . . . . . . . . . . . . . . . 12 85 7.2. Recommendations . . . . . . . . . . . . . . . . . . . . . 12 86 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 87 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 88 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 89 10.1. Normative References . . . . . . . . . . . . . . . . . . . 13 90 10.2. Informative References . . . . . . . . . . . . . . . . . . 14 91 Appendix A. Changes from RFC 6106 . . . . . . . . . . . . . . . . 15 93 1. Introduction 95 The purpose of this document is to standardize IPv6 Router 96 Advertisement (RA) options (DNS RA options) for DNS Recursive Server 97 Addresses used for the DNS name resolution in IPv6 hosts, and also 98 for a DNS Search List of domain suffixes. 100 Neighbor Discovery (ND) for IP version 6 and IPv6 Stateless Address 101 Autoconfiguration (SLAAC) provide ways to configure either fixed or 102 mobile nodes with one or more IPv6 addresses, default routers, and 103 some other parameters [RFC4861][RFC4862]. 105 It is infeasible to manually configure nomadic hosts each time they 106 connect to a different network. While a one-time static 107 configuration is possible, it is generally not desirable on general- 108 purpose hosts such as laptops. For instance, locally defined name 109 spaces would not be available to the host if it were to run its own 110 recursive name server directly connected to the global DNS. 112 The DNS information can also be provided through DHCPv6 [RFC3315] 113 [RFC3736][RFC3646]. However, the access to DNS is a fundamental 114 requirement for almost all hosts, so IPv6 stateless autoconfiguration 115 cannot stand on its own as an alternative deployment model in any 116 practical network without any support for DNS configuration. 118 These issues are not pressing in dual-stack networks as long as a DNS 119 server is available on the IPv4 side, but they become more critical 120 with the deployment of IPv6-only networks. As a result, this 121 document defines a mechanism based on DNS RA options to allow IPv6 122 hosts to perform the automatic DNS configuration. 124 1.1. Applicability Statements 126 RA-based DNS configuration is a useful alternative in networks where 127 an IPv6 host's address is autoconfigured through IPv6 stateless 128 address autoconfiguration and where there is either no DHCPv6 129 infrastructure at all or some hosts do not have a DHCPv6 client. The 130 intention is to enable the full configuration of basic networking 131 information for hosts without requiring DHCPv6. However, for 132 networks that need to distribute additional information, DHCPv6 is 133 likely to be employed. In these networks, RA-based DNS configuration 134 may not be needed. 136 RA-based DNS configuration allows an IPv6 host to acquire the DNS 137 configuration (i.e., DNS recursive server addresses and DNS Search 138 List) for the link(s) to which the host is connected. Furthermore, 139 the host learns this DNS configuration from the same RA message that 140 provides configuration information for the link. 142 The advantages and disadvantages of the RA-based approach are 143 discussed in [RFC4339] along with other approaches, such as the DHCP 144 and well-known anycast address approaches. 146 1.2. Coexistence of RA Options and DHCP Options for DNS Configuration 148 Two protocols exist to configure the DNS information on a host, the 149 Router Advertisement options specified in this document and the 150 DHCPv6 options specified in [RFC3646]. They can be used together. 151 The rules governing the decision to use stateful configuration 152 mechanisms are specified in [RFC4861]. Hosts conforming to this 153 specification MUST extract DNS information from Router Advertisement 154 messages, unless static DNS configuration has been specified by the 155 user. If there is DNS information available from multiple Router 156 Advertisements and/or from DHCP, the host MUST maintain an ordered 157 list of this information as specified in Section 5.3.1. 159 2. Requirements Language 161 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 162 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 163 document are to be interpreted as described in [RFC2119]. 165 3. Terminology 167 This document uses the terminology defined in [RFC4861] and 168 [RFC4862]. In addition, four new terms are defined below: 170 o Recursive DNS Server (RDNSS): Server that provides a recursive DNS 171 resolution service for translating domain names into IP addresses 172 or resolving PTR records, as defined in [RFC1034] and [RFC1035]. 