use Net::Pcap;

my $err;
my($address, $netmask);
my $dev = Net::Pcap::lookupdev(\$err);
print "dev is $dev\n";

if(Net::Pcap::lookupnet($dev, \$address, \$netmask, \$err)) {
    die "Failed to look up dev info on $dev";
}

print "address=$address netmask=$netmask\n";

##</code><code>##

dev is eth0
address=-1062731776 netmask=-256