GNUnet is a framework for secure peer-to-peer networking. The primary application implemented within the GNUnet framework is anonymous for censorship-resistant file-sharing.
Communication
Gnunet uses TCP protocol. Gnunet will try TCP port 2086,1080,2088,2186 and 13881 to login.
If all login ports are blocked, then Gnunet will failed to login.
How to block Gnunet?
Because Gnunet login port is only TCP port 2086,1080,2088,2186 and 13881, so you can block them only by
disable the ports in the firewall.