transparent proxy servers

I am wondering exactly how transparent proxy servers work, I can find breif definitions but nothting in detail. From what I understand so far

"transparent proxy servers relay data on behalf of the client, without altering any data traveling to a web page for example that the user or client is visiting"

this is my understanding, this may be wrong. But if that is what a transparent proxy server does i have alot of quetsions.

-if the client is requesting a page and the proxy server is responsible for sending the page back to the user? how does the proxy server know the ip address of the web page, is the web pages ip put into the data of the packet, because the proxy servers address would need to be in the header. And when the proxy server itself forwards the request for the site does it take the info from the data section of the packet and put it in the header, and map the ip address of the client to its (the proxy servers ip) and a port address like NAT - and then change the destination ip again when its sending the data back to the client.

If anyone can understand this please try and explain. I have no real reason for needing to know this i would just feel better if i had a more solid foundation of knowing how things worked.


Thanks

*Moved from Tutorials*

Essentially, a transparent proxy server is a combination of a normal proxy server, and some NAT rules on a router somewhere.

A normal connection outgoing to port 80, has its destination address NAT'd by the router, to turn up on the port which a "normal" proxy server listens on.

The proxy server then behaves slightly differently because it has to realise the connection has been NAT'd, and it impersonates the destination web server while proxying the request.

So it's "transparent" because as far as the client (web browser) is concerned, the proxy isn't even there. The client just sees itself connecting to the server directly, but the NAT ensures that this doesn't happen.

*loads* of ISPs use them. It makes good sense too, as if they can cache 10% of web traffic, they can save themselves a lot of money.

Persuading novice users of different OS, browsers, machines etc to use a normal proxy server would be a support nightmare.

Slarty