You can use the route
command to determine your gateway (router) IP:
me@pc ~ $ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.1.254 0.0.0.0 UG 2 0 0 eth0
127.0.0.0 127.0.0.1 255.0.0.0 UG 0 0 0 lo
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
Reference: How do I find out my Linux gateway / router IP address?