[PLUG] Hey IPv6ers, about this netstat -nt output

[Tim]

> recent curiosity point:
> 
>   michael at post:/etc/bind/zones$ netstat -nt
>   Active Internet connections (w/o servers)
>   Proto Recv-Q Send-Q Local Address           Foreign Address         State      
>   tcp6       0      0 64.105.252.42:22        64.105.252.44:58721     ESTABLISHED
>   tcp6       0      0 64.105.252.42:22        64.105.252.44:58279     ESTABLISHED
>   tcp6       0      0 64.105.252.42:22        64.105.252.44:54908     ESTABLISHED
>   tcp6       0      0 64.105.252.42:22        64.105.252.44:55373     ESTABLISHED
> 
> tcp6 and ip4 addresses?  That is kinda unexpected.
> Any handy explanations?

In order to make application development for IPv6 a little easier,
operating systems have implemented various ways to listen on a single
socket for both v4 and v6 simultaneously.  A good overview is here:

  http://utcc.utoronto.ca/~cks/space/blog/linux/Ipv6DualBinding

So you can actually see a program bind to v6, and if the kernel
settings (or manual socket settings) are right, it can accept v4
connections.  This probably explains the odd netstat output you're
seeing. 

tim