Proxy auto configuration example: proxy.pac

function FindProxyForURL(url, host) {
 if(isInNet(host, "198.168.0.0", "255.255.0.0") || 
    isInNet(host, "172.23.65.0", "255.255.255.0") || 
    isInNet(host, "127.0.0.0", "255.255.255.0") {
  return "DIRECT";
 } else {
  return "PROXY wwwproxy1.yourorg.org:3128; PROXY wwwproxy2.yourorg.org:3128; DIRECT";
 }
}