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diff --git a/doc/draft/draft-ietf-behave-dns64-01.txt b/doc/draft/draft-ietf-behave-dns64-01.txt deleted file mode 100644 index 25a6dd4d0726..000000000000 --- a/doc/draft/draft-ietf-behave-dns64-01.txt +++ /dev/null @@ -1,1624 +0,0 @@ - - - -BEHAVE WG M. Bagnulo -Internet-Draft UC3M -Intended status: Standards Track A. Sullivan -Expires: April 22, 2010 Shinkuro - P. Matthews - Alcatel-Lucent - I. van Beijnum - IMDEA Networks - October 19, 2009 - - -DNS64: DNS extensions for Network Address Translation from IPv6 Clients - to IPv4 Servers - draft-ietf-behave-dns64-01 - -Status of this Memo - - This Internet-Draft is submitted to IETF in full conformance with the - provisions of BCP 78 and BCP 79. - - Internet-Drafts are working documents of the Internet Engineering - Task Force (IETF), its areas, and its working groups. Note that - other groups may also distribute working documents as Internet- - Drafts. - - Internet-Drafts are draft documents valid for a maximum of six months - and may be updated, replaced, or obsoleted by other documents at any - time. It is inappropriate to use Internet-Drafts as reference - material or to cite them other than as "work in progress." - - The list of current Internet-Drafts can be accessed at - http://www.ietf.org/ietf/1id-abstracts.txt. - - The list of Internet-Draft Shadow Directories can be accessed at - http://www.ietf.org/shadow.html. - - This Internet-Draft will expire on April 22, 2010. - -Copyright Notice - - Copyright (c) 2009 IETF Trust and the persons identified as the - document authors. All rights reserved. - - This document is subject to BCP 78 and the IETF Trust's Legal - Provisions Relating to IETF Documents in effect on the date of - publication of this document (http://trustee.ietf.org/license-info). - Please review these documents carefully, as they describe your rights - and restrictions with respect to this document. - - - -Bagnulo, et al. Expires April 22, 2010 [Page 1] - -Internet-Draft DNS64 October 2009 - - -Abstract - - DNS64 is a mechanism for synthesizing AAAA records from A records. - DNS64 is used with an IPv6/IPv4 translator to enable client-server - communication between an IPv6-only client and an IPv4-only server, - without requiring any changes to either the IPv6 or the IPv4 node, - for the class of applications that work through NATs. This document - specifies DNS64, and provides suggestions on how it should be - deployed in conjunction with IPv6/IPv4 translators. - - -Table of Contents - - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3. Background to DNS64 - DNSSEC interaction . . . . . . . . . . . 6 - 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8 - 5. DNS64 Normative Specification . . . . . . . . . . . . . . . . 9 - 5.1. Resolving AAAA queries and the answer section . . . . . . 9 - 5.1.1. The answer when there is AAAA data available . . . . . 9 - 5.1.2. The answer when there is an error . . . . . . . . . . 9 - 5.1.3. Data for the answer when performing synthesis . . . . 9 - 5.1.4. Performing the synthesis . . . . . . . . . . . . . . . 10 - 5.1.5. Querying in parallel . . . . . . . . . . . . . . . . . 11 - 5.2. Generation of the IPv6 representations of IPv4 - addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 - 5.3. Handling other RRs . . . . . . . . . . . . . . . . . . . . 12 - 5.3.1. PTR queries . . . . . . . . . . . . . . . . . . . . . 12 - 5.3.2. Handling the additional section . . . . . . . . . . . 13 - 5.3.3. Other records . . . . . . . . . . . . . . . . . . . . 13 - 5.4. Assembling a synthesized response to a AAAA query . . . . 14 - 5.5. DNSSEC processing: DNS64 in recursive server mode . . . . 14 - 5.6. DNS64 and multihoming . . . . . . . . . . . . . . . . . . 15 - 6. Deployment notes . . . . . . . . . . . . . . . . . . . . . . . 16 - 6.1. DNS resolvers and DNS64 . . . . . . . . . . . . . . . . . 16 - 6.2. DNSSEC validators and DNS64 . . . . . . . . . . . . . . . 16 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 - 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16 - 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 - 10.1. Normative References . . . . . . . . . . . . . . . . . . . 17 - 10.2. Informative References . . . . . . . . . . . . . . . . . . 18 - Appendix A. Deployment scenarios and examples . . . . . . . . . . 20 - A.1. Embed and Zero-Pad algorithm description . . . . . . . . . 21 - A.2. An-IPv6-network-to-IPv4-Internet setup with DNS64 in - DNS server mode . . . . . . . . . . . . . . . . . . . . . 22 - A.3. An-IPv6-network-to-IPv4-Internet setup with DNS64 in - stub-resolver mode . . . . . . . . . . . . . . . . . . . . 23 - - - -Bagnulo, et al. Expires April 22, 2010 [Page 2] - -Internet-Draft DNS64 October 2009 - - - A.4. IPv6-Internet-to-an-IPv4-network setup DNS64 in DNS - server mode . . . . . . . . . . . . . . . . . . . . . . . 25 - Appendix B. Motivations and Implications of synthesizing AAAA - RR when real AAAA RR exists . . . . . . . . . . . . . 27 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 3] - -Internet-Draft DNS64 October 2009 - - -1. Introduction - - This document specifies DNS64, a mechanism that is part of the - toolbox for IPv6-IPv4 transition and co-existence. DNS64, used - together with an IPv6/IPv4 translator such as NAT64 - [I-D.bagnulo-behave-nat64], allows an IPv6-only client to initiate - communications by name to an IPv4-only server. - - DNS64 is a mechanism for synthesizing AAAA resource records (RRs) - from A RRs. A synthetic AAAA RR created by the DNS64 from an - original A RR contains the same FQDN of the original A RR but it - contains an IPv6 address instead of an IPv4 address. The IPv6 - address is an IPv6 representation of the IPv4 address contained in - the original A RR. The IPv6 representation of the IPv4 address is - algorithmically generated from the IPv4 address returned in the A RR - and a set of parameters configured in the DNS64 (typically, an IPv6 - prefix used by IPv6 representations of IPv4 addresses and optionally - other parameters). - - Together with a IPv6/IPv4 translator, these two mechanisms allow an - IPv6-only client to initiate communications to an IPv4-only server - using the FQDN of the server. - - These mechanisms are expected to play a critical role in the IPv4- - IPv6 transition and co-existence. Due to IPv4 address depletion, it - is likely that in the future, many IPv6-only clients will want to - connect to IPv4-only servers. In the typical case, the approach only - requires the deployment of IPv6/IPv4 translators that connect an - IPv6-only network to an IPv4-only network, along with the deployment - of one or more DNS64-enabled name servers. However, some advanced - features require performing the DNS64 function directly by the end- - hosts themselves. - - -2. Overview - - This section provides a non-normative introduction to the DNS64 - mechanism. - - We assume that we have an IPv6/IPv4 translator box connecting an IPv4 - network and an IPv6 network. The IPv6/IPv4 translator device - provides translation services between the two networks enabling - communication between IPv4-only hosts and IPv6-only hosts. (NOTE: By - IPv6-only hosts we mean hosts running IPv6-only applications, hosts - that can only use IPv6, as well as the cases where only IPv6 - connectivity is available to the client. By IPv4-only servers we - mean servers running IPv4-only applications, servers that can only - use IPv4, as well as the cases where only IPv4 connectivity is - - - -Bagnulo, et al. Expires April 22, 2010 [Page 4] - -Internet-Draft DNS64 October 2009 - - - available to the server). The IPv6/IPv4 translator used in - conjunction with DNS64 must allow communications initiated from the - IPv6-only host to the IPv4-only host. - - To allow an IPv6 initiator to do a standard