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diff --git a/doc/draft/draft-ietf-behave-dns64-11.txt b/doc/draft/draft-ietf-behave-dns64-11.txt new file mode 100644 index 00000000..3c5ac813 --- /dev/null +++ b/doc/draft/draft-ietf-behave-dns64-11.txt @@ -0,0 +1,1792 @@ + + + +BEHAVE WG M. Bagnulo +Internet-Draft UC3M +Intended status: Standards Track A. Sullivan +Expires: April 4, 2011 Shinkuro + P. Matthews + Alcatel-Lucent + I. van Beijnum + IMDEA Networks + October 1, 2010 + + +DNS64: DNS extensions for Network Address Translation from IPv6 Clients + to IPv4 Servers + draft-ietf-behave-dns64-11 + +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. + +Status of this Memo + + This Internet-Draft is submitted in full conformance with the + provisions of BCP 78 and BCP 79. + + Internet-Drafts are working documents of the Internet Engineering + Task Force (IETF). Note that other groups may also distribute + working documents as Internet-Drafts. The list of current Internet- + Drafts is at http://datatracker.ietf.org/drafts/current/. + + 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." + + This Internet-Draft will expire on April 4, 2011. + +Copyright Notice + + Copyright (c) 2010 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 + + + +Bagnulo, et al. Expires April 4, 2011 [Page 1] + +Internet-Draft DNS64 October 2010 + + + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 2] + +Internet-Draft DNS64 October 2010 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 3. Background to DNS64-DNSSEC interaction . . . . . . . . . . . . 8 + 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 10 + 5. DNS64 Normative Specification . . . . . . . . . . . . . . . . 11 + 5.1. Resolving AAAA queries and the answer section . . . . . . 11 + 5.1.1. The answer when there is AAAA data available . . . . . 12 + 5.1.2. The answer when there is an error . . . . . . . . . . 12 + 5.1.3. Dealing with timeouts . . . . . . . . . . . . . . . . 12 + 5.1.4. Special exclusion set for AAAA records . . . . . . . . 13 + 5.1.5. Dealing with CNAME and DNAME . . . . . . . . . . . . . 13 + 5.1.6. Data for the answer when performing synthesis . . . . 13 + 5.1.7. Performing the synthesis . . . . . . . . . . . . . . . 14 + 5.1.8. Querying in parallel . . . . . . . . . . . . . . . . . 14 + 5.2. Generation of the IPv6 representations of IPv4 + addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 + 5.3. Handling other Resource Records and the Additional + Section . . . . . . . . . . . . . . . . . . . . . . . . . 16 + 5.3.1. PTR Resource Record . . . . . . . . . . . . . . . . . 16 + 5.3.2. Handling the additional section . . . . . . . . . . . 17 + 5.3.3. Other Resource Records . . . . . . . . . . . . . . . . 17 + 5.4. Assembling a synthesized response to a AAAA query . . . . 18 + 5.5. DNSSEC processing: DNS64 in validating resolver mode . . . 18 + 6. Deployment notes . . . . . . . . . . . . . . . . . . . . . . . 19 + 6.1. DNS resolvers and DNS64 . . . . . . . . . . . . . . . . . 19 + 6.2. DNSSEC validators and DNS64 . . . . . . . . . . . . . . . 20 + 6.3. DNS64 and multihomed and dual-stack hosts . . . . . . . . 20 + 6.3.1. IPv6 multihomed hosts . . . . . . . . . . . . . . . . 20 + 6.3.2. Accidental dual-stack DNS64 use . . . . . . . . . . . 21 + 6.3.3. Intentional dual-stack DNS64 use . . . . . . . . . . . 21 + 7. Deployment scenarios and examples . . . . . . . . . . . . . . 22 + 7.1. Example of An-IPv6-network-to-IPv4-Internet setup with + DNS64 in DNS server mode . . . . . . . . . . . . . . . . . 22 + 7.2. An example of an-IPv6-network-to-IPv4-Internet setup + with DNS64 in stub-resolver mode . . . . . . . . . . . . . 24 + 7.3. Example of IPv6-Internet-to-an-IPv4-network setup + DNS64 in DNS server mode . . . . . . . . . . . . . . . . . 25 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 27 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 + 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 28 + 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 + 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 + 12.1. Normative References . . . . . . . . . . . . . . . . . . . 28 + 12.2. Informative References . . . . . . . . . . . . . . . . . . 29 + Appendix A. Motivations and Implications of synthesizing AAAA + Resource Records when real AAAA Resource Records + + + +Bagnulo, et al. Expires April 4, 2011 [Page 3] + +Internet-Draft DNS64 October 2010 + + + exist . . . . . . . . . . . . . . . . . . . . . . . . 30 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 4] + +Internet-Draft DNS64 October 2010 + + +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 stateful NAT64 + [I-D.ietf-behave-v6v4-xlate-stateful], 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 owner name 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 an 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 features + require performing the DNS64 function directly in the end-hosts + themselves. + + This document is structured as follows: section 2 provides a non- + normative overview of the behaviour of DNS64. Section 3 provides a + non-normative background required to understand the interaction + between DNS64 and DNSSEC. The normative specification of DNS64 is + provided in sections 4, 5 and 6. Section 4 defines the terminology, + section 5 is the actual DNS64 specification and section 6 covers + deployments issues. Section 7 is non-normative and provides a set of + examples and typical deployment scenarios. + + +2. Overview + + This section provides an introduction to the DNS64 mechanism. + + We assume that we have one or more IPv6/IPv4 translator boxes + + + +Bagnulo, et al. Expires April 4, 2011 [Page 5] + +Internet-Draft DNS64 October 2010 + + + 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 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 cases where only IPv4 connectivity is + available to the server). Each 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 cannot retrieve a AAAA