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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Behave WG T. Savolainen 3 Internet-Draft Nokia 4 Intended status: Standards Track J. Korhonen 5 Expires: January 11, 2012 Nokia Siemens Networks 6 July 10, 2011 8 Discovery of a Network-Specific NAT64 Prefix using a Well-Known Name 9 draft-ietf-behave-nat64-discovery-heuristic-02.txt 11 Abstract 13 This document describes a method for detecting presence of DNS64 and 14 for learning IPv6 prefix used for protocol translation on an access 15 network without explicit support from the access network. The method 16 depends on existence of a known IPv4-only domain name. The 17 information learned enables applications and hosts to perform local 18 IPv6 address synthesis and on dual-stack accesses avoid traversal 19 through NAT64. 21 Status of this Memo 23 This Internet-Draft is submitted 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). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 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 This Internet-Draft will expire on January 11, 2012. 38 Copyright Notice 40 Copyright (c) 2011 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Requirements and Terminology . . . . . . . . . . . . . . . . . 3 57 2.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 3 58 2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. Host behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 3.1. Connectivity test . . . . . . . . . . . . . . . . . . . . . 5 61 4. Considerations for hosting the IPv4-only well-known name . . . 6 62 5. DNS(64) entity considerations . . . . . . . . . . . . . . . . . 6 63 6. Exit strategy . . . . . . . . . . . . . . . . . . . . . . . . . 6 64 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 65 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 66 8.1. About IPv4 address for the well-known name . . . . . . . . 7 67 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 68 10. Normative References . . . . . . . . . . . . . . . . . . . . . 7 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 71 1. Introduction 73 As part of the transition to IPv6 NAT64 [RFC6146] and DNS64 [RFC6147] 74 technologies will be utilized by some access networks to provide IPv4 75 connectivity for IPv6-only hosts. The DNS64 utilizes IPv6 address 76 synthesis to create local IPv6 presentations of peers having only 77 IPv4 addresses, hence allowing DNS-using IPv6-only hosts to 78 communicate with IPv4-only peers. 80 However, DNS64 cannot serve applications not using DNS, such as those 81 receiving IPv4 address literals as referrals. Such applications 82 could nevertheless be able to work through NAT64, provided they are 83 able to create locally valid IPv6 presentations of peers' IPv4 84 addresses. 86 Additionally, DNS64 is not able to do IPv6 address synthesis for 87 hosts running validating DNSSEC enabled resolvers, but instead the 88 synthetization must be done by the hosts. In order to perform IPv6 89 synthesis hosts have to learn the IPv6 prefix(es) used on the access 90 network for protocol translation. 92 This document describes a best effort method for advanced 93 applications and hosts to learn the information required to perform 94 local IPv6 address synthesis. An example application is a browser 95 encountering an IPv4 address literal in an IPv6-only access network. 96 Another example is a host running validating security aware DNS 97 resolver. 99 The knowledge of IPv6 address synthetization taking place may also be 100 useful if DNS64 and NAT64 are present in dual-stack enabled access 101 network. In such cases hosts may choose to prefer IPv4 in order to 102 avoid traversal through protocol translators. 104 The described method is intented for the scenarios where network 105 assisted NAT64 and prefix discovery solutions are not available. 107 2. Requirements and Terminology 109 2.1. Requirements 111 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 112 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 113 document are to be interpreted as described in [RFC2119]. 115 2.2. Terminology 117 Well-Known IPv4-only Name: a fully qualified domain name well-known 118 to have only A record. 120 Well-Known IPv4 Address: an IPv4 address that is well-known and 121 mapped to the well-known name. 123 3. Host behavior 125 A host requiring information about presence of NAT64 and the IPv6 126 prefix used for protocol translation shall send a DNS query for AAAA 127 records of a known IPv4-only fully qualified domain name. This may 128 happen, for example, at the moment the host is configured an IPv6 129 address of a DNS server. This may also happen at the time when first 130 DNS query for AAAA record is initiated. The host may perform this 131 check in both IPv6-only and dual-stack access networks. 133 When sending AAAA query for the known name a host MUST set "Checking 134 Disabled (CD)" bit to zero, as otherwise the DNS64 will not perform 135 IPv6 address synthesis hence does not reveal the IPv6 prefix(es) used 136 for protocol translation. 138 A DNS reply with one or more non-empty AAAA records indicates that 139 the access network is utilizing IPv6 address synthesis. A host MUST 140 look through all of the received AAAA records to collect all 141 available prefixes. The prefixes may include Well-Known Prefix or 142 one or more Network-Specific Prefixes. In the case of NSPs the host 143 SHALL search for the IPv4 address inside of the received IPv6 144 addresses to determine used address format. 146 An IPv4 address inside synthesized IPv6 address should be found at 147 some of the locations described in [RFC6052]. If the searched IPv4 148 address is not found on any of the standard locations the network 149 must be using different formatting. Developers may over time learn 150 on IPv6 translated address formats that are extensions or 151 alternatives to the standard formats. Developers MAY at that point 152 add additional steps to the described discovery procedures. The 153 additional steps are outside the scope of the present document. 155 The host should ensure a 32-bit IPv4 address value is present only 156 once in an IPv6 address. In case another instance of the value is 157 found inside the IPv6, the host shall repeat the search with another 158 IPv4 address, if possible. 