如何设置squid使外网也可以通过代理服务器上网，并且使用代理服务器的ip地址

按照配置文件内网可以通过服务器上网，显示的ip是本机ip，外网不能通过服务器，现在想让外网可以通过代理服务器，并且使用服务器的ip，请问该怎么配置？ 谢谢！

http_port 3128 
visible_hostname No1.proxy
cache_mgr 
cache_dir ufs /usr/local/squid/var/cache 512 16 256
cache_mem 512 MB
cache_swap_low 90
cache_swap_high 95
access_log /usr/local/squid/var/logs/access.log squid 
cache_log /usr/local/squid/var/logs/cache.log
cache_store_log /usr/local/squid/var/logs/store.log
pid_filename /usr/local/squid/var/logs/squid.pid
maximum_object_size 4096 KB 
hierarchy_stoplist cgi-bin ?
hierarchy_stoplist -i ^https:\\ ?
acl QUERY urlpath_regex -i cgi-bin \? \.asp \.php \.jsp \.cgi
acl QUERY urlpath_regex cgi-bin .php .cgi .avi .wmv .rm .ram .mpg .mpeg .zip .exe
cache deny QUERY
acl denyssl urlpath_regex -i ^https:\\
no_cache deny QUERY
no_cache deny denyssl
ipcache_size 1024
ipcache_low 90
ipcache_high 95
fqdncache_size 1024
dns_nameservers ********
cache_effective_user squid squid

http_access allow all