From 13174b302f0e809bb5279bb4767dc07369dba93c Mon Sep 17 00:00:00 2001 From: Mark Andrews Date: Mon, 19 Oct 2009 23:42:52 +0000 Subject: [PATCH] new draft --- doc/draft/draft-ietf-behave-dns64-01.txt | 1624 ++++++++++++++++++++++ 1 file changed, 1624 insertions(+) create mode 100644 doc/draft/draft-ietf-behave-dns64-01.txt diff --git a/doc/draft/draft-ietf-behave-dns64-01.txt b/doc/draft/draft-ietf-behave-dns64-01.txt new file mode 100644 index 0000000000..25a6dd4d07 --- /dev/null +++ b/doc/draft/draft-ietf-behave-dns64-01.txt @@ -0,0 +1,1624 @@ + + + +BEHAVE WG M. Bagnulo +Internet-Draft UC3M +Intended status: Standards Track A. Sullivan +Expires: April 22, 2010 Shinkuro + P. Matthews + Alcatel-Lucent + I. van Beijnum + IMDEA Networks + October 19, 2009 + + +DNS64: DNS extensions for Network Address Translation from IPv6 Clients + to IPv4 Servers + draft-ietf-behave-dns64-01 + +Status of this Memo + + This Internet-Draft is submitted to IETF in full conformance with the + provisions of BCP 78 and BCP 79. + + Internet-Drafts are working documents of the Internet Engineering + Task Force (IETF), its areas, and its working groups. Note that + other groups may also distribute working documents as Internet- + Drafts. + + Internet-Drafts are draft documents valid for a maximum of six months + and may be updated, replaced, or obsoleted by other documents at any + time. It is inappropriate to use Internet-Drafts as reference + material or to cite them other than as "work in progress." + + The list of current Internet-Drafts can be accessed at + http://www.ietf.org/ietf/1id-abstracts.txt. + + The list of Internet-Draft Shadow Directories can be accessed at + http://www.ietf.org/shadow.html. + + This Internet-Draft will expire on April 22, 2010. + +Copyright Notice + + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents in effect on the date of + publication of this document (http://trustee.ietf.org/license-info). + Please review these documents carefully, as they describe your rights + and restrictions with respect to this document. + + + +Bagnulo, et al. Expires April 22, 2010 [Page 1] + +Internet-Draft DNS64 October 2009 + + +Abstract + + DNS64 is a mechanism for synthesizing AAAA records from A records. + DNS64 is used with an IPv6/IPv4 translator to enable client-server + communication between an IPv6-only client and an IPv4-only server, + without requiring any changes to either the IPv6 or the IPv4 node, + for the class of applications that work through NATs. This document + specifies DNS64, and provides suggestions on how it should be + deployed in conjunction with IPv6/IPv4 translators. + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 3. Background to DNS64 - DNSSEC interaction . . . . . . . . . . . 6 + 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8 + 5. DNS64 Normative Specification . . . . . . . . . . . . . . . . 9 + 5.1. Resolving AAAA queries and the answer section . . . . . . 9 + 5.1.1. The answer when there is AAAA data available . . . . . 9 + 5.1.2. The answer when there is an error . . . . . . . . . . 9 + 5.1.3. Data for the answer when performing synthesis . . . . 9 + 5.1.4. Performing the synthesis . . . . . . . . . . . . . . . 10 + 5.1.5. Querying in parallel . . . . . . . . . . . . . . . . . 11 + 5.2. Generation of the IPv6 representations of IPv4 + addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 + 5.3. Handling other RRs . . . . . . . . . . . . . . . . . . . . 12 + 5.3.1. PTR queries . . . . . . . . . . . . . . . . . . . . . 12 + 5.3.2. Handling the additional section . . . . . . . . . . . 13 + 5.3.3. Other records . . . . . . . . . . . . . . . . . . . . 13 + 5.4. Assembling a synthesized response to a AAAA query . . . . 14 + 5.5. DNSSEC processing: DNS64 in recursive server mode . . . . 14 + 5.6. DNS64 and multihoming . . . . . . . . . . . . . . . . . . 15 + 6. Deployment notes . . . . . . . . . . . . . . . . . . . . . . . 16 + 6.1. DNS resolvers and DNS64 . . . . . . . . . . . . . . . . . 16 + 6.2. DNSSEC validators and DNS64 . . . . . . . . . . . . . . . 16 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 + 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16 + 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 + 10.1. Normative References . . . . . . . . . . . . . . . . . . . 17 + 10.2. Informative References . . . . . . . . . . . . . . . . . . 18 + Appendix A. Deployment scenarios and examples . . . . . . . . . . 20 + A.1. Embed and Zero-Pad algorithm description . . . . . . . . . 21 + A.2. An-IPv6-network-to-IPv4-Internet setup with DNS64 in + DNS server mode . . . . . . . . . . . . . . . . . . . . . 22 + A.3. An-IPv6-network-to-IPv4-Internet setup with DNS64 in + stub-resolver mode . . . . . . . . . . . . . . . . . . . . 23 + + + +Bagnulo, et al. Expires April 22, 2010 [Page 2] + +Internet-Draft DNS64 October 2009 + + + A.4. IPv6-Internet-to-an-IPv4-network setup DNS64 in DNS + server mode . . . . . . . . . . . . . . . . . . . . . . . 25 + Appendix B. Motivations and Implications of synthesizing AAAA + RR when real AAAA RR exists . . . . . . . . . . . . . 27 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 3] + +Internet-Draft DNS64 October 2009 + + +1. Introduction + + This document specifies DNS64, a mechanism that is part of the + toolbox for IPv6-IPv4 transition and co-existence. DNS64, used + together with an IPv6/IPv4 translator such as NAT64 + [I-D.bagnulo-behave-nat64], allows an IPv6-only client to initiate + communications by name to an IPv4-only server. + + DNS64 is a mechanism for synthesizing AAAA resource records (RRs) + from A RRs. A synthetic AAAA RR created by the DNS64 from an + original A RR contains the same FQDN of the original A RR but it + contains an IPv6 address instead of an IPv4 address. The IPv6 + address is an IPv6 representation of the IPv4 address contained in + the original A RR. The IPv6 representation of the IPv4 address is + algorithmically generated from the IPv4 address returned in the A RR + and a set of parameters configured in the DNS64 (typically, an IPv6 + prefix used by IPv6 representations of IPv4 addresses and optionally + other parameters). + + Together with a IPv6/IPv4 translator, these two mechanisms allow an + IPv6-only client to initiate communications to an IPv4-only server + using the FQDN of the server. + + These mechanisms are expected to play a critical role in the IPv4- + IPv6 transition and co-existence. Due to IPv4 address depletion, it + is likely that in the future, many IPv6-only clients will want to + connect to IPv4-only servers. In the typical case, the approach only + requires the deployment of IPv6/IPv4 translators that connect an + IPv6-only network to an IPv4-only network, along with the deployment + of one or more DNS64-enabled name servers. However, some advanced + features require performing the DNS64 function directly by the end- + hosts themselves. + + +2. Overview + + This section provides a non-normative introduction to the DNS64 + mechanism. + + We assume that we have an IPv6/IPv4 translator box connecting an IPv4 + network and an IPv6 network. The IPv6/IPv4 translator device + provides translation services between the two networks enabling + communication between IPv4-only hosts and IPv6-only hosts. (NOTE: By + IPv6-only hosts we mean hosts running IPv6-only applications, hosts + that can only use IPv6, as well as the cases where only IPv6 + connectivity is available to the client. By IPv4-only servers we + mean servers running IPv4-only applications, servers that can only + use IPv4, as well as the cases where only IPv4 connectivity is + + + +Bagnulo, et al. Expires April 22, 2010 [Page 4] + +Internet-Draft DNS64 October 2009 + + + available to the server). The IPv6/IPv4 translator used in + conjunction with DNS64 must allow communications