diff --git a/doc/draft/draft-ietf-behave-dns64-08.txt b/doc/draft/draft-ietf-behave-dns64-08.txt deleted file mode 100644 index c83849c0f3..0000000000 --- a/doc/draft/draft-ietf-behave-dns64-08.txt +++ /dev/null @@ -1,1792 +0,0 @@ - - - -BEHAVE WG M. Bagnulo -Internet-Draft UC3M -Intended status: Standards Track A. Sullivan -Expires: September 23, 2010 Shinkuro - P. Matthews - Alcatel-Lucent - I. van Beijnum - IMDEA Networks - March 22, 2010 - - -DNS64: DNS extensions for Network Address Translation from IPv6 Clients - to IPv4 Servers - draft-ietf-behave-dns64-08 - -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 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 September 23, 2010. - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 1] - -Internet-Draft DNS64 March 2010 - - -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 - 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 BSD License. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 2] - -Internet-Draft DNS64 March 2010 - - -Table of Contents - - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 3. Background to DNS64-DNSSEC interaction . . . . . . . . . . . . 8 - 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5. DNS64 Normative Specification . . . . . . . . . . . . . . . . 10 - 5.1. Resolving AAAA queries and the answer section . . . . . . 11 - 5.1.1. The answer when there is AAAA data available . . . . . 11 - 5.1.2. The answer when there is an error . . . . . . . . . . 11 - 5.1.3. Dealing with timeouts . . . . . . . . . . . . . . . . 12 - 5.1.4. Special exclusion set for AAAA records . . . . . . . . 12 - 5.1.5. Dealing with CNAME and DNAME . . . . . . . . . . . . . 12 - 5.1.6. Data for the answer when performing synthesis . . . . 13 - 5.1.7. Performing the synthesis . . . . . . . . . . . . . . . 13 - 5.1.8. Querying in parallel . . . . . . . . . . . . . . . . . 14 - 5.2. Generation of the IPv6 representations of IPv4 - addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 - 5.3. Handling other Resource Records and the Additional - Section . . . . . . . . . . . . . . . . . . . . . . . . . 15 - 5.3.1. PTR Resource Record . . . . . . . . . . . . . . . . . 15 - 5.3.2. Handling the additional section . . . . . . . . . . . 16 - 5.3.3. Other Resource Records . . . . . . . . . . . . . . . . 16 - 5.4. Assembling a synthesized response to a AAAA query . . . . 17 - 5.5. DNSSEC processing: DNS64 in recursive resolver mode . . . 17 - 6. Deployment notes . . . . . . . . . . . . . . . . . . . . . . . 18 - 6.1. DNS resolvers and DNS64 . . . . . . . . . . . . . . . . . 18 - 6.2. DNSSEC validators and DNS64 . . . . . . . . . . . . . . . 19 - 6.3. DNS64 and multihomed and dual-stack hosts . . . . . . . . 19 - 6.3.1. IPv6 multihomed hosts . . . . . . . . . . . . . . . . 19 - 6.3.2. Accidental dual-stack DNS64 use . . . . . . . . . . . 20 - 6.3.3. Intentional dual-stack DNS64 use . . . . . . . . . . . 20 - 7. Deployment scenarios and examples . . . . . . . . . . . . . . 21 - 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 . . . . . . . . . . . . . 23 - 7.3. Example of IPv6-Internet-to-an-IPv4-network setup - DNS64 in DNS server mode . . . . . . . . . . . . . . . . . 25 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 27 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 - 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 27 - 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 September 23, 2010 [Page 3] - -Internet-Draft DNS64 March 2010 - - - exist . . . . . . . . . . . . . . . . . . . . . . . . 30 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 4] - -Internet-Draft DNS64 March 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 advanced - features require performing the DNS64 function directly in the end- - hosts themselves. - - -2. Overview - - This section provides a non-normative introduction to the DNS64 - mechanism. - - We assume that we have one or more IPv6/IPv4 translator boxes - 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 - - - -Bagnulo, et al. Expires September 23, 2010 [Page 5] - -Internet-Draft DNS64 March 2010 - - - 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. - - 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 - - - -Bagnulo, et al. Expires September 23, 2010 [Page 6] - -Internet-Draft DNS64 March 2010 - - - 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 - 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 advanced functions like - - - -Bagnulo, et al. Expires September 23, 2010 [Page 7] - -Internet-Draft DNS64 March 2010 - - - 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: - - 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. - - 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. - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 8] - -Internet-Draft DNS64 March 2010 - - - 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 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 (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 node receives a query with - the DO bit set and CD clear. This ought to work 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 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. - - -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]. - - - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 9] - -Internet-Draft DNS64 March 2010 - - - 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 DNS (e.g., A records containing IPv4 - addresses). - - DNS64 recursor: 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. - - 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. - - 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. - - 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]. - - -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. - - 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]. Support of - multicast address handling is out of the scope of this document. A - possible approach is specified in [I-D.venaas-behave-mcast46]. - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 10] - -Internet-Draft DNS64 March 2010 - - - 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. DNS64 operation for classes - other than IN is undefined, and a DNS64 MUST behave as though no - DNS64 function is configured. - -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 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. - - 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. - - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 11] - -Internet-Draft DNS64 March 2010 - - -5.1.3. Dealing with timeouts - - If the query receives no answer before the timeout, it is treated as - RCODE=2 (Server failure). - -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, the original CNAME or DNAME RR is - included as part of the answer, and the synthetic AAAA, if - appropriate, is included. - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 12] - -Internet-Draft DNS64 March 2010 - - -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 - 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, - depending on the mode and operation of the underlying 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 5.1.7. 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 default value of 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.) - - 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 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. - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 13] - -Internet-Draft DNS64 March 2010 - - -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. However, this would result - in performing unnecessary A RR queries in the case where 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 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 the 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 - - [[anchor8: Note in document: The value 64:FF9B::/96 is proposed as - the value for the Well-Known prefix and needs to be confirmed - - - -Bagnulo, et al. Expires September 23, 2010 [Page 14] - -Internet-Draft DNS64 March 2010 - - - 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 - 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. 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. 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 - - - -Bagnulo, et al. Expires September 23, 2010 [Page 15] - -Internet-Draft DNS64 March 2010 - - - 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. In addition, the generated CNAME could correspond to an - unpopulated in-addr.arpa zone, so the CNAME would provide a - reference to a non-existent record. - - 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. - - 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. - -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 September 23, 2010 [Page 16] - -Internet-Draft DNS64 March 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. - -5.5. DNSSEC processing: DNS64 in recursive 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 - 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 - - - -Bagnulo, et al. Expires September 23, 2010 [Page 17] - -Internet-Draft DNS64 March 2010 - - - 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 - 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 - - - -Bagnulo, et al. Expires September 23, 2010 [Page 18] - -Internet-Draft DNS64 March 2010 - - - will be unable to answer the necessary AAAA queries. - -6.2. DNSSEC validators and DNS64 - - Existing DNSSEC validators (i.e. that are 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 recursor 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| - +---------------+ +-------------+ - - 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. For more discussion of - this topic, see [I-D.savolainen-mif-dns-server-selection]. - - Note that the issue is not that there are two interfaces, but that - there are two networks involved. The same results could be achieved - with a single interface routed to two different networks. - - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 19] - -Internet-Draft DNS64 March 2010 - - -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| - +---------------+ +-------------+ - - 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. - - +---------------+ +-------------+ - | i1 (IPv6)+----NAT64--------+IPv4 Internet| - | | +-------------+ - | host | - | | - | i2 (IPv4)+---(local LAN only) - - - -Bagnulo, et al. Expires September 23, 2010 [Page 20] - -Internet-Draft DNS64 March 2010 - - - +---------------+ - - 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 walk through some sample scenarios that are - expected to be common deployment cases. It should be noted that this - 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.ietf-behave-address-format]. - - 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 - [I-D.ietf-behave-v6v4-framework]. 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 - [I-D.ietf-behave-v6v4-framework]. 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 IPv4 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 September 23, 2010 [Page 21] - -Internet-Draft DNS64 March 2010 - - - 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 - -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: - - - +---------------------+ +---------------+ - |IPv6 network | | IPv4 | - | | +-------------+ | Network | - | |--| Name server |--| | - | | | with DNS64 | | +----+ | - | +----+ | +-------------+ | | H2 | | - | | H1 |---| | | +----+ | - | +----+ | +-------+ | 192.0.2.1 | - | |------| NAT64 |----| | - | | +-------+ | | - | | | | | - +---------------------+ +---------------+ - - The figure shows an IPv6 node H1 and an IPv4 node H2 with IPv4 - address 192.0.2.1 and FQDN h2.example.com - - A IPv6/IPv4 Translator connects the IPv6 network to the IPv4 - Internet. This 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, as defined in - [I-D.ietf-behave-address-format]. - - 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 is configured to represent the whole IPv4 - unicast space with using the WKP 64:FF9B::/96. For the purpose of - this example, we assume it learns this through manual configuration. - - - -Bagnulo, et al. Expires September 23, 2010 [Page 22] - -Internet-Draft DNS64 March 2010 - - - 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 queries for A records for H2 and gets - back a single A records containing the IPv4 address 192.0.2.1. - The name server then synthesizes a AAAA records. 