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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 5006 (Obsoleted by RFC 6106) 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 Brocade/ETRI 4 Obsoletes: 5006 (if approved) S. Park 5 Intended status: Standards Track SAMSUNG Electronics 6 Expires: January 27, 2011 L. Beloeil 7 France Telecom R&D 8 S. Madanapalli 9 Ordyn Technologies 10 July 26, 2010 12 IPv6 Router Advertisement Options for DNS Configuration 13 draft-ietf-6man-dns-options-bis-07 15 Abstract 17 This document specifies IPv6 Router Advertisement options to allow 18 IPv6 routers to advertise a list of DNS recursive server addresses 19 and a DNS search list to IPv6 hosts. 21 Status of This Memo 23 This Internet-Draft is submitted to IETF in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF), its areas, and its working groups. Note that 28 other groups may also distribute working documents as Internet- 29 Drafts. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 The list of current Internet-Drafts can be accessed at 37 http://www.ietf.org/ietf/1id-abstracts.txt. 39 The list of Internet-Draft Shadow Directories can be accessed at 40 http://www.ietf.org/shadow.html. 42 This Internet-Draft will expire on January 27, 2011. 44 Copyright Notice 46 Copyright (c) 2010 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.1. Applicability Statements . . . . . . . . . . . . . . . . . 3 63 1.2. Coexistence of RA Options and DHCP Options for DNS 64 Configuration . . . . . . . . . . . . . . . . . . . . . . 4 65 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 66 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 68 5. Neighbor Discovery Extension . . . . . . . . . . . . . . . . . 5 69 5.1. Recursive DNS Server Option . . . . . . . . . . . . . . . 5 70 5.2. DNS Search List Option . . . . . . . . . . . . . . . . . . 7 71 5.3. Procedure of DNS Configuration . . . . . . . . . . . . . . 8 72 5.3.1. Procedure in IPv6 Host . . . . . . . . . . . . . . . . 8 73 5.3.2. Warnings for DNS Options Configuration . . . . . . . . 9 74 6. Implementation Considerations . . . . . . . . . . . . . . . . 10 75 6.1. DNS Repository Management . . . . . . . . . . . . . . . . 10 76 6.2. Synchronization between DNS Server List and Resolver 77 Repository . . . . . . . . . . . . . . . . . . . . . . . . 11 78 6.3. Synchronization between DNS Search List and Resolver 79 Repository . . . . . . . . . . . . . . . . . . . . . . . . 12 80 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 81 7.1. Security Threats . . . . . . . . . . . . . . . . . . . . . 13 82 7.2. Recommendations . . . . . . . . . . . . . . . . . . . . . 14 83 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 84 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15 85 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 86 10.1. Normative References . . . . . . . . . . . . . . . . . . . 15 87 10.2. Informative References . . . . . . . . . . . . . . . . . . 16 88 Appendix A. Changes from RFC 5006 . . . . . . . . . . . . . . . . 17 90 1. Introduction 92 The purpose of this document is to standardize IPv6 Router 93 Advertisement (RA) option for DNS configuration in IPv6 hosts 94 specified in an earlier experimental specification [RFC5006] and also 95 to define a new RA option for Domain Name Search lists. 97 Neighbor Discovery (ND) for IP Version 6 and IPv6 Stateless Address 98 Autoconfiguration provide ways to configure either fixed or mobile 99 nodes with one or more IPv6 addresses, default routers and some other 100 parameters [RFC4861][RFC4862]. Most Internet services are identified 101 by using a DNS name. The two RA options defined in this document 102 provide the DNS information needed for an IPv6 host to reach Internet 103 services. 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 name server software directly connected to the global DNS. 112 The DNS information can also be provided through DHCP 113 [RFC3315][RFC3736][RFC3646]. However, the access to DNS is a 114 fundamental requirement for almost all hosts, so IPv6 stateless 115 autoconfiguration cannot stand on its own as an alternative 116 deployment model in any practical network without any support for DNS 117 configuration. 119 These issues are not pressing in dual stack networks as long as a DNS 120 server is available on the IPv4 side, but become more critical with 121 the deployment of IPv6-only networks. As a result, this document 122 defines a mechanism based on IPv6 RA options to allow IPv6 hosts to 123 perform the automatic DNS configuration. 