ifconfig
Shows network adapters, IP addresses, and can be used to bring adapters up and down.
sudo dhclient -r
DHCP release of IP address. Equivalent to ipconfig/release on Windows.
sudo dhclient
DHCP renew or request of IP address. Equivalent to ipconfig/renew on Windows.
sudo netstat -tap
Shows processes that are listening, and other active network connections. You must run as super user to see the owning processes.
sudo nmap -p1-65535 -sS -sV -O -PI -PT <IP / Hostname>
Initiates a port scan of all ports and reports which unfiltered ports are open or closed.
iptables
Enforces table-based rules to implementing a firewall. Check out this iptables example.