initiated from the + IPv6-only host to the IPv4-only host. + + To allow an IPv6 initiator to do a standard AAAA RR DNS lookup to + learn the address of the responder, DNS64 is used to synthesize a + AAAA record from an A record containing a real IPv4 address of the + responder, whenever the DNS64 service cannot retrieve a AAAA record + for the requested host name. The DNS64 device appears as a regular + recursive resolver for the IPv6 initiator. The DNS64 box receives an + AAAA DNS query generated by the IPv6 initiator. It first attempts a + recursive resolution for the requested AAAA records. If there is no + AAAA record available for the target node (which is the normal case + when the target node is an IPv4-only node), DNS64 performs a query + for A records. If any A records are discovered, DNS64 creates a + synthetic AAAA RR from the information retrieved in each A RR. + + The FQDN of a synthetic AAAA RR is the same as that of the original A + RR, but an IPv6 representation of the IPv4 address contained in the + original A RR is included in the AAAA RR. The IPv6 representation of + the IPv4 address is algorithmically generated from the IPv4 address + and additional parameters configured in the DNS64. Among those + parameters configured in the DNS64, there is at least one IPv6 + prefix, called Pref64::/n. The IPv6 address representing IPv4 + addresses included in the AAAA RR synthesized by the DNS64 function + contain Pref64::/n and they also embed the original IPv4 address. + + The same algorithm and the same Pref64::/n prefix or prefixes must be + configured both in the DNS64 device and the IPv6/IPv4 translator, so + that both can algorithmically generate the same IPv6 representation + for a given IPv4 address. In addition, it is required that IPv6 + packets addressed to an IPv6 destination that contains the Pref64::/n + be delivered to the IPv6/IPv4 translator, so they can be translated + into IPv4 packets. + + Once the DNS64 has synthesized the AAAA RR, the synthetic AAAA RR is + passed back to the IPv6 initiator, which will initiate an IPv6 + communication with the IPv6 address associated with the IPv4 + receiver. The packet will be routed to the IPv6/IPv4 translator + which will forward it to the IPv4 network . + + In general, the only shared state between the DNS64 and the IPv6/IPv4 + translator is the Pref64::/n and an optional set of static + parameters. The Pref64::/n and the set of static parameters must be + configured to be the same on both; there is no communication between + the DNS64 device and IPv6/IPv4 translator functions. The mechanism + to be used for configuring the parameters of the DNS64 is beyond the + scope of this memo. + + + +Bagnulo, et al. Expires April 22, 2010 [Page 5] + +Internet-Draft DNS64 October 2009 + + + The DNS64 function can be performed in two places. + + One option is to locate the DNS64 function in recursive name + servers serving end hosts. In this case, when an IPv6-only host + queries the name server for AAAA RRs for an IPv4-only host, the + name server can perform the synthesis of AAAA RRs and pass them + back to the IPv6 only initiator. The main advantage of this mode + is that current IPv6 nodes can use this mechanism without + requiring any modification. This mode is called "DNS64 in DNS + server mode". + + The other option is to place the DNS64 function in the end hosts + themselves, coupled to the local stub resolver. In this case, the + stub resolver will try to obtain (real) AAAA RRs and in case they + are not available, the DNS64 function will synthesize AAAA RRs for + internal usage. This mode is compatible with some advanced + functions like DNSSEC validation in the end host. The main + drawback of this mode is its deployability, since it requires + changes in the end hosts. This mode is called "DNS64 in stub- + resolver mode"". + + +3. Background to DNS64 - DNSSEC interaction + + DNSSEC presents a special challenge for DNS64, because DNSSEC is + designed to detect changes to DNS answers, and DNS64 may alter + answers coming from an authoritative server. + + A recursive resolver can be security-aware or security-oblivious. + Moreover, a security-aware recursive name server can be validating or + non-validating, according to operator policy. In the cases below, + the recursive server is also performing DNS64, and has a local policy + to validate. We call this general case vDNS64, but in all the cases + below the DNS64 functionality should be assumed needed. + + DNSSEC includes some signaling bits that offer some indicators of + what the query originator understands. + + If a query arrives at a vDNS64 device with the DO bit set, the query + originator is signaling that it understands DNSSEC. The DO bit does + not indicate that the query originator will validate the response. + It only means that the query originator can understand responses + containing DNSSEC data. Conversely, if the DO bit is clear, that is + evidence that the querying agent is not aware of DNSSEC. + + If a query arrives at a vDNS64 device with the CD bit set, it is an + indication that the querying agent wants all the validation data so + it can do checking itself. By local policy, vDNS64 could still + + + +Bagnulo, et al. Expires April 22, 2010 [Page 6] + +Internet-Draft DNS64 October 2009 + + + validate, but it must return all data to the querying agent anyway. + + Here are the possible cases: + + 1. A security-oblivious DNS64 node receives a query with the DO bit + clear. In this case, DNSSEC is not a concern, because the + querying agent does not understand DNSSEC responses. + + 2. A security-oblivious DNS64 node receives a query with the DO bit + set, and the CD bit clear. This is just like the case of a non- + DNS64 case: the server doesn't support it, so the querying agent + is out of luck. + + 3. A security-aware and non-validating DNS64 node receives a query + with the DO bit set and the CD bit clear. Such a resolver is not + validating responses, likely due to local policy (see [RFC4035], + section 4.2). For that reason, this case amounts to the same as + the previous case, and no validation happens. + + 4. A security-aware and non-validating DNS64 node receives a query + with the DO bit set and the CD bit set. In this case, the + resolver is supposed to pass on all the data it gets to the query + initiator (see section 3.2.2 of [RFC4035]). This case will be + problematic with DNS64. If the DNS64 server modifies the record, + the client will get the data back and try to validate it, and the + data will be invalid as far as the client is concerned. + + 5. A security-aware and validating DNS64 node receives a query with + the DO bit clear and CD clear. In this case, the resolver + validates the data. If it fails, it returns RCODE 2 (SERVFAIL); + otherwise, it returns the answer. This is the ideal case for + vDNS64. The resolver validates the data, and then synthesizes + the new record and passes that to the client. The client, which + is presumably not validating (else it would have set DO and CD), + cannot tell that DNS64 is involved. + + 6. A security-aware and validating DNS64 node receives a query with + the DO bit set and CD clear. In principle, this ought to work + like the previous case, except that the resolver should also set + the AD bit on the response. + + 7. A security-aware and validating DNS64 node receives a query with + the DO bit set and CD set. This is effectively the same as the + case where a security-aware and non-validating recursive resolver + receives a similar query, and the same thing will happen: the + downstream validator will mark the data as invalid if DNS64 has + performed synthesis. + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 7] + +Internet-Draft DNS64 October 2009 + + +4. Terminology + + This section provides definitions for the special terms used in the + document. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [RFC2119]. + + Authoritative server: A DNS server that can answer authoritatively a + given DNS question. + + DNS64: A logical function that synthesizes DNS resource records (e.g + AAAA records containing IPv6 addresses) from DNS resource records + actually contained in the global DNS (e.g. A records containing + IPv4 addresses). + + DNS64 recursor: A recursive resolver that provides the DNS64 + functionality as part of its operation. + + Recursive resolver: A DNS server that accepts requests from one + resolver, and asks another resolver for the answer on behalf of + the first resolver. In the context of this document, "the + recursive resolver" means a recursive resolver immediately next in + the DNS resolution chain from an end point. The end point usually + has only a stub resolver available.[[anchor5: I can't actually + remember why we needed the sentences following "In the context of + this document. . ." Unless someone has a reason, I'll take it + out. --ajs@shinkuro.com]] + + Synthetic RR: A DNS resource record (RR) that is not contained in + any zone data file, but has been synthesized from other RRs. An + example is a synthetic AAAA record created from an A record. + + Stub resolver: A resolver with minimum functionality, typically for + use in end points that depend on a recursive resolver. Most end + points on the Internet as of this writing use stub + resolvers.[[anchor6: Do we need this in the document? I don't + think so. 1034 defines this term. --ajs@shinkuro.com]] + + IPv6/IPv4 translator: A device that translates IPv6 packets to IPv4 + packets and vice-versa. It is only required that the + communication initiated from the IPv6 side be supported. + + For a detailed understanding of this document, the reader should also + be familiar with DNS terminology from [RFC1034],[RFC1035] and current + NAT terminology from [RFC4787]. Some parts of this document assume + familiarity with the terminology of the DNS security extensions + + + +Bagnulo, et al. Expires April 22, 2010 [Page 8] + +Internet-Draft DNS64 October 2009 + + + outlined in [RFC4035]. + + +5. DNS64 Normative Specification + + A DNS64 is a logical function that synthesizes AAAA records from A + records. The DNS64 function may be implemented in a stub resolver, + in a recursive resolver, or in an authoritative name server. + + The implementation SHOULD support mapping of IPv4 address ranges to + separate IPv6 prefixes for AAAA record synthesis. This allows + handling of special use IPv4 addresses [I-D.iana-rfc3330bis]. + Multicast address handling is further specified in + [I-D.venaas-behave-mcast46]. + +5.1. Resolving AAAA queries and the answer section + + When the DNS64 receives a query for RRs of type AAAA and class IN, it + first attempts to retrieve non-synthetic RRs of this type and class, + either by performing a query or, in the case of an authoritative + server, by examining its own results. + +5.1.1. The answer when there is AAAA data available + + If the query results in one or more AAAA records in the answer + section, the result is returned to the requesting client as per + normal DNS semantics (except in the case where the AAAA falls in the + ::ffff/96 network; see below for treatment of that network). In this + case, DNS64 SHOULD NOT include synthetic AAAA RRs in the response + (see Appendix B for an analysis of the motivations for and the + implications of not complying with this recommendation). By default + DNS64 implementations MUST NOT synthesize AAAA RRs when real AAAA RRs + exist. + +5.1.2. The answer when there is an error + + If the query results in a response with an error code other than 0, + the result is handled according to normal DNS operation -- that is, + either the resolver tries again using a different server from the + authoritative NS RRSet, or it returns the error to the client. This + stage is still prior to any synthesis having happened, so a response + to be returned to the client does not need any special assembly than + would usually happen in DNS operation. + +5.1.3. Data for the answer when performing synthesis + + If the query results in no error but an empty answer section in the + response, the DNS64 resolver attempts to retrieve A records for the + + + +Bagnulo, et al. Expires April 22, 2010 [Page 9] + +Internet-Draft DNS64 October 2009 + + + name in question. If this new A RR query results in an empty answer + or in an error, then the empty result or error is used as the basis + for the answer returned to the querying client. (Transient errors + may result in retrying the query, depening on the operation of the + resolver; this is just as in Section 5.1.2.) If instead the query + results in one or more A RRs, the DNS64 synthesizes AAAA RRs based on + the A RRs according to the procedure outlined in Section 5.1.4. The + DNS64 resolver then returns the synthesized AAAA records in the + answer section to the client, removing the A records that form the + basis of the synthesis. + + As an exception to the general rule about always returning the AAAA + records if they are returned in the answer, AAAA records with + addresses in the ::ffff/96 network are treated just like the case + where there is neither an error nor an empty answer section. This is + because a real IPv6-only node will not be any more able to reach the + addresses in ::ffff/96 than it is able to reach an IPv4 address + without assistance. An implementation MAY use the address in + ::ffff/96 as the basis of synthesis without querying for an A record, + by using the last 32 bits of the address provided in the AAAA record. + [[anchor10: I changed this to say "neither. . .nor" because the + previous version suggested that it would return the error-or-empty- + answer to the querying client, and that can't be right. Correct? + --ajs@shinkuro.com]] + +5.1.4. Performing the synthesis + + A synthetic AAAA record is created from an A record as follows: + + o The NAME field is set to the NAME field from the A record + + o The TYPE field is set to 28 (AAAA) + + o The CLASS field is set to 1 (IN) + + o The TTL field is set to the minimum of the TTL of the original A + RR and the SOA RR for the queried domain. (Note that in order to + obtain the TTL of the SOA RR the DNS64 does not need to perform a + new query, but it can remember the TTL from the SOA RR in the + negative response to the AAAA query). + + o The RDLENGTH field is set to 16 + + o The RDATA field is set to the IPv6 representation of the IPv4 + address from the RDATA field of the A record. The DNS64 SHOULD + check each A RR against IPv4 address ranges and select the + corresponding IPv6 prefix to use in synthesizing the AAAA RR. See + Section 5.2 for discussion of the algorithms to be used in + + + +Bagnulo, et al. Expires April 22, 2010 [Page 10] + +Internet-Draft DNS64 October 2009 + + + effecting the transformation. + +5.1.5. Querying in parallel + + DNS64 MAY perform the query for the AAAA RR and for the A RR in + parallel, in order to minimize the delay. However, this would result + in performing unnecessary A RR queries in the case no AAAA RR + synthesis is required. A possible trade-off would be to perform them + sequentially but with a very short interval between them, so if we + obtain a fast reply, we avoid doing the additional query. (Note that + this discussion is relevant only if the DNS64 function needs to + perform external queries to fetch the RR. If the needed RR + information is available locally, as in the case of an authoritative + server, the issue is no longer relevant.) + +5.2. Generation of the IPv6 representations of IPv4 addresses + + DNS64 supports multiple algorithms for the generation of the IPv6 + representation of an IPv4 address. The constraints imposed on the + generation algorithms are the following: + + The same algorithm to create an IPv6 address from an IPv4 address + MUST be used by both the DNS64 to create the IPv6 address to be + returned in the synthetic AAAA RR from the IPv4 address contained + in original A RR, and by the IPv6/IPv4 translator to create the + IPv6 address to be included in the destination address field of + the outgoing IPv6 packets from the IPv4 address included in the + destination address field of the incoming IPv4 packet. + + The algorithm MUST be reversible, i.e. it MUST be possible to + extract the original IPv4 address from the IPv6 representation. + + The input for the algorithm MUST be limited to the IPv4 address, + the IPv6 prefix (denoted Pref64::/n) used in the IPv6 + representations and optionally a set of stable parameters that are + configured in the DNS64 (such as fixed string to be used as a + suffix). + + If we note n the length of the prefix Pref64::/n, then n MUST + the less or equal than 96. If a Pref64::/n is configured + through any means in the DNS64 (such as manually configured, or + other automatic mean not specified in this document), the + default algorithm MUST use this prefix. If no prefix is + available, the algorithm MUST use the Well-Known prefix TBD1 + defined in [I-D.thaler-behave-translator-addressing] + + [[anchor12: Note in document: TBD1 in the passage above is to be + substituted by whatever prefix is assigned by IANA to be the well- + + + +Bagnulo, et al. Expires April 22, 2010 [Page 11] + +Internet-Draft DNS64 October 2009 + + + known prefix.]] + + DNS64 MUST support the following algorithms for generating IPv6 + representations of IPv4 addresses defined in + [I-D.thaler-behave-translator-addressing]: + + Zero-Pad And Embed, defined in section 3.2.3 of + [I-D.thaler-behave-translator-addressing] + + Compensation-Pad And Embed, defined in section of 3.2.4 of + [I-D.thaler-behave-translator-addressing] + + Embed And Zero-Pad, defined in section of 3.2.5 of + [I-D.thaler-behave-translator-addressing] + + Preconfigured Mapping Table, defined in section of 3.2.6 of + [I-D.thaler-behave-translator-addressing] + + The default algorithm used by DNS64 must be Embed and Zero-Pad. + While the normative description of the algorithms is provided in + [I-D.thaler-behave-translator-addressing], an sample description of + the algorithm and its application to different scenarios is provided + in Appendix A for illustration purposes. + +5.3. Handling other RRs + +5.3.1. PTR queries + + If a DNS64 nameserver receives a PTR query for a record in the + IP6.ARPA domain, it MUST strip the IP6.ARPA labels from the QNAME, + reverse the address portion of the QNAME according to the encoding + scheme outlined in section 2.5 of [RFC3596] , and examine the + resulting address to see whether its prefix matches the locally- + configured Pref64::/n. There are two alternatives for a DNS64 + nameserver to respond to such PTR queries. A DNS64 node MUST provide + one of these, and SHOULD NOT provide both at the same time unless + different IP6.ARPA zones require answers of different sorts. + + The first option is for the DNS64 nameserver to respond + authoritatively for its prefixes. If the address prefix matches any + Pref64::/n used in the site, either a LIR prefix or a well-known + prefix used for NAT64 as defined in + [I-D.thaler-behave-translator-addressing], then the DNS64 server MAY + answer the query using locally-appropriate RDATA. The DNS64 server + MAY use the same RDATA for all answers. Note that the requirement is + to match any Pref64::/n used at the site, and not merely the locally- + configured Pref64::/n. This is because end clients could ask for a + PTR record matching an address received through a different (site- + + + +Bagnulo, et al. Expires April 22, 2010 [Page 12] + +Internet-Draft DNS64 October 2009 + + + provided) DNS64, and if this strategy is in effect, those queries + should never be sent to the global DNS. The advantage of this + strategy is that it makes plain to the querying client that the + prefix is one operated by the DNS64 site, and that the answers the + client is getting are generated by the DNS64. The disadvantage is + that any useful reverse-tree information that might be in the global + DNS is unavailable to the clients querying the DNS64. + + The second option is for the DNS64 nameserver to synthesize a CNAME + mapping the IP6.ARPA namespace to the corresponding IN-ADDR.ARPA + name. The rest of the response would be the normal DNS processing. + The CNAME can be signed on the fly if need be. The advantage of this + approach is that any useful information in the reverse tree is + available to the querying client. The disadvantage is that it adds + additional load to the DNS64 (because CNAMEs have to be synthesized + for each PTR query that matches the Pref64::/n), and that it may + require signing on the fly. [[anchor15: what are we supposed to do + here when the in-addr.arpa zone is unmaintained, as it may be. If + there is no data at the target name, then we'll get a CNAME with a + map to an empty namespace, I think? Isn't that bad? + --ajs@shinkuro.com]] + + If the address prefix does not match any of the Pref64::/n, then the + DNS64 server MUST process the query as though it were any other query + -- i.e. a recursive nameserver MUST attempt to resolve the query as + though it were any other (non-A/AAAA) query, and an authoritative + server MUST respond authoritatively or with a referral, as + appropriate. + +5.3.2. Handling the additional section + + DNS64 synthesis MUST NOT be performed on any records in the + additional section of synthesized answers. The DNS64 MUST pass the + additional section unchanged. + + [[anchor16: We had some discussion, as an alternative to the above, + of allowing the DNS64 to truncate the additional section completely, + on the grounds that the additional section could break mixed-mode + iterative/forwarding resolvers that happen to end up behind DNS64. + Nobody else seemed to like that plan, so I haven't included it. + --ajs@shinkuro.com]] + +5.3.3. Other records + + If the DNS64 is in recursive resolver mode, then it SHOULD also serve + the zones specified in [I-D.ietf-dnsop-default-local-zones], rather + than forwarding those queries elsewhere to be handled. + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 13] + +Internet-Draft DNS64 October 2009 + + + All other RRs MUST be returned unchanged. + +5.4. Assembling a synthesized response to a AAAA query + + The DNS64 uses different pieces of data to build the response + returned to the querying client. + + The query that is used as the basis for synthesis results either in + an error, an answer that can be used as a basis for synthesis, or an + empty (authoritative) answer. If there is an empty answer, then the + DNS64 responds to the original querying client with the answer the + DNS64 received to the original AAAA query. Otherwise, the response + is assembled as follows. + + The header fields are set according to the usual rules for recursive + or authoritative servers, depending on the role that the DNS64 is + serving. The question section is copied from the original AAAA + query. The answer section is populated according to the rules in + Section 5.1.4. The authority section is copied from the response to + the A query that the DNS64 performed. The additional section is + populated according to the rules in Section 5.3.2. + + [[anchor18: The cross-reference to how to do the additional section + can be removed, and replaced by "copied from the response to the A + query that the DNS64 performed" if we don't want to allow the DNS64 + to truncate the additional section. See the note above. If I hear + no