Most of the access providers, can't quickly move to dual-stack. It may be a
problem of existing equipment or even L2 technology (as the cable/DOCSIS 2.0
The bigger issue is upgrading the CPEs. Lack of plans in the last years,
didn't helped the low cost vendors to deliver them with dual-stack. Yes,
there are open source alternatives, but they don't work so easily for all,
as not all the users are able to do that upgrade, and otherwise it may mean
a hard support cost. Obviously this will be challenged by those ISPs that
want to start providing new services based on IPv6 (surveillance, home
automation, IPTV, etc.).
So having a CPE typically means either the user has a single PC and the CPE
may be configured as bridge and then the user PC has the public IPv4 address
(case for 6to4), or the user PCs are behind NAT (caser for Teredo).
The alternative will be softwires (L2TP), but is not yet fully supported
(I'm not even sure if Vista support it form Microsoft, for XP I think not
So providing a combination of 6to4 relay and Teredo server+relay, is a
simple way to offer IPv6 connectivity at a very low cost and improve
performance vs. using relays somewhere else.
Of course, this will be more obvious as more applications use IPv6, and in
fact, my suggestion will be, once we have some more relays across all
Internet, that XP and Vista get one of those updated changing the setup of
the address selection table, so Teredo and 6to4 become preferred to IPv4
In fact, it will be quite easy to, at boot time, do a quick test (ICMPv6 +
ICMPv4) of the "availability" of a good relay, to decide if the policy table
prefers by default Teredo/6to4 instead of IPv4.
Of course all this is assuming that you can't provide native IPv6 !
Also one very important issue will be to make sure that Windows 2003 (which
runs lots of websites with IIS), is updated with Teredo Server/Relay
function or at least that Teredo host-specific relay functionality works by
PS: What it will be good is to get at least some of the MS servers
dual-stacked and you know, if help is needed, I don't mind to spare some
time for that !