125 1.1. Applicability Statements 127 RA-based DNS configuration is a useful alternative in networks where 128 an IPv6 host's address is autoconfigured through IPv6 stateless 129 address autoconfiguration, and where there is either no DHCPv6 130 infrastructure at all or some hosts do not have a DHCPv6 client. The 131 intention is to enable the full configuration of basic networking 132 information for hosts without requiring DHCPv6. However, when in 133 many networks some additional information needs to be distributed, 134 those networks are likely to employ DHCPv6. In these networks RA- 135 based DNS configuration may not be needed. 137 RA-based DNS configuration allows an IPv6 host to acquire the DNS 138 configuration (i.e., DNS recursive server addresses and DNS search 139 list) for the link(s) to which the host is connected. Furthermore, 140 the host learns this DNS configuration from the same RA message that 141 provides configuration information for the link, thereby avoiding 142 also running DHCPv6. 144 The advantages and disadvantages of the RA-based approach are 145 discussed in [RFC4339] along with other approaches, such as the DHCP 146 and well-known anycast addresses approaches. 148 1.2. Coexistence of RA Options and DHCP Options for DNS Configuration 150 Two protocols exist to configure the DNS information on a host, the 151 Router Advertisement options described in this document and the 152 DHCPv6 options described in [RFC3646]. They can be used together. 153 The rules governing the decision to use stateful configuration 154 mechanisms are specified in [RFC4861]. Hosts conforming to this 155 specification MUST extract DNS information from Router Advertisement 156 messages, unless static DNS configuration has been specified by the 157 user. If there is DNS information available from multiple Router 158 Advertisements and/or from DHCP, the host MUST maintain an ordered 159 list of this information as specified in Section 5.3.1. 161 2. Requirements Language 163 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 164 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 165 document are to be interpreted as described in [RFC2119]. 167 3. Terminology 169 This document uses the terminology described in [RFC4861] and 170 [RFC4862]. In addition, four new terms are defined below: 172 o Recursive DNS Server (RDNSS): Server which provides a recursive 173 DNS resolution service for translating domain names into IP 174 addresses as defined in [RFC1034] and [RFC1035]. 176 o RDNSS Option: IPv6 RA option to deliver the RDNSS information to 177 IPv6 hosts [RFC4861]. 179 o DNS Search List (DNSSL): The list of DNS suffix domain names used 180 by IPv6 hosts when they perform DNS query searches for short, 181 unqualified domain names. 183 o DNSSL Option: IPv6 RA option to deliver the DNSSL information to 184 IPv6 hosts. 186 o DNS Repository: Two data structures for managing DNS Configuration 187 Information in the IPv6 protocol stack in addition to Neighbor 188 Cache and Destination Cache for Neighbor Discovery [RFC4861]. The 189 first data structure is the DNS Server List for RDNSS addresses 190 and the second is the DNS Search List for DNS search domain names. 192 o Resolver Repository: Configuration repository with RDNSS addresses 193 and a DNS search list that a DNS resolver on the host uses for DNS 194 name resolution; for example, the Unix resolver file (i.e., /etc/ 195 resolv.conf) and Windows registry. 197 4. Overview 199 This document standardizes the ND option called the RDNSS option 200 defined in [RFC5006] that contains the addresses of recursive DNS 201 servers. This document also defines a new ND option called the DNSSL 202 option for Domain Search List. This is to maintain parity with the 203 DHCPv6 options and to ensure that there is necessary functionality to 204 determine the search domains. 206 The existing ND message (i.e., Router Advertisement) is used to carry 207 this information. An IPv6 host can configure the IPv6 addresses of 208 one or more RDNSSes via RA messages. Through the RDNSS and DNSSL 209 options, along with the prefix information option based on the ND 210 protocol ([RFC4861] and [RFC4862]), an IPv6 host can perform the 211 network configuration of its IPv6 address and the DNS information 212 simultaneously without needing DHCPv6 for the DNS configuration. The 213 RA options for RDNSS and DNSSL can be used on any network that 214 supports the use of ND. 216 This approach requires the manual configuration or other automatic 217 mechanisms (e.g., DHCPv6 or vendor proprietary configuration 218 mechanisms) to configure the DNS information in routers sending the 219 advertisements. The automatic configuration of RDNSS addresses and a 220 DNS search list in routers is out of scope for this document. 