Quoting Steve Litt (slitt@???):

> A program called ip. It has commands such as ip route, ip addr, ip
> link, and several others. It's confusing and underdocumented, but so is
> ifconfig (which I never even began to master).

I have a knowledgebase item 'iproute2 transition' on
http://linuxmafia.com/kb/Network_Other/ pointing to a good LWN.net
article on this subject.