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6to4 and 'campus' networks
Many university campus networks (and large businesses that have been
around for some time, etc.) run non-RFC1918 addresses internally.
They then NAT, proxy or statefully filter traffic through their
border. If someone has a better name than "campus" for this, then
then I'm all ears - I realise it's not accurate at all.
My understanding of Windows (and to some extent some Linuxes and
BSDs) 6to4 behaviour is that when they detect an interface with a non-
RFC1918 IPv4 address, they bring up 6to4.
While this is fine for networks that don't filter or otherwise mess
with IP protocol 41, this causes big problems for users behind
networks that filter or NAT.
When I recently turned on AAAA records on a fairly decently sized
traffic website of mine, the most comments about reachability came
from people on 'campus' style networks, as described above. AAAA
records are now turned off for that site, for obvious reasons. These
were all non-technical users with Vista on their machines.
Has anyone given thought to a 6to4 'qualification' procedure for auto-
configured 6to4? Such a procedure could be as simple as sending an
ICMPv6 echo request to 2002:c058:6301:: (220.127.116.11) and bringing
the interface up if there is an acceptable response.
Note that I accept that in an ideal world, administrators of networks
like this would block traffic to 18.104.22.168, and return an ICMP
unreachable message of some flavour, so that when we try and reach an
IPv6 connected host, we instantly realise 6to4 is unusable (and maybe
even fall back to Teredo or something, instead of IPv4). In the real
world however, expecting all the administrators of these types of
networks to make changes like this is fairly unreasonable, and as I
mention, it's a fairly big problem for anyone wanting to roll out
AAAA records to production stuff, right now.