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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 1, 2011 L. Beloeil 7 France Telecom R&D 8 S. Madanapalli 9 Ordyn Technologies 10 June 30, 2010 12 IPv6 Router Advertisement Options for DNS Configuration 13 draft-ietf-6man-dns-options-bis-05 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 1, 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 6. Implementation Considerations . . . . . . . . . . . . . . . . 9 74 6.1. DNS Repository Management . . . . . . . . . . . . . . . . 10 75 6.2. Synchronization between DNS Server List and Resolver 76 Repository . . . . . . . . . . . . . . . . . . . . . . . . 10 77 6.3. Synchronization between DNS Search List and Resolver 78 Repository . . . . . . . . . . . . . . . . . . . . . . . . 12 79 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 80 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 81 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 82 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 83 10.1. Normative References . . . . . . . . . . . . . . . . . . . 14 84 10.2. Informative References . . . . . . . . . . . . . . . . . . 15 85 Appendix A. Changes from RFC 5006 . . . . . . . . . . . . . . . . 15 87 1. Introduction 89 The purpose of this document is to standardize IPv6 Router 90 Advertisement (RA) option for DNS configuration in IPv6 hosts 91 specified in an earlier experimental specification [RFC5006] and also 92 to define a new RA option for Domain Name Search lists. 94 Neighbor Discovery (ND) for IP Version 6 and IPv6 Stateless Address 95 Autoconfiguration provide ways to configure either fixed or mobile 96 nodes with one or more IPv6 addresses, default routers and some other 97 parameters [RFC4861][RFC4862]. Most Internet services are identified 98 by using a DNS name. The two RA options defined in this document 99 provide the DNS information needed for an IPv6 host to reach Internet 100 services. 102 It is infeasible to manually configure nomadic hosts each time they 103 connect to a different network. While a one-time static 104 configuration is possible, it is generally not desirable on general- 105 purpose hosts such as laptops. For instance, locally defined name 106 spaces would not be available to the host if it were to run its own 107 name server software directly connected to the global DNS. 109 The DNS information can also be provided through DHCP 110 [RFC3315][RFC3736][RFC3646]. However, the access to DNS is a 111 fundamental requirement for almost all hosts, so IPv6 stateless 112 autoconfiguration cannot stand on its own as an alternative 113 deployment model in any practical network without any support for DNS 114 configuration. 116 These issues are not pressing in dual stack networks as long as a DNS 117 server is available on the IPv4 side, but become more critical with 118 the deployment of IPv6-only networks. As a result, this document 119 defines a mechanism based on IPv6 RA options to allow IPv6 hosts to 120 perform the automatic DNS configuration. 122 1.1. Applicability Statements 124 RA-based DNS configuration is a useful alternative in networks where 125 an IPv6 host's address is autoconfigured through IPv6 stateless 126 address autoconfiguration, and where there is either no DHCPv6 127 infrastructure at all or some hosts do not have a DHCPv6 client. The 128 intention is to enable the full configuration of basic networking 129 information for hosts without requiring DHCPv6. However, when in 130 many networks some additional information needs to be distributed, 131 those networks are likely to employ DHCPv6. In these networks RA- 132 based DNS configuration may not be needed. 134 RA-based DNS configuration allows an IPv6 host to acquire the DNS 135 configuration (i.e., DNS recursive server addresses and DNS search 136 list) for the link(s) to which the host is connected. Furthermore, 137 the host learns this DNS configuration from the same RA message that 138 provides configuration information for the link, thereby avoiding 139 also running DHCPv6. 141 The advantages and disadvantages of the RA-based approach are 142 discussed in [RFC4339] along with other approaches, such as the DHCP 143 and well-known anycast addresses approaches. 145 1.2. Coexistence of RA Options and DHCP Options for DNS Configuration 147 Two protocols exist to configure the DNS information on a host, the 148 Router Advertisement options described in this document and the 149 DHCPv6 options described in [RFC3646]. They can be used together. 