222 5. Neighbor Discovery Extension 224 The IPv6 DNS configuration mechanism in this document needs two new 225 ND options in Neighbor Discovery: (i) the Recursive DNS Server 226 (RDNSS) option and (ii) the DNS Search List (DNSSL) option. 228 5.1. Recursive DNS Server Option 230 The RDNSS option contains one or more IPv6 addresses of recursive DNS 231 servers. All of the addresses share the same lifetime value. If it 232 is desirable to have different lifetime values, multiple RDNSS 233 options can be used. Figure 1 shows the format of the RDNSS option. 235 0 1 2 3 236 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 1 237 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 238 | Type | Length | Reserved | 239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 240 | Lifetime | 241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 242 | | 243 : Addresses of IPv6 Recursive DNS Servers : 244 | | 245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 247 Figure 1: Recursive DNS Server (RDNSS) Option Format 249 Fields: 250 Type 8-bit identifier of the RDNSS option type as assigned 251 by the IANA: 25 253 Length 8-bit unsigned integer. The length of the option 254 (including the Type and Length fields) is in units of 255 8 octets. The minimum value is 3 if one IPv6 address 256 is contained in the option. Every additional RDNSS 257 address increases the length by 2. The Length field 258 is used by the receiver to determine the number of 259 IPv6 addresses in the option. 261 Lifetime 32-bit unsigned integer. The maximum time, in 262 seconds (relative to the time the packet is sent), 263 over which this RDNSS address MAY be used for name 264 resolution. Hosts MAY send a Router Solicitation to 265 ensure the RDNSS information is fresh before the 266 interval expires. In order to provide fixed hosts 267 with stable DNS service and allow mobile hosts to 268 prefer local RDNSSes to remote RDNSSes, the value of 269 Lifetime SHOULD be bounded as MaxRtrAdvInterval <= 270 Lifetime <= 2*MaxRtrAdvInterval where 271 MaxRtrAdvInterval is the Maximum RA Interval defined 272 in [RFC4861]. A value of all one bits (0xffffffff) 273 represents infinity. A value of zero means that 274 the RDNSS address MUST no longer be used. 276 Addresses of IPv6 Recursive DNS Servers 277 One or more 128-bit IPv6 addresses of the recursive 278 DNS servers. The number of addresses is determined 279 by the Length field. That is, the number of 280 addresses is equal to (Length - 1) / 2. 282 5.2. DNS Search List Option 284 The DNSSL option contains one or more domain names of DNS suffixes. 285 All of the domain names share the same lifetime value. If it is 286 desirable to have different lifetime values, multiple DNSSL options 287 can be used. Figure 2 shows the format of the DNSSL option. 289 0 1 2 3 290 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 1 291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 | Type | Length | Reserved | 293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 294 | Lifetime | 295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 | | 297 : Domain Names of DNS Search List : 298 | | 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 Figure 2: DNS Search List (DNSSL) Option Format 303 Fields: 304 Type 8-bit identifier of the DNSSL option type as assigned 305 by the IANA: (TBD) 307 Length 8-bit unsigned integer. The length of the option 308 (including the Type and Length fields) is in units of 309 8 octets. The minimum value is 2 if at least one 310 domain name is contained in the option. The Length 311 field is set to a multiple of 8 octets to accommodate 312 all the domain names in the field of Domain Names of 313 DNS Search List. 315 Lifetime 32-bit unsigned integer. The maximum time, in 316 seconds (relative to the time the packet is sent), 317 over which this DNSSL domain name MAY be used for 318 name resolution. The Lifetime value has the same 319 semantics as with RDNSS option. That is, Lifetime 320 SHOULD be bounded as follows: MaxRtrAdvInterval <= 321 Lifetime <= 2*MaxRtrAdvInterval. A value of all one 322 bits (0xffffffff) represents infinity. A value of 323 zero means that the DNSSL domain name MUST no longer 324 be used. 326 Domain Names of DNS Search List 327 One or more domain names of DNS search list that MUST 328 be encoded using the technique described in Section 329 3.1 of [RFC1035]. By this technique, each domain 330 name is represented as a sequence of labels ending in 331 a zero octet, defined as domain name representation. 