174 o RDNSS Option: IPv6 RA option to deliver the RDNSS information to 175 IPv6 hosts [RFC4861]. 177 o DNS Search List (DNSSL): The list of DNS suffix domain names used 178 by IPv6 hosts when they perform DNS query searches for short, 179 unqualified domain names. 181 o DNSSL Option: IPv6 RA option to deliver the DNSSL information to 182 IPv6 hosts. 184 o DNS Repository: Two data structures for managing DNS Configuration 185 Information in the IPv6 protocol stack in addition to Neighbor 186 Cache and Destination Cache for Neighbor Discovery [RFC4861]. The 187 first data structure is the DNS Server List for RDNSS addresses 188 and the second is the DNS Search List for DNS search domain names. 190 o Resolver Repository: Configuration repository with RDNSS addresses 191 and a DNS Search List that a DNS resolver on the host uses for DNS 192 name resolution; for example, the Unix resolver file (i.e., /etc/ 193 resolv.conf) and Windows registry. 195 4. Overview 197 This document standardizes the ND option called the RDNSS option that 198 contains the addresses of recursive DNS servers. This document also 199 standardizes the ND option called the DNSSL option that contains the 200 Domain Search List. This is to maintain parity with the DHCPv6 201 options and to ensure that there is necessary functionality to 202 determine the search domains. 204 The existing ND message (i.e., Router Advertisement) is used to carry 205 this information. An IPv6 host can configure the IPv6 addresses of 206 one or more RDNSSes via RA messages. Through the RDNSS and DNSSL 207 options, along with the prefix information option based on the ND 208 protocol ([RFC4861] and [RFC4862]), an IPv6 host can perform the 209 network configuration of its IPv6 address and the DNS information 210 simultaneously without needing DHCPv6 for the DNS configuration. The 211 RA options for RDNSS and DNSSL can be used on networks that support 212 the use of ND. 214 This approach requires the manual configuration or other automatic 215 mechanisms (e.g., DHCPv6 or vendor proprietary configuration 216 mechanisms) to configure the DNS information in routers sending the 217 advertisements. The automatic configuration of RDNSS addresses and a 218 DNS Search List in routers is out of scope for this document. 220 5. Neighbor Discovery Extension 222 The IPv6 DNS configuration mechanism in this document needs two ND 223 options in Neighbor Discovery: (i) the Recursive DNS Server (RDNSS) 224 option and (ii) the DNS Search List (DNSSL) option. 226 5.1. Recursive DNS Server Option 228 The RDNSS option contains one or more IPv6 addresses of recursive DNS 229 servers. All of the addresses share the same Lifetime value. If it 230 is desirable to have different Lifetime values, multiple RDNSS 231 options can be used. Figure 1 shows the format of the RDNSS option. 233 0 1 2 3 234 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 1 235 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 236 | Type | Length | Reserved | 237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 238 | Lifetime | 239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 240 | | 241 : Addresses of IPv6 Recursive DNS Servers : 242 | | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 245 Figure 1: Recursive DNS Server (RDNSS) Option Format 247 Fields: 248 Type 8-bit identifier of the RDNSS option type as assigned 249 by the IANA: 25 251 Length 8-bit unsigned integer. The length of the option 252 (including the Type and Length fields) is in units of 253 8 octets. The minimum value is 3 if one IPv6 address 254 is contained in the option. Every additional RDNSS 255 address increases the length by 2. The Length field 256 is used by the receiver to determine the number of 257 IPv6 addresses in the option. 259 Lifetime 32-bit unsigned integer. The maximum time in 260 seconds (relative to the time the packet is received) 261 over which these RDNSS addresses MAY be used for name 262 resolution. The value of Lifetime SHOULD by default 263 be at least 3 * MaxRtrAdvInterval where 264 MaxRtrAdvInterval is the Maximum RA Interval defined 265 in [RFC4861]. A value of all one bits (0xffffffff) 266 represents infinity. A value of zero means that the 267 RDNSS addresses MUST no longer be used. 269 Addresses of IPv6 Recursive DNS Servers 270 One or more 128-bit IPv6 addresses of the recursive 271 DNS servers. The number of addresses is determined 272 by the Length field. That is, the number of 273 addresses is equal to (Length - 1) / 2. 