150 The rules governing the decision to use stateful configuration 151 mechanisms are specified in [RFC4861]. Hosts conforming to this 152 specification MUST extract DNS information from Router Advertisement 153 messages, unless static DNS configuration has been specified by the 154 user. If there is DNS information available from multiple Router 155 Advertisements and/or from DHCP, the host MUST maintain an ordered 156 list of this information as specified in Section 5.3.1. 158 2. Requirements Language 160 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 161 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 162 document are to be interpreted as described in [RFC2119]. 164 3. Terminology 166 This document uses the terminology described in [RFC4861] and 167 [RFC4862]. In addition, four new terms are defined below: 169 o Recursive DNS Server (RDNSS): Server which provides a recursive 170 DNS resolution service for translating domain names into IP 171 addresses as defined in [RFC1034] and [RFC1035]. 173 o RDNSS Option: IPv6 RA option to deliver the RDNSS information to 174 IPv6 hosts [RFC4861]. 176 o DNS Search List (DNSSL): The list of DNS suffix domain names used 177 by IPv6 hosts when they perform DNS query searches for short, 178 unqualified domain names. 180 o DNSSL Option: IPv6 RA option to deliver the DNSSL information to 181 IPv6 hosts. 183 o DNS Repository: Two data structures for managing DNS Configuration 184 Information in the IPv6 protocol stack in addition to Neighbor 185 Cache and Destination Cache for Neighbor Discovery [RFC4861]. The 186 first data structure is the DNS Server List for RDNSS addresses 187 and the second is the DNS Search List for DNS search domain names. 189 o Resolver Repository: Configuration repository with RDNSS addresses 190 and a DNS search list that a DNS resolver on the host uses for DNS 191 name resolution; for example, the Unix resolver file (i.e., /etc/ 192 resolv.conf) and Windows registry. 194 4. Overview 196 This document standardizes the ND option called the RDNSS option 197 defined in [RFC5006] that contains the addresses of recursive DNS 198 servers. This document also defines a new ND option called the DNSSL 199 option for Domain Search List. This is to maintain parity with the 200 DHCPv6 options and to ensure that there is necessary functionality to 201 determine the search domains. 203 The existing ND message (i.e., Router Advertisement) is used to carry 204 this information. An IPv6 host can configure the IPv6 addresses of 205 one or more RDNSSes via RA messages. Through the RDNSS and DNSSL 206 options, along with the prefix information option based on the ND 207 protocol ([RFC4861] and [RFC4862]), an IPv6 host can perform the 208 network configuration of its IPv6 address and the DNS information 209 simultaneously without needing DHCPv6 for the DNS configuration. The 210 RA options for RDNSS and DNSSL can be used on any network that 211 supports the use of ND. 213 This approach requires the manual configuration or other automatic 214 mechanisms (e.g., DHCPv6 or vendor proprietary configuration 215 mechanisms) to configure the DNS information in routers sending the 216 advertisements. The automatic configuration of RDNSS addresses and a 217 DNS search list in routers is out of scope for this document. 219 5. Neighbor Discovery Extension 221 The IPv6 DNS configuration mechanism in this document needs two new 222 ND options in Neighbor Discovery: (i) the Recursive DNS Server 223 (RDNSS) option and (ii) the DNS Search List (DNSSL) option. 225 5.1. Recursive DNS Server Option 227 The RDNSS option contains one or more IPv6 addresses of recursive DNS 228 servers. All of the addresses share the same lifetime value. If it 229 is desirable to have different lifetime values, multiple RDNSS 230 options can be used. Figure 1 shows the format of the RDNSS option. 232 0 1 2 3 233 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 1 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 235 | Type | Length | Reserved | 236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 237 | Lifetime | 238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 239 | | 240 : Addresses of IPv6 Recursive DNS Servers : 241 | | 242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 Figure 1: Recursive DNS Server (RDNSS) Option Format 246 Fields: 247 Type 8-bit identifier of the RDNSS option type as assigned 248 by the IANA: 25 250 Length 8-bit unsigned integer. The length of the option 251 (including the Type and Length fields) is in units of 252 8 octets. The minimum value is 3 if one IPv6 address 253 is contained in the option. Every additional RDNSS 254 address increases the length by 2. The Length field 255 is used by the receiver to determine the number of 256 IPv6 addresses in the option. 