332 For more than one domain name, the corresponding 333 domain name representations are concatenated as they 334 are. Note that for the simple decoding, the domain 335 names MUST NOT be encoded in a compressed form, as 336 described in Section 4.1.4 of [RFC1035]. Because the 337 size of this field MUST be a multiple of 8 octets, 338 for the minimum multiple including the domain name 339 representations, the remaining octets other than the 340 encoding parts of the domain name representations 341 MUST be padded with zeros. 343 Note: An RDNSS address or a DNSSL domain name MUST be used only as 344 long as both the RA router lifetime (advertised by a Router 345 Advertisement message [RFC4861]) and the corresponding option 346 lifetime have not expired. The reason is that in the current 347 network to which an IPv6 host is connected, the RDNSS may not be 348 currently reachable, that the DNSSL domain name is not valid any 349 more, or that these options do not provide service to the host's 350 current address (e.g., due to network ingress filtering 351 [RFC2827][RFC5358]). 353 5.3. Procedure of DNS Configuration 355 The procedure of DNS configuration through the RDNSS and DNSSL 356 options is the same as with any other ND option [RFC4861]. 358 5.3.1. Procedure in IPv6 Host 360 When an IPv6 host receives DNS options (i.e., RDNSS option and DNSSL 361 option) through RA messages, it processes the options as follows: 363 o The validity of DNS options is checked with the Length field; that 364 is, the value of the Length field in the RDNSS option is greater 365 than or equal to the minimum value (3) and also the value of the 366 Length field in the DNSSL option is greater than or equal to the 367 minimum value (2). 369 o If the DNS options are valid, the host SHOULD copy the values of 370 the options into the DNS Repository and the Resolver Repository in 371 order. Otherwise, the host MUST discard the options. Refer to 372 Section 6 for the detailed procedure. 374 When the IPv6 host has gathered a sufficient number (e.g., three) of 375 RDNSS addresses (or DNS search domain names), it SHOULD maintain 376 RDNSS addresses (or DNS search domain names) by the sufficient number 377 such that the latest received RDNSS or DNSSL is more preferred to the 378 old ones; that is, when the number of RDNSS addresses (or DNS search 379 domain names) is already the sufficient number, the new one replaces 380 the old one that will expire first in terms of Lifetime. As an 381 exceptional case, if the received RDNSS addresses (or DNS search 382 domain names) already exist in the IPv6 host, their Lifetime fields 383 update their expiration time, that is, when the corresponding DNS 384 information expires in the IPv6 host; note that when the Lifetime 385 field has zero, the corresponding RDNSS (or DNS search domain name) 386 is deleted from the IPv6 host. Except for this update, the IPv6 host 387 SHOULD ignore other RDNSS addresses (or DNS search domain names) 388 within an RDNSS (or a DNSSL) option and/or additional RDNSS (or 389 DNSSL) options within an RA. Refer to Section 6 for the detailed 390 procedure. Note that the sufficient number is a system parameter, so 391 it can be determined by a local policy. Also, separate parameters 392 can be specified for the sufficient number of RDNSS addresses and 393 that of DNS search domain names, respectively. In this document, 394 three is RECOMMENDED as a sufficient number considering both the 395 robust DNS query and the reasonably time-bounded recognition of the 396 unreachability of DNS servers. 398 In the case where the DNS options of RDNSS and DNSSL can be obtained 399 from multiple sources, such as RA and DHCP, the IPv6 host SHOULD keep 400 some DNS options from all sources. Unless explicitly specified for 401 the discovery mechanism, the exact number of addresses and domain 402 names to keep is a matter of local policy and implementation choice. 403 However, it is RECOMMENDED that at least three RDNSS addresses (or 404 DNSSL domain names) can be stored from at least two different 405 sources. The DNS options from Router Advertisements and DHCP SHOULD 406 be stored into DNS Repository and Resolver Repository so that 407 information from DHCP appears there first and therefore takes 408 precedence. Thus, the DNS information from DHCP takes precedence 409 over that from RA for DNS queries. On the other hand, for DNS 410 options announced by RA, if some RAs use the Secure Neighbor 411 Discovery (SEND) protocol [RFC3971] for RA security, they MUST be 412 preferred over those which do not use SEND. Refer to Section 7 for 413 the detailed discussion on SEND for RA DNS options. 