record for the + queried name. The DNS64 service appears as a regular DNS server or + resolver to the IPv6 initiator. The DNS64 receives a AAAA DNS query + generated by the IPv6 initiator. It first attempts a resolution for + the requested AAAA records. If there are no AAAA records 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. For each A + record discovered, DNS64 creates a synthetic AAAA RR from the + information retrieved in the A RR. + + The owner name 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. If not explicitly mentioned, all prefixes are treated + equally and the operations described in this document are performed + using the prefixes available. So as to be general, we will call any + of these prefixes Pref64::/n, and describe the operations made with + the generic prefix Pref64::/n. The IPv6 address representing IPv4 + addresses included in the AAAA RR synthesized by the DNS64 contain + Pref64::/n and they also embed the original IPv4 address. + + The same algorithm and the same Pref64::/n prefix(es) must be + configured both in the DNS64 device and the IPv6/IPv4 translator(s), + 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 address that + contains the Pref64::/n be delivered to an IPv6/IPv4 translator that + has that particular Pref64::/n configured, so they can be translated + into IPv4 packets. + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 6] + +Internet-Draft DNS64 October 2010 + + + Once the DNS64 has synthesized the AAAA RRs, the synthetic AAAA RRs + are 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 an 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. + + The prefixes to be used as Pref64::/n and their applicability are + discussed in [I-D.ietf-behave-address-format]. There are two types + of prefixes that can be used as Pref64::/n. + + The Pref64::/n can be the Well-Known Prefix 64:FF9B::/96 reserved + by [I-D.ietf-behave-address-format] for the purpose of + representing IPv4 addresses in IPv6 address space. + + The Pref64::/n can be a Network-Specific Prefix (NSP). An NSP is + an IPv6 prefix assigned by an organization to create IPv6 + representations of IPv4 addresses. + + The main difference in the nature of the two types of prefixes is + that the NSP is a locally assigned prefix that is under control of + the organization that is providing the translation services, while + the Well-Known Prefix is a prefix that has a global meaning since it + has been assigned for the specific purpose of representing IPv4 + addresses in IPv6 address space. + + The DNS64 function can be performed in any of three places. The + terms below are more formally defined in Section 4. + + The first option is to locate the DNS64 function in authoritative + servers for a zone. In this case, the authoritative server provides + synthetic AAAA RRs for an IPv4-only host in its zone. This is one + type of DNS64 server. + + Another 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 recursive resolver + + + +Bagnulo, et al. Expires April 4, 2011 [Page 7] + +Internet-Draft DNS64 October 2010 + + + mode". This is a second type of DNS64 server, and it is also one + type of DNS64 resolver. + + The last option is to place the DNS64 function in the end hosts, + 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 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". This is the second type of + DNS64 resolver. + + +3. Background to DNS64-DNSSEC interaction + + DNSSEC ([RFC4033], [RFC4034], [RFC4035]) 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 resolver can be validating or + non-validating, according to operator policy. In the cases below, + the recursive resolver 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 "DNSSEC OK" (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 "Checking Disabled" + (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 validate, but it must return all data to the + querying agent anyway. + + Here are the possible cases: + + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 8] + +Internet-Draft DNS64 October 2010 + + + 1. A DNS64 (DNSSEC-aware or DNSSEC-oblivious) 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. The + DNS64 can do validation of the response, if dictated by its local + policy. + + 2. A security-oblivious DNS64 receives a query with the DO bit set, + and the CD bit clear or set. 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 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 receives a query with + the DO bit set and the CD bit set. In this case, the DNS64 is + supposed to pass on all the data it gets to the query initiator + (see section 3.2.2 of [RFC4035]). This case will not work with + DNS64, unless the validating resolver is prepared to do DNS64 + itself. If the DNS64 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 resolver 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 (Server + failure); 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 should have + set DO and CD), cannot tell that DNS64 is involved. + + 6. A security-aware and validating DNS64 resolver receives a query + with the DO bit set and CD clear. This works like the previous + case, except that the resolver should also set the "Authentic + Data" (AD) bit on the response. + + 7. A security-aware and validating DNS64 resolver 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. The node needs to do DNS64 + itself, or else communication will fail. + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 9] + +Internet-Draft DNS64 October 2010 + + +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 request. + + DNS64: A logical function that synthesizes DNS resource records (e.g + AAAA records containing IPv6 addresses) from DNS resource records + actually contained in the DNS (e.g., A records containing IPv4 + addresses). + + DNS64 recursive resolver: A recursive resolver that provides the + DNS64 functionality as part of its operation. This is the same + thing as "DNS64 in recursive