more feedback on this topic, then I'll make this change in the + next version. --ajs@shinkuro.com]] + +5.5. DNSSEC processing: DNS64 in recursive server mode + + We consider the case where the recursive server that is performing + DNS64 also has a local policy to validate the answers according to + the procedures outlined in [RFC4035] Section 5. We call this general + case vDNS64. + + The vDNS64 uses the presence of the DO and CD bits to make some + decisions about what the query originator needs, and can react + accordingly: + + 1. If CD is not set and DO is not set, vDNS64 SHOULD perform + validation and do synthesis as needed. + + 2. If CD is not set and DO is set, then vDNS64 SHOULD perform + validation. Whenever vDNS64 performs validation, it MUST + validate the negative answer for AAAA queries before proceeding + to query for A records for the same name, in order to be sure + that there is not a legitimate AAAA record on the Internet. + + + +Bagnulo, et al. Expires April 22, 2010 [Page 14] + +Internet-Draft DNS64 October 2009 + + + Failing to observe this step would allow an attacker to use DNS64 + as a mechanism to circumvent DNSSEC. If the negative response + validates, and the response to the A query validates, then the + vDNS64 MAY perform synthesis and SHOULD set the AD bit in the + answer to the client. This is acceptable, because [RFC4035], + section 3.2.3 says that the AD bit is set by the name server side + of a security-aware recursive name server if and only if it + considers all the RRSets in the Answer and Authority sections to + be authentic. In this case, the name server has reason to + believe the RRSets are all authentic, so it SHOULD set the AD + bit. If the data does not validate, the vDNS64 MUST respond with + RCODE=2 (server failure). + A security-aware end point might take the presence of the AD bit + as an indication that the data is valid, and may pass the DNS + (and DNSSEC) data to an application. If the application attempts + to validate the synthesized data, of course, the validation will + fail. One could argue therefore that this approach is not + desirable. But security aware stub resolvers MUST NOT place any + reliance on data received from resolvers and validated on their + behalf without certain criteria established by [RFC4035], section + 4.9.3. An application that wants to perform validation on its + own should use the CD bit. + + 3. If the CD bit is set and DO is set, then vDNS64 MAY perform + validation, but MUST NOT perform synthesis. It MUST hand the + data back to the query initiator, just like a regular recursive + resolver, and depend on the client to do the validation and the + synthesis itself. + The disadvantage to this approach is that an end point that is + translation-oblivious but security-aware and validating will not + be able to use the DNS64 functionality. In this case, the end + point will not have the desired benefit of NAT64. In effect, + this strategy means that any end point that wishes to do + validation in a NAT64 context must be upgraded to be translation- + aware as well. + +5.6. DNS64 and multihoming + + Synthetic AAAA records may be constructed on the basis of the network + context in which they were constructed. Therefore, a synthetic AAAA + received from one interface MUST NOT be used to resolve hosts via + another network interface. [[anchor21: This seems to be the result of + the discussion on-list starting with message id 18034D4D7FE9AE48BF19A + B1B0EF2729F3EF0E69687@NOK-EUMSG-01.mgdnok.nokia.com, but it's pretty + strange when stated baldly. In particular, how is the multi-homed + host supposed to know that a given AAAA is synthetic? + --ajs@shinkuro.com]] + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 15] + +Internet-Draft DNS64 October 2009 + + +6. Deployment notes + + While DNS64 is intended to be part of a strategy for aiding IPv6 + deployment in an internetworking environment with some IPv4-only and + IPv6-only networks, it is important to realise that it is + incompatible with some things that may be deployed in an IPv4-only or + dual-stack context. + +6.1. DNS resolvers and DNS64 + + Full-service resolvers that are unaware of the DNS64 function can be + (mis)configured to act as mixed-mode iterative and forwarding + resolvers. In a native-IPv4 context, this sort of configuration may + appear to work. It is impossible to make it work properly without it + being aware of the DNS64 function, because it will likely at some + point obtain IPv4-only glue records and attempt to use them for + resolution. The result that is returned will contain only A records, + and without the ability to perform the DNS64 function the resolver + will simply be unable to answer the necessary AAAA queries. + +6.2. DNSSEC validators and DNS64 + + Existing DNSSEC validators (i.e. that are unaware of DNS64) will + reject all the data that comes from the DNS64 as having been tampered + with. If it is necessary to have validation behind the DNS64, then + the validator must know how to perform the DNS64 function itself. + Alternatively, the validating host may establish a trusted connection + with the DNS64, and allow the DNS64 to do all validation on its + behalf. + + +7. Security Considerations + + See the discussion on the usage of DNSSEC and DNS64 described in the + document. + + +8. Contributors + + Dave Thaler + + Microsoft + + dthaler@windows.microsoft.com + + + + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 16] + +Internet-Draft DNS64 October 2009 + + +9. Acknowledgements + + This draft contains the result of discussions involving many people, + including the participants of the IETF BEHAVE Working Group. The + following IETF participants made specific contributions to parts of + the text, and their help is gratefully acknowledged: Mark Andrews, + Jari Arkko, Rob Austein, Timothy Baldwin, Fred Baker, Marc Blanchet, + Cameron Byrne, Brian Carpenter, Hui Deng, Francis Dupont, Ed + Jankiewicz, Peter Koch, Suresh Krishnan, Ed Lewis, Xing Li, Matthijs + Mekking, Hiroshi Miyata, Simon Perrault, Teemu Savolainen, Jyrki + Soini, Dave Thaler, Mark Townsley, Stig Venaas, Magnus Westerlund, + Florian Weimer, Dan Wing, Xu Xiaohu. + + Marcelo Bagnulo and Iljitsch van Beijnum are partly funded by + Trilogy, a research project supported by the European Commission + under its Seventh Framework Program. + + +10. References + +10.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", + STD 13, RFC 1034, November 1987. + + [RFC1035] Mockapetris, P., "Domain names - implementation and + specification", STD 13, RFC 1035, November 1987. + + [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", + RFC 2671, August 1999. + + [RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection", + RFC 2672, August 1999. + + [RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm + (SIIT)", RFC 2765, February 2000. + + [RFC4787] Audet, F. and C. Jennings, "Network Address Translation + (NAT) Behavioral Requirements for Unicast UDP", BCP 127, + RFC 4787, January 2007. + + [I-D.ietf-behave-tcp] + Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. + Srisuresh, "NAT Behavioral Requirements for TCP", + draft-ietf-behave-tcp-08 (work in progress), + + + +Bagnulo, et al. Expires April 22, 2010 [Page 17] + +Internet-Draft DNS64 October 2009 + + + September 2008. + + [I-D.ietf-behave-nat-icmp] + Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT + Behavioral Requirements for ICMP protocol", + draft-ietf-behave-nat-icmp-12 (work in progress), + January 2009. + + [I-D.thaler-behave-translator-addressing] + Thaler, D., "IPv6 Addressing of IPv6/IPv4 Translators", + draft-thaler-behave-translator-addressing-00 (work in + progress), July 2009. + +10.2. Informative References + + [I-D.bagnulo-behave-nat64] + Bagnulo, M., Matthews, P., and