275 Note: The addresses for recursive DNS servers in the RDNSS option 276 MAY be link-local addresses. Such link-local addresses SHOULD be 277 registered into the resolver repository along with the 278 corresponding link zone indices of the links that receive the 279 RDNSS option(s) for them. The link-local addresses MAY be 280 represented in the resolver repository with their link zone 281 indices in the textual format for scoped addresses as described in 282 [RFC4007]. When a resolver sends a DNS query message to an RDNSS 283 identified by a link-local address, it MUST use the corresponding 284 link. 286 5.2. DNS Search List Option 288 The DNSSL option contains one or more domain names of DNS suffixes. 289 All of the domain names share the same Lifetime value. If it is 290 desirable to have different Lifetime values, multiple DNSSL options 291 can be used. Figure 2 shows the format of the DNSSL option. 293 0 1 2 3 294 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 1 295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 | Type | Length | Reserved | 297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 298 | Lifetime | 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 300 | | 301 : Domain Names of DNS Search List : 302 | | 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 305 Figure 2: DNS Search List (DNSSL) Option Format 307 Fields: 308 Type 8-bit identifier of the DNSSL option type as assigned 309 by the IANA: 31 311 Length 8-bit unsigned integer. The length of the option 312 (including the Type and Length fields) is in units of 313 8 octets. The minimum value is 2 if at least one 314 domain name is contained in the option. The Length 315 field is set to a multiple of 8 octets to accommodate 316 all the domain names in the field of Domain Names of 317 DNS Search List. 319 Lifetime 32-bit unsigned integer. The maximum time in 320 seconds (relative to the time the packet is received) 321 over which these DNSSL domain names MAY be used for 322 name resolution. The Lifetime value has the same 323 semantics as with the RDNSS option. That is, 324 Lifetime SHOULD by default be at least 325 3 * MaxRtrAdvInterval. A value of all one bits 326 (0xffffffff) represents infinity. A value of zero 327 means that the DNSSL domain names MUST no longer be 328 used. 330 Domain Names of DNS Search List 331 One or more domain names of DNS Search List that MUST 332 be encoded as described in Section 3.1 of [RFC1035]. 333 By this technique, each domain name is represented as 334 a sequence of labels ending in a zero octet, defined 335 as domain name representation. For more than one 336 domain name, the corresponding domain name 337 representations are concatenated as they are. Note 338 that for the simple decoding, the domain names MUST 339 NOT be encoded in a compressed form, as described in 340 Section 4.1.4 of [RFC1035]. Because the size of this 341 field MUST be a multiple of 8 octets, for the minimum 342 multiple including the domain name representations, 343 the remaining octets other than the encoding parts of 344 the domain name representations MUST be padded with 345 zeros. 347 5.3. Procedure of DNS Configuration 349 The procedure of DNS configuration through the RDNSS and DNSSL 350 options is the same as with any other ND option [RFC4861]. 352 5.3.1. Procedure in IPv6 Hosts 354 When an IPv6 host receives DNS options (i.e., RDNSS and DNSSL 355 options) through RA messages, it processes the options as follows: 357 o The validity of DNS options is checked with the Length field; that 358 is, the value of the Length field in the RDNSS option is greater 359 than or equal to the minimum value (3), and satisfies that (Length 360 - 1) % 2 == 0. The value of the Length field in the DNSSL option 361 is greater than or equal to the minimum value (2). Also, the 362 validity of the RDNSS option is checked with the "Addresses of 363 IPv6 Recursive DNS Servers" field; that is, the addresses should 364 be unicast addresses. 366 o If the DNS options are valid, the host SHOULD copy the values of 367 the options into the DNS Repository and the Resolver Repository in 368 order. Otherwise, the host MUST discard the options. Refer to 369 Section 6 for the detailed procedure. 