resolver mode". + + DNS64 resolver: Any resolver (stub resolver or recursive resolver) + that provides the DNS64 function. + + DNS64 server: Any server providing the DNS64 function. This + includes the server portion of a recursive resolver when it is + providing the DNS64 function. + + IPv4-only server: Servers running IPv4-only applications, servers + that can only use IPv4, as well as cases where only IPv4 + connectivity is available to the server. + + IPv6-only hosts: Hosts running IPv6-only applications, hosts that + can only use IPv6, as well as cases where only IPv6 connectivity + is available to the client. + + Recursive resolver: A DNS server that accepts requests from one + resolver, and asks another server (of some description) for the + answer on behalf of the first resolver. Full discussion of DNS + recursion is beyond the scope of this document; see [RFC1034] and + [RFC1035] for full details. + + Synthetic RR: A DNS resource record (RR) that is not contained in + the authoritative servers' zone data, but which is instead + synthesized from other RRs in the same zone. An example is a + synthetic AAAA record created from an A record. + + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 10] + +Internet-Draft DNS64 October 2010 + + + 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 outlined in [RFC4035]. It is worth emphasizing that while + DNS64 is a logical function separate from the DNS, it is nevertheless + closely associated with that protocol. It depends on the DNS + protocol, and some behavior of DNS64 will interact with regular DNS + responses. + + +5. DNS64 Normative Specification + + 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. It + works within those DNS functions, and appears on the network as + though it were a "plain" DNS resolver or name server conforming to + [RFC1034], and [RFC1035]. + + The implementation SHOULD support mapping of separate IPv4 address + ranges to separate IPv6 prefixes for AAAA record synthesis. This + allows handling of special use IPv4 addresses [RFC5735]. + + DNS messages contain several sections. The portion of a DNS message + that is altered by DNS64 is the Answer section, which is discussed + below in section Section 5.1. The resulting synthetic answer is put + together with other sections, and that creates the message that is + actually returned as the response to the DNS query. Assembling that + response is covered below in section Section 5.4. + + DNS64 also responds to PTR queries involving addresses containing any + of the IPv6 prefixes it uses for synthesis of AAAA RRs. + +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. The query may be answered from + a local cache, if one is available. DNS64 operation for classes + other than IN is undefined, and a DNS64 MUST behave as though no + DNS64 function is configured. + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 11] + +Internet-Draft DNS64 October 2010 + + +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 any of the AAAA + records match a special exclusion set of prefixes, considered in + Section 5.1.4. If there is (non-excluded) AAAA data available, DNS64 + SHOULD NOT include synthetic AAAA RRs in the response (see Appendix A + 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 RCODE other than 0 (No error + condition), then there are two possibilities. A result with RCODE=3 + (Name Error) is handled according to normal DNS operation (which is + normally to return 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. + + Any other RCODE is treated as though the RCODE were 0 (see sections + Section 5.1.6 and Section 5.1.7) and the answer section were empty. + This is because of the large number of different responses from + deployed name servers when they receive AAAA queries without a AAAA + record being available (see [RFC4074]). Note that this means, for + practical purposes, that several different classes of error in the + DNS are all treated as though a AAAA record is not available for that + owner name. + + It is important to note that, as of this writing, some servers + respond with RCODE=3 to a AAAA query even if there is an A record + available for that owner name. Those servers are in clear violation + of the meaning of RCODE 3, and it is expected that they will decline + in use as IPv6 deployment increases. + +5.1.3. Dealing with timeouts + + If the query receives no answer before the timeout (which might be + the timeout from every authoritative server, depending on whether the + DNS64 is in recursive resolver mode), it is treated as RCODE=2 + (Server failure). + + + + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 12] + +Internet-Draft DNS64 October 2010 + + +5.1.4. Special exclusion set for AAAA records + + Some IPv6 addresses are not actually usable by IPv6-only hosts. If + they are returned to IPv6-only querying agents as AAAA records, + therefore, the goal of decreasing the number of failure modes will + not be attained. Examples include AAAA records with addresses in the + ::ffff:0:0/96 network, and possibly (depending on the context) AAAA + records with the site's Pref::64/n or the Well-Known Prefix (see + below for more about the Well-Known Prefix). A DNS64 implementation + SHOULD provide a mechanism to specify IPv6 prefix ranges to be + treated as though the AAAA containing them were an empty answer. An + implementation SHOULD include the ::ffff/96 network in that range by + default. Failure to provide this facility will mean that clients + querying the DNS64 function may not be able to communicate with hosts + that would be reachable from a dual-stack host. + + When the DNS64 performs its initial AAAA query, if it receives an + answer with only AAAA records containing addresses in the excluded + range(s), then it MUST treat the answer as though it were an empty + answer, and proceed accordingly. If it receives an answer with at + least one AAAA record containing an address outside any of the + excluded