IF proxy_ip does not start with "127.0" or "192.168" or "10." or "169.254":

There are other special/private IP blocks that you'll probably want filtered. This RFC contains the full list for IPv4: https://tools.ietf.org/html/rfc5735#section-4 And the equivalent for IPv6: https://tools.ietf.org/html/rfc5156