415 5.3.2. Warnings for DNS Options Configuration 417 There are two warnings for DNS options configuration: (i) warning for 418 multiple sources of DNS options and (ii) warning for multiple network 419 interfaces. First, in the case of multiple sources for DNS options 420 (e.g., RA and DHCP), an IPv6 host can configure its IP addresses from 421 these sources. In this case, it is not possible to control how the 422 host uses DNS information and what source addresses it uses to send 423 DNS queries. As a result, configurations where different information 424 is provided by different sources may lead to problems. Therefore, 425 the network administrator needs to configure DNS options in multiple 426 sources in order to prevent such problems from happening. 428 Second, if different DNS information is provided on different network 429 interfaces, this can lead to inconsistent behavior. The IETF is 430 working on solving this problem for both DNS and other information in 431 Multiple Interfaces (MIF) working group. 433 6. Implementation Considerations 435 Note: This non-normative section gives some hints for implementing 436 the processing of the RDNSS and DNSSL options in an IPv6 host. 438 For the configuration and management of DNS information, the 439 advertised DNS configuration information can be stored and managed in 440 both the DNS Repository and the Resolver Repository. 442 In environments where the DNS information is stored in user space and 443 ND runs in the kernel, it is necessary to synchronize the DNS 444 information (i.e., RDNSS addresses and DNS search domain names) in 445 kernel space and the Resolver Repository in user space. For the 446 synchronization, an implementation where ND works in the kernel 447 should provide a write operation for updating DNS information from 448 the kernel to the Resolver Repository. One simple approach is to 449 have a daemon (or a program that is called at defined intervals) that 450 keeps monitoring the lifetimes of RDNSS addresses and DNS search 451 domain names all the time. Whenever there is an expired entry in the 452 DNS Repository, the daemon can delete the corresponding entry from 453 the Resolver Repository. 455 6.1. DNS Repository Management 457 For DNS repository management, the kernel or user-space process 458 (depending on where RAs are processed) should maintain two data 459 structures: (i) DNS Server List that keeps the list of RDNSS 460 addresses and (ii) DNS Search List that keeps the list of DNS search 461 domain names. Each entry in these two lists consists of a pair of an 462 RDNSS address (or DNSSL domain name) and Expiration-time as follows: 464 o RDNSS address for DNS Server List: IPv6 address of the Recursive 465 DNS Server, which is available for recursive DNS resolution 466 service in the network advertising the RDNSS option. 468 o DNSSL domain name for DNS Search List: DNS suffix domain names, 469 which is used to perform DNS query searches for short, unqualified 470 domain names in the network advertising the DNSSL option. 472 o Expiration-time for DNS Server List or DNS Search List: The time 473 when this entry becomes invalid. Expiration-time is set to the 474 value of the Lifetime field of the RDNSS option or DNSSL option 475 plus the current system time. Whenever a new RDNSS option with 476 the same address (or DNSSL option with the same domain name) is 477 received on the same interface as a previous RDNSS option (or 478 DNSSL option), this field is updated to have a new expiration 479 time. When Expiration-time becomes less than the current system 480 time, this entry is regarded as expired. 482 6.2. Synchronization between DNS Server List and Resolver Repository 484 When an IPv6 host receives the information of multiple RDNSS 485 addresses within a network (e.g., campus network and company network) 486 through an RA message with RDNSS option(s), it stores the RDNSS 487 addresses (in order) into both the DNS Server List and the Resolver 488 Repository. The processing of the RDNSS consists of (i) the 489 processing of RDNSS option(s) included in an RA message and (ii) the 490 handling of expired RDNSSes. The processing of RDNSS option(s) is as 491 follows: 493 Step (a): Receive and parse the RDNSS option(s). For the RDNSS 494 addresses in each RDNSS option, perform Step (b) through Step (d). 496 Step (b): For each RDNSS address, check the following: If the 497 RDNSS address already exists in the DNS Server List and the RDNSS 498 option's Lifetime field is set to zero, delete the corresponding 499 RDNSS entry from both the DNS Server List and the Resolver 500 Repository in order to prevent the RDNSS address from being used 501 any more for certain reasons in network management, e.g., the 502 termination of the RDNSS or a renumbering situation. That is, the 503 RDNSS can resign from its DNS service because the machine running 504 the RDNSS is out of service intentionally or unintentionally. 