I. Beijnum, "NAT64: Network + Address and Protocol Translation from IPv6 Clients to IPv4 + Servers", draft-bagnulo-behave-nat64-03 (work in + progress), March 2009. + + [RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address + Translation - Protocol Translation (NAT-PT)", RFC 2766, + February 2000. + + [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, + "Dynamic Updates in the Domain Name System (DNS UPDATE)", + RFC 2136, April 1997. + + [RFC1858] Ziemba, G., Reed, D., and P. Traina, "Security + Considerations for IP Fragment Filtering", RFC 1858, + October 1995. + + [RFC3128] Miller, I., "Protection Against a Variant of the Tiny + Fragment Attack (RFC 1858)", RFC 3128, June 2001. + + [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network + Address Translator (Traditional NAT)", RFC 3022, + January 2001. + + [RFC3484] Draves, R., "Default Address Selection for Internet + Protocol version 6 (IPv6)", RFC 3484, February 2003. + + [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, + "DNS Extensions to Support IP Version 6", RFC 3596, + October 2003. + + [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. + + + +Bagnulo, et al. Expires April 22, 2010 [Page 18] + +Internet-Draft DNS64 October 2009 + + + Rose, "DNS Security Introduction and Requirements", + RFC 4033, March 2005. + + [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. + Rose, "Resource Records for the DNS Security Extensions", + RFC 4034, March 2005. + + [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. + Rose, "Protocol Modifications for the DNS Security + Extensions", RFC 4035, March 2005. + + [RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network + Address Translator - Protocol Translator (NAT-PT) to + Historic Status", RFC 4966, July 2007. + + [I-D.iana-rfc3330bis] + Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses", + draft-iana-rfc3330bis-06 (work in progress), + February 2009. + + [I-D.ietf-mmusic-ice] + Rosenberg, J., "Interactive Connectivity Establishment + (ICE): A Protocol for Network Address Translator (NAT) + Traversal for Offer/Answer Protocols", + draft-ietf-mmusic-ice-19 (work in progress), October 2007. + + [I-D.ietf-6man-addr-select-sol] + Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama, + "Solution approaches for address-selection problems", + draft-ietf-6man-addr-select-sol-01 (work in progress), + June 2008. + + [RFC3498] Kuhfeld, J., Johnson, J., and M. Thatcher, "Definitions of + Managed Objects for Synchronous Optical Network (SONET) + Linear Automatic Protection Switching (APS) + Architectures", RFC 3498, March 2003. + + [I-D.wing-behave-learn-prefix] + Wing, D., Wang, X., and X. Xu, "Learning the IPv6 Prefix + of an IPv6/IPv4 Translator", + draft-wing-behave-learn-prefix-02 (work in progress), + May 2009. + + [I-D.miyata-behave-prefix64] + Miyata, H. and M. Bagnulo, "PREFIX64 Comparison", + draft-miyata-behave-prefix64-02 (work in progress), + March 2009. + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 19] + +Internet-Draft DNS64 October 2009 + + + [I-D.venaas-behave-mcast46] + Venaas, S., "An IPv4 - IPv6 multicast translator", + draft-venaas-behave-mcast46-00 (work in progress), + December 2008. + + [I-D.ietf-dnsop-default-local-zones] + Andrews, M., "Locally-served DNS Zones", + draft-ietf-dnsop-default-local-zones-08 (work in + progress), February 2009. + + +Appendix A. Deployment scenarios and examples + + In this section, we first provide a description of the default + address transformation algorithm and then we walk through some sample + scenarios that are expected to be common deployment cases. It should + be noted that is provided for illustrative purposes and this section + is not normative. The normative definition of DNS64 is provided in + Section 5 and the normative definition of the address transformation + algorithm is provided in [I-D.thaler-behave-translator-addressing]. + + There are two main different setups where DNS64 is expected to be + used (other setups are possible as well, but these two are the main + ones identified at the time of this writing). + + One possible setup that is expected to be common is the case of an + end site or an ISP that is providing IPv6-only connectivity or + connectivity to IPv6-only hosts that wants to allow the + communication from these IPv6-only connected hosts to the IPv4 + Internet. This case is called An-IPv6-network-to-IPv4-Internet. + In this case, the IPv6/IPv4 Translator is used to connect the end + site or the ISP to the IPv4 Internet and the DNS64 function is + provided by the end site or the ISP. + + The other possible setup that is expected is an IPv4 site that + wants that its IPv4 servers to be reachable from the IPv6 + Internet. This case is called IPv6-Internet-to-an-IPv4-network. + It should be noted that the IPv4 addresses used in the IPv4 site + can be either public or private. In this case, the IPv6/IPv4 + Translator is used to connect the IPv4 end site to the IPv6 + Internet and the DNS64 function is provided by the end site + itself. + + In this section we illustrate how the DNS64 behaves in the different + scenarios that are expected to be common. We consider then 3 + possible scenarios, namely: + + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 20] + +Internet-Draft DNS64 October 2009 + + + 1. An-IPv6-network-to-IPv4-Internet setup with DNS64 in DNS server + mode + + 2. An-IPv6-network-to-IPv4-Internet setup with DNS64 in stub- + resolver mode + + 3. IPv6-Internet-to-an-IPv4-network setup with DNS64 in DNS server + mode + + The notation used is the following: upper case letters are IPv4 + addresses; upper case letters with a prime(') are IPv6 addresses; + lower case letters are ports; prefixes are indicated by "P::X", which + is an IPv6 address built from an IPv4 address X by adding the prefix + P, mappings are indicated as "(X,x) <--> (Y',y)". + +A.1. Embed and Zero-Pad algorithm description + + In this section we describe the default algorithm for the generation + of IPv6 address from IPv4 address to be implemented in the DNS64. + + The only parameter required by the default algorithm is an IPv6 + prefix. This prefix is used to map IPv4 addresses into IPv6 + addresses, and is denoted Pref64. If we note n the length of the + prefix Pref64, then n must the less or equal than 96. If an Pref64 + is configured through any means in the DNS64 (such as manually + configured, or other automatic mean not specified in this document), + the default algorithm must use this prefix. If no prefix is + available the algorithm must use the Well-Know prefix (include here + the prefix to be assigned by IANA) defined in + [I-D.thaler-behave-translator-addressing] + + The input for the algorithm are: + + The IPv4 address: X + + The IPv6 prefix: Pref64::/n + + The IPv6 address is generated by concatenating the prefix Pref64::/n, + the IPv4 address X and optionally (in case n is strictly smaller than + 96) an all-zero suffix. So, the resulting IPv6 address would be + Pref64:X:: + + Reverse algorithm + + We next describe the reverse algorithm of the algorithm described in + the previous section. This algorithm allows to generate and IPv4 + address from an IPv6 address. This reverse algorithm is NOT + implemented by the DNS64 but it is implemented in the IPv6/IPv4 + + + +Bagnulo, et al. Expires April 22, 2010 [Page 21] + +Internet-Draft DNS64 October 2009 + + + translator that is serving the same domain the DNS64. + + The only parameter required by the default algorithm is an IPv6 + prefix. This prefix is the one originally used to map IPv4 addresses + into IPv6 addresses, and is denoted Pref64. + + The input for the algorithm are: + + The IPv6 address: X' + + The IPv6 prefix: Pref64::/n + + First, the algorithm checks that the fist n bits of the IPv6 address + X' match