160 In the case only one IPv6 prefix was present in the DNS response: a 161 host shall use that IPv6 prefix for both local synthetization and for 162 detecting synthesis done by the DNS64 entity on the network. 164 In the case multiple IPv6 prefixes were present in the DNS response: 165 a host SHOULD use all received prefixes when determining whether 166 other received IPv6 addresses are synthetic. However, for selecting 167 prefix for the local IPv6 address synthesis host MUST use the 168 following prioritization order, of which purpose is to avoid use of 169 prefixes containing suffixes reserved for the future [RFC6052]: 171 1. Use NSP having /96 prefix 173 2. Use WKP prefix 175 3. Use longest available NSP prefix 177 In the case of NXDOMAIN or empty AAAA reply: the DNS64 is not 178 available on the access network, network filtered the well-known 179 query on purpose, or something went wrong in the DNS resolution. All 180 unsuccesful cases result in unavailability of a host to perform local 181 IPv6 address synthesis. The host MAY periodically resend AAAA query 182 to check if DNS64 has become available or temporary problem cleared. 183 The host MAY perform A query for the well-known name to learn whether 184 the service is available at all (see section 6 about Exit Strategy). 185 The host MAY also continue monitoring DNS replies with IPv6 addresses 186 constructed from WKP, in which case the host MAY use the WKP as if it 187 were learned during the query for well-known name. 189 To save Internet's resources, if possible, a host should perform 190 NAT64 discovery only when needed (e.g. when local synthesis is 191 required, cached reply timeouts, new network interface is started, 192 and so forth. Furthermore, the host SHOULD cache the replies it 193 receives and honor TTLs. 195 3.1. Connectivity test 197 After the host has obtained a candidate prefix and format for the 198 IPv6 address synthesis it may locally synthesize an IPv6 address, by 199 using a publicly routable IPv4 address, and test connectivity with 200 the resulting IPv6 address. The connectivity test may be conducted 201 e.g. with ICMPv6 or with a transport layer protocol. 203 This connectivity test ensures local address synthetization results 204 in functional and protocol translatable IPv6 addresses. 206 The host MUST NOT perform connectivity test for the well-known IPv4 207 address of the well-known name, but instead to some other destination 208 such as host vendor servers. 210 4. Considerations for hosting the IPv4-only well-known name 212 The authoritative nameserver for the well-known name shall have DNS 213 record TTL set to a long value in order to improve effectiveness of 214 DNS caching. The exact value depends on availability time for the 215 used public IPv4 address, but should not be longer than one year. 217 5. DNS(64) entity considerations 219 DNS(64) servers MUST NOT interfere or perform special procedures for 220 the queries related to the well-known name until the time has arrived 221 for the exit strategy to be deployed. 223 6. Exit strategy 225 A day will come when this tool is no longer needed or is replaced by 226 some other tool. 228 In global scope the exit strategy includes sending NXDOMAIN replies 229 by the authoritative nameserver of the well-known name with very long 230 TTL. 232 In local scope, after network administrators have determined there is 233 no longer need for this tool in their network, they may start locally 234 serving A and AAAA queries for the well-known name with NXDOMAIN 235 reply. 237 A client implementation receiving NXDOMAIN for the AAAA query for the 238 well-known name is either not talking to DNS64 or this tool has been 239 disabled. NXDOMAIN response also for the A query for the well-known 240 name means this tool has been disabled. 242 7. Security Considerations 244 No security considerations have been identified. 246 8. IANA Considerations 248 A well-known name should be defined and a public IPv4 address 249 allocated (by IANA? IETF? Someone else?). 251 8.1. About IPv4 address for the well-known name 253 The global IPv4 address for the well-known, if possible, should be 254 chosen so that it is unlikely to appear more than once within an IPv6 255 address and also as easy as possible to find from within the 256 synthetic IPv6 address. A global address is required as otherwise 257 DNS64 entity will not perform AAAA record synthesis. The address 258 does not have to be routable as no communications are initiated to 259 the IPv4 address. 261 Allocating two IPv4 addresses would improve the heuristics in cases 262 where the primary IPv4 address' bit pattern appears more than once in 263 the synthetic IPv6 address (NSP prefix contains the same bit pattern 264 as the IPv4 address). 266 If no well-known IPv4 address is allocated for this method, the 267 heuristic requires sending additional A query to learn the IPv4 268 address that is sought inside the received IPv6 address. Without 269 knowing IPv4 address it is impossible to determine address format 270 used by DNS64. 272 9. Acknowledgements 274 Authors would like to thank Andrew Sullivan, Dan Wing, Washam Fan, 275 Cameron Byrne, Zhenqiang Li, and Christian Huitema for significant 276 improvement ideas and comments. 278 10. Normative References 280 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 281 Requirement Levels", BCP 14, RFC 2119, March 1997. 283 [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. 284 Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, 285 October 2010. 287 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 288 NAT64: Network Address and Protocol Translation from IPv6 289 Clients to IPv4 Servers", RFC 6146, April 2011. 291 [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van 292 Beijnum, "DNS64: DNS Extensions for Network Address 293 Translation from IPv6 Clients to IPv4 Servers", RFC 6147, 294 April 2011. 296 Authors' Addresses 298 Teemu Savolainen 299 Nokia 300 Hermiankatu 12 D 301 FI-33720 Tampere 302 Finland 304 Email: teemu.savolainen@nokia.com 306 Jouni Korhonen 307 Nokia Siemens Networks 308 Linnoitustie 6 309 FI-02600 Espoo 310 Finland 312 Email: jouni.nospam@gmail.com