Router(config)#ip route [ip] [subnetmask]{interface or ip]

example:

Router(config)#ip route 172.16.1.1 255.255.255.0 serial 0/1/0

or

Router(config)#ip route 172.16.1.1 255.255.255.0 16.16.16.1

 default route:

Router(config)#ip route 0.0.0.0 0.0.0.0 [interface or ip ]

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for monitoring:

Router#show ip route