505 Also, under the renumbering situation, the RDNSS's IPv6 address 506 will be changed, so the previous RDNSS address should not be used 507 any more. The processing of this RDNSS address is finished here. 508 Otherwise, go to Step (c). 510 Step (c): For each RDNSS address, if it already exists in the DNS 511 Server List, then just update the value of the Expiration-time 512 field according to the procedure specified in the third bullet of 513 Section 6.1. Otherwise, go to Step (d). 515 Step (d): For each RDNSS address, if it does not exist in the DNS 516 Server List, register the RDNSS address and lifetime with the DNS 517 Server List and then insert the RDNSS address in front of the 518 Resolver Repository. In the case where the data structure for the 519 DNS Server List is full of RDNSS entries (that is, has more 520 RDNSSes than the sufficient number discussed in Section 5.3.1), 521 delete from the DNS Server List the entry with the shortest 522 expiration time (i.e., the entry that will expire first). The 523 corresponding RDNSS address is also deleted from the Resolver 524 Repository. For the ordering of RDNSS addresses in an RDNSS 525 option, position the first RDNSS address in the RDNSS option as 526 the first one in the Resolver Repository, the second RDNSS address 527 in the option as the second one in the repository, and so on. 528 This ordering allows the RDNSS addresses in the RDNSS option to be 529 preferred according to their order in the RDNSS option for the DNS 530 name resolution. The processing of these RDNSS addresses is 531 finished here. 533 The handling of expired RDNSSes is as follows: Whenever an entry 534 expires in the DNS Server List, the expired entry is deleted from the 535 DNS Server List, and also the RDNSS address corresponding to the 536 entry is deleted from the Resolver Repository. 538 6.3. Synchronization between DNS Search List and Resolver Repository 540 When an IPv6 host receives the information of multiple DNSSL domain 541 names within a network (e.g., campus network and company network) 542 through an RA message with DNSSL option(s), it stores the DNSSL 543 domain names (in order) into both the DNS Search List and the 544 Resolver Repository. The processing of the DNSSL consists of (i) the 545 processing of DNSSL option(s) included in an RA message and (ii) the 546 handling of expired DNSSLs. The processing of DNSSL option(s) is as 547 follows: 549 Step (a): Receive and parse the DNSSL option(s). For the DNSSL 550 domain names in each DNSSL option, perform Step (b) through Step 551 (d). 553 Step (b): For each DNSSL domain name, check the following: If the 554 DNSSL domain name already exists in the DNS Search List and the 555 DNSSL option's Lifetime field is set to zero, delete the 556 corresponding DNSSL entry from both the DNS Search List and the 557 Resolver Repository in order to prevent the DNSSL domain name from 558 being used any more for certain reasons in network management, 559 e.g., the termination of the RDNSS or a renaming situation. That 560 is, the RDNSS can resign from its DNS service because the machine 561 running the RDNSS is out of service intentionally or 562 unintentionally. Also, under the renaming situation, the DNSSL 563 domain names will be changed, so the previous domain names should 564 not be used any more. The processing of this DNSSL domain name is 565 finished here. Otherwise, go to Step (c). 567 Step (c): For each DNSSL domain name, if it already exists in the 568 DNS Server List, then just update the value of the Expiration-time 569 field according to the procedure specified in the third bullet of 570 Section 6.1. Otherwise, go to Step (d). 572 Step (d): For each DNSSL domain name, if it does not exist in the 573 DNS Search List, register the DNSSL domain name and lifetime with 574 the DNS Search List and then insert the DNSSL domain name in front 575 of the Resolver Repository. In the case where the data structure 576 for the DNS Search List is full of DNSSL domain name entries (that 577 is, has more DNSSL domain names than the sufficient number 578 discussed in Section 5.3.1), delete from the DNS Server List the 579 entry with the shortest expiration time (i.e., the entry that will 580 expire first). The corresponding DNSSL domain name is also 581 deleted from the Resolver Repository. For the ordering of DNSSL 582 domain names in a DNSSL option, position the first DNSSL domain 583 name in the DNSSL option as the first one in the Resolver 584 Repository, the second DNSSL domain name in the option as the 585 second one in the repository, and so on. This ordering allows the 586 DNSSL domain names in the DNSSL option to be preferred according 587 to their order in the DNSSL option for the DNS domain name used by 588 the DNS query. The processing of these DNSSL domain name is 589 finished here. 591 The handling of expired DNSSLs is as follows: Whenever an entry 592 expires in the DNS Search List, the expired entry is deleted from 593 the DNS Search List, and also the DNSSL domain name corresponding 594 to the entry is deleted from the Resolver Repository. 