Question

I am looking for a function to determine whether a given IPv4 address is in a given network.

It will be similar to this; however, I do not want to install a complete framework or reinvent the wheel if it is not necessary.

The idea would be similar to the following:

function IsInNetwork($givenIP, $networkIP, $netmask) {
   // ???
}

$valid = IsInNetwork("10.0.9.35", "10.0.8.0", "255.255.254.0");

— EDIT —

With Rich Adams help, he pointed me in the right direction and came up with the following:

function IsInNetwork2($givenIP, $networkIP, $netmask) 
{
    $ipaddr = ip2long($givenIP);
    $netip = ip2long($networkIP);
    $netmask = (ip2long($netmask) * -1) + $netip;

    if ($ipaddr >= $netip && $ipaddr <= $netmask){
        return true;
    } else {
        return false;
    }
}

Answer 1

Something like this should work,

function IsInNetwork($givenIP, $networkIP, $netmask)
{
    return ((ip2long($givenIP) & ip2long($networkIP)) == ip2long($network));
}

$valid = IsInNetwork("10.0.9.35", "10.0.8.0", "255.255.254.0"); // true