range(s), then it MAY build an answer section for a response + including only the AAAA record(s) that do not contain any of the + addresses inside the excluded ranges. That answer section is used in + the assembly of a response as detailed in Section 5.4. + Alternatively, it MAY treat the answer as though it were an empty + answer, and proceed accordingly. It MUST NOT return the offending + AAAA records as part of a response. + +5.1.5. Dealing with CNAME and DNAME + + If the response contains a CNAME or a DNAME, then the CNAME or DNAME + chain is followed until the first terminating A or AAAA record is + reached. This may require the DNS64 to ask for an A record, in case + the response to the original AAAA query is a CNAME or DNAME without a + AAAA record to follow. The resulting AAAA or A record is treated + like any other AAAA or A case, as appropriate. + + When assembling the answer section, any chains of CNAME or DNAME RRs + are included as part of the answer along with the synthetic AAAA (if + appropriate). + +5.1.6. Data for the answer when performing synthesis + + If the query results in no error but an empty answer section in the + response, the DNS64 attempts to retrieve A records for the name in + question, either by performing another query or, in the case of an + authoritative server, by examining its own results. If this new A RR + + + +Bagnulo, et al. Expires April 4, 2011 [Page 13] + +Internet-Draft DNS64 October 2010 + + + 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. 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 5.1.7. The DNS64 returns the + synthesized AAAA records in the answer section, removing the A + records that form the basis of the synthesis. + +5.1.7. 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 the original CLASS field, 1. Under this + specification, DNS64 for any CLASS other than 1 is undefined. + + 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. If the SOA RR was not + delivered with the negative response to the AAAA query, then the + DNS64 SHOULD use a the minimum of the TTL of the original A RR and + 600 seconds. It is possible instead to query explicitly for the + SOA RR and use the result of that query, but this will increase + query load and time to resolution for little additional benefit.) + This is in keeping with the approach used in negative caching + ([RFC2308]. + + 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 MUST + check each A RR against configured 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 + effecting the transformation. + +5.1.8. Querying in parallel + + The DNS64 MAY perform the query for the AAAA RR and for the A RR in + parallel, in order to minimize the delay. + + Note: Querying in parallel will result in performing unnecessary A RR + queries in the case where no AAAA RR synthesis is required. A + + + +Bagnulo, et al. Expires April 4, 2011 [Page 14] + +Internet-Draft DNS64 October 2010 + + + 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 + t 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 a DNS64 to create the IPv6 address to be + returned in the synthetic AAAA RR from the IPv4 address contained + in an original A RR, and by a IPv6/IPv4 translator to create the + IPv6 address to be included in the source address field of the + outgoing IPv6 packets from the IPv4 address included in the source + address field of the incoming IPv4 packet. + + The algorithm MUST be reversible; i.e., it MUST be possible to + derive 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 and in the NAT64 (such as fixed string to + be used as a suffix). + + For each prefix Pref64::/n, n MUST be less than or equal to 96. + If one or more Pref64::/n are configured in the DNS64 through + any means (such as manually configured, or other automatic + means not specified in this document), the default algorithm + MUST use these prefixes (and not use the Well-Known Prefix). + If no prefix is available, the algorithm MUST use the Well- + Known Prefix 64:FF9B::/96 defined in + [I-D.ietf-behave-address-format] to represent the IPv4 unicast + address range + + [[anchor6: Note in document: The value 64:FF9B::/96 is proposed as + the value for the Well-Known prefix and needs to be confirmed + whenis published as RFC.]][I-D.ietf-behave-address-format] + + A DNS64 MUST support the algorithm for generating IPv6 + representations of IPv4 addresses defined in Section 2 of + [I-D.ietf-behave-address-format]. Moreover, the aforementioned + + + +Bagnulo, et al. Expires April 4, 2011 [Page 15] + +Internet-Draft DNS64 October 2010 + + + algorithm MUST be the default algorithm used by the DNS64. While the + normative description of the algorithm is provided in + [I-D.ietf-behave-address-format], a sample description of the + algorithm and its application to different scenarios is provided in + Section 7 for illustration purposes. + +5.3. Handling other Resource Records and the Additional Section + +5.3.1. PTR Resource Record + + If a DNS64 server 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 any of the locally- + configured Pref64::/n or the default Well-known prefix. There are + two alternatives for a DNS64 server to respond to such PTR queries. + A DNS64 server MUST provide one of these, and SHOULD NOT provide both + at the same time unless different IP6.ARPA zones require answers of + different sorts: + + 1. The first option is for the DNS64 server to respond + authoritatively for its prefixes. If the address prefix matches + any Pref64::/n used in the site, either a NSP or the Well-Known + Prefix (i.e. 64:FF9B::/96), 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-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 + 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. + + 2. The second option is for the DNS64 nameserver to synthesize a + CNAME mapping the IP6.ARPA namespace to the corresponding IN- + ADDR.ARPA name. In this case, the DNS64 nameserver SHOULD ensure + that there is RDATA at the PTR of the corresponding IN-ADDR.ARPA + name, and that there is not an existing CNAME at that name. This + is in order to avoid synthesizing a CNAME that makes a CNAME + chain longer or that does not actually point to anything. 