596 7. Security Considerations 598 In this section, we analyze security threats related to DNS options 599 and then suggest recommendations to cope with such security threats. 601 7.1. Security Threats 603 For RDNSS option, an attacker could send an RA with a fraudulent 604 RDNSS address, misleading IPv6 hosts into contacting an unintended 605 DNS server for DNS name resolution. Also, for DNSSL option, an 606 attacker can let IPv6 hosts resolve a host name without DNS suffix 607 into an unintended host's IP address with a fraudulent DNS search 608 list. 610 These attacks are similar to Neighbor Discovery attacks that use 611 Redirect or Neighbor Advertisement messages to redirect traffic to 612 individual addresses of malicious parties. That is, as a rogue 613 router, a malicious node on a LAN can promiscuously receive packets 614 for any router's MAC address and send packets with the router's MAC 615 address as the source MAC address in the L2 header. As a result, L2 616 switches send packets addressed to the router to the malicious node. 617 Also, this attack can send redirects that tell the hosts to send 618 their traffic somewhere else. The malicious node can send 619 unsolicited RA or Neighbor Advertisement (NA) replies, answer RS or 620 Neighbor Solicitation (NS) requests, etc. Thus, the attacks related 621 to RDNSS and DNSSL are similar to both Neighbor Discovery attacks and 622 attacks against unauthenticated DHCP, as both can be used for both 623 "wholesale" traffic redirection and more specific attacks. 625 However, the security of these RA options for DNS configuration does 626 not affect ND protocol security [RFC4861]. This is because learning 627 DNS information via the RA options cannot be worse than learning bad 628 router information via the RA options. Therefore, the vulnerability 629 of ND is not worse and is a subset of the attacks that any node 630 attached to a LAN can do independently of ND. 632 7.2. Recommendations 634 The Secure Neighbor Discovery (SEND) protocol [RFC3971] is used as a 635 security mechanism for ND. It is RECOMMENDED that ND use SEND to 636 allow all the ND options including the RDNSS and DNSSL options to be 637 automatically included in the signatures. Through SEND, the 638 transport for the RA options is integrity-protected; that is, SEND 639 can prevent the spoofing of these DNS options with signatures. Also, 640 SEND enables an IPv6 host to verify that the sender of an RA is 641 actually a router authorized to act as a router. However, since any 642 valid SEND router can still insert RDNSS and DNSSL options, the 643 current SEND cannot verify which one is or is not authorized to send 644 the options. Thus, this verification of the authorized routers for 645 ND options will be required. [ID-csi-send-cert] specifies the usage 646 of extended key for the certificate deployed in SEND. This document 647 defines the roles of routers (i.e., routers acting as proxy and 648 address owner) and explains the authorization of the roles. The 649 mechanism in this document can be extended to verify which routers 650 are authorized to insert RDNSS and DNSSL options. 652 It is common for network devices such as switches to include 653 mechanisms to block unauthorized ports from running a DHCPv6 server 654 to provide protection from rogue DHCP servers. That means that an 655 attacker on other ports cannot insert bogus DNS servers using DHCPv6. 656 The corresponding technique for network devices is RECOMMENDED to 657 block rogue Router Advertisement messages including the RDNSS and 658 DNSSL options from unauthorized nodes. 660 An attacker may provide a bogus DNS Search List option in order to 661 cause the victim to send DNS queries to a specific DNS server when 662 the victim queries non-fully qualified domain names. For this 663 attack, the DNS resolver in IPv6 hosts can mitigate the vulnerability 664 with the recommendations mentioned in [RFC1535], [RFC1536], and 665 [RFC3646]. 