# for 192.168.*.*
my @netmask_a = qw ( 255 255 0 0 );
my @sample_a  = qw ( 192 168 0 0 );
my $netmask = unpack("N", pack("C*", @netmask_a));
my $sample = unpack("N", pack("C*", @sample_a));
my $addr = int rand(2**32);
$addr &= ~ $netmask;
$addr ^= $sample;
# Dotted quad form:
my $dottedaddr = join(".", unpack("C*", pack("N", $addr)));