with the prefix Pref64::/n i.e. verifies that Pref64::/n = + X'/n. + + If this is not the case, the algorithm ends and no IPv4 address is + generated. + + If the verification is successful, then the bits between the n+1 + and the n+32 of the IPv6 address X' are extracted to form the IPv4 + address. + +A.2. An-IPv6-network-to-IPv4-Internet setup with DNS64 in DNS server + mode + + In this example, we consider an IPv6 node located in an IPv6-only + site that initiates a communication to an IPv4 node located in the + IPv4 Internet. + + The scenario for this case is depicted in the following figure: + + + +---------------------------------------+ +-----------+ + |IPv6 site +-------------+ |IP Addr: | | + | +----+ | Name server | +-------+ T | IPv4 | + | | H1 | | with DNS64 | |64Trans|------| Internet | + | +----+ +-------------+ +-------+ +-----------+ + | |IP addr: Y' | | | |IP addr: X + | --------------------------------- | +----+ + +---------------------------------------+ | H2 | + +----+ + + The figure shows an IPv6 node H1 which has an IPv6 address Y' and an + IPv4 node H2 with IPv4 address X. + + A IPv6/IPv4 Translator connects the IPv6 network to the IPv4 + Internet. This IPv6/IPv4 Translator has a prefix (called Pref64::/n) + + + +Bagnulo, et al. Expires April 22, 2010 [Page 22] + +Internet-Draft DNS64 October 2009 + + + an IPv4 address T assigned to its IPv4 interface. + + The other element involved is the local name server. The name server + is a dual-stack node, so that H1 can contact it via IPv6, while it + can contact IPv4-only name servers via IPv4. + + The local name server needs to know the prefix assigned to the local + IPv6/IPv4 Translator (Pref64::/n). For the purpose of this example, + we assume it learns this through manual configuration. + + For this example, assume the typical DNS situation where IPv6 hosts + have only stub resolvers, and always query a name server that + performs recursive lookups (henceforth called "the recursive + nameserver"). + + The steps by which H1 establishes communication with H2 are: + + 1. H1 does a DNS lookup for FQDN(H2). H1 does this by sending a DNS + query for an AAAA record for H2 to the recursive name server. + The recursive name server implements DNS64 functionality. + + 2. The recursive name server resolves the query, and discovers that + there are no AAAA records for H2. + + 3. The recursive name server queries for an A record for H2 and gets + back an A record containing the IPv4 address X. The name server + then synthesizes an AAAA record. The IPv6 address in the AAAA + record contains the prefix assigned to the IPv6/IPv4 Translator + in the upper n bits then the IPv4 address X and then an all-zero + padding i.e. the resulting IPv6 address is Pref64:X:: + + 4. H1 receives the synthetic AAAA record and sends a packet towards + H2. The packet is sent from a source transport address of (Y',y) + to a destination transport address of (Pref64:X::,x), where y and + x are ports chosen by H2. + + 5. The packet is routed to the IPv6 interface of the IPv6/IPv4 + Translator and the subsequent communication flows by means of the + IPv6/IPv4 Translator mechanisms. + +A.3. An-IPv6-network-to-IPv4-Internet setup with DNS64 in stub-resolver + mode + + The scenario for this case is depicted in the following figure: + + + + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 23] + +Internet-Draft DNS64 October 2009 + + + +---------------------------------------+ +-----------+ + |IPv6 site +-------+ |IP addr: | | + | +---------------+ | Name | +-------+ T | IPv4 | + | | H1 with DNS64 | | Server| |64Trans|------| Internet | + | +---------------+ +-------+ +-------+ +-----------+ + | |IP addr: Y' | | | |IP addr: X + | --------------------------------- | +----+ + +---------------------------------------+ | H2 | + +----+ + + The figure shows an IPv6 node H1 which has an IPv6 address Y' and an + IPv4 node H2 with IPv4 address X. Node H1 is implementing the DNS64 + function. + + A IPv6/IPv4 Translator connects the IPv6 network to the IPv4 + Internet. This IPv6/IPv4 Translator has a prefix (called Pref64::/n) + and an IPv4 address T assigned to its IPv4 interface. + + H1 needs to know the prefix assigned to the local IPv6/IPv4 + Translator (Pref64::/n). For the purpose of this example, we assume + it learns this through manual configuration. + + Also shown is a name server. For the purpose of this example, we + assume that the name server is a dual-stack node, so that H1 can + contact it via IPv6, while it can contact IPv4-only name servers via + IPv4. + + For this example, assume the typical situation where IPv6 hosts have + only stub resolvers and always query a name server that provides + recursive lookups (henceforth called "the recursive name server"). + The recursive name server does not perform the DNS64 function. + + The steps by which H1 establishes communication with H2 are: + + 1. H1 does a DNS lookup for FQDN(H2). H1 does this by sending a DNS + query for a AAAA record for H2 to the recursive name server. + + 2. The recursive DNS server resolves the query, and returns the + answer to H1. Because there are no AAAA records in the global + DNS for H2, the answer is empty. + + 3. The stub resolver at H1 then queries for an A record for H2 and + gets back an A record containing the IPv4 address X. The DNS64 + function within H1 then synthesizes a AAAA record. The IPv6 + address in the AAAA record contains the prefix assigned to the + IPv6/IPv4 Translator in the upper n bits, then the IPv4 address X + and then an all-zero padding i.e. the resulting IPv6 address is + Pref64:X::. + + + +Bagnulo, et al. Expires April 22, 2010 [Page 24] + +Internet-Draft DNS64 October 2009 + + + 4. H1 sends a packet towards H2. The packet is sent from a source + transport address of (Y',y) to a destination transport address of + (Pref64:X::,x), where y and x are ports chosen by H2. + + 5. The packet is routed to the IPv6 interface of the IPv6/IPv4 + Translator and the subsequent communication flows using the IPv6/ + IPv4 Translator mechanisms. + +A.4. IPv6-Internet-to-an-IPv4-network setup DNS64 in DNS server mode + + In this example, we consider an IPv6 node located in the IPv6 + Internet site that initiates a communication to a IPv4 node located + in the IPv4 site. + + This scenario can be addressed without using any form of DNS64 + function. This is so because it is possible to assign a fixed IPv6 + address to each of the IPv4 servers. Such an IPv6 address would be + constructed as the Pref64::/n concatenated with the IPv4 address of + the IPv4 server and an all-zero padding. Note that the IPv4 address + can be a public or a private address; the latter does not present any + additional difficulty, since the LIR prefix must be used a Pref64 (in + this scenario the usage of the WK prefix is not supported). Once + these IPv6 addresses have been assigned to represent the IPv4 servers + in the IPv6 Internet, real AAAA RRs containing these addresses can be + published in the DNS under the site's domain. This is the + recommended approach to handle this scenario, because it does not + involve synthesizing AAAA records at the time of query. Such a + configuration is easier to troubleshoot in the event of problems, + because it always provides the same answer to every query. + + However, there are some more dynamic scenarios, where synthesizing + AAAA RRs in this setup may be needed. In particular, when DNS Update + [RFC2136] is used in the IPv4 site to update the A RRs for the IPv4 + servers, there are two options: One option is to modify the server + that receives the dynamic DNS updates. That would normally be the + authoritative server for the zone. So the authoritative zone would + have normal AAAA RRs that are synthesized as dynamic updates occur. + The