Display Current Config for all NIC's: ifconfig
Display Current Config for eth0: ifconfig eth0
Assign IP: ifconfig eth0 192.168.1.2
Ping: ping -c 3 192.168.1.1
Assign multiple IP's: ifconfig eth0:0 192.168.1.2
Assign second IP: ifconfig eth0:1 192.168.1.3
Disable network card: ifconfig eth0 down
Enable network card: ifconfig eth0 up
View current routing table: route "or" route -n
View arp cache: arp "or" arp -n
Assign IP/Subnet: ifconfig eth0 192.168.1.2 netmask 255.255.255.0
Assign Default Gateway: route add default gw 192.168.1.1
Trace Route: traceroute www.whatismyip.com
Trace Path: tracepath www.whatismyip.com
DNS Test: host www.whatismyip.com
Advanced DNS Test: dig www.whatismyip.com
Reverse Lookup: host 66.11.119.69
Advanced Reverse Lookup: dig -x 66.11.119.69
*You MUST be at the ROOT user to make/save any changes. Linux users, your distribution will determine the location of your network config file which will need to be updated and saved in order for the changes to remain in effect after rebooting. Network cards are referred to as eth0, eth1, eth2, etc based on their position on the PCI bus.
*Special thanks to Gergely for the Linux commands!