1. The DLCI number defines a single virtual connection through the WAN and are the Frame Relay equivalent to a hardware address.
Periodically, through the exchange of signaling messages, a network may announce a new virtual circuit with its corresponding DLCI number. However, protocol addressing is not included in the announcement. The station receiving such an indication will learn of the new connection, but will not be able to address the other side. Without a new configuration or mechanism for discovering the protocol address of the other side, this new virtual circuit is unusable.
For this reason, Inverse Address Resolution Protocol (Inverse ARP) was developed. Inverse ARP allows a Frame Relay network to discover the protocol address associated with the virtual circuit.
Inverse ARP is used instead of the "frame-relay map" command which allows you to define the mappings between a specific protocol and address and a specific DLCI. Usually you would only select Inverse ARP if you want to configure an interface for multipoint communication. You would not need to select Inverse ARP if you have a point-to-point interface because there is only a single destination and discovery is not required.
2. If you do not have the IP address space to use many subinterfaces, you can use IP unnumbered on each subinterface. You need to use static routes or dynamic routing for your traffic to get routed. And you must use point-to-point subinterfaces. For more information, refer to:
http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1831/products_configuration_guide_chapter09186a0080087d01.html#1003234
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Regards
Rajat Chauhan
