Know to setup a network with a modem, router and a few client computers.
Understand how IP addresses work in a private network vs public Internet situation.
A general understanding of masking/subnetting.
Understand what your Gateway is.
Understand how DHCP works and also know how to setup a basic computer to computer network.
Understand how and when to use static IPs.
Know how to forward ports.
If wireless is involved, know how to apply encryption, understand signal strengths and how it can be improved.   _{Your Comment}