 subinterfaces can have only one DLCI active on them, while multipoint subinter- faces can have many. Multipoint subinterfaces behave in much the same way that physical interfaces do: you can have a mix of point-to-point and multipoint subinter- faces on a physical interface. It is even possible to have some DLCIs assigned to subinterfaces, and others to the physical interface. As mentioned earlier, one of the main benefits of frame-relay subinterfaces is the elimination of split-horizon issues with routing protocols. Creating multiple point- to-point subinterfaces, and assigning each of the PVCs to one of them, enables each PVC to be considered a different interface. Subinterfaces are created with the global interface command. Specify the name you'd like the subinterface to have, along with the keyword point-to-point or multipoint: Router-A(config)# int s0/0.102 point-to-point Router-A(config-subif)# You're now in interface configuration mode for the newly created subinterface, and can configure this subinterface as you would a physical interface. Be careful when you choose your subinterface type. If you choose the wrong type by mistake, the only way to change it is to negate the defining command in the configuration, save the config minus the subinterface, and reboot the router. As a result, the following error message will be displayed when you remove a frame-relay subinter- face: Not all config may be removed and may reappear after reactivating the sub-interface. Chapter 22: Frame Relay You now need to assign specific virtual circuits to the subinterface. This can be done with the frame-relay interface-dlci subinterface command, or by mapping a DLCI to a layer-3 address with the frame-relay map subinterface command. If you're adding a subinterface after you've already configured the DLCI on the physical interface, you'll need to remove the maps on the physical interface before proceeding. Mapping an IP address to a VC is a little different when using subinterfaces and the interface-dlci command: interface Ser