So you’re having a problem with the Internet daemon you wrote. You’re convinced the firewall, or some other magic, in your modern Linux distribution is eating your packets.
First, make sure your daemon is actually running and has successfully bound to the address and port in question:
sudo netstat -atnup
If your application is not listed there you have a problem with it
binding its server socket. Check the return values from
If you’re still suspecting the firewall, or some other magic, test your
theory with netcat. First start a server, with your relevant address
and port, remember you need to be root, or have
CAP_NET_ADMIN, to use
ports <= 4096:
nc -l -u -p 9999
Here we bind to 0.0.0.0:9999. Now, start a client to test if the server can receive any data:
nc -u 127.0.0.1 9999
Type something on the console and press enter to send it to the server. If you receive the data then there’s no magic, execpt from bugs in you application, preventing your appplication from working.