This is the infrastructure of the Crazy Canvas Challenges at Hacktoberfest 2023.
To make sure the participants can only test with the test pixelflut server and not the challenge one a iptable rule needs to be applied.
This will block the port 1234 from the outside of localhost.
Since the challenges are all communicating from inside the host, this is fine.
The command for that:
sudo iptables -I INPUT --proto tcp --source localhost --destination 10.201.77.56 --dport 1234 -j ACCEPT
sudo iptables -I INPUT --proto tcp --destination 10.201.77.56 --dport 1234 -j REJECT