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 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: - - - - - - - - - - - - - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 23] - -Internet-Draft DNS64 March 2010 - - - +---------------------+ +---------------+ - |IPv6 network | | IPv4 | - | | +--------+ | Network | - | |-----| Name |----| | - | +-----+ | | server | | +----+ | - | | H1 | | +--------+ | | H2 | | - | |with |---| | | +----+ | - | |DNS64| | +-------+ | 192.0.2.1 | - | +----+ |------| NAT64 |----| | - | | +-------+ | | - | | | | | - +---------------------+ +---------------+ - - - 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 - - A IPv6/IPv4 Translator connects the IPv6 network to the IPv4 - Internet. This IPv6/IPv4 Translator is using the WKP 64:FF9B::/96 - and an IPv4 address T 203.0.113.1 assigned to its IPv4 interface. - - H1 needs to know the prefix assigned to the local IPv6/IPv4 - Translator (64:FF9B::/96). 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 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 - - - -Bagnulo, et al. Expires September 23, 2010 [Page 24] - -Internet-Draft DNS64 March 2010 - - - 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 in principle 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 - [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 -- - - - -Bagnulo, et al. Expires September 23, 2010 [Page 25] - -Internet-Draft DNS64 March 2010 - - - 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. 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 |------| NAT64 |-----|---| H2 | | - | | +-------+ | +----+ | - | | | | 192.0.2.1 | - | | +------------+ | | - | |----| Name server|--| | - | | | with DNS64 | | | - +-----------+ +------------+ | | - | | | | - +----+ | | - | H1 | +----------------------+ - +----+ - - The figure shows an IPv6 node H1 and an IPv4 node H2 with IPv4 - address X 192.0.2.1 and FQDN h2.example.com. - - A IPv6/IPv4 translator connects the IPv4 network to the IPv6 - Internet. This IPv6/IPv4 translator has a NSP 2001:DB8::/96. - - 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 (2001:DB8::/96). For the purpose of this - example, we assume it learns this through manual configuration. - - The steps by which H1 establishes communication with H2 are: - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 26] - -Internet-Draft DNS64 March 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. 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 functions 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 by its very functioning 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. - - -9. IANA Considerations - - This memo makes no request of IANA. - - -10. Contributors - - Dave Thaler - - Microsoft - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 27] - -Internet-Draft DNS64 March 2010 - - - 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, Ed Jankiewicz, Peter - Koch, Suresh Krishnan, 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, 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. - - [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. - - [I-D.ietf-behave-address-format] - Huitema, C., Bao, C., Bagnulo, M., Boucadair, M., and X. - Li, "IPv6 Addressing of IPv4/IPv6 Translators", - draft-ietf-behave-address-format-04 (work in progress), - January 2010. - - - - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 28] - -Internet-Draft DNS64 March 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-08 (work in - progress), January 2010. - - [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, - "Dynamic Updates in the Domain Name System (DNS UPDATE)", - RFC 2136, April 1997. - - [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. - Rose, "Protocol Modifications for the DNS Security - Extensions", RFC 4035, March 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-07 (work in progress), - February 2010. - - [I-D.venaas-behave-mcast46] - Venaas, S., Asaeda, H., SUZUKI, S., and T. Fujisaki, "An - IPv4 - IPv6 multicast translator", - draft-venaas-behave-mcast46-01 (work in progress), - July 2009. - - [I-D.ietf-dnsop-default-local-zones] - - - -Bagnulo, et al. Expires September 23, 2010 [Page 29] - -Internet-Draft DNS64 March 2010 - - - Andrews, M., "Locally-served DNS Zones", - draft-ietf-dnsop-default-local-zones-09 (work in - progress), November 2009. - - [I-D.savolainen-mif-dns-server-selection] - Savolainen, T., "DNS Server Selection on Multi-Homed - Hosts", draft-savolainen-mif-dns-server-selection-02 (work - in progress), February 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 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 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 - 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. - - - - -Bagnulo, et al. Expires September 23, 2010 [Page 30] - -Internet-Draft DNS64 March 2010 - - - 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. - - So this option introduces problems in the following cases: - - An IPv6 network to the IPv4 internet with an NSP - - IPv6 to IPv4 in the same network when reaching external - destinations and an NSP 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. - - -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 September 23, 2010 [Page 31] - -Internet-Draft DNS64 March 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 September 23, 2010 [Page 32] -