371 In the case where the DNS information of RDNSS and DNSSL can be 372 obtained from multiple sources, such as RA and DHCP, the IPv6 host 373 SHOULD keep some DNS options from all sources. Unless explicitly 374 specified for the discovery mechanism, the exact number of addresses 375 and domain names to keep is a matter of local policy and 376 implementation choice as a local configuration option. However, in 377 the case of multiple sources, the ability to store a total of at 378 least three RDNSS addresses (or DNSSL domain names) from the multiple 379 sources is RECOMMENDED. The DNS options from Router Advertisements 380 and DHCP SHOULD be stored into the DNS Repository and Resolver 381 Repository so that information from DHCP appears there first and 382 therefore takes precedence. Thus, the DNS information from DHCP 383 takes precedence over that from RA for DNS queries. On the other 384 hand, for DNS options announced by RA, if some RAs use the Secure 385 Neighbor Discovery (SEND) protocol [RFC3971] for RA security, they 386 MUST be preferred over those that do not use SEND. Also, DNS options 387 announced by RA via SEND MUST be preferred over those announced by 388 un-authenticated DHCP [RFC3118]. Refer to Section 7 for the detailed 389 discussion on SEND for DNS RA options. 391 5.3.2. Warnings for DNS Options Configuration 393 There are two warnings for DNS options configuration: (i) warning for 394 multiple sources of DNS options and (ii) warning for multiple network 395 interfaces. First, in the case of multiple sources for DNS options 396 (e.g., RA and DHCP), an IPv6 host can configure its IP addresses from 397 these sources. In this case, it is not possible to control how the 398 host uses DNS information and what source addresses it uses to send 399 DNS queries. As a result, configurations where different information 400 is provided by different mechanisms for autoconfiguration may lead to 401 problems. Therefore, the network administrator needs to carefully 402 configure different DNS options in the multiple mechanisms for 403 autoconfiguration in order to minimize the impact of such problems 404 [DHCPv6-SLAAC]. 406 Second, if different DNS information is provided on different network 407 interfaces, this can lead to inconsistent behavior. The IETF worked 408 on solving this problem for both DNS and other information obtained 409 by multiple interfaces [RFC6418][RFC6419], and standardized the 410 solution for RDNSS selection for multi-interfaced nodes in [RFC6731], 411 which is based on DHCP. 413 6. Implementation Considerations 415 The implementation considerations in this document include the 416 following three: (i) DNS repository management, (ii) synchronization 417 between DNS server list and resolver repository, and (iii) 418 synchronization between DNS search list and resolver repository. 420 6.1. DNS Repository Management 422 For DNS repository management, the following two data structures 423 SHOULD be synchronized with the resolver repository: (i) DNS Server 424 List that keeps the list of RDNSS addresses and (ii) DNS Search List 425 that keeps the list of DNS search domain names. Each entry in these 426 two lists consists of a pair of an RDNSS address (or DNSSL domain 427 name) and Expiration-time as follows: 429 o RDNSS address for DNS Server List: IPv6 address of the Recursive 430 DNS Server which is available for recursive DNS resolution service 431 in the network advertising the RDNSS option. 433 o DNSSL domain name for DNS Search List: DNS suffix domain name 434 which is used to perform DNS query searches for short, unqualified 435 domain names. 437 o Expiration-time for DNS Server List or DNS Search List: The time 438 when this entry becomes invalid. Expiration-time is set to the 439 value of the Lifetime field of the RDNSS option or DNSSL option 440 plus the current time. Whenever a new RDNSS option with the same 441 address (or DNSSL option with the same domain name) is received on 442 the same interface as a previous RDNSS option (or DNSSL option), 443 this field is updated to have a new Expiration-time. When the 444 current time becomes larger than Expiration-time, this entry is 445 regarded as expired. Note that the DNS information for the RDNSS 446 and DNSSL options need not be dropped if the expiry of the RA 447 router lifetime happens. This is because these options have their 448 own lifetime values. 