netcat UDP

gistfile1.txt

# Start up netcat server
nc -kluv localhost 9000

# Check it with lsof
$ lsof -Pni :9000
COMMAND   PID        USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
nc      59231 markneedham    5u  IPv6 0xd2ab0eedