I had a problem with calling this function with REMOTE_ADDR on my lighttpd web server. Turned out that IPv6 was installed on this server, so even though REMOTE_ADDR was an IPv4 address, it was being formatted using IPv6's IPv4 compatibility mode. For example, 10.0.0.1 was becoming ::ffff:10.0.0.1, which caused iplong to report the address as invalid instead of parsing it correctly.
The correct fix would of course be to update my infrastructure so that it's properly IPv6-compatible; but in the context of my particular situation, this would involve a lot of re-engineering. So in the meantime, I worked around the issue using this quick and dirty hack:
<?php
$ip = htmlspecialchars($_SERVER['REMOTE_ADDR']);
if (strpos($ip, '::') === 0) {
$ip = substr($ip, strrpos($ip, ':')+1);
}
$host = ip2long($ip);
?>
Ugly but functional.