450 6.2. Synchronization between DNS Server List and Resolver Repository 452 When an IPv6 host receives the information of multiple RDNSS 453 addresses within a network (e.g., campus network and company network) 454 through an RA message with RDNSS option(s), it stores the RDNSS 455 addresses (in order) into both the DNS Server List and the Resolver 456 Repository. The processing of the RDNSS consists of (i) the 457 processing of RDNSS option(s) included in an RA message and (ii) the 458 handling of expired RDNSSes. The processing of RDNSS option(s) is as 459 follows: 461 Step (a): Receive and parse the RDNSS option(s). For the RDNSS 462 addresses in each RDNSS option, perform Steps (b) through (d). 464 Step (b): For each RDNSS address, check the following: If the 465 RDNSS address already exists in the DNS Server List and the RDNSS 466 option's Lifetime field is set to zero, delete the corresponding 467 RDNSS entry from both the DNS Server List and the Resolver 468 Repository in order to prevent the RDNSS address from being used 469 any more for certain reasons in network management, e.g., the 470 termination of the RDNSS or a renumbering situation. That is, the 471 RDNSS can resign from its DNS service because the machine running 472 the RDNSS is out of service intentionally or unintentionally. 473 Also, under the renumbering situation, the RDNSS's IPv6 address 474 will be changed, so the previous RDNSS address should not be used 475 any more. The processing of this RDNSS address is finished here. 476 Otherwise, go to Step (c). 478 Step (c): For each RDNSS address, if it already exists in the DNS 479 Server List and the RDNSS option's Lifetime field is not set to 480 zero, then just update the value of the Expiration-time field 481 according to the procedure specified in the third bullet of 482 Section 6.1. Otherwise, go to Step (d). 484 Step (d): For each RDNSS address, if it does not exist in the DNS 485 Server List, register the RDNSS address and Lifetime with the DNS 486 Server List and then insert the RDNSS address as the first one in 487 the Resolver Repository. In the case where the data structure for 488 the DNS Server List is full of RDNSS entries (that is, has more 489 RDNSSes than the sufficient number discussed in Section 5.3.1), 490 delete from the DNS Server List the entry with the shortest 491 Expiration-time (i.e., the entry that will expire first). The 492 corresponding RDNSS address is also deleted from the Resolver 493 Repository. For the ordering of RDNSS addresses in an RDNSS 494 option, position the first RDNSS address in the RDNSS option as 495 the first one in the Resolver Repository, the second RDNSS address 496 in the option as the second one in the repository, and so on. 497 This ordering allows the RDNSS addresses in the RDNSS option to be 498 preferred according to their order in the RDNSS option for the DNS 499 name resolution. The processing of these RDNSS addresses is 500 finished here. 502 The handling of expired RDNSSes is as follows: Whenever an entry 503 expires in the DNS Server List, the expired entry is deleted from the 504 DNS Server List, and also the RDNSS address corresponding to the 505 entry is deleted from the Resolver Repository. 507 6.3. Synchronization between DNS Search List and Resolver Repository 509 When an IPv6 host receives the information of multiple DNSSL domain 510 names within a network through an RA message with DNSSL option(s), it 511 stores the DNSSL domain names (in order) into both the DNS Search 512 List and the Resolver Repository. The processing of the DNSSL 513 consists of (i) the processing of DNSSL option(s) included in an RA 514 message and (ii) the handling of expired DNSSLs. The processing of 515 DNSSL option(s) is the same with that of RDNSS option(s) in Section 516 6.2. 518 7. Security Considerations 520 In this section, we analyze security threats related to DNS options 521 and then suggest recommendations to cope with such security threats. 523 7.1. Security Threats 525 For the RDNSS option, an attacker could send an RA with a fraudulent 526 RDNSS address, misleading IPv6 hosts into contacting an unintended 527 DNS server for DNS name resolution. Also, for the DNSSL option, an 528 attacker can let IPv6 hosts resolve a host name without a DNS suffix 529 into an unintended host's IP address with a fraudulent DNS Search 530 List. These attacks are similar to ND attacks specified in [RFC4861] 531 that use Redirect or Neighbor Advertisement messages to redirect 532 traffic to individual addresses of malicious parties. 