Figure 1 shows the previous topology but using point-to-point subinterfaces. Each PVC is a separate subnetwork. The router’s physical interfaces are divided into subinterfaces, with each subinterface on a separate subnetwork.
In Figure 2, R1 has two point-to-point subinterfaces. The s0/0/1.102 subinterface connects to R2, and the s0/0/1.103 subinterface connects to R3. Each subinterface is on a different subnet.
To configure subinterfaces on a physical interface, the following steps are required:
Step 1. Remove any network layer address assigned to the physical interface. If the physical interface has an address, frames are not received by the local subinterfaces.
Step 2. Configure Frame Relay encapsulation on the physical interface using the encapsulation frame-relay command.
Step 3. For each of the defined PVCs, create a logical subinterface. Specify the port number, followed by a period (.) and the subinterface number. To make troubleshooting easier, it is suggested that the subinterface number matches the DLCI number.
Step 4. Configure an IP address for the interface and set the bandwidth.
Step 5. Configure the local DLCI on the subinterface using the frame-relay interface-dlci command. Recall that the Frame Relay service provider assigns the DLCI numbers.
Use the Syntax Checker in Figure 3 to configure router R2’s physical interface into point-to-point subinterfaces with the appropriate Frame Relay configuration.