258 Lifetime 32-bit unsigned integer. The maximum time, in 259 seconds (relative to the time the packet is sent), 260 over which this RDNSS address MAY be used for name 261 resolution. Hosts MAY send a Router Solicitation to 262 ensure the RDNSS information is fresh before the 263 interval expires. In order to provide fixed hosts 264 with stable DNS service and allow mobile hosts to 265 prefer local RDNSSes to remote RDNSSes, the value of 266 Lifetime SHOULD be bounded as MaxRtrAdvInterval <= 267 Lifetime <= 2*MaxRtrAdvInterval where 268 MaxRtrAdvInterval is the Maximum RA Interval defined 269 in [RFC4861]. A value of all one bits (0xffffffff) 270 represents infinity. A value of zero means that 271 the RDNSS address MUST no longer be used. 273 Addresses of IPv6 Recursive DNS Servers 274 One or more 128-bit IPv6 addresses of the recursive 275 DNS servers. The number of addresses is determined 276 by the Length field. That is, the number of 277 addresses is equal to (Length - 1) / 2. 279 5.2. DNS Search List Option 281 The DNSSL option contains one or more domain names of DNS suffixes. 282 All of the domain names share the same lifetime value. If it is 283 desirable to have different lifetime values, multiple DNSSL options 284 can be used. Figure 2 shows the format of the DNSSL option. 286 0 1 2 3 287 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 1 288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 289 | Type | Length | Reserved | 290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 291 | Lifetime | 292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 293 | | 294 : Domain Names of DNS Search List : 295 | | 296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 298 Figure 2: DNS Search List (DNSSL) Option Format 300 Fields: 301 Type 8-bit identifier of the DNSSL option type as assigned 302 by the IANA: (TBD) 304 Length 8-bit unsigned integer. The length of the option 305 (including the Type and Length fields) is in units of 306 8 octets. The minimum value is 2 if at least one 307 domain name is contained in the option. The Length 308 field is set to a multiple of 8 octets to accommodate 309 all the domain names in the field of Domain Names of 310 DNS Search List. 312 Lifetime 32-bit unsigned integer. The maximum time, in 313 seconds (relative to the time the packet is sent), 314 over which this DNSSL domain name MAY be used for 315 name resolution. The Lifetime value has the same 316 semantics as with RDNSS option. That is, Lifetime 317 SHOULD be bounded as follows: MaxRtrAdvInterval <= 318 Lifetime <= 2*MaxRtrAdvInterval. A value of all one 319 bits (0xffffffff) represents infinity. A value of 320 zero means that the DNSSL domain name MUST no longer 321 be used. 323 Domain Names of DNS Search List 324 One or more domain names of DNS search list that MUST 325 be encoded using the technique described in Section 326 3.1 of [RFC1035]. By this technique, each domain 327 name is represented as a sequence of labels ending in 328 a zero octet, defined as domain name representation. 329 For more than one domain name, the corresponding 330 domain name representations are concatenated as they 331 are. Note that for the simple decoding, the domain 332 names MUST NOT be encoded in a compressed form, as 333 described in Section 4.1.4 of [RFC1035]. Because the 334 size of this field MUST be a multiple of 8 octets, 335 for the minimum multiple including the domain name 336 representations, the remaining octets other than the 337 encoding parts of the domain name representations 338 MUST be padded with zeros. 340 Note: An RDNSS address or a DNSSL domain name MUST be used only as 341 long as both the RA router lifetime (advertised by a Router 342 Advertisement message [RFC4861]) and the corresponding option 343 lifetime have not expired. The reason is that in the current 344 network to which an IPv6 host is connected, the RDNSS may not be 345 currently reachable, that the DNSSL domain name is not valid any 346 more, or that these options do not provide service to the host's 347 current address (e.g., due to network ingress filtering 348 [RFC2827][RFC5358]). 350 5.3. Procedure of DNS Configuration 352 The procedure of DNS configuration through the RDNSS and DNSSL 353 options is the same as with any other ND option [RFC4861]. 355 5.3.1. Procedure in IPv6 Host 357 When an IPv6 host receives DNS options (i.e., RDNSS option and DNSSL 358 option) through RA messages, it processes the options as follows: 360 o The validity of DNS options is checked with the Length field; that 361 is, the value of the Length field in the RDNSS option is greater 362 than or equal to the minimum value (3) and also the value of the 363 Length field in the DNSSL option is greater than or equal to the 364 minimum value (2). 