other option is modify the authoritative server to generate + synthetic AAAA records for a zone, possibly based on additional + constraints, upon the receipt of a DNS query for the AAAA RR. The + first option -- in which the AAAA is synthesized when the DNS update + message is received, and the data published in the relevant zone -- + is recommended over the second option (i.e. the synthesis upon + receipt of the AAAA DNS query). This is because it is usually easier + to solve problems of misconfiguration and so on when the DNS + responses are not being generated dynamically. For completeness, the + DNS64 behavior that we describe in this section covers the case of + synthesizing the AAAA RR when the DNS query arrives. Nevertheless, + + + +Bagnulo, et al. Expires April 22, 2010 [Page 25] + +Internet-Draft DNS64 October 2009 + + + such a configuration is NOT RECOMMENDED. Troubleshooting + configurations that change the data depending on the query they + receive is notoriously hard, and the IPv4/IPv6 translation scenario + is complicated enough without adding additional opportunities for + possible malfunction. + + The scenario for this case is depicted in the following figure: + + + +-----------+ +----------------------------------------+ + | | | IPv4 site +-------------+ | + | IPv6 | +-------+ +----+ | Name server | | + | Internet |------|64Trans| | H2 | | with DNS64 | | + +-----------+ +-------+ +----+ +-------------+ | + |IP addr: Y' | | |IP addr: X | | + +----+ | ----------------------------------- | + | H1 | +----------------------------------------+ + +----+ + + The figure shows an IPv6 node H1 which has an IPv6 address Y' and an + IPv4 node H2 with IPv4 address X. + + A IPv6/IPv4 Translator connects the IPv4 network to the IPv6 + Internet. This IPv6/IPv4 Translator has a prefix (called + Pref64::/n). + + Also shown is the authoritative name server for the local domain with + DNS64 functionality. For the purpose of this example, we assume that + the name server is a dual-stack node, so that H1 or a recursive + resolver acting on the request of H1 can contact it via IPv6, while + it can be contacted by IPv4-only nodes to receive dynamic DNS updates + via IPv4. + + The local name server needs to know the prefix assigned to the local + IPv6/IPv4 Translator (Pref64::/n). For the purpose of this example, + we assume it learns this through manual configuration. + + The steps by which H1 establishes communication with H2 are: + + 1. H1 does a DNS lookup for FQDN(H2). H1 does this by sending a DNS + query for an AAAA record for H2. The query is eventually + forwarded to the server in the IPv4 site. + + 2. The local DNS server resolves the query (locally), and discovers + that there are no AAAA records for H2. + + 3. The name server verifies that FQDN(H2) and its A RR are among + those that the local policy defines as allowed to generate a AAAA + + + +Bagnulo, et al. Expires April 22, 2010 [Page 26] + +Internet-Draft DNS64 October 2009 + + + RR from. If that is the case, the name server synthesizes an + AAAA record from the A RR and the relevant Pref64::/n. The IPv6 + address in the AAAA record contains the prefix assigned to the + IPv6/IPv4 Translator in the first n bits and the IPv4 address X + and then an all-zero padding. + + 4. H1 receives the synthetic AAAA record and sends a packet towards + H2. The packet is sent from a source transport address of (Y',y) + to a destination transport address of (Pref64:X::,x), where y and + x are ports chosen by H2. + + 5. The packet is routed through the IPv6 Internet to the IPv6 + interface of the IPv6/IPv4 Translator and the communication flows + using the IPv6/IPv4 Translator mechanisms. + + +Appendix B. Motivations and Implications of synthesizing AAAA RR when + real AAAA RR exists + + The motivation for synthesizing AAAA RR when a real AAAA RR exists is + to support the following scenario: + + An IPv4-only server application (e.g. web server software) is + running on a dual-stack host. There may also be dual-stack server + applications also running on the same host. That host has fully + routable IPv4 and IPv6 addresses and hence the authoritative DNS + server has an A and a AAAA record as a result. + + An IPv6-only client (regardless of whether the client application + is IPv6-only, the client stack is IPv6-only, or it only has an + IPv6 address) wants to access the above server. + + The client issues a DNS query to a DNS64 recursor. + + If the DNS64 only generates a synthetic AAAA if there's no real AAAA, + then the communication will fail. Even though there's a real AAAA, + the only way for communication to succeed is with the translated + address. So, in order to support this scenario, the administrator of + a DNS64 service may want to enable the synthesis of AAAA RR even when + real AAAA RR exist. + + The implication of including synthetic AAAA RR when real AAAA RR + exist is that translated connectivity may be preferred over native + connectivity in some cases where the DNS64 is operated in DNS server + mode. + + RFC3484 [RFC3484] rules use longest prefix match to select which is + the preferred destination address to use. So, if the DNS64 recursor + + + +Bagnulo, et al. Expires April 22, 2010 [Page 27] + +Internet-Draft DNS64 October 2009 + + + returns both the synthetic AAAA RR and the real AAAA RR, then if the + DNS64 is operated by the same domain as the initiating host, and a + global unicast prefix (called the LIR prefix as defined in + [I-D.thaler-behave-translator-addressing]) is used, then the + synthetic AAAA RR is likely to be preferred. + + This means that without further configuration: + + In the case of An IPv6 network to the IPv4 internet, the host will + prefer translated connectivity if LIR prefix is used. If the + Well-Known (WK) prefix defined in + [I-D.thaler-behave-translator-addressing] is used, it will + probably prefer native connectivity. + + In the case of the IPv6 Internet to an IPv4 network, it is + possible to bias the selection towards the real AAAA RR if the + DNS64 recursor returns the real AAAA first in the DNS reply, when + the LIR prefix is used (the WK prefix usage is not recommended in + this case) + + In the case of the IPv6 to IPv4 in the same network, for local + destinations (i.e., target hosts inside the local site), it is + likely that the LIR prefix and the destination prefix are the + same, so we can use the order of RR in the DNS reply to bias the + selection through native connectivity. If a WK prefix is used, + the longest prefix match rule will select native connectivity. + + So this option introduces problems in the following cases: + + An IPv6 network to the IPv4 internet with the LIR prefix + + IPv6 to IPv4 in the same network when reaching external + destinations and the LIR prefix is used. + + In any case, the problem can be solved by properly configuring the + RFC3484 [RFC3484] policy table, but this requires effort on the part + of the site operator. + + + + + + + + + + + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 28] + +Internet-Draft DNS64 October 2009 + + +Authors' Addresses + + Marcelo Bagnulo + UC3M + Av. Universidad 30 + Leganes, Madrid 28911 + Spain + + Phone: +34-91-6249500 + Fax: + Email: marcelo@it.uc3m.es + URI: http://www.it.uc3m.es/marcelo + + + Andrew Sullivan + Shinkuro + 4922 Fairmont Avenue, Suite 250 + Bethesda, MD 20814 + USA + + Phone: +1 301 961 3131 + Email: ajs@shinkuro.com + + + Philip Matthews + Unaffiliated + 600 March Road + Ottawa, Ontario + Canada + + Phone: +1 613-592-4343 x224 + Fax: + Email: philip_matthews@magma.ca + URI: + + + Iljitsch van Beijnum + IMDEA Networks + Av. Universidad 30 + Leganes, Madrid 28911 + Spain + + Phone: +34-91-6246245 + Email: iljitsch@muada.com + + + + + + + +Bagnulo, et al. Expires April 22, 2010 [Page 29] +