use ipv4
ipv6 i think isn't even implemented in x yet
when a client tries to use ipv6 and the server is using ipv4 like almost everything is still using
they have to talk extra
client says in ipv6 "hey give me a connection"
server using ipv4 says "huuuuh, could you rephrase that in some way that makes sense"
cliient responds with ipv4
results are slow connections
one of the things ipv6 addresses is a larger address space
http://www.ipv6.org/specs.html