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 When the IPv6 host has gathered a sufficient number (e.g., three) of 372 RDNSS addresses (or DNS search domain names), it SHOULD maintain 373 RDNSS addresses (or DNS search domain names) by the sufficient number 374 such that the latest received RDNSS or DNSSL is more preferred to the 375 old ones; that is, when the number of RDNSS addresses (or DNS search 376 domain names) is already the sufficient number, the new one replaces 377 the old one that will expire first in terms of Lifetime. As an 378 exceptional case, if the received RDNSS addresses (or DNS search 379 domain names) already exist in the IPv6 host, their Lifetime fields 380 update their expiration time, that is, when the corresponding DNS 381 information expires in the IPv6 host; note that when the Lifetime 382 field has zero, the corresponding RDNSS (or DNS search domain name) 383 is deleted from the IPv6 host. Except for this update, the IPv6 host 384 SHOULD ignore other RDNSS addresses (or DNS search domain names) 385 within an RDNSS (or a DNSSL) option and/or additional RDNSS (or 386 DNSSL) options within an RA. Refer to Section 6 for the detailed 387 procedure. Note that the sufficient number is a system parameter, so 388 it can be determined by a local policy. Also, separate parameters 389 can be specified for the sufficient number of RDNSS addresses and 390 that of DNS search domain names, respectively. In this document, 391 three is RECOMMENDED as a sufficient number considering both the 392 robust DNS query and the reasonably time-bounded recognition of the 393 unreachability of DNS servers. 395 In the case where the DNS options of RDNSS and DNSSL can be obtained 396 from multiple sources, such as RA and DHCP, the IPv6 host SHOULD keep 397 some DNS options from all sources. Unless explicitly specified for 398 the discovery mechanism, the exact number of addresses and domain 399 names to keep is a matter of local policy and implementation choice. 400 However, it is RECOMMENDED that at least three RDNSS addresses (or 401 DNSSL domain names) can be stored from at least two different 402 sources. The DNS options from Router Advertisements and DHCP SHOULD 403 be stored into DNS Repository and Resolver Repository so that 404 information from DHCP appears there first and therefore takes 405 precedence. 407 6. Implementation Considerations 409 Note: This non-normative section gives some hints for implementing 410 the processing of the RDNSS and DNSSL options in an IPv6 host. 412 For the configuration and management of DNS information, the 413 advertised DNS configuration information can be stored and managed in 414 both the DNS Repository and the Resolver Repository. 416 In environments where the DNS information is stored in user space and 417 ND runs in the kernel, it is necessary to synchronize the DNS 418 information (i.e., RDNSS addresses and DNS search domain names) in 419 kernel space and the Resolver Repository in user space. For the 420 synchronization, an implementation where ND works in the kernel 421 should provide a write operation for updating DNS information from 422 the kernel to the Resolver Repository. One simple approach is to 423 have a daemon (or a program that is called at defined intervals) that 424 keeps monitoring the lifetimes of RDNSS addresses and DNS search 425 domain names all the time. Whenever there is an expired entry in the 426 DNS Repository, the daemon can delete the corresponding entry from 427 the Resolver Repository. 429 6.1. DNS Repository Management 431 For DNS repository management, the kernel or user-space process 432 (depending on where RAs are processed) should maintain two data 433 structures: (i) DNS Server List that keeps the list of RDNSS 434 addresses and (ii) DNS Search List that keeps the list of DNS search 435 domain names. Each entry in these two lists consists of a pair of an 436 RDNSS address (or DNSSL domain name) and Expiration-time as follows: 438 o RDNSS address for DNS Server List: IPv6 address of the Recursive 439 DNS Server, which is available for recursive DNS resolution 440 service in the network advertising the RDNSS option. 442 o DNSSL domain name for DNS Search List: DNS suffix domain names, 443 which is used to perform DNS query searches for short, unqualified 444 domain names in the network advertising the DNSSL option. 446 o Expiration-time for DNS Server List or DNS Search List: The time 447 when this entry becomes invalid. Expiration-time is set to the 448 value of the Lifetime field of the RDNSS option or DNSSL option 449 plus the current system time. Whenever a new RDNSS option with 450 the same address (or DNSSL option with the same domain name) is 451 received on the same interface as a previous RDNSS option (or 452 DNSSL option), this field is updated to have a new expiration 453 time. When Expiration-time becomes less than the current system 454 time, this entry is regarded as expired. 