Point-to-Point Leased Lines
Point-to-point leased lines are established across synchronous point-to-point serial links. These synchronous point-to-point links include a cable from a service provider, with the service including the capability to send and receive bits across that cable at a predetermined speed. The physical connection includes a CSU/DSU on each end of the link. After the CSU/DSUs are configured and the lines are installed, only a small amount of configuration is required on the routers to get the two routers working. You only need to configure IP addresses on each router and run a no shutdown command on each interface to enable them to ping each other across the link. The IP addresses of the two routers at either end of the synchronous point-to-point serial link must be in the same subnet because the two routers' interfaces are not separated by some other IP router. Generally, the no shutdown command is not required but if a Cisco router comes up, and the physical WAN link is not working, the router might place a shutdown command on the interface configuration. So the no shutdown interface subcommand would be needed to put the interface in service.