AAAA RR DNS lookup to - learn the address of the responder, DNS64 is used to synthesize a - AAAA record from an A record containing a real IPv4 address of the - responder, whenever the DNS64 service cannot retrieve a AAAA record - for the requested host name. The DNS64 device appears as a regular - recursive resolver for the IPv6 initiator. The DNS64 box receives an - AAAA DNS query generated by the IPv6 initiator. It first attempts a - recursive resolution for the requested AAAA records. If there is no - AAAA record available for the target node (which is the normal case - when the target node is an IPv4-only node), DNS64 performs a query - for A records. If any A records are discovered, DNS64 creates a - synthetic AAAA RR from the information retrieved in each A RR. - - The FQDN of a synthetic AAAA RR is the same as that of the original A - RR, but an IPv6 representation of the IPv4 address contained in the - original A RR is included in the AAAA RR. The IPv6 representation of - the IPv4 address is algorithmically generated from the IPv4 address - and additional parameters configured in the DNS64. Among those - parameters configured in the DNS64, there is at least one IPv6 - prefix, called Pref64::/n. The IPv6 address representing IPv4 - addresses included in the AAAA RR synthesized by the DNS64 function - contain Pref64::/n and they also embed the original IPv4 address. - - The same algorithm and the same Pref64::/n prefix or prefixes must be - configured both in the DNS64 device and the IPv6/IPv4 translator, so - that both can algorithmically generate the same IPv6 representation - for a given IPv4 address. In addition, it is required that IPv6 - packets addressed to an IPv6 destination that contains the Pref64::/n - be delivered to the IPv6/IPv4 translator, so they can be translated - into IPv4 packets. - - Once the DNS64 has synthesized the AAAA RR, the synthetic AAAA RR is - passed back to the IPv6 initiator, which will initiate an IPv6 - communication with the IPv6 address associated with the IPv4 - receiver. The packet will be routed to the IPv6/IPv4 translator - which will forward it to the IPv4 network . - - In general, the only shared state between the DNS64 and the IPv6/IPv4 - translator is the Pref64::/n and an optional set of static - parameters. The Pref64::/n and the set of static parameters must be - configured to be the same on both; there is no communication between - the DNS64 device and IPv6/IPv4 translator functions. The mechanism - to be used for configuring the parameters of the DNS64 is beyond the - scope of this memo. - - - -Bagnulo, et al. Expires April 22, 2010 [Page 5] - -Internet-Draft DNS64 October 2009 - - - The DNS64 function can be performed in two places. - - One option is to locate the DNS64 function in recursive name - servers serving end hosts. In this case, when an IPv6-only host - queries the name server for AAAA RRs for an IPv4-only host, the - name server can perform the synthesis of AAAA RRs and pass them - back to the IPv6 only initiator. The main advantage of this mode - is that current IPv6 nodes can use this mechanism without - requiring any modification. This mode is called "DNS64 in DNS - server mode". - - The other option is to place the DNS64 function in the end hosts - themselves, coupled to the local stub resolver. In this case, the - stub resolver will try to obtain (real) AAAA RRs and in case they - are not available, the DNS64 function will synthesize AAAA RRs for - internal usage. This mode is compatible with some advanced - functions like DNSSEC validation in the end host. The main - drawback of this mode is its deployability, since it requires - changes in the end hosts. This mode is called "DNS64 in stub- - resolver mode"". - - -3. Background to DNS64 - DNSSEC interaction - - DNSSEC presents a special challenge for DNS64, because DNSSEC is - designed to detect changes to DNS answers, and DNS64 may alter - answers coming from an authoritative server. - - A recursive resolver can be security-aware or security-oblivious. - Moreover, a security-aware recursive name server can be validating or - non-validating, according to operator policy. In the cases below, - the recursive server is also performing DNS64, and has a local policy - to validate. We call this general case vDNS64, but in all the cases - below the DNS64 functionality should be assumed needed. - - DNSSEC includes some signaling bits that offer some indicators of - what the query originator understands. - - If a query arrives at a vDNS64 device with the DO bit set, the query - originator is signaling that it understands DNSSEC. The DO bit does - not indicate that the query originator will validate the response. - It only means that the query originator can understand responses - containing DNSSEC data. Conversely, if the DO bit is clear, that is - evidence that the querying agent is not aware of DNSSEC. - - If a query arrives at a vDNS64 device with the CD bit set, it is an - indication that the querying agent wants all the validation data so - it can do checking itself. By local policy, vDNS64 could still - - - -Bagnulo, et al. Expires April 22, 2010 [Page 6] - -Internet-Draft DNS64 October 2009 - - - validate, but it must return all data to the querying agent anyway. - - Here are the possible cases: - - 1. A security-oblivious DNS64 node receives a query with the DO bit - clear. In this case, DNSSEC is not a concern, because the - querying agent does not understand DNSSEC responses. - - 2. A security-oblivious DNS64 node receives a query with the DO bit - set, and the CD bit clear. This is just like the case of a non- - DNS64 case: the server doesn't support it, so the querying agent - is out of luck. - - 3. A security-aware and non-validating DNS64 node receives a query - with the DO bit set and the CD bit clear. Such a resolver is not - validating responses, likely due to local policy (see [RFC4035], - section 4.2). For that reason, this case amounts to the same as - the previous case, and no validation happens. - - 4. A security-aware and non-validating DNS64 node receives a query - with the DO bit set and the CD bit set. In this case, the - resolver is supposed to pass on all the data it gets to the query - initiator (see section 3.2.2 of [RFC4035]). This case will be - problematic with DNS64. If the DNS64 server modifies the record, - the client will get the data back and try to validate it, and the - data will be invalid as far as the client is concerned. - - 5. A security-aware and validating DNS64 node receives a query with - the DO bit clear and CD clear. In this case, the resolver - validates the data. If it fails, it returns RCODE 2 (SERVFAIL); - otherwise, it returns the answer. This is the ideal case for - vDNS64. The resolver validates the data, and then synthesizes - the new record and passes that to the client. The client, which - is presumably not validating (else it would have set DO and CD), - cannot tell that DNS64 is involved. - - 6. A security-aware and validating DNS64 node receives a query with - the DO bit set and CD clear. In principle, this ought to work - like the previous case, except that the resolver should also set - the AD bit on the response. - - 7. A security-aware and validating DNS64 node receives a query with - the DO bit set and CD set. This is effectively the same as the - case where a security-aware and non-validating recursive resolver - receives a similar query, and the same thing will happen: the - downstream validator will mark the data as invalid if DNS64 has - performed synthesis. - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 7] - -Internet-Draft DNS64 October 2009 - - -4. Terminology - - This section provides definitions for the special terms used in the - document. - - The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", - "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this - document are to be interpreted as described in RFC 2119 [RFC2119]. - - Authoritative server: A DNS server that can answer authoritatively a - given DNS question. - - DNS64: A logical function that synthesizes DNS resource records (e.g - AAAA records containing IPv6 addresses) from DNS resource records - actually contained in the global DNS (e.g. A records containing - IPv4 addresses). - - DNS64 recursor: A recursive resolver that provides the DNS64 - functionality as part of its operation. - - Recursive resolver: A DNS server that accepts requests from one - resolver, and asks another resolver for the answer on behalf of - the first resolver. In the context of this document, "the - recursive resolver" means a recursive resolver immediately next in - the DNS resolution chain from an end point. The end point usually - has only a stub resolver available.