I want to block a certain IP address at my firewall which is connected to my PC, but I don't know what it looks like.
Is there any way I can see a list of all IPs having connections with my PC?
So far I tried
netstat -b -n in the command line, but from the list I get the only one showing appears to be the IP of a server that I don't want to block.
Yes, there is. A command-line approach to this is using
netstat. See this how-to.
netstatis very similar to using netstat on Unix-based systems, by the way, so this applies not only for Windows.