Does anybody have insights of how teamviewer manages to work over port 80?
I would expect that port 80 would then be claimed while I am using a teamviewer session, which would prevent me to communicate over port 80 (http e.g.). That's obviously not the case, so how does this work?
When you make a connection to another machine over the network, you have a source port and a destination port.
The source port can be any port, meaning it doesn't have to match the destination port.
So while I can listen on port 80, I can connect to another system on port 80 using a local port of, say, 45000. In fact, most of the time the system will allocate a source port (also called a bind port) for you automatically when calling connect().
Needless to say, you don't have to listen on a port in order to connect to another system on that port, hence why TeamViewer - or whatever other application - can listen to port 80 on your machine without hindering your browser from making requests to other systems that are also listening to port 80.
The machine you CONNECT TO with teamviewer works on port 80. So for your machine it is like accessing yet another website.
