Subject: I-D ACTION:draft-moore-6to4-dns-03.txt

From: [email-masked]
Date: Mon, 21 Oct 2002 08:05:26 -0400

A New Internet-Draft is available from the on-line Internet-Drafts directories.

	Title		: 6to4 and DNS
	Author(s)	: K. Moore
	Filename	: draft-moore-6to4-dns-03.txt
	Pages		: 11
	Date		: 2002-10-18
	
6to4 [1] defines a mechanism for allowing sites to communicate
using IPv6 over the public IPv4 Internet.  It does so by assigning a
block of IPv6 addresses corresponding to any 'public' (globally-scoped)
IPv4 address, and a means of tunneling IPv6 traffic destined for such
addresses over the IPv4 Internet.  In this way, any site which is
connected to the IPv4 Internet and which has at least one global IPv4
address assigned to it, can communicate with IPv6.
The advantage of 6to4 is that it decouples deployment of IPv6 by
the core of the network (e.g. Internet Service Providers or ISPs) from
deployment of IPv6 at the edges (e.g. customer sites), allowing each
site or ISP to deploy IPv6 support in its own time frame according to
its own priorities.  With 6to4, the edges may communicate with one
another using IPv6 even if one or more of their ISPs do not yet provide
native IPv6 service.  In addition, the principal cost of the 6to4
transition mechanism is borne by those who benefit from it.
However, the ability to perform so-called 'reverse lookups'
(lookups of IP addresses rather than domain names) in DNS requires that
there be a delegation path for the IP address being queried, from the
DNS root to the servers for the DNA zone which provides the PTR records
for that IP address.  For ordinary IPv6 addresses, the necessary DNS
servers and records for IPv6 reverse lookups would be maintained by the
each organization to which an address block is delegated; the delegation
path of DNS records reflects the delegation of address blocks
themselves.  However, for IPv6 addresses beginning with the 6to4 address
prefix, the DNS records would need to reflect IPv4 address delegation.
Since the entire motivation of 6to4 is to decouple site deployment of
IPv6 from infrastructure deployment of IPv6, such records cannot be
expected to be present for a site using 6to4 - especially for a site
whose ISP did not yet support IPv6 in any form.
This memo discusses several potential mechanisms for locating the
DNS servers which are assumed to provide 'reverse lookup' of 6to4
addresses.

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