456 6.2. Synchronization between DNS Server List and Resolver Repository 458 When an IPv6 host receives the information of multiple RDNSS 459 addresses within a network (e.g., campus network and company network) 460 through an RA message with RDNSS option(s), it stores the RDNSS 461 addresses (in order) into both the DNS Server List and the Resolver 462 Repository. The processing of the RDNSS consists of (i) the 463 processing of RDNSS option(s) included in an RA message and (ii) the 464 handling of expired RDNSSes. The processing of RDNSS option(s) is as 465 follows: 467 Step (a): Receive and parse the RDNSS option(s). For the RDNSS 468 addresses in each RDNSS option, perform Step (b) through Step (d). 470 Step (b): For each RDNSS address, check the following: If the 471 RDNSS address already exists in the DNS Server List and the RDNSS 472 option's Lifetime field is set to zero, delete the corresponding 473 RDNSS entry from both the DNS Server List and the Resolver 474 Repository in order to prevent the RDNSS address from being used 475 any more for certain reasons in network management, e.g., the 476 termination of the RDNSS or a renumbering situation. That is, the 477 RDNSS can resign from its DNS service because the machine running 478 the RDNSS is out of service intentionally or unintentionally. 479 Also, under the renumbering situation, the RDNSS's IPv6 address 480 will be changed, so the previous RDNSS address should not be used 481 any more. The processing of this RDNSS address is finished here. 482 Otherwise, go to Step (c). 484 Step (c): For each RDNSS address, if it already exists in the DNS 485 Server List, then just update the value of the Expiration-time 486 field according to the procedure specified in the third bullet of 487 Section 6.1. Otherwise, go to Step (d). 489 Step (d): For each RDNSS address, if it does not exist in the DNS 490 Server List, register the RDNSS address and lifetime with the DNS 491 Server List and then insert the RDNSS address in front of the 492 Resolver Repository. In the case where the data structure for the 493 DNS Server List is full of RDNSS entries (that is, has more 494 RDNSSes than the sufficient number discussed in Section 5.3.1), 495 delete from the DNS Server List the entry with the shortest 496 expiration time (i.e., the entry that will expire first). The 497 corresponding RDNSS address is also deleted from the Resolver 498 Repository. For the ordering of RDNSS addresses in an RDNSS 499 option, position the first RDNSS address in the RDNSS option as 500 the first one in the Resolver Repository, the second RDNSS address 501 in the option as the second one in the repository, and so on. 502 This ordering allows the RDNSS addresses in the RDNSS option to be 503 preferred according to their order in the RDNSS option for the DNS 504 name resolution. The processing of these RDNSS addresses is 505 finished here. 507 The handling of expired RDNSSes is as follows: Whenever an entry 508 expires in the DNS Server List, the expired entry is deleted from the 509 DNS Server List, and also the RDNSS address corresponding to the 510 entry is deleted from the Resolver Repository. 512 6.3. Synchronization between DNS Search List and Resolver Repository 514 When an IPv6 host receives the information of multiple DNSSL domain 515 names within a network (e.g., campus network and company network) 516 through an RA message with DNSSL option(s), it stores the DNSSL 517 domain names (in order) into both the DNS Search List and the 518 Resolver Repository. The processing of the DNSSL consists of (i) the 519 processing of DNSSL option(s) included in an RA message and (ii) the 520 handling of expired DNSSLs. The processing of DNSSL option(s) is as 521 follows: 523 Step (a): Receive and parse the DNSSL option(s). For the DNSSL 524 domain names in each DNSSL option, perform Step (b) through Step 525 (d). 527 Step (b): For each DNSSL domain name, check the following: If the 528 DNSSL domain name already exists in the DNS Search List and the 529 DNSSL option's Lifetime field is set to zero, delete the 530 corresponding DNSSL entry from both the DNS Search List and the 531 Resolver Repository in order to prevent the DNSSL domain name from 532 being used any more for certain reasons in network management, 533 e.g., the termination of the RDNSS or a renaming situation. That 534 is, the RDNSS can resign from its DNS service because the machine 535 running the RDNSS is out of service intentionally or 536 unintentionally. Also, under the renaming situation, the DNSSL 537 domain names will be changed, so the previous domain names should 538 not be used any more. The processing of this DNSSL domain name is 539 finished here. Otherwise, go to Step (c). 