This could be the last IPv6 post of the week

*COULD BE*

Ok, this is a quick one and it makes perfect logical sense. If a machine is running dual stacks (v4 and v6) the machine will try to connect with another dual stack device via IPv6 first and then it will try IPv4 should v6 be unable to connect for some reason.

I had it all backwards thinking the dual stack machine would connect via IPv4 first then v6. But if you think it about the reason for having that the other way around is kind of obvious. Obvious or not it slipped past me. Whoops. Let's try some hosts:

For a single stack host a name lookup will return only IPv4 addresses:
host cnn.com
cnn.com has address 157.166.226.25
cnn.com has address 157.166.226.26
cnn.com has address 157.166.224.25
cnn.com has address 157.166.224.26

However if a host is running dual IP stacks both addresses will be returned:
host m0n0.ch
m0n0.ch has address 80.254.71.228
m0n0.ch has IPv6 address 2a02:200:3:1::101

The requesting machine, being a part of the "in crowd" running IPv6 will try that address first. So, in the end, you don't have to point the same query to the same machine if you don't want; just set up DNS however you'd like**. This could be useful for v4 and v6 load balancers or who knows what.

Thanks for everyone for setting me straight on that one (including M0n0wall's maintainer Manuel Kasper).

** DNS and IPv6.. oh boy, that's a post for another day.