Does a transparent proxy just mean when traffic is redirected to port 3128?
Is there any problem with just telling people to use port 3128?

For example, I could redirect all traffic on 8080 to 3128.

A transparent proxy is when the client requires no configuration to be proxied.
The way to achieve this is to create fw rules on the gateway that redirect packets with the one destination port, to anther port, generally where the proxy software is listening.

The classic example is for your gateway firewall to redirect packets destinated for port 80 to 3128 or 8080 where they are handled by the proxy server/filter and then passed (if necessary) to the actual destination server/port.

The reason for it is to prevent people un-proxying their http (or whatever) connections.

So this is really only useful for within networks behind a firewall where you want internet connections to go through the proxy first?

If I have a proxy available to anyone on the internet they still need its IP address and I would forward connections on port 80 to 3128?
Why not just tell them to connect to 3128?

Because they might decide not to... particularly where the proxy also includes some form of filtering/scanning.

Yes. But then that's the whole point (or at least one of
the major points) of having a proxy.

Because it requires *no* set-up on the client?



Cheers,
Tink

Well, it does in an environemtn where people are connecting to a proxy outside of thir network. For example, to hide their IP or spoof the fact that they are in their own country.
For this, the user has to set up the IP address in their browser anyway don't they?
I guess giving them a different port hides the proxy server port?