campbe13 / sockets-lab

created to be used in a lab for 440 2022

code for creating sockets

For teaching/learning about sockets, playing with the underlying TCP transport layer communications. TCP is the transport used for a lot of application layer protocols.

If you would like to try this you will need to install (or check for)

1. Python V 3 (preferred) python3 --version or python --version
2. netcat nc on *nix

echo server

see server.py when you run the server the process logs to socket.log (it appends, does not overwrite so you may want to delete old versions as needed)

server side

Run the server code, it will bind to tcp (stream) & ip & port

• run in background ./server.py &
  • binds to 127.0.0.1:8111
  • check it with netstat -lan |less note the state LISTEN
  • if it crashes or has just ended the ip&port may still be bound, in a TIME_WAIT status instead of LISTEN, you can see this through netstat, you will have to wa,it for it to end
  • you can see the comms via socket.log in the cwd

client side, talk to server

On the same system, use netcat (nc) to act as a client & make the socket pair

• fake out client comms with netcat
  • talk to the server nc -v -n 127.0.0.1 8111
  • it will echo the data you type in back at you, as long as the socket pair is live
  • quit will end the connection on the server side
  • you will have to hit enter again after entering quit as that will signal nc to stop
  • check the socket source & dest while you are talking to the server netstat -lan|less and after you quit (you may see TIME_WAIT)

Use the code in a lab exercise

Follow the instructions in lab-questions to play with and learn about TCP sockets.

Teacher's version in

restricted, gitlab