534 However, the security of these RA options for DNS configuration does 535 not affect ND protocol security [RFC4861]. This is because learning 536 DNS information via the RA options cannot be worse than learning bad 537 router information via the RA options. Therefore, the vulnerability 538 of ND is not worse and is a subset of the attacks that any node 539 attached to a LAN can do. 541 7.2. Recommendations 543 The Secure Neighbor Discovery (SEND) protocol [RFC3971] is designed 544 as a security mechanism for ND. In this case, ND can use SEND to 545 allow all the ND options including the RDNSS and DNSSL options to be 546 automatically signed with digital signatures. 548 It is common for network devices such as switches to include 549 mechanisms to block unauthorized ports from running a DHCPv6 server 550 to provide protection from rogue DHCPv6 servers [RFC7610]. That 551 means that an attacker on other ports cannot insert bogus DNS servers 552 using DHCPv6. The corresponding technique for network devices is 553 RECOMMENDED to block rogue Router Advertisement messages [RFC6104] 554 including the RDNSS and DNSSL options from unauthorized nodes. 556 An attacker may provide a bogus DNS Search List option in order to 557 cause the victim to send DNS queries to a specific DNS server when 558 the victim queries non-FQDNs (fully qualified domain names). For 559 this attack, the DNS resolver in IPv6 hosts can mitigate the 560 vulnerability with the recommendations mentioned in [RFC1535], 561 [RFC1536], and [RFC3646]. 563 8. IANA Considerations 565 The RDNSS option defined in this document uses the IPv6 Neighbor 566 Discovery Option type defined in RFC 6106 [RFC6106], which was 567 assigned by the IANA as follows: 569 Option Name Type 570 Recursive DNS Server Option 25 572 The DNSSL option defined in this document uses the IPv6 Neighbor 573 Discovery Option type defined in RFC 6106 [RFC6106], which was 574 assigned by the IANA as follows: 576 Option Name Type 577 DNS Search List Option 31 579 These options have been registered in the "Internet Control Message 580 Protocol version 6 (ICMPv6) Parameters" registry [ICMPv6]. 582 9. Acknowledgements 584 This document has greatly benefited from inputs by Robert Hinden, 585 Pekka Savola, Iljitsch van Beijnum, Brian Haberman, Tim Chown, Erik 586 Nordmark, Dan Wing, Jari Arkko, Ben Campbell, Vincent Roca, Tony 587 Cheneau, Fernando Gont, Jen Linkova, Ole Troan, Mark Smith, Tatuya 588 Jinmei, Lorenzo Colitti, Tore Anderson, David Farmer, Bing Liu, and 589 Tassos Chatzithomaoglou. The authors sincerely appreciate their 590 contributions. 592 This document was supported by Institute for Information & 593 communications Technology Promotion (IITP) grant funded by the Korea 594 government (MSIP) [10041244, Smart TV 2.0 Software Platform]. 596 10. References 598 10.1. Normative References 600 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 601 Requirement Levels", BCP 14, RFC 2119, March 1997. 603 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. 604 Soliman, "Neighbor Discovery for IP version 6 605 (IPv6)", RFC 4861, September 2007. 607 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 608 Stateless Address Autoconfiguration", RFC 4862, 609 September 2007. 611 [RFC1035] Mockapetris, P., "Domain names - implementation and 612 specification", STD 13, RFC 1035, November 1987. 614 [RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., 615 and B. Zill, "IPv6 Scoped Address Architecture", 616 RFC 4007, March 2005. 618 10.2. Informative References 620 [RFC1034] Mockapetris, P., "Domain names - concepts and 621 facilities", STD 13, RFC 1034, November 1987. 623 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, 624 C., and M. Carney, "Dynamic Host Configuration 625 Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. 627 [RFC3736] Droms, R., "Stateless Dynamic Host Configuration 628 Protocol (DHCP) Service for IPv6", RFC 3736, 629 April 2004. 631 [RFC3646] Droms, R., "DNS Configuration options for Dynamic 632 Host Configuration Protocol for IPv6 (DHCPv6)", 633 RFC 3646, December 2003. 635 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 636 "IPv6 Router Advertisement Options for DNS 637 Configuration", RFC 6106, November 2010. 639 [RFC4339] Jeong, J., "IPv6 Host Configuration of DNS Server 640 Information Approaches", RFC 4339, February 2006. 