Question

I have a PHP page I need to limit execution access of
to only clients inside our firewall.

How would I write a php-script that can look up the clients
ip-address and match it to a ip-range (for instance 10...* or 200.10.10.*).

Answer 1

You can use ip2long to convert dotted quads to long values, then just perform some arithmetic to check a given network/mask combination:

$network=ip2long("200.10.10.0");
$mask=ip2long("255.255.255.0");

$remote=ip2long($_SERVER['REMOTE_ADDR']);

if (($remote & $mask) == $network)
{
   //match!
}
else
{
   //does not match!
}