(PHP 4, PHP 5, PHP 7, PHP 8)
gethostbyaddr — Get the Internet host name corresponding to a given IP address
   Returns the host name of the Internet host specified by
   ip.
  
ipThe host IP address.
   Returns the host name on success, the unmodified ip
   on failure, or false on malformed input.
  
Example #1 A simple gethostbyaddr() example
<?php
$hostname = gethostbyaddr($_SERVER['REMOTE_ADDR']);
echo $hostname;
?>