The TCP wrappers provides a classical unix mechanism which has been designed to check if the remote client is able to connect from the given IP address.
Tcpwrap is currently available through PECL http://pecl.php.net/package/tcpwrap.
If PEAR is available on your *nix-like system you can use the pear installer to install the tcpwrap extension, by the following command: pear -v install tcpwrap.
You can always download the tar.gz package and install tcpwrap by hand:
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