because of the difference in http server in handling IPv4 mapped
	address (IPv4 traffic goes into the system into AF_INET6 socket),
	the peer's address passed by $REMOTE_ADDR to CGI script can vary
	between the http server.
	some http server would pass IPv4 mapped address as is (::ffff:10.1.1.1),
	and some http server would pass IPv4 mapped address converted into
	IPv4 address (10.1.1.1).  this complexity could confuse CGI program
	writers and could open up vulnerability if CGI program uses
	$REMOTE_ADDR for authentication.

	solution: do not accept IPv4 traffic by using AF_INET6 socket.  use
	AF_INET socket (http server should listen to AF_INET and AF_INET6
	socket explicitly).  draft-cmetz-v6ops-v4mapped-api-harmful-01.txt
	talks more about this issue.

itojun