642 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, 643 "SEcure Neighbor Discovery (SEND)", RFC 3971, 644 March 2005. 646 [RFC3118] Droms, R. and W. Arbaugh, "", RFC 3118, June 2001. 648 [RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router 649 Advertisement Problem Statement", RFC 6104, 650 February 2011. 652 [RFC7610] Gont, F., Liu, W., and G. Van de Velde, "DHCPv6- 653 Shield: Protecting against Rogue DHCPv6 Servers", 654 RFC 7610, August 2015. 656 [RFC1535] Gavron, E., "A Security Problem and Proposed 657 Correction With Widely Deployed DNS Software", 658 RFC 1535, October 1993. 660 [RFC1536] Kumar, A., Postel, J., Neuman, C., Danzig, P., and S. 661 Miller, "Common DNS Implementation Errors and 662 Suggested Fixes", RFC 1536, October 1993. 664 [DHCPv6-SLAAC] Liu, B., Jiang, S., Gong, X., Wang, W., and E. Rey, 665 "DHCPv6/SLAAC Interaction Problems on Address and DNS 666 Configuration", Work in Progress, February 2016. 668 [RFC6418] Blanchet, M. and P. Seite, "Multiple Interfaces and 669 Provisioning Domains Problem Statement", RFC 6418, 670 November 2011. 672 [RFC6419] Wasserman, M. and P. Seite, "Current Practices for 673 Multiple-Interface Hosts", RFC 6419, November 2011. 675 [RFC6731] Savolainen, T., Kato, J., and T. Lemon, "Improved 676 Recursive DNS Server Selection for Multi-Interfaced 677 Nodes", RFC 6731, December 2012. 679 [ICMPv6] ICMPv6 Parameters Registry, "http://www.iana.org/ 680 assignments/icmpv6-parameters/ 681 icmpv6-parameters.xhtml#icmpv6-parameters-5". 683 Appendix A. Changes from RFC 6106 685 The following changes were made from RFC 6106 "IPv6 Router 686 Advertisement Options for DNS Configuration": 688 o This document allows a higher default value of the lifetime of the 689 DNS RA options than RFC 6106 in order to avoid the frequent expiry 690 of the options on links with a relatively high rate of packet 691 loss, and also making additional clarifications. The lifetime's 692 lower bound of 2 * MaxRtrAdvInterval was shown to lead to the 693 expiry of these options on links with a relatively high rate of 694 packet loss. This revision relaxes the lower bound and sets a 695 higher default value of 3 * MaxRtrAdvInterval to avoid this 696 problem. 698 o The generation of Router Solicitation to ensure that the RDNSS 699 information is fresh before the expiry of the RDNSS option is 700 removed in order to prevent multicast traffic on the link from 701 increasing. 703 o The addresses for recursive DNS servers in the RDNSS option can be 704 not only global addresses, but also link-local addresses. The 705 link-local addresses for RDNSSes should be registered into the 706 resolver repository along with the corresponding link zone 707 indices. 709 o The recommendation that at most three RDNSS addresses to maintain 710 by RDNSS options should be limited is removed. By this removal, 711 the number of RDNSSes to maintain is up to an implementer's local 712 policy. 714 o The recommendation that at most three DNS domains to maintain by 715 DNSSL options should be limited is removed. By this removal, when 716 the set of unique DNSSL values are not equivalent, none of them 717 are ignored for hostname lookups. 719 o The guidance of the specific implementation for the 720 synchronization of the DNS Repository and Resolver Repository on 721 the kernel space and user space is removed. 723 o The usage of the keywords of SHOULD and RECOMMENDED in RFC 2119 is 724 removed in the recommendation of using SEND for secure ND. 725 Instead of using these keywords, SEND is specified as only a 726 possible solution for secure ND. 728 Authors' Addresses 730 Jaehoon Paul Jeong 731 Department of Software 732 Sungkyunkwan University 733 2066 Seobu-Ro, Jangan-Gu 734 Suwon, Gyeonggi-Do 16419 735 Republic of Korea 737 Phone: +82 31 299 4957 738 Fax: +82 31 290 7996 739 EMail: pauljeong@skku.edu 740 URI: http://iotlab.skku.edu/people-jaehoon-jeong.php 741 Soohong Daniel Park 742 Software R&D Center 743 Samsung Electronics 744 Seoul R&D Campus D-Tower, 56, Seongchon-Gil, Seocho-Gu 745 Seoul 06765 746 Republic of Korea 748 EMail: soohong.park@samsung.com 750 Luc Beloeil 751 France Telecom R&D 752 42, rue des coutures 753 BP 6243 754 14066 CAEN Cedex 4 755 France 757 Phone: +33 2 40 44 97 40 758 EMail: luc.beloeil@orange-ftgroup.com 760 Syam Madanapalli 761 iRam Technologies 762 #H304, Shriram Samruddhi, Thubarahalli 763 Bangalore - 560066 764 India 766 EMail: smadanapalli@gmail.com