At the command line interface type:
$ ip addr show
Either of these commands will show all of your interfaces and their IP addresses and Defalt Gateways.
A cable connection would be "eth0" a wireless connection would bd "wlan" and a dialup modem connection would be "ppp0"
If you have an ethernet cable connection to your router and you don't see an eth0 entry then either the ethernet interface is down or is not pulling an ip address from your router.
if that is the case:
"ifup ehth0" will bring eth0 up and dhclient will cause it to pull an ip address
at that point redo
or ip addr show
this will show you if eth0 is up and pulling an IP address from the router.
If your router is a linksys, then look for 192.168.1.1 as the default gateway and 18.104.22.168 as the "src" or IP address for the linux box.
Good luck with it