How does a Web Proxy work?

Question

Consider a case that there is a Proxy in my Organization, I need to enter the Proxy details in my IE. If I remove these details from the browser, I am no longer able to access the Internet. So I assume that all the Internet traffic goes through the Proxy that has been set for the Organization. Correct??

Now my real problem is that when I programmatically try to access the Internet(using Java), I have the option to specify Proxy=Yes or No. If I choose Proxy=Yes, I need to give the username and password, if I choose Proxy=No, it establishes a direct connection and still lets me access the Internet. Please refer the below Java API doc

http://download.oracle.com/javase/6/docs/technotes/guides/net/proxies.html and search for the string "which represents a direct connection, or absence of proxy".

I want to know what is this DIRECT connection ? How is it established ? Does not all the external world(Internet) traffic route through the Proxy in an Organization ?

Answer 1

It depends on your organisation.

If your browser (Internet Explorer, in your case) does work with a proxy, and does not work without a proxy, it's possible that

• all direct outgoing connections are blocked (safest)
• only certain direct outgoing connections are blocked (more flexible, less safe)

You can test this by trying to establish different connections to servers on the web. Try HTTP to google.com:80; try FTP to an open FTP server; try IRC to an IRC server, try setting your own nameservers (Google has nice DNS-servers); try connecting to your home machine.

If your Java application is able to make a direct connection, then probably not all traffic is blocked. Maybe only traffic to servers on certain ports (80, HTTP ; 21, FTP; ...) is blocked.

Edit: reading list

You want to learn more about connections, internet and proxies?

• Learn about the OSI Model and look at the TCP/IP Model.
• Checkout the RFC's for HTTP/1.1; HTTP/1.0; FTP; IRC and SMTP.
• Try using TELNET to make a connection to a HTTP/FTP/IRC/SMTP server.
• Write small programs to make connections to those servers.
• Install a packet monitor such as Wireshark to see what traffic passes. Inspect HTTP/FTP/IRC traffic and see how it works.
• Install Linux/BSD and setup a webserver and/or proxy server or install a LAMP/WAMP.