[[anchor5: I can't actually - remember why we needed the sentences following "In the context of - this document. . ." Unless someone has a reason, I'll take it - out. --ajs@shinkuro.com]] - - Synthetic RR: A DNS resource record (RR) that is not contained in - any zone data file, but has been synthesized from other RRs. An - example is a synthetic AAAA record created from an A record. - - Stub resolver: A resolver with minimum functionality, typically for - use in end points that depend on a recursive resolver. Most end - points on the Internet as of this writing use stub - resolvers.[[anchor6: Do we need this in the document? I don't - think so. 1034 defines this term. --ajs@shinkuro.com]] - - IPv6/IPv4 translator: A device that translates IPv6 packets to IPv4 - packets and vice-versa. It is only required that the - communication initiated from the IPv6 side be supported. - - For a detailed understanding of this document, the reader should also - be familiar with DNS terminology from [RFC1034],[RFC1035] and current - NAT terminology from [RFC4787]. Some parts of this document assume - familiarity with the terminology of the DNS security extensions - - - -Bagnulo, et al. Expires April 22, 2010 [Page 8] - -Internet-Draft DNS64 October 2009 - - - outlined in [RFC4035]. - - -5. DNS64 Normative Specification - - A DNS64 is a logical function that synthesizes AAAA records from A - records. The DNS64 function may be implemented in a stub resolver, - in a recursive resolver, or in an authoritative name server. - - The implementation SHOULD support mapping of IPv4 address ranges to - separate IPv6 prefixes for AAAA record synthesis. This allows - handling of special use IPv4 addresses [I-D.iana-rfc3330bis]. - Multicast address handling is further specified in - [I-D.venaas-behave-mcast46]. - -5.1. Resolving AAAA queries and the answer section - - When the DNS64 receives a query for RRs of type AAAA and class IN, it - first attempts to retrieve non-synthetic RRs of this type and class, - either by performing a query or, in the case of an authoritative - server, by examining its own results. - -5.1.1. The answer when there is AAAA data available - - If the query results in one or more AAAA records in the answer - section, the result is returned to the requesting client as per - normal DNS semantics (except in the case where the AAAA falls in the - ::ffff/96 network; see below for treatment of that network). In this - case, DNS64 SHOULD NOT include synthetic AAAA RRs in the response - (see Appendix B for an analysis of the motivations for and the - implications of not complying with this recommendation). By default - DNS64 implementations MUST NOT synthesize AAAA RRs when real AAAA RRs - exist. - -5.1.2. The answer when there is an error - - If the query results in a response with an error code other than 0, - the result is handled according to normal DNS operation -- that is, - either the resolver tries again using a different server from the - authoritative NS RRSet, or it returns the error to the client. This - stage is still prior to any synthesis having happened, so a response - to be returned to the client does not need any special assembly than - would usually happen in DNS operation. - -5.1.3. Data for the answer when performing synthesis - - If the query results in no error but an empty answer section in the - response, the DNS64 resolver attempts to retrieve A records for the - - - -Bagnulo, et al. Expires April 22, 2010 [Page 9] - -Internet-Draft DNS64 October 2009 - - - name in question. If this new A RR query results in an empty answer - or in an error, then the empty result or error is used as the basis - for the answer returned to the querying client. (Transient errors - may result in retrying the query, depening on the operation of the - resolver; this is just as in Section 5.1.2.) If instead the query - results in one or more A RRs, the DNS64 synthesizes AAAA RRs based on - the A RRs according to the procedure outlined in Section 5.1.4. The - DNS64 resolver then returns the synthesized AAAA records in the - answer section to the client, removing the A records that form the - basis of the synthesis. - - As an exception to the general rule about always returning the AAAA - records if they are returned in the answer, AAAA records with - addresses in the ::ffff/96 network are treated just like the case - where there is neither an error nor an empty answer section. This is - because a real IPv6-only node will not be any more able to reach the - addresses in ::ffff/96 than it is able to reach an IPv4 address - without assistance. An implementation MAY use the address in - ::ffff/96 as the basis of synthesis without querying for an A record, - by using the last 32 bits of the address provided in the AAAA record. - [[anchor10: I changed this to say "neither. . .nor" because the - previous version suggested that it would return the error-or-empty- - answer to the querying client, and that can't be right. Correct? - --ajs@shinkuro.com]] - -5.1.4. Performing the synthesis - - A synthetic AAAA record is created from an A record as follows: - - o The NAME field is set to the NAME field from the A record - - o The TYPE field is set to 28 (AAAA) - - o The CLASS field is set to 1 (IN) - - o The TTL field is set to the minimum of the TTL of the original A - RR and the SOA RR for the queried domain. (Note that in order to - obtain the TTL of the SOA RR the DNS64 does not need to perform a - new query, but it can remember the TTL from the SOA RR in the - negative response to the AAAA query). - - o The RDLENGTH field is set to 16 - - o The RDATA field is set to the IPv6 representation of the IPv4 - address from the RDATA field of the A record. The DNS64 SHOULD - check each A RR against IPv4 address ranges and select the - corresponding IPv6 prefix to use in synthesizing the AAAA RR. See - Section 5.2 for discussion of the algorithms to be used in - - - -Bagnulo, et al. Expires April 22, 2010 [Page 10] - -Internet-Draft DNS64 October 2009 - - - effecting the transformation. - -5.1.5. Querying in parallel - - DNS64 MAY perform the query for the AAAA RR and for the A RR in - parallel, in order to minimize the delay. However, this would result - in performing unnecessary A RR queries in the case no AAAA RR - synthesis is required. A possible trade-off would be to perform them - sequentially but with a very short interval between them, so if we - obtain a fast reply, we avoid doing the additional query. (Note that - this discussion is relevant only if the DNS64 function needs to - perform external queries to fetch the RR. If the needed RR - information is available locally, as in the case of an authoritative - server, the issue is no longer relevant.) - -5.2. Generation of the IPv6 representations of IPv4 addresses - - DNS64 supports multiple algorithms for the generation of the IPv6 - representation