How to Configure Default Route

A default route, also known as the gateway of last resort, is the network route used by a router when no other known route exists for a given IP packet's destination address. All the packets for destinations not known by the router's routing table are sent to the default route. This route generally leads to another router, which treats the packet the same way: If the route is known, the packet will get forwarded to the known route. If not, the packet is forwarded to the default-route of that router which generally leads to another router. And so on. Each router traversal adds a one-hop distance to the route

Configuration Command:

Router(config)#ip route 0.0.0.0 0.0.0.0 serial 0/0/0    >> exit interface OR

Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.10.2   >> next hope (router) address

Cisco ASA  Configuration Command:
ASA(Config)#route outside 0.0.0.0 0.0.0.0 10.100.200.1 1