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 + + + +Bagnulo, et al. Expires April 4, 2011 [Page 16] + +Internet-Draft DNS64 October 2010 + + + 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. + + If the address prefix does not match any 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. + + NOTE: It may appear that adding synthetic records to the + additional section is desirable, because clients sometimes use the + data in the additional section to proceed without having to re- + query. There is in general no promise, however, that the + additional section will contain all the relevant records, so any + client that depends on the additional section being able to + satisfy its needs (i.e. without additional queries) is necessarily + broken. An IPv6-only client that needs a AAAA record, therefore, + will send a query for the necessary AAAA record if it is unable to + find such a record in the additional section of an answer it is + consuming. For a correctly-functioning client, the effect would + be no different if the additional section were empty.The + alternative, of removing the A records in the additional section + and replacing them with synthetic AAAA records, may cause a host + behind a NAT64 to query directly a nameserver that is unaware of + the NAT64 in question. The result in this case will be resolution + failure anyway, only later in the resolution operation. The + prohibition on synthetic data in the additional section reduces, + but does not eliminate, the possibility of resolution failures due + to cached DNS data from behind the DNS64. See Section 6. + +5.3.3. Other Resource Records + + If the DNS64 is in recursive resolver mode, then considerations + outlined in [I-D.ietf-dnsop-default-local-zones] may be relevant. + + All other RRs MUST be returned unchanged. This includes responses to + queries for A RRs. + + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 17] + +Internet-Draft DNS64 October 2010 + + +5.4. Assembling a synthesized response to a AAAA query + + A 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 (initiator's) 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 + (initiator's) query. The answer section is populated according to + the rules in Section 5.1.7. The authority and additional sections + are copied from the response to the final query that the DNS64 + performed, and used as the basis for synthesis. + + The final response from the DNS64 is subject to all the standard DNS + rules, including truncation [RFC1035] and EDNS0 handling [RFC2671]. + +5.5. DNSSEC processing: DNS64 in validating resolver mode + + We consider the case where a recursive resolver 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. See the next item for + rules about how to do validation and synthesis. In this case, + however, vDNS64 MUST NOT set the AD bit in any response. + + 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. + 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 + + + +Bagnulo, et al. Expires April 4, 2011 [Page 18] + +Internet-Draft DNS64 October 2010 + + + 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 return the + data 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. + + +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 + + + +Bagnulo, et al. Expires April 4, 2011 [Page 19] + +Internet-Draft DNS64 October 2010 + + + 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 be unable to answer the necessary AAAA queries. + +6.2. DNSSEC validators and DNS64 + + An existing DNSSEC validator (i.e. that is unaware of DNS64) might + reject all the data that comes from DNS64 as having been tampered + with (even if it did not set CD when querying). 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 a DNS64, and allow the + DNS64 recursive resolver to do all validation on its behalf. + +6.3. DNS64 and multihomed and dual-stack hosts + +6.3.1. IPv6 multihomed hosts + + Synthetic AAAA records may be constructed on the basis of the network + context in which they were constructed. If a host sends DNS queries + to resolvers in multiple networks, it is possible that some of them + will receive answers from a DNS64 without all of them being connected + via a NAT64. For instance, suppose a system has two interfaces, i1 + and i2. Whereas i1 is connected to the IPv4 Internet via NAT64, i2 + has native IPv6 connectivity only. I1 might receive a AAAA answer + from a DNS64 that is configured for a particular NAT64; the IPv6 + address contained in that AAAA answer will not connect with anything + via i2. + + +---------------+ +-------------+ + | i1 (IPv6)+----NAT64--------+IPv4 Internet| + | | +-------------+ + | host | + | | +-------------+ + | i2 (IPv6)+-----------------+IPv6 Internet| + +---------------+ +-------------+ + + Figure 1: IPv6 multihomed hosts + + This example illustrates why it is generally preferable that hosts + treat DNS answers from one interface as local to that interface. The + answer received on one interface will not work on the other + interface. Hosts that attempt to use DNS answers globally may + encounter surprising failures in these cases. + + Note that the issue is not that there are two interfaces, but that + there are two networks involved. The same results could be achieved + + + +Bagnulo, et al. Expires April 4, 2011 [Page 20] + +Internet-Draft DNS64 October 2010 + + + with a single interface routed to two different networks. + +6.3.2. Accidental dual-stack DNS64 use + + Similarly, suppose that i1 has IPv6 connectivity and can connect to + the IPv4 Internet through NAT64, but i2 has native IPv4 connectivity. + In this case, i1 could receive an IPv6 address from a synthetic AAAA + that would better be reached via native IPv4. Again, it is worth + emphasising