The internal IP address of the main router (Gateway to the Internet) is usually very stable, and always available.

Inside a campus/building, the number of routing hops to that router is usually very small .. typically less than 3.

You could send a "ping" to that address and check if it is found in 2 hops or less, to verify internal reachability.

? Of course, this can be spoofed, if the user knows what the code is looking for.

A more secure way would be to establish a server on the network, and require login , or canned credentials to be retrieved from the server before processing.

        What is the sound of Perl? Is it not the sound of a wall that people have stopped banging their heads against?
              -Larry Wall, 1992

In reply to Re: verify presence in a given network by NetWallah
in thread verify presence in a given network by Anonymous Monk

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