541 Step (c): For each DNSSL domain name, if it already exists in the 542 DNS Server List, then just update the value of the Expiration-time 543 field according to the procedure specified in the third bullet of 544 Section 6.1. Otherwise, go to Step (d). 546 Step (d): For each DNSSL domain name, if it does not exist in the 547 DNS Search List, register the DNSSL domain name and lifetime with 548 the DNS Search List and then insert the DNSSL domain name in front 549 of the Resolver Repository. In the case where the data structure 550 for the DNS Search List is full of DNSSL domain name entries (that 551 is, has more DNSSL domain names than the sufficient number 552 discussed in Section 5.3.1), delete from the DNS Server List the 553 entry with the shortest expiration time (i.e., the entry that will 554 expire first). The corresponding DNSSL domain name is also 555 deleted from the Resolver Repository. For the ordering of DNSSL 556 domain names in a DNSSL option, position the first DNSSL domain 557 name in the DNSSL option as the first one in the Resolver 558 Repository, the second DNSSL domain name in the option as the 559 second one in the repository, and so on. This ordering allows the 560 DNSSL domain names in the DNSSL option to be preferred according 561 to their order in the DNSSL option for the DNS domain name used by 562 the DNS query. The processing of these DNSSL domain name is 563 finished here. 565 The handling of expired DNSSLs is as follows: Whenever an entry 566 expires in the DNS Search List, the expired entry is deleted from 567 the DNS Search List, and also the DNSSL domain name corresponding 568 to the entry is deleted from the Resolver Repository. 570 7. Security Considerations 572 The security of the RA options for DNS configuration does not affect 573 ND protocol security [RFC4861]. This is because learning DNS 574 information via the RA options cannot be worse than learning bad 575 router information via the RA options. Thus, the vulnerability of ND 576 is not worse and is a subset of the attacks that any node attached to 577 a LAN can do independently of ND. A malicious node on a LAN can 578 promiscuously receive packets for any router's MAC address and send 579 packets with the router's MAC address as the source MAC address in 580 the L2 header. As a result, L2 switches send packets addressed to 581 the router to the malicious node. Also, this attack can send 582 redirects that tell the hosts to send their traffic somewhere else. 583 The malicious node can send unsolicited RA or Neighbor Advertisement 584 (NA) replies, answer RS or Neighbor Solicitation (NS) requests, etc. 585 Also, an attacker could send an RA with a fraudulent RDNSS address, 586 which is presumably an easier avenue of attack than becoming a rogue 587 router and having to process all traffic for the subnet. This attack 588 is similar to Neighbor Discovery attacks that use Redirect or 589 Neighbor Advertisement messages to redirect traffic to individual 590 addresses to malicious parties. In general, the attacks related to 591 RDNSS and DNSSL are similar to both Neighbor Discovery attacks and 592 attacks against unauthenticated DHCP, as both can be used for both 593 "wholesale" traffic redirection and more specific attacks. 595 It is common for network devices such as switches to include 596 mechanisms to block unauthorized ports from running a DHCPv6 server 597 to provide protection from rogue DHCP servers. That means that an 598 attacker on other ports cannot insert bogus DNS servers using DHCPv6. 599 The corresponding technique for network devices is recommended to 600 block rogue Router Advertisement messages including the RDNSS and 601 DNSSL options from unauthorized nodes. 603 An attacker may provide a bogus DNS Search List option in order to 604 cause the victim to send DNS queries to a specific DNS server when 605 the victim queries non-fully qualified domain names. For this 606 attack, the DNS resolver in IPv6 hosts can mitigate the vulnerability 607 with the recommendations in [RFC1535], [RFC1536], and [RFC3646]. 609 If the Secure Neighbor Discovery (SEND) protocol is used as a 610 security mechanism for ND, all the ND options including the RDNSS and 611 DNSSL options are automatically included in the signatures [RFC3971], 612 so the transport for the RA options is integrity-protected. However, 613 since any valid SEND router can still insert RDNSS and DNSSL options, 614 SEND cannot verify which one is or is not authorized to send the 615 options. 