that this arises because there are two networks involved. + + +---------------+ +-------------+ + | i1 (IPv6)+----NAT64--------+IPv4 Internet| + | | +-------------+ + | host | + | | +-------------+ + | i2 (IPv4)+-----------------+IPv4 Internet| + +---------------+ +-------------+ + + Figure 2: Accidental dual-stack DNS64 use + + The default configuration of dual-stack hosts is that IPv6 is + preferred over IPv4 ([RFC3484]). In that arrangement the host will + often use the NAT64 when native IPv4 would be more desirable. For + this reason, hosts with IPv4 connectivity to the Internet should + avoid using DNS64. This can be partly resolved by ISPs when + providing DNS resolvers to clients, but that is not a guarantee that + the NAT64 will never be used when a native IPv4 connection should be + used. There is no general-purpose mechanism to ensure that native + IPv4 transit will always be preferred, because to a DNS64-oblivious + host, the DNS64 looks just like an ordinary DNS server. Operators of + a NAT64 should expect traffic to pass through the NAT64 even when it + is not necessary. + +6.3.3. Intentional dual-stack DNS64 use + + Finally, consider the case where the IPv4 connectivity on i2 is only + with a LAN, and not with the IPv4 Internet. The IPv4 Internet is + only accessible using the NAT64. In this case, it is critical that + the DNS64 not synthesize AAAA responses for hosts in the LAN, or else + that the DNS64 be aware of hosts in the LAN and provide context- + sensitive answers ("split view" DNS answers) for hosts inside the + LAN. As with any split view DNS arrangement, operators must be + prepared for data to leak from one context to another, and for + failures to occur because nodes accessible from one context are not + accessible from the other. + + + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 21] + +Internet-Draft DNS64 October 2010 + + + +---------------+ +-------------+ + | i1 (IPv6)+----NAT64--------+IPv4 Internet| + | | +-------------+ + | host | + | | + | i2 (IPv4)+---(local LAN only) + +---------------+ + + Figure 3: Intentional dual-stack DNS64 use + + It is important for deployers of DNS64 to realise that, in some + circumstances, making the DNS64 available to a dual-stack host will + cause the host to prefer to send packets via NAT64 instead of via + native IPv4, with the associated loss of performance or functionality + (or both) entailed by the NAT. At the same time, some hosts are not + able to learn about DNS servers provisioned on IPv6 addresses, or + simply cannot send DNS packets over IPv6. + + +7. Deployment scenarios and examples + + In this section we illustrate how the DNS64 behaves in different + scenarios that are expected to be common. In particular we will + consider the following scenarios defined in + [I-D.ietf-behave-v6v4-framework]: the an-IPv6-network-to-IPv4- + Internet scenario (both with DNS64 in DNS server mode and in stub- + resolver mode) and the IPv6-Internet-to-an-IPv4-network setup (with + DNS64 in DNS server mode only). + + In all the examples below, there is a IPv6/IPv4 translator connecting + the IPv6 domain to the IPv4 one. Also there is a name server that is + a dual-stack node, so it can communicate with IPv6 hosts using IPv6 + and with IPv4 nodes using IPv4. In addition, we assume that in the + examples, the DNS64 function learns which IPv6 prefix it needs to use + to map the IPv4 address space through manual configuration. + +7.1. Example of 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: + + + + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 22] + +Internet-Draft DNS64 October 2010 + + + +---------------------+ +---------------+ + |IPv6 network | | IPv4 | + | | +-------------+ | Internet | + | |--| Name server |--| | + | | | with DNS64 | | +----+ | + | +----+ | +-------------+ | | H2 | | + | | H1 |---| | | +----+ | + | +----+ | +------------+ | 192.0.2.1 | + | |---| IPv6/IPv4 |--| | + | | | Translator | | | + | | +------------+ | | + | | | | | + +---------------------+ +---------------+ + + Figure 4: An-IPv6-network-to-IPv4-Internet setup with DNS64 in DNS + server mode + + The figure shows an IPv6 node H1 and an IPv4 node H2 with IPv4 + address 192.0.2.1 and FQDN h2.example.com. + + The IPv6/IPv4 Translator has an IPv4 address 203.0.113.1 assigned to + its IPv4 interface and it is using the WKP 64:FF9B::/96 to create + IPv6 representations of IPv4 addresses. The same prefix is + configured in the DNS64 function in the local name server. + + For this example, assume the typical DNS situation where IPv6 hosts + have only stub resolvers, and they are configured with the IP address + of a name server that they always have to query and 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 h2.example.com. H1 does this by sending + a DNS query for a 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 performs an A-record query for H2 and + gets back an RRset containing a single A record with the IPv4 + address 192.0.2.1. The name server then synthesizes a AAAA + record. The IPv6 address in the AAAA record contains the prefix + assigned to the IPv6/IPv4 Translator in the upper 96 bits and the + received IPv4 address in the lower 32 bits i.e. the resulting + IPv6 address is 64:FF9B::192.0.2.1. + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 23] + +Internet-Draft DNS64 October 2010 + + + 4. H1 receives the synthetic AAAA record and sends a packet towards + H2. The packet is sent to the destination address 64:FF9B:: + 192.0.2.1. + + 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. + +7.2. An example of an-IPv6-network-to-IPv4-Internet setup with DNS64 in + stub-resolver mode + + This case is depicted in the following figure: + + + +---------------------+ +---------------+ + |IPv6 network | | IPv4 | + | | +--------+ | Internet | + | |-----| Name |----| | + | +-----+ | | server | | +----+ | + | | H1 | | +--------+ | | H2 | | + | |with |---| | | +----+ | + | |DNS64| | +------------+ | 