you mentioned in this course that the router firewall by default is blocking the inbound request (request from internet to the pc), and it is just allow the revers connection , i ma wondering how the team-viewer application is allowing the inbound request, does this make sense??
Good question and I cover this on the course in volume 3 bypassing firewalls.
Remote access tools such as teamviewer and LogMeIn use reverse connections.
You install these on the network that you want to access. Your office Pc for example.
These remote admin tools connect out of ports that are open on the firewall such as port 80 and 443 to central servers. Your client then connects to the their servers which allows the connection to be forwarded onto your client. The client never needs to initiate a connection into the network. The teamviewer or logmein software within the network maintains an active connection out through allowed ports in order to bypass the firewalls inbound filters.
This is why you don’t need to open up a port on the firewall or change NAT settings if you use teamviewer and LogMeIn on your local network.