of an IPv4 address. The constraints imposed on the - generation algorithms are the following: - - The same algorithm to create an IPv6 address from an IPv4 address - MUST be used by both the DNS64 to create the IPv6 address to be - returned in the synthetic AAAA RR from the IPv4 address contained - in original A RR, and by the IPv6/IPv4 translator to create the - IPv6 address to be included in the destination address field of - the outgoing IPv6 packets from the IPv4 address included in the - destination address field of the incoming IPv4 packet. - - The algorithm MUST be reversible, i.e. it MUST be possible to - extract the original IPv4 address from the IPv6 representation. - - The input for the algorithm MUST be limited to the IPv4 address, - the IPv6 prefix (denoted Pref64::/n) used in the IPv6 - representations and optionally a set of stable parameters that are - configured in the DNS64 (such as fixed string to be used as a - suffix). - - If we note n the length of the prefix Pref64::/n, then n MUST - the less or equal than 96. If a Pref64::/n is configured - through any means in the DNS64 (such as manually configured, or - other automatic mean not specified in this document), the - default algorithm MUST use this prefix. If no prefix is - available, the algorithm MUST use the Well-Known prefix TBD1 - defined in [I-D.thaler-behave-translator-addressing] - - [[anchor12: Note in document: TBD1 in the passage above is to be - substituted by whatever prefix is assigned by IANA to be the well- - - - -Bagnulo, et al. Expires April 22, 2010 [Page 11] - -Internet-Draft DNS64 October 2009 - - - known prefix.]] - - DNS64 MUST support the following algorithms for generating IPv6 - representations of IPv4 addresses defined in - [I-D.thaler-behave-translator-addressing]: - - Zero-Pad And Embed, defined in section 3.2.3 of - [I-D.thaler-behave-translator-addressing] - - Compensation-Pad And Embed, defined in section of 3.2.4 of - [I-D.thaler-behave-translator-addressing] - - Embed And Zero-Pad, defined in section of 3.2.5 of - [I-D.thaler-behave-translator-addressing] - - Preconfigured Mapping Table, defined in section of 3.2.6 of - [I-D.thaler-behave-translator-addressing] - - The default algorithm used by DNS64 must be Embed and Zero-Pad. - While the normative description of the algorithms is provided in - [I-D.thaler-behave-translator-addressing], an sample description of - the algorithm and its application to different scenarios is provided - in Appendix A for illustration purposes. - -5.3. Handling other RRs - -5.3.1. PTR queries - - If a DNS64 nameserver receives a PTR query for a record in the - IP6.ARPA domain, it MUST strip the IP6.ARPA labels from the QNAME, - reverse the address portion of the QNAME according to the encoding - scheme outlined in section 2.5 of [RFC3596] , and examine the - resulting address to see whether its prefix matches the locally- - configured Pref64::/n. There are two alternatives for a DNS64 - nameserver to respond to such PTR queries. A DNS64 node MUST provide - one of these, and SHOULD NOT provide both at the same time unless - different IP6.ARPA zones require answers of different sorts. - - The first option is for the DNS64 nameserver to respond - authoritatively for its prefixes. If the address prefix matches any - Pref64::/n used in the site, either a LIR prefix or a well-known - prefix used for NAT64 as defined in - [I-D.thaler-behave-translator-addressing], then the DNS64 server MAY - answer the query using locally-appropriate RDATA. The DNS64 server - MAY use the same RDATA for all answers. Note that the requirement is - to match any Pref64::/n used at the site, and not merely the locally- - configured Pref64::/n. This is because end clients could ask for a - PTR record matching an address received through a different (site- - - - -Bagnulo, et al. Expires April 22, 2010 [Page 12] - -Internet-Draft DNS64 October 2009 - - - provided) DNS64, and if this strategy is in effect, those queries - should never be sent to the global DNS. The advantage of this - strategy is that it makes plain to the querying client that the - prefix is one operated by the DNS64 site, and that the answers the - client is getting are generated by the DNS64. The disadvantage is - that any useful reverse-tree information that might be in the global - DNS is unavailable to the clients querying the DNS64. - - The second option is for the DNS64 nameserver to synthesize a CNAME - mapping the IP6.ARPA namespace to the corresponding IN-ADDR.ARPA - name. The rest of the response would be the normal DNS processing. - The CNAME can be signed on the fly if need be. The advantage of this - approach is that any useful information in the reverse tree is - available to the querying client. The disadvantage is that it adds - additional load to the DNS64 (because CNAMEs have to be synthesized - for each PTR query that matches the Pref64::/n), and that it may - require signing on the fly. [[anchor15: what are we supposed to do - here when the in-addr.arpa zone is unmaintained, as it may be. If - there is no data at the target name, then we'll get a CNAME with a - map to an empty namespace, I think? Isn't that bad? - --ajs@shinkuro.com]] - - If the address prefix does not match any of the Pref64::/n, then the - DNS64 server MUST process the query as though it were any other query - -- i.e. a recursive nameserver MUST attempt to resolve the query as - though it were any other (non-A/AAAA) query, and an authoritative - server MUST respond authoritatively or with a referral, as - appropriate. - -5.3.2. Handling the additional section - - DNS64 synthesis MUST NOT be performed on any records in the - additional section of synthesized answers. The DNS64 MUST pass the - additional section unchanged. - - [[anchor16: We had some discussion, as an alternative to the above, - of allowing the DNS64 to truncate the additional section completely, - on the grounds that the additional section could break mixed-mode - iterative/forwarding resolvers that happen to end up behind DNS64. - Nobody else seemed to like that plan, so I haven't included it. - --ajs@shinkuro.com]] - -5.3.3. Other records - - If the DNS64 is in recursive resolver mode, then it SHOULD also serve - the zones specified in [I-D.ietf-dnsop-default-local-zones], rather - than forwarding those queries elsewhere to be handled. - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 13] - -Internet-Draft DNS64 October 2009 - - - All other RRs MUST be returned unchanged. - -5.4. Assembling a synthesized response to a AAAA query - - The DNS64 uses different pieces of data to build the response - returned to the querying client. - - The query that is used as the basis for synthesis results either in - an error, an answer that can be used as a basis for synthesis, or an - empty (authoritative) answer. If there is an empty answer, then the - DNS64 responds to the original querying client with the answer the - DNS64 received to the original AAAA query. Otherwise, the response - is assembled as follows. - - The header fields are set according to the usual rules for recursive - or authoritative servers, depending on the role that the DNS64 is - serving. The question section is copied from the original AAAA - query. The answer section is populated according to the rules in - Section 5.1.4. The authority section is copied from the response to - the A query that the DNS64 performed. The additional section is - populated according to the rules in Section 5.3.2. - - [[anchor18: The cross-reference to how to do the additional section - can be removed, and replaced by "copied from the response to the A - query that the DNS64 performed" if we don't want to allow the DNS64 - to truncate the additional section. See the note above. If I hear - no more feedback on this topic, then