This sample configuration is for a Cisco 1602 router with a point-to-point leased line configuraiton, but can be easily adapted to other Cisco routers.

Using 684 out of 7506 bytes
!
version 11.2
no service udp-small-servers
no service tcp-small-servers
!
hostname customer-gw
!
enable secret 5 $1$KO/5$Exw2XJ7TgoqPnTVOvBR8V1
enable password giscustomer
!
!
interface Ethernet0
 ip address 216.41.70.193 255.255.255.0
!
interface Serial0
 description Point-to-point to GIS
 ip unnumbered Ethernet0
 no ip mroute-cache
 no fair-queue
!
no ip classless
ip route 0.0.0.0 0.0.0.0 Serial0
!
line con 0
line vty 0 4
 password giscustomer
 login
!
end