Behave WG                                                  T. Savolainen
Internet-Draft                                                     Nokia
Intended status: Standards Track                             J. Korhonen
Expires: November 24, 2011                        Nokia Siemens Networks
                                                            May 23, 2011

  Discovery of a Network-Specific NAT64 Prefix using a Well-Known Name


   This document describes a method for detecting presence of DNS64 and
   for learning IPv6 prefix used for protocol translation on an access
   network without explicit support from the access network.  The method
   depends on existence of a known IPv4-only domain name.  The
   information learned enables applications and hosts to perform local
   IPv6 address synthesis and on dual-stack accesses avoid traversal
   through NAT64.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on November 24, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   ( in effect on the date of
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements and Terminology  . . . . . . . . . . . . . . . . . 3
     2.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . 3
     2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Host behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Connectivity test . . . . . . . . . . . . . . . . . . . . . 5
     3.2.  IPv4 addresses of the known name  . . . . . . . . . . . . . 5
     3.3.  Non-standard IPv6 address formats . . . . . . . . . . . . . 6
   4.  Hosting of an IPv4-only name(s) . . . . . . . . . . . . . . . . 6
   5.  Required IPv4 addresses . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

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1.  Introduction

   As part of the transition to IPv6 NAT64 [RFC6146] and DNS64 [RFC6147]
   technologies will be utilized by some access networks to provide IPv4
   connectivity for IPv6-only hosts.  The DNS64 utilizes IPv6 address
   synthesis to create local IPv6 presentations of peers having only
   IPv4 addresses, hence allowing DNS-using IPv6-only hosts to
   communicate with IPv4-only peers.

   However, DNS64 cannot serve applications not using DNS, such as those
   receiving IPv4 address literals as referrals.  Such applications
   could nevertheless be able to work through NAT64, provided they are
   able to create locally valid IPv6 presentations of peers' IPv4

   Additionally, DNS64 is not able to do IPv6 address synthesis for
   hosts running validating DNSSEC enabled resolvers, but instead the
   synthetization must be done by the hosts.  In order to perform IPv6
   synthesis hosts have to learn the IPv6 prefix(es) used on the access
   network for protocol translation.

   This document describes a best effort method for advanced
   applications and hosts to learn the information required to perform
   local IPv6 address synthesis.  An example application is a browser
   encountering an IPv4 address literal in an IPv6-only access network.
   Another example is a host running validating security aware DNS

   The knowledge of IPv6 address synthetization taking place may also be
   useful if DNS64 and NAT64 are present in dual-stack enabled access
   network.  In such cases hosts may choose to prefer IPv4 in order to
   avoid traversal through protocol translators.

   The described method is intented for the scenarios where network
   assisted NAT64 and prefix discovery solutions are not available.

2.  Requirements and Terminology

2.1.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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2.2.  Terminology

   Known Name: a fully qualified domain name known by the implementation
   to have only an A record.  Implementation knows it by hard-coding or
   e.g. via some provisioning technology.  The name is not known by

   Well-Known IPv4-only Name: a fully qualified domain name well-known
   to have only A record.

3.  Host behavior

   A host requiring information about presence of NAT64 and the IPv6
   prefix used for protocol translation shall send a DNS query for AAAA
   records of a known IPv4-only fully qualified domain name.  This may
   happen, for example, at the moment the host is configured an IPv6
   address of a DNS server.  This may also happen at the time when first
   DNS query for AAAA record is initiated.  The host may perform this
   check in both IPv6-only and dual-stack access networks.

   When sending AAAA query for the known name a host MUST set "Checking
   Disabled (CD)" bit to zero, as otherwise the DNS64 will not perform
   IPv6 address synthesis hence does not reveal the IPv6 prefix(es) used
   for protocol translation.

   A DNS reply with one or more non-empty AAAA records indicates that
   the access network is utilizing IPv6 address synthesis.  A host MUST
   look through all of the received AAAA records to collect all
   available prefixes.  The prefixes may include Well-Known Prefix or
   one or more Network-Specific Prefixes.  In the case of NSPs the host
   SHALL search for the IPv4 address inside of the received IPv6
   addresses to determine used address format.

   An IPv4 address inside synthesized IPv6 address should be found at
   some of the locations described in [RFC6052].  If the searched IPv4
   address is not found on any of the standard locations the network
   must be using different formatting.  In such case the host may try to
   find out the IPv4 address at some other location.