617 8. IANA Considerations 619 The RDNSS option defined in this document is using the IPv6 Neighbor 620 Discovery Option type in RFC 5006 [RFC5006] assigned by the IANA as 621 follows: 623 Option Name Type 624 RDNSS option 25 626 The IANA is requested to assign a new IPv6 Neighbor Discovery Option 627 type for the DNSSL option defined in this document: 629 Option Name Type 630 DNSSL option (TBD) 632 The IANA registry for these options is: 634 http://www.iana.org/assignments/icmpv6-parameters 636 9. Acknowledgements 638 This document has greatly benefited from inputs by Robert Hinden, 639 Pekka Savola, Iljitsch van Beijnum, Brian Haberman, Tim Chown, Erik 640 Nordmark, Dan Wing, and Jari Arkko. The authors sincerely appreciate 641 their contributions. 643 10. References 645 10.1. Normative References 647 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 648 Requirement Levels", BCP 14, RFC 2119, March 1997. 650 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 651 "Neighbor Discovery for IP Version 6 (IPv6)", RFC 4861, 652 September 2007. 654 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 655 Address Autoconfiguration", RFC 4862, September 2007. 657 [RFC1035] Mockapetris, P., "Domain Names - Implementation and 658 Specification", RFC 1035, November 1987. 660 10.2. Informative References 662 [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", 663 RFC 1034, November 1987. 665 [RFC3315] Droms, R., Ed., "Dynamic Host Configuration Protocol for 666 IPv6 (DHCPv6)", RFC 3315, July 2003. 668 [RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol 669 (DHCP) Service for IPv6", RFC 3736, April 2004. 671 [RFC3646] Droms, R., Ed., "DNS Configuration options for Dynamic 672 Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, 673 December 2003. 675 [RFC5006] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 676 "IPv6 Router Advertisement Option for DNS Configuration", 677 RFC 5006, September 2007. 679 [RFC4339] Jeong, J., Ed., "IPv6 Host Configuration of DNS Server 680 Information Approaches", RFC 4339, February 2006. 682 [RFC3971] Arkko, J., Ed., "SEcure Neighbor Discovery (SEND)", 683 RFC 3971, March 2005. 685 [RFC5358] Damas, J. and F. Neves, "Preventing Use of Recursive 686 Nameservers in Reflector Attacks", BCP 140, RFC 5358, 687 October 2008. 689 [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: 690 Defeating Denial of Service Attacks which employ IP Source 691 Address Spoofing", BCP 38, RFC 2827, May 2000. 693 [RFC1535] Gavron, E., "A Security Problem and Proposed Correction 694 With Widely Deployed DNS Software", RFC 1535, 695 October 1993. 697 [RFC1536] Kumar, A., Postel, J., Neuman, C., Danzig, P., and S. 698 Miller, "Common DNS Implementation Errors and Suggested 699 Fixes", RFC 1536, October 1993. 701 Appendix A. Changes from RFC 5006 703 The following changes were made from RFC 5006 "IPv6 Router 704 Advertisement Option for DNS Configuration": 706 o Added DNS Search List (DNSSL) Option to support the advertisement 707 of DNS suffixes used in the DNS search along with RDNSS Option in 708 RFC 5006. 710 o Clarified the coexistence of RA options and DHCP options for DNS 711 configuration. 713 o Modified the procedure in IPv6 host: 715 * Clarified the procedure for DNS options in an IPv6 host. 717 * Specified a sufficient number of RDNSS addresses or DNS search 718 domain names as three. 720 * Specified a way to deal with DNS options from multiple sources, 721 such as RA and DHCP. 723 o Modified implementation considerations for DNSSL Option handling. 725 o Modified security considerations to consider more attack scenarios 726 and the corresponding possible solutions. 728 o Modified IANA considerations to require another IPv6 Neighbor 729 Discovery Option type for DNSSL option. 731 Authors' Addresses 733 Jaehoon Paul Jeong 734 Brocade Communications Systems/ETRI 735 6000 Nathan Ln N 736 Plymouth, MN 55442 737 USA 739 Phone: +1 763 268 7173 740 Fax: +1 763 268 6800 741 EMail: pjeong@brocade.com 742 URI: http://www.cs.umn.edu/~jjeong/ 743 Soohong Daniel Park 744 Mobile Platform Laboratory 745 SAMSUNG Electronics 746 416 Maetan-3dong, Yeongtong-Gu 747 Suwon, Gyeonggi-Do 443-742 748 Korea 750 Phone: +82 31 200 4508 751 EMail: soohong.park@samsung.com 753 Luc Beloeil 754 France Telecom R&D 755 42, rue des coutures 756 BP 6243 757 14066 CAEN Cedex 4 758 France 760 Phone: +33 2 40 44 97 40 761 EMail: luc.beloeil@orange-ftgroup.com 763 Syam Madanapalli 764 Ordyn Technologies 765 1st Floor, Creator Building, ITPL 766 Bangalore - 560066 767 India 769 Phone: +91-80-40383000 770 EMail: smadanapalli@gmail.com