667 8. IANA Considerations 669 The RDNSS option defined in this document is using the IPv6 Neighbor 670 Discovery Option type in RFC 5006 [RFC5006] assigned by the IANA as 671 follows: 673 Option Name Type 674 RDNSS option 25 676 The IANA is requested to assign a new IPv6 Neighbor Discovery Option 677 type for the DNSSL option defined in this document: 679 Option Name Type 680 DNSSL option (TBD) 682 The IANA registry for these options is: 684 http://www.iana.org/assignments/icmpv6-parameters 686 9. Acknowledgements 688 This document has greatly benefited from inputs by Robert Hinden, 689 Pekka Savola, Iljitsch van Beijnum, Brian Haberman, Tim Chown, Erik 690 Nordmark, Dan Wing, Jari Arkko, Ben Campbell, Vincent Roca, and Tony 691 Cheneau. The authors sincerely appreciate their contributions. 693 10. References 695 10.1. Normative References 697 [RFC2119] Bradner, S., "Key words for use in RFCs to 698 Indicate Requirement Levels", BCP 14, RFC 2119, 699 March 1997. 701 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. 702 Soliman, "Neighbor Discovery for IP Version 6 703 (IPv6)", RFC 4861, September 2007. 705 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 706 Stateless Address Autoconfiguration", RFC 4862, 707 September 2007. 709 [RFC1035] Mockapetris, P., "Domain Names - Implementation 710 and Specification", RFC 1035, November 1987. 712 10.2. Informative References 714 [RFC1034] Mockapetris, P., "Domain Names - Concepts and 715 Facilities", RFC 1034, November 1987. 717 [RFC3315] Droms, R., Ed., "Dynamic Host Configuration 718 Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. 720 [RFC3736] Droms, R., "Stateless Dynamic Host Configuration 721 Protocol (DHCP) Service for IPv6", RFC 3736, 722 April 2004. 724 [RFC3646] Droms, R., Ed., "DNS Configuration options for 725 Dynamic Host Configuration Protocol for IPv6 726 (DHCPv6)", RFC 3646, December 2003. 728 [RFC5006] Jeong, J., Park, S., Beloeil, L., and S. 729 Madanapalli, "IPv6 Router Advertisement Option 730 for DNS Configuration", RFC 5006, September 2007. 732 [RFC4339] Jeong, J., Ed., "IPv6 Host Configuration of DNS 733 Server Information Approaches", RFC 4339, 734 February 2006. 736 [RFC3971] Arkko, J., Ed., "SEcure Neighbor Discovery 737 (SEND)", RFC 3971, March 2005. 739 [RFC5358] Damas, J. and F. Neves, "Preventing Use of 740 Recursive Nameservers in Reflector Attacks", 741 BCP 140, RFC 5358, October 2008. 743 [RFC2827] Ferguson, P. and D. Senie, "Network Ingress 744 Filtering: Defeating Denial of Service Attacks 745 which employ IP Source Address Spoofing", BCP 38, 746 RFC 2827, May 2000. 748 [RFC1535] Gavron, E., "A Security Problem and Proposed 749 Correction With Widely Deployed DNS Software", 750 RFC 1535, October 1993. 752 [RFC1536] Kumar, A., Postel, J., Neuman, C., Danzig, P., 753 and S. Miller, "Common DNS Implementation Errors 754 and Suggested Fixes", RFC 1536, October 1993. 756 [ID-csi-send-cert] Gagliano, R., Krishnan, S., and A. Kukec, 757 "Certificate profile and certificate management 758 for SEND", Work in Progress, June 2010. 760 Appendix A. Changes from RFC 5006 762 The following changes were made from RFC 5006 "IPv6 Router 763 Advertisement Option for DNS Configuration": 765 o Added DNS Search List (DNSSL) Option to support the advertisement 766 of DNS suffixes used in the DNS search along with RDNSS Option in 767 RFC 5006. 769 o Clarified the coexistence of RA options and DHCP options for DNS 770 configuration. 772 o Modified the procedure in IPv6 host: 774 * Clarified the procedure for DNS options in an IPv6 host. 776 * Specified a sufficient number of RDNSS addresses or DNS search 777 domain names as three. 779 * Specified a way to deal with DNS options from multiple sources, 780 such as RA and DHCP. 782 o Modified implementation considerations for DNSSL Option handling. 784 o Modified security considerations to consider more attack scenarios 785 and the corresponding possible solutions. 787 o Modified IANA considerations to require another IPv6 Neighbor 788 Discovery Option type for DNSSL option. 790 Authors' Addresses 792 Jaehoon Paul Jeong 793 Brocade Communications Systems/ETRI 794 6000 Nathan Ln N 795 Plymouth, MN 55442 796 USA 798 Phone: +1 763 268 7173 799 Fax: +1 763 268 6800 800 EMail: pjeong@brocade.com 801 URI: http://www.cs.umn.edu/~jjeong/ 802 Soohong Daniel Park 803 Mobile Platform Laboratory 804 SAMSUNG Electronics 805 416 Maetan-3dong, Yeongtong-Gu 806 Suwon, Gyeonggi-Do 443-742 807 Korea 809 Phone: +82 31 200 4508 810 EMail: soohong.park@samsung.com 812 Luc Beloeil 813 France Telecom R&D 814 42, rue des coutures 815 BP 6243 816 14066 CAEN Cedex 4 817 France 819 Phone: +33 2 40 44 97 40 820 EMail: luc.beloeil@orange-ftgroup.com 822 Syam Madanapalli 823 Ordyn Technologies 824 1st Floor, Creator Building, ITPL 825 Bangalore - 560066 826 India 828 Phone: +91-80-40383000 829 EMail: smadanapalli@gmail.com