How are they blocking RDP on port 80?

Question

I'm on a corporate computer that is behind a very restrictive firewall, and trying to connect to my home computer. I configured my router to forward port 80 to 3389 (RDP port). My idea was to try to connect with port 80 since the regular RDP port might be blocked. However I found out that it's not working. RDP on port 80 is blocked as well.

My router's IP address is not blocked, since I can access the config interface on <router IP address>:8080 . Remote Desktop itself also works for connections to hosts within the internal domain.

I was wondering how are they blocking that kind of traffic (RDP on port 80 towards external IPs)? What kind of firewall rule is used?

Answer 1

It is likely they are using either a proxy server directly in the browser settings, or they are using a transparent proxy in the path.

A proxy server will check that valid HTTP traffic is passing through and discard anything that isn't (if only because it doesn't know how to process non-http traffic).

In either case, your work PC does not have direct access to the internet, it just appears to.