The What is my IP? utility script checks all available IPs in the HTTP request (including proxy IPs).

  # RegExp for IPs

  # Basic decimal digit

  my $ReIpNum = qr{([01]?\d\d?|2[0-4]\d|25[0-5])};

  # Standard IP

  my $ip_match = qr{^$ReIpNum\.$ReIpNum\.$ReIpNum\.$ReIpNum$};

  # Special IPs   

  my $ip_private1 = qr{^10\.$ReIpNum\.$ReIpNum\.$ReIpNum$}; # RFC 3330/1918

  my $ip_private2 = qr{^172\.(1[6-9|2[0-9]|3[01])\.$ReIpNum\.$ReIpNum$}; # RFC 3300/1918

  my $ip_private3 = qr{^192\.168\.$ReIpNum\.$ReIpNum$}; # RFC 3330/1918

  my $ip_loopback = qr{^127\.$ReIpNum\.$ReIpNum\.$ReIpNum$}; # RFC3330/1700

  my $ip_testnet =  qr{^192\.0\.2\.$ReIpNum$}; # RFC 3330