   The host should ensure a 32-bit IPv4 address value is present only
   once in an IPv6 address.  In case another instance of the value is
   found inside the IPv6, the host shall repeat the search with another
   IPv4 address.

   In the case only one IPv6 prefix was present in the DNS response: a
   host shall use that IPv6 prefix for both local synthetization and for
   detecting synthesis done by the DNS64 entity on the network.

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   In the case multiple IPv6 prefixes were present in the DNS response:
   a host SHOULD use all received prefixes when determining whether
   other received IPv6 addresses are synthetic.  However, for selecting
   prefix for the local IPv6 address synthesis host MUST use the
   following prioritization order, of which purpose is to avoid use of
   prefixes containing suffixes reserved for the future [RFC6052]:

   1.  Use NSP having /96 prefix

   2.  Use WKP prefix

   3.  Use longest available NSP prefix

   In the case of NXDOMAIN or empty AAAA reply: the DNS64 is not
   available on the access network, network filtered the well-known AAAA
   query on purpose, or something went wrong in the DNS resolution.  All
   unsuccesful cases result in unavailability of a host to perform local
   IPv6 address synthesis.  The host MAY periodically resend AAAA query
   to check if DNS64 has become available or temporary problem cleared.
   The host MAY also continue monitoring DNS replies with IPv6 addresses
   constructed from WKP, in which case the host MAY use the WKP as if it
   were learned during the query for well-known name.

3.1.  Connectivity test

   After the host has obtained a candidate prefix and format for the
   IPv6 address synthesis it may locally synthesize an IPv6 address, by
   using a publicly routable IPv4 address, and test connectivity with
   the resulting IPv6 address.  The connectivity test may be conducted
   e.g. with ICMPv6 or with a transport layer protocol.  The used public
   IPv4 address may be learned via separate A query.

   This connectivity test ensures local address synthetization results
   in functional and protocol translatable IPv6 addresses.

3.2.  IPv4 addresses of the known name

   The IPv4 addresses of the known name should be such that they are
   unlikely to appear more than once within an IPv6 address and also as
   easy as possible to find from within the synthetic IPv6 address.
   Good addresses might be as a primary and as a secondary.  The secondary address is needed in
   the case multiple instaces of primary address are present in a
   synthetic IPv6 address.  The IPv4 addresses can, however, be publicly
   routable especially if also used for the connectivity test.

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3.3.  Non-standard IPv6 address formats

   A node may need to perform more complex heuristics to cope with
   networks possibly using non-standard IPv6 address formats.  Non-
   standard approaches might include for example:

   1.  Non-standard location: IPv4 address in one piece at non-standard
       location.  Can be found by pattern matching.

   2.  Fragmented: IPv4 address in multiple pieces around the IPv6
       address.  May be found by pattern matching.

   3.  Obfuscated address: IPv4 address is obfuscated, for example
       xorred.  May potentially be found especially if standard addess
       format is used, but as this is an indication of access network's
       unwillingness to support host based synthetization the host
       should not try to decipher the IPv6 prefix.

4.  Hosting of an IPv4-only name(s)

   The required IPv4-only name has to be hosted by someone.  While
   IANA(?) might host one (?), it may be safest for device, operating
   system, and/or application vendors to host IPv4-only names for their
   own uses.  The name should have two A records in order to manage in
   situations where the first IPv4 address appears more than once within
   synthetic IPv6 address.  Another name may be needed for connectivity
   test purposes.

5.  Required IPv4 addresses

   A prefix detection without connectivity test does not require any
   routable IPv4 addresses.  The connectivity test requires a routable
   IPv4 address on the server side.

6.  Security Considerations

   No security considerations have been identified.

7.  IANA Considerations

   IANA(?) should define a name and an IPv4 address for a Well-Known
   IPv4-only Name.

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8.  Acknowledgements

   Authors would like to thank Dan Wing, Washam Fan, Cameron Byrne, and
   Christian Huitema for improvement ideas and comments.

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              April 2011.

Authors' Addresses

   Teemu Savolainen
   Hermiankatu 12 D
   FI-33720 Tampere


   Jouni Korhonen
   Nokia Siemens Networks
   Linnoitustie 6
   FI-02600 Espoo


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