I'll make this change in the - next version. --ajs@shinkuro.com]] - -5.5. DNSSEC processing: DNS64 in recursive server mode - - We consider the case where the recursive server that is performing - DNS64 also has a local policy to validate the answers according to - the procedures outlined in [RFC4035] Section 5. We call this general - case vDNS64. - - The vDNS64 uses the presence of the DO and CD bits to make some - decisions about what the query originator needs, and can react - accordingly: - - 1. If CD is not set and DO is not set, vDNS64 SHOULD perform - validation and do synthesis as needed. - - 2. If CD is not set and DO is set, then vDNS64 SHOULD perform - validation. Whenever vDNS64 performs validation, it MUST - validate the negative answer for AAAA queries before proceeding - to query for A records for the same name, in order to be sure - that there is not a legitimate AAAA record on the Internet. - - - -Bagnulo, et al. Expires April 22, 2010 [Page 14] - -Internet-Draft DNS64 October 2009 - - - Failing to observe this step would allow an attacker to use DNS64 - as a mechanism to circumvent DNSSEC. If the negative response - validates, and the response to the A query validates, then the - vDNS64 MAY perform synthesis and SHOULD set the AD bit in the - answer to the client. This is acceptable, because [RFC4035], - section 3.2.3 says that the AD bit is set by the name server side - of a security-aware recursive name server if and only if it - considers all the RRSets in the Answer and Authority sections to - be authentic. In this case, the name server has reason to - believe the RRSets are all authentic, so it SHOULD set the AD - bit. If the data does not validate, the vDNS64 MUST respond with - RCODE=2 (server failure). - A security-aware end point might take the presence of the AD bit - as an indication that the data is valid, and may pass the DNS - (and DNSSEC) data to an application. If the application attempts - to validate the synthesized data, of course, the validation will - fail. One could argue therefore that this approach is not - desirable. But security aware stub resolvers MUST NOT place any - reliance on data received from resolvers and validated on their - behalf without certain criteria established by [RFC4035], section - 4.9.3. An application that wants to perform validation on its - own should use the CD bit. - - 3. If the CD bit is set and DO is set, then vDNS64 MAY perform - validation, but MUST NOT perform synthesis. It MUST hand the - data back to the query initiator, just like a regular recursive - resolver, and depend on the client to do the validation and the - synthesis itself. - The disadvantage to this approach is that an end point that is - translation-oblivious but security-aware and validating will not - be able to use the DNS64 functionality. In this case, the end - point will not have the desired benefit of NAT64. In effect, - this strategy means that any end point that wishes to do - validation in a NAT64 context must be upgraded to be translation- - aware as well. - -5.6. DNS64 and multihoming - - Synthetic AAAA records may be constructed on the basis of the network - context in which they were constructed. Therefore, a synthetic AAAA - received from one interface MUST NOT be used to resolve hosts via - another network interface. [[anchor21: This seems to be the result of - the discussion on-list starting with message id 18034D4D7FE9AE48BF19A - B1B0EF2729F3EF0E69687@NOK-EUMSG-01.mgdnok.nokia.com, but it's pretty - strange when stated baldly. In particular, how is the multi-homed - host supposed to know that a given AAAA is synthetic? - --ajs@shinkuro.com]] - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 15] - -Internet-Draft DNS64 October 2009 - - -6. Deployment notes - - While DNS64 is intended to be part of a strategy for aiding IPv6 - deployment in an internetworking environment with some IPv4-only and - IPv6-only networks, it is important to realise that it is - incompatible with some things that may be deployed in an IPv4-only or - dual-stack context. - -6.1. DNS resolvers and DNS64 - - Full-service resolvers that are unaware of the DNS64 function can be - (mis)configured to act as mixed-mode iterative and forwarding - resolvers. In a native-IPv4 context, this sort of configuration may - appear to work. It is impossible to make it work properly without it - being aware of the DNS64 function, because it will likely at some - point obtain IPv4-only glue records and attempt to use them for - resolution. The result that is returned will contain only A records, - and without the ability to perform the DNS64 function the resolver - will simply be unable to answer the necessary AAAA queries. - -6.2. DNSSEC validators and DNS64 - - Existing DNSSEC validators (i.e. that are unaware of DNS64) will - reject all the data that comes from the DNS64 as having been tampered - with. If it is necessary to have validation behind the DNS64, then - the validator must know how to perform the DNS64 function itself. - Alternatively, the validating host may establish a trusted connection - with the DNS64, and allow the DNS64 to do all validation on its - behalf. - - -7. Security Considerations - - See the discussion on the usage of DNSSEC and DNS64 described in the - document. - - -8. Contributors - - Dave Thaler - - Microsoft - - dthaler@windows.microsoft.com - - - - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 16] - -Internet-Draft DNS64 October 2009 - - -9. Acknowledgements - - This draft contains the result of discussions involving many people, - including the participants of the IETF BEHAVE Working Group. The - following IETF participants made specific contributions to parts of - the text, and their help is gratefully acknowledged: Mark Andrews, - Jari Arkko, Rob Austein, Timothy Baldwin, Fred Baker, Marc Blanchet, - Cameron Byrne, Brian Carpenter, Hui Deng, Francis Dupont, Ed - Jankiewicz, Peter Koch, Suresh Krishnan, Ed Lewis, Xing Li, Matthijs - Mekking, Hiroshi Miyata, Simon Perrault, Teemu Savolainen, Jyrki - Soini, Dave Thaler, Mark Townsley, Stig Venaas, Magnus Westerlund, - Florian Weimer, Dan Wing, Xu Xiaohu. - - Marcelo Bagnulo and Iljitsch van Beijnum are partly funded by - Trilogy, a research project supported by the European Commission - under its Seventh Framework Program. - - -10. References - -10.1. Normative References - - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, March 1997. - - [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", - STD 13, RFC 1034, November 1987. - - [RFC1035] Mockapetris, P., "Domain names - implementation and - specification", STD 13, RFC 1035, November 1987. - - [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", - RFC 2671, August 1999. - - [RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection", - RFC 2672, August 1999. - - [RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm - (SIIT)", RFC 2765, February 2000. - - [RFC4787] Audet, F. and C. Jennings, "Network Address Translation - (NAT) Behavioral Requirements for Unicast UDP", BCP 127, - RFC 4787, January 2007. - - [I-D.ietf-behave-tcp] - Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. - Srisuresh, "NAT Behavioral Requirements for TCP", - draft-ietf-behave-tcp-08 (work in progress), - - - -Bagnulo, et al. Expires April 22, 2010 [Page 17] - -Internet-Draft DNS64 October 2009 - - - September 2008. - - [I-D.ietf-behave-nat-icmp] - Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT - Behavioral Requirements for ICMP protocol", - draft-ietf-behave-nat-icmp-12 (work in progress), - January 2009. - - [I-D.thaler-behave-translator-addressing] - Thaler, D., "IPv6 Addressing of IPv6/IPv4 Translators", - draft-thaler-behave-translator-addressing-00 (work in - progress), July 2009. - -10.2. Informative References - - [I-D.bagnulo-behave-nat64] - Bagnulo, M., Matthews, P., and I. Beijnum, "NAT64: Network - Address and Protocol Translation from IPv6 Clients to IPv4 - Servers", draft-bagnulo-behave-nat64-03 (work in - progress), March 2009. - - [RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address - Translation - Protocol Translation (NAT-PT)", RFC 2766, - February 2000. - - [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, - "Dynamic Updates in the Domain Name System (DNS UPDATE)", - RFC 2136, April 1997. - - [RFC1858] Ziemba, G., Reed, D., and P. Traina, "Security - Considerations for IP Fragment Filtering", RFC 1858, - October 1995. - - [RFC3128] Miller, I., "Protection Against a Variant of the Tiny - Fragment Attack (RFC 1858)", RFC 3128, June 2001. - - [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network - Address Translator (Traditional NAT)", RFC 3022, - January 2001. - - [RFC3484] Draves, R., "Default Address Selection for Internet - Protocol version 6 (IPv6)", RFC 3484, February 2003. - - [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, - "DNS Extensions to Support IP Version 6", RFC 3596, - October 2003. - - [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. - - - -Bagnulo, et al. Expires April 22, 2010 [Page 18] - -Internet-Draft DNS64 October 2009 - - - Rose, "DNS Security Introduction and Requirements", - RFC 4033, March 2005. - - [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. - Rose, "Resource Records for the DNS Security Extensions", - RFC 4034, March 2005. - - [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. - Rose, "Protocol Modifications for the DNS Security - Extensions", RFC 4035, March 2005. - - [RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network - Address Translator - Protocol Translator (NAT-PT) to - Historic Status", RFC 4966, July 2007. - - [I-D.iana-rfc3330bis] - Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses", - draft-iana-rfc3330bis-06 (work in progress), - February 2009. - - [I-D.ietf-mmusic-ice] - Rosenberg, J., "Interactive Connectivity Establishment - (ICE): A Protocol for Network Address Translator (NAT) - Traversal for Offer/Answer Protocols", - draft-ietf-mmusic-ice-19 (work in progress), October 2007. - - [I-D.ietf-6man-addr-select-sol] - Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama, - "Solution approaches for address-selection problems", - draft-ietf-6man-addr-select-sol-01 (work in progress), - June 2008. - - [RFC3498] Kuhfeld, J., Johnson, J., and M. Thatcher, "Definitions of - Managed Objects for Synchronous Optical Network (SONET) - Linear Automatic Protection Switching (APS) - Architectures", RFC 3498, March 2003. - - [I-D.wing-behave-learn-prefix] - Wing, D., Wang, X., and X. Xu, "Learning the IPv6 Prefix - of an IPv6/IPv4 Translator", - draft-wing-behave-learn-prefix-02 (work in progress), - May 2009. - - [I-D.miyata-behave-prefix64] - Miyata, H. and M. Bagnulo, "PREFIX64 Comparison", - draft-miyata-behave-prefix64-02 (work in progress), - March 2009. - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 19] - -Internet-Draft DNS64 October 2009 - - - [I-D.venaas-behave-mcast46] - Venaas, S., "An IPv4 - IPv6 multicast translator", - draft-venaas-behave-mcast46-00 (work in progress), - December 2008. - - [I-D.ietf-dnsop-default-local-zones] - Andrews, M., "Locally-served DNS Zones", - draft-ietf-dnsop-default-local-zones-08 (work in - progress), February 2009. - - -Appendix A. Deployment scenarios and examples - - In this section, we first provide a description of the default - address transformation algorithm and then we walk through some sample - scenarios that are expected to be common deployment cases. It should - be noted that is provided for illustrative purposes and this section - is not normative. The normative definition of DNS64 is provided in - Section 5 and the normative definition of the address transformation - algorithm is provided in [I-D.thaler-behave-translator-addressing]. - - There are two main different setups where DNS64 is expected to be - used (other setups are possible as well, but these two are the main - ones identified at the time of this writing). - - One possible setup that is expected to be common is the case of an - end site or an ISP that is providing IPv6-only connectivity or - connectivity to IPv6-only hosts that wants to allow the - communication from these IPv6-only connected hosts to the IPv4 - Internet. This case is called An-IPv6-network-to-IPv4-Internet. - In this case, the IPv6/IPv4 Translator is used to connect the end - site or the ISP to the IPv4 Internet and the DNS64 function is - provided by the end site or the ISP. - - The other possible setup that is expected is an IPv4 site that - wants that its IPv4 servers to be reachable from the IPv6 - Internet. This case is called IPv6-Internet-to-an-IPv4-network. - It should be noted that the IPv4 addresses used in the IPv4 site - can be either public or private. In this case, the IPv6/IPv4 - Translator is used to connect the IPv4 end site to the IPv6 - Internet and the DNS64 function is provided by the end site - itself. - - In this section we illustrate how the DNS64 behaves in the different - scenarios that are expected to be common. We consider then 3 - possible scenarios, namely: - - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 20] - -Internet-Draft DNS64 October 2009 - - - 1. An-IPv6-network-to-IPv4-Internet setup with DNS64 in DNS server - mode - - 2. An-IPv6-network-to-IPv4-Internet setup with DNS64 in stub- - resolver mode - - 3. IPv6-Internet-to-an-IPv4-network setup with DNS64 in DNS server - mode - - The notation used is the following: upper case letters are IPv4 - addresses; upper case letters with a prime(') are IPv6 addresses; - lower case letters are ports; prefixes are indicated by "P::X", which - is an IPv6 address built from an IPv4 address X by adding the prefix - P, mappings are indicated as "(X,x) <--> (Y',y)". - -A.1. Embed and Zero-Pad algorithm description - - In this section we describe the default algorithm for the generation - of IPv6 address from IPv4 address to be implemented in the DNS64. - - The only parameter required by the default algorithm is an IPv6 - prefix. This prefix is used to map IPv4 addresses into IPv6 - addresses, and is denoted Pref64. If we note n the length of the - prefix Pref64, then n must the less or equal than 96. If an Pref64 - is configured through any means in the DNS64 (such as manually - configured, or other automatic mean not specified in this document), - the default algorithm must use this prefix. If no prefix is - available the algorithm must use the Well-Know prefix (include here - the prefix to be assigned by IANA) defined in - [I-D.thaler-behave-translator-addressing] - - The input for the algorithm are: - - The IPv4 address: X - - The IPv6 prefix: Pref64::/n - - The IPv6 address is generated by concatenating the prefix Pref64::/n, - the IPv4 address X and optionally (in case n is strictly smaller than - 96) an all-zero suffix. So, the resulting IPv6 address would be - Pref64:X:: - - Reverse algorithm - - We next describe the reverse algorithm of the algorithm described in - the previous section. This algorithm allows to generate and IPv4 - address from an IPv6 address. This reverse algorithm is NOT - implemented by the DNS64 but it is implemented in the IPv6/IPv4 - - - -Bagnulo, et al. Expires April 22, 2010 [Page 21] - -Internet-Draft DNS64 October 2009 - - - translator that is serving the same domain the DNS64. - - The only parameter required by the default algorithm is an IPv6 - prefix. This prefix is the one originally used to map IPv4 addresses - into IPv6 addresses, and is denoted Pref64. - - The input for the algorithm are: - - The IPv6 address: X' - - The IPv6 prefix: Pref64::/n - - First, the algorithm checks that the fist n bits of the IPv6 address - X' match with the prefix Pref64::/n i.e. verifies that Pref64::/n = - X'/n. - - If this is not the case, the algorithm ends and no IPv4 address is - generated. - - If the verification is successful, then the bits between the n+1 - and the n+32 of the IPv6 address X' are extracted to form the IPv4 - address. - -A.2. An-IPv6-network-to-IPv4-Internet setup with DNS64 in DNS server - mode - - In this example, we consider an IPv6 node located in an IPv6-only - site that initiates a communication to an IPv4 node located in the - IPv4 Internet. - - The scenario for this case is depicted in the following figure: - - - +---------------------------------------+ +-----------+ - |IPv6 site +-------------+ |IP Addr: | | - | +----+ | Name server | +-------+ T | IPv4 | - | | H1 | | with DNS64 | |64Trans|------| Internet | - | +----+ +-------------+ +-------+ +-----------+ - | |IP addr: Y' | | | |IP addr: X - | --------------------------------- | +----+ - +---------------------------------------+ | H2 | - +----+ - - The figure shows an IPv6 node H1 which has an IPv6 address Y' and an - IPv4 node H2 with IPv4 address X. - - A IPv6/IPv4 Translator connects the IPv6 network to the IPv4 - Internet. This IPv6/IPv4 Translator has a prefix (called Pref64::/n) - - - -Bagnulo, et al. Expires April 22, 2010 [Page 22] - -Internet-Draft DNS64 October 2009 - - - an IPv4 address T assigned to its IPv4 interface. - - The other element involved is the local name server. The name server - is a dual-stack node, so that H1 can contact it via IPv6, while it - can contact IPv4-only name servers via IPv4. - - The local name server needs to know the prefix assigned to the local - IPv6/IPv4 Translator (Pref64::/n). For the purpose of this example, - we assume it learns this through manual configuration. - - For this example, assume the typical DNS situation where IPv6 hosts - have only stub resolvers, and always query a name server that - performs recursive lookups (henceforth called "the recursive - nameserver"). - - The steps by which H1 establishes communication with H2 are: - - 1. H1 does a DNS lookup for FQDN(H2). H1 does this by sending a DNS - query for an AAAA record for H2 to the recursive name server. - The recursive name server implements DNS64 functionality. - - 2. The recursive name server resolves the query, and discovers that - there are no AAAA records for H2. - - 3. The recursive name server queries for an A record for H2 and gets - back an A record containing the IPv4 address X. The name server - then synthesizes an AAAA record. The IPv6 address in the AAAA - record contains the prefix assigned to the IPv6/IPv4 Translator - in the upper n bits then the IPv4 address X and then an all-zero - padding i.e. the resulting IPv6 address is Pref64:X:: - - 4. H1 receives the synthetic AAAA record and sends a packet towards - H2. The packet is sent from a source transport address of (Y',y) - to a destination transport address of (Pref64:X::,x), where y and - x are ports chosen by H2. - - 5. The packet is routed to the IPv6 interface of the IPv6/IPv4 - Translator and the subsequent communication flows by means of the - IPv6/IPv4 Translator mechanisms. - -A.3. An-IPv6-network-to-IPv4-Internet setup with DNS64 in stub-resolver - mode - - The scenario for this case is depicted in the following figure: - - - - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 23] - -Internet-Draft DNS64 October 2009 - - - +---------------------------------------+ +-----------+ - |IPv6 site +-------+ |IP addr: | | - | +---------------+ | Name | +-------+ T | IPv4 | - | | H1 with DNS64 | | Server| |64Trans|------| Internet | - | +---------------+ +-------+ +-------+ +-----------+ - | |IP addr: Y' | | | |IP addr: X - | --------------------------------- | +----+ - +---------------------------------------+ | H2 | - +----+ - - The figure shows an IPv6 node H1 which has an IPv6 address Y' and an - IPv4 node H2 with IPv4 address X. Node H1 is implementing the DNS64 - function. - - A IPv6/IPv4 Translator connects the IPv6 network to the IPv4 - Internet. This IPv6/IPv4 Translator has a prefix (called Pref64::/n) - and an IPv4 address T assigned to its IPv4 interface. - - H1 needs to know the prefix assigned to the local IPv6/IPv4 - Translator (Pref64::/n). For the purpose of this example, we assume - it learns this through manual configuration. - - Also shown is a name server. For the purpose of this example, we - assume that the name server is a dual-stack node, so that H1 can - contact it via IPv6, while it can contact IPv4-only name servers via - IPv4. - - For this example, assume the typical situation where IPv6 hosts have - only stub resolvers and always query a name server that provides - recursive lookups (henceforth called "the recursive name server"). - The recursive name server does not perform the DNS64 function. - - The steps by which H1 establishes communication with H2 are: - - 1. H1 does a DNS lookup for FQDN(H2). H1 does this by sending a DNS - query for a AAAA record for H2 to the recursive name server. - - 2. The recursive DNS server resolves the query, and returns the - answer to H1. Because there are no AAAA records in the global - DNS for H2, the answer is empty. - - 3. The stub resolver at H1 then queries for an A record for H2 and - gets back an A record containing the IPv4 address X. The DNS64 - function within H1 then synthesizes a AAAA record. The IPv6 - address in the AAAA record contains the prefix assigned to the - IPv6/IPv4 Translator in the upper n bits, then the IPv4 address X - and then an all-zero padding i.e. the resulting IPv6 address is - Pref64:X::. - - - -Bagnulo, et al. Expires April 22, 2010 [Page 24] - -Internet-Draft DNS64 October 2009 - - - 4. H1 sends a packet towards H2. The packet is sent from a source - transport address of (Y',y) to a destination transport address of - (Pref64:X::,x), where y and x are ports chosen by H2. - - 5. The packet is routed to the IPv6 interface of the IPv6/IPv4 - Translator and the subsequent communication flows using the IPv6/ - IPv4 Translator mechanisms. - -A.4. IPv6-Internet-to-an-IPv4-network setup DNS64 in DNS server mode - - In this example, we consider an IPv6 node located in the IPv6 - Internet site that initiates a communication to a IPv4 node located - in the IPv4 site. - - This scenario can be addressed without using any form of DNS64 - function. This is so because it is possible to assign a fixed IPv6 - address to each of the IPv4 servers. Such an IPv6 address would be - constructed as the Pref64::/n concatenated with the IPv4 address of - the IPv4 server and an all-zero padding. Note that the IPv4 address - can be a public or a private address; the latter does not present any - additional difficulty, since the LIR prefix must be used a Pref64 (in - this scenario the usage of the WK prefix is not supported). Once - these IPv6 addresses have been assigned to represent the IPv4 servers - in the IPv6 Internet, real AAAA RRs containing these addresses can be - published in the DNS under the site's domain. This is the - recommended approach to handle this scenario, because it does not - involve synthesizing AAAA records at the time of query. Such a - configuration is easier to troubleshoot in the event of problems, - because it always provides the same answer to every query. - - However, there are some more dynamic scenarios, where synthesizing - AAAA RRs in this setup may be needed. In particular, when DNS Update - [RFC2136] is used in the IPv4 site to update the A RRs for the IPv4 - servers, there are two options: One option is to modify the server - that receives the dynamic DNS updates. That would normally be the - authoritative server for the zone. So the authoritative zone would - have normal AAAA RRs that are synthesized as dynamic updates occur. - The other option is modify the authoritative server to generate - synthetic AAAA records for a zone, possibly based on additional - constraints, upon the receipt of a DNS query for the AAAA RR. The - first option -- in which the AAAA is synthesized when the DNS update - message is received, and the data published in the relevant zone -- - is recommended over the second option (i.e. the synthesis upon - receipt of the AAAA DNS query). This is because it is usually easier - to solve problems of misconfiguration and so on when the DNS - responses are not being generated dynamically. For completeness, the - DNS64 behavior that we describe in this section covers the case of - synthesizing the AAAA RR when the DNS query arrives. Nevertheless, - - - -Bagnulo, et al. Expires April 22, 2010 [Page 25] - -Internet-Draft DNS64 October 2009 - - - such a configuration is NOT RECOMMENDED. Troubleshooting - configurations that change the data depending on the query they - receive is notoriously hard, and the IPv4/IPv6 translation scenario - is complicated enough without adding additional opportunities for - possible malfunction. - - The scenario for this case is depicted in the following figure: - - - +-----------+ +----------------------------------------+ - | | | IPv4 site +-------------+ | - | IPv6 | +-------+ +----+ | Name server | | - | Internet |------|64Trans| | H2 | | with DNS64 | | - +-----------+ +-------+ +----+ +-------------+ | - |IP addr: Y' | | |IP addr: X | | - +----+ | ----------------------------------- | - | H1 | +----------------------------------------+ - +----+ - - The figure shows an IPv6 node H1 which has an IPv6 address Y' and an - IPv4 node H2 with IPv4 address X. - - A IPv6/IPv4 Translator connects the IPv4 network to the IPv6 - Internet. This IPv6/IPv4 Translator has a prefix (called - Pref64::/n). - - Also shown is the authoritative name server for the local domain with - DNS64 functionality. For the purpose of this example, we assume that - the name server is a dual-stack node, so that H1 or a recursive - resolver acting on the request of H1 can contact it via IPv6, while - it can be contacted by IPv4-only nodes to receive dynamic DNS updates - via IPv4. - - The local name server needs to know the prefix assigned to the local - IPv6/IPv4 Translator (Pref64::/n). For the purpose of this example, - we assume it learns this through manual configuration. - - The steps by which H1 establishes communication with H2 are: - - 1. H1 does a DNS lookup for FQDN(H2). H1 does this by sending a DNS - query for an AAAA record for H2. The query is eventually - forwarded to the server in the IPv4 site. - - 2. The local DNS server resolves the query (locally), and discovers - that there are no AAAA records for H2. - - 3. The name server verifies that FQDN(H2) and its A RR are among - those that the local policy defines as allowed to generate a AAAA - - - -Bagnulo, et al. Expires April 22, 2010 [Page 26] - -Internet-Draft DNS64 October 2009 - - - RR from. If that is the case, the name server synthesizes an - AAAA record from the A RR and the relevant Pref64::/n. The IPv6 - address in the AAAA record contains the prefix assigned to the - IPv6/IPv4 Translator in the first n bits and the IPv4 address X - and then an all-zero padding. - - 4. H1 receives the synthetic AAAA record and sends a packet towards - H2. The packet is sent from a source transport address of (Y',y) - to a destination transport address of (Pref64:X::,x), where y and - x are ports chosen by H2. - - 5. The packet is routed through the IPv6 Internet to the IPv6 - interface of the IPv6/IPv4 Translator and the communication flows - using the IPv6/IPv4 Translator mechanisms. - - -Appendix B. Motivations and Implications of synthesizing AAAA RR when - real AAAA RR exists - - The motivation for synthesizing AAAA RR when a real AAAA RR exists is - to support the following scenario: - - An IPv4-only server application (e.g. web server software) is - running on a dual-stack host. There may also be dual-stack server - applications also running on the same host. That host has fully - routable IPv4 and IPv6 addresses and hence the authoritative DNS - server has an A and a AAAA record as a result. - - An IPv6-only client (regardless of whether the client application - is IPv6-only, the client stack is IPv6-only, or it only has an - IPv6 address) wants to access the above server. - - The client issues a DNS query to a DNS64 recursor. - - If the DNS64 only generates a synthetic AAAA if there's no real AAAA, - then the communication will fail. Even though there's a real AAAA, - the only way for communication to succeed is with the translated - address. So, in order to support this scenario, the administrator of - a DNS64 service may want to enable the synthesis of AAAA RR even when - real AAAA RR exist. - - The implication of including synthetic AAAA RR when real AAAA RR - exist is that translated connectivity may be preferred over native - connectivity in some cases where the DNS64 is operated in DNS server - mode. - - RFC3484 [RFC3484] rules use longest prefix match to select which is - the preferred destination address to use. So, if the DNS64 recursor - - - -Bagnulo, et al. Expires April 22, 2010 [Page 27] - -Internet-Draft DNS64 October 2009 - - - returns both the synthetic AAAA RR and the real AAAA RR, then if the - DNS64 is operated by the same domain as the initiating host, and a - global unicast prefix (called the LIR prefix as defined in - [I-D.thaler-behave-translator-addressing]) is used, then the - synthetic AAAA RR is likely to be preferred. - - This means that without further configuration: - - In the case of An IPv6 network to the IPv4 internet, the host will - prefer translated connectivity if LIR prefix is used. If the - Well-Known (WK) prefix defined in - [I-D.thaler-behave-translator-addressing] is used, it will - probably prefer native connectivity. - - In the case of the IPv6 Internet to an IPv4 network, it is - possible to bias the selection towards the real AAAA RR if the - DNS64 recursor returns the real AAAA first in the DNS reply, when - the LIR prefix is used (the WK prefix usage is not recommended in - this case) - - In the case of the IPv6 to IPv4 in the same network, for local - destinations (i.e., target hosts inside the local site), it is - likely that the LIR prefix and the destination prefix are the - same, so we can use the order of RR in the DNS reply to bias the - selection through native connectivity. If a WK prefix is used, - the longest prefix match rule will select native connectivity. - - So this option introduces problems in the following cases: - - An IPv6 network to the IPv4 internet with the LIR prefix - - IPv6 to IPv4 in the same network when reaching external - destinations and the LIR prefix is used. - - In any case, the problem can be solved by properly configuring the - RFC3484 [RFC3484] policy table, but this requires effort on the part - of the site operator. - - - - - - - - - - - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 28] - -Internet-Draft DNS64 October 2009 - - -Authors' Addresses - - Marcelo Bagnulo - UC3M - Av. Universidad 30 - Leganes, Madrid 28911 - Spain - - Phone: +34-91-6249500 - Fax: - Email: marcelo@it.uc3m.es - URI: http://www.it.uc3m.es/marcelo - - - Andrew Sullivan - Shinkuro - 4922 Fairmont Avenue, Suite 250 - Bethesda, MD 20814 - USA - - Phone: +1 301 961 3131 - Email: ajs@shinkuro.com - - - Philip Matthews - Unaffiliated - 600 March Road - Ottawa, Ontario - Canada - - Phone: +1 613-592-4343 x224 - Fax: - Email: philip_matthews@magma.ca - URI: - - - Iljitsch van Beijnum - IMDEA Networks - Av. Universidad 30 - Leganes, Madrid 28911 - Spain - - Phone: +34-91-6246245 - Email: iljitsch@muada.com - - - - - - - -Bagnulo, et al. Expires April 22, 2010 [Page 29] - |