Determining the Interface
The interface that interfaces the Frame Relay network is the one that should be configured. Once the interface has been selected, you should change to the appropriate interface configuration mode in the router. You should decide whether subinterfaces should be implemented. For a single point-to-point implementation, it might not be necessary to use subinterfaces; however, this implementation does not scale. If future sites are planned, it is best to use subinterfaces from the beginning.
To create a subinterface, use the following command to change to the desired interface:
interface interface_type interface_number.subinterface_number
For example, to create subinterface 1 on Serial 0, use the command interface serial 0.1. You must also determine the nature, or cast type, of the subinterface to be created, i.e., decide whether the subinterface will act as a point-to-point connection or a point-to-multipoint connection. If not specified, the subinterface defaults to a multipoint connection. To specify the cast type, add the keywords point-to-point or multipoint to the end of the previous command.