192.0.2.1 | + | +----+ |---| IPv6/IPv4 |--| | + | | | Translator | | | + | | +------------+ | | + | | | | | + +---------------------+ +---------------+ + + + Figure 5: An-IPv6-network-to-IPv4-Internet setup with DNS64 in stub- + resolver mode + + The figure shows an IPv6 node H1 implementing the DNS64 function and + an IPv4 node H2 with IPv4 address 192.0.2.1 and FQDN h2.example.com. + + The IPv6/IPv4 Translator has an IPv4 address 203.0.113.1 assigned to + its IPv4 interface and it is using the WKP 64:FF9B::/96 to create + IPv6 representations of IPv4 addresses. The same prefix is + configured in the DNS64 function in H1. + + For this example, assume the typical DNS situation where IPv6 hosts + have only stub resolvers, and they are configured with the IP address + of a name server that they always have to query and that performs + recursive lookups (henceforth called "the recursive nameserver"). + The recursive name server does not perform the DNS64 function. + + The steps by which H1 establishes communication with H2 are: + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 24] + +Internet-Draft DNS64 October 2010 + + + 1. H1 does a DNS lookup for h2.example.com. 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 192.0.2.1. 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 96 bits, then the received + IPv4 address i.e. the resulting IPv6 address is 64:FF9B:: + 192.0.2.1. + + 4. H1 sends a packet towards H2. The packet is sent to the + destination address 64:FF9B::192.0.2.1. + + 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. + +7.3. Example of 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 that initiates a communication to an IPv4 node located in + the IPv4 site. + + In some cases, 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 nodes. Such an IPv6 address + would be constructed using the address transformation algorithm + defined in [I-D.ietf-behave-address-format] that takes as input the + Pref64::/96 and the IPv4 address of the IPv4 node. Note that the + IPv4 address can be a public or a private address; the latter does + not present any additional difficulty, since an NSP must be used as + Pref64::/96 (in this scenario the usage of the Well-Known prefix is + not supported as discussed in [I-D.ietf-behave-address-format]). + Once these IPv6 addresses have been assigned to represent the IPv4 + nodes 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. + + However, there are some more dynamic scenarios, where synthesizing + AAAA RRs in this setup may be needed. In particular, when DNS Update + + + +Bagnulo, et al. Expires April 4, 2011 [Page 25] + +Internet-Draft DNS64 October 2010 + + + [RFC2136] is used in the IPv4 site to update the A RRs for the IPv4 + nodes, there are two options: One option is to modify the DNS 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 all the authoritative servers 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 when the DNS responses are not + being generated dynamically. However, it may be the case where the + primary server (that receives all the updates) cannot be upgraded for + whatever reason, but where a secondary can be upgraded in order to + handle the (comparatively small amount) of AAAA queries. In such + case, it is possible to use the DNS64 as described next. The DNS64 + behavior that we describe in this section covers the case of + synthesizing the AAAA RR when the DNS query arrives. + + The scenario for this case is depicted in the following figure: + + + +-----------+ +----------------------+ + | | | IPv4 site | + | IPv6 | +------------+ | +----+ | + | Internet |----| IPv6/IPv4 |--|---| H2 | | + | | | Translator | | +----+ | + | | +------------+ | | + | | | | 192.0.2.1 | + | | +------------+ | | + | |----| Name server|--| | + | | | with DNS64 | | | + +-----------+ +------------+ | | + | | | | + +----+ | | + | H1 | +----------------------+ + +----+ + + Figure 6: IPv6-Internet-to-an-IPv4-network setup DNS64 in DNS server + mode + + The figure shows an IPv6 node H1 and an IPv4 node H2 with IPv4 + address 192.0.2.1 and FQDN h2.example.com. + + The IPv6/IPv4 Translator is using a NSP 2001:DB8::/96 to create IPv6 + representations of IPv4 addresses. The same prefix is configured in + + + +Bagnulo, et al. Expires April 4, 2011 [Page 26] + +Internet-Draft DNS64 October 2010 + + + the DNS64 function in the local name server. The name server that + implements the DNS64 function is the authoritative name server for + the local domain. + + The steps by which H1 establishes communication with H2 are: + + 1. H1 does a DNS lookup for h2.example.com. H1 does this by sending + a DNS query for a 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 h2.example.com and its A RR are + among those that the local policy defines as allowed to generate + a AAAA RR from. If that is the case, the name server synthesizes + a AAAA record from the A RR and the prefix 2001:DB8::/96. The + IPv6 address in the AAAA record is 2001:DB8::192.0.2.1. + + 4. H1 receives the synthetic AAAA record and sends a packet towards + H2. The packet is sent to the destination address 2001:DB8:: + 192.0.2.1. + + 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. + + +8. Security Considerations + + DNS64 operates in combination with the DNS, and is therefore subject + to whatever security considerations are appropriate to the DNS mode + in which the DNS64 is operating (i.e. authoritative, recursive, or + stub resolver mode). + + DNS64 has the potential to interfere with the functioning of DNSSEC, + because DNS64 modifies DNS answers, and DNSSEC is designed to detect + such modification and to treat modified answers as bogus. See the + discussion above in Section 3, Section 5.5, and Section 6.2. + + Additionally, for the correct functioning of the translation + services, the DNS64 and the NAT64 need to use the same Pref64. If an + attacker manages to change the Pref64 used by the DNS64, the traffic + generated by the host that receives the synthetic reply will be + delivered to the altered Pref64. This can result in either a DoS + attack (if resulting IPv6 addresses are not assigned to any device) + or in a flooding attack (if the resulting IPv6 addresses are assigned + to devices that do not wish to receive the traffic) or in + + + +Bagnulo, et al. Expires April 4, 2011 [Page 27] + +Internet-Draft DNS64 October 2010 + + + eavesdropping attack (in case the Pref64 is routed through the + attacker). + + +9. IANA Considerations + + This memo makes no request of IANA. + + +10. Contributors + + Dave Thaler + + Microsoft + + dthaler@windows.microsoft.com + + +11. 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: Jaap Akkerhuis, + Mark Andrews, Jari Arkko, Rob Austein, Timothy Baldwin, Fred Baker, + Doug Barton, Marc Blanchet, Cameron Byrne, Brian Carpenter, Zhen Cao, + Hui Deng, Francis Dupont, Patrik Faltstrom, David Harrington, Ed + Jankiewicz, Peter Koch, Suresh Krishnan, Martti Kuparinen, Ed Lewis, + Xing Li, Bill Manning, Matthijs Mekking, Hiroshi Miyata, Simon + Perrault, Teemu Savolainen, Jyrki Soini, Dave Thaler, Mark Townsley, + Rick van Rein, Stig Venaas, Magnus Westerlund, Jeff Westhead, Florian + Weimer, Dan Wing, Xu Xiaohu, Xiangsong Cui. + + Marcelo Bagnulo and Iljitsch van Beijnum are partly funded by + Trilogy, a research project supported by the European Commission + under its Seventh Framework Program. + + +12. References + +12.1. 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. + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 28] + +Internet-Draft DNS64 October 2010 + + + [RFC1035] Mockapetris, P., "Domain names - implementation and + specification", STD 13, RFC 1035, November 1987. + + [RFC4787] Audet, F. and C. Jennings, "Network Address Translation + (NAT) Behavioral Requirements for Unicast UDP", BCP 127, + RFC 4787, January 2007. + + [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", + RFC 2671, August 1999. + + [I-D.ietf-behave-address-format] + Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. + Li, "IPv6 Addressing of IPv4/IPv6 Translators", + draft-ietf-behave-address-format-10 (work in progress), + August 2010. + +12.2. Informative References + + [I-D.ietf-behave-v6v4-xlate-stateful] + Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful + NAT64: Network Address and Protocol Translation from IPv6 + Clients to IPv4 Servers", + draft-ietf-behave-v6v4-xlate-stateful-12 (work in + progress), July 2010. + + [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, + "Dynamic Updates in the Domain Name System (DNS UPDATE)", + RFC 2136, April 1997. + + [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS + NCACHE)", RFC 2308, March 1998. + + [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. + 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. + + + +Bagnulo, et al. Expires April 4, 2011 [Page 29] + +Internet-Draft DNS64 October 2010 + + + Rose, "Protocol Modifications for the DNS Security + Extensions", RFC 4035, March 2005. + + [RFC4074] Morishita, Y. and T. Jinmei, "Common Misbehavior Against + DNS Queries for IPv6 Addresses", RFC 4074, May 2005. + + [RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses", + BCP 153, RFC 5735, January 2010. + + [I-D.ietf-behave-v6v4-framework] + Baker, F., Li, X., Bao, C., and K. Yin, "Framework for + IPv4/IPv6 Translation", + draft-ietf-behave-v6v4-framework-10 (work in progress), + August 2010. + + [I-D.ietf-dnsop-default-local-zones] + Andrews, M., "Locally-served DNS Zones", + draft-ietf-dnsop-default-local-zones-14 (work in + progress), September 2010. + + +Appendix A. Motivations and Implications of synthesizing AAAA Resource + Records when real AAAA Resource Records exist + + The motivation for synthesizing AAAA RRs when real AAAA RRs exist 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 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. + + 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 resolver. + + 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 RRs even + when real AAAA RRs exist. + + The implication of including synthetic AAAA RRs when real AAAA RRs + exist is that translated connectivity may be preferred over native + + + +Bagnulo, et al. Expires April 4, 2011 [Page 30] + +Internet-Draft DNS64 October 2010 + + + connectivity in some cases where the DNS64 is operated in DNS server + mode. + + RFC3484 [RFC3484] rules use longest prefix match to select the + preferred destination address to use. So, if the DNS64 resolver + returns both the synthetic AAAA RRs and the real AAAA RRs, then if + the DNS64 is operated by the same domain as the initiating host, and + a global unicast prefix (called an NSP in + [I-D.ietf-behave-address-format]) is used, then a synthetic AAAA RR + is likely to be preferred. + + This means that without further configuration: + + In the "An IPv6 network to the IPv4 Internet" scenario, the host + will prefer translated connectivity if an NSP is used. If the + Well-Known Prefix defined in [I-D.ietf-behave-address-format] is + used, it will probably prefer native connectivity. + + In the "IPv6 Internet to an IPv4 network" scenario, it is possible + to bias the selection towards the real AAAA RR if the DNS64 + resolver returns the real AAAA first in the DNS reply, when an NSP + is used (the Well-Known Prefix usage is not supported in this + case) + + In the "An IPv6 network to IPv4 network" scenario, for local + destinations (i.e., target hosts inside the local site), it is + likely that the NSP 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 the Well-Known Prefix is used, + the longest prefix match rule will select native connectivity. + + The problem can be solved by properly configuring the RFC3484 + [RFC3484] policy table. + + +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 + + + + +Bagnulo, et al. Expires April 4, 2011 [Page 31] + +Internet-Draft DNS64 October 2010 + + + 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 4, 2011 [Page 32] + |