Hi, I am using Applet client and servlet in the server side. The applet uses URL Connection for communicating with the servlet. My machine is not registered with a naming host(DNS). I am setting the url parameter as "localhost" for creating the URL class object.Then it is working perfect in my machine. That is URL url=new URL("http://localhost:8080/km/servlet/ChatServlet"); URLConnection con=url.openConnection(); But I want to test it from another machine, keeping my machine as the server (I am using Tomcat server).It is a multicast application. So I changed the url to my machine's domain name. I tried both domain and IP address for the url. When I set the url parameter like this, It is throwing some security exception, when the applet client tries to open the URL Connection to the servlet. That is URL url=new URL("http://elizabeth:8080/km/servlet/ChatServlet"); or URL url=new URL("http://192.168.1.22:8080/km/servlet/ChatServlet"); Even when I tested the above url with the applet client running in my machine , it is throwing the same exception. The applet client is opening the connection when it is run in my machine (where the server is running)setting the url to "localhost". But when I test it with "localhost", I cannot run the applet client in another machine. Is this because, my machine is not registered with DNS, so that when the URL is resolved, it is not finding such a server and throw the exception? Or is it because of any other problem? Please give me a solution.. It is very urgent.. Thanks Elizabeth.