For non-broadcast multiple access (NBMA)–based WAN technologies such as X.25, frame relay, and ATM, the Network Interface Layer address is not a MAC address but a virtual circuit identifier. For example, for frame relay, the virtual circuit identifier is the Frame Relay Data Link Connection Identifier (DLCI). To address frames for a given destination, the Frame Relay header’s DLCI is set to the value that corresponds to the virtual circuit over which the frame is traveling. With NMBA technologies, the virtual circuit identifier is known but the IP address of the interface on the other end of the virtual circuit is not.

InARP is used to resolve the IP address on the other end of a virtual circuit based on a known Frame Relay ...

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