getnetbyaddr

getnetbyaddr 
address
, [
addrtype
]

Retrieves the network name or names of the given network address . ( addrtype indicates the type of address. Often this function is used for IP addresses, where the type is not needed.) The return value in list context is:

($name, $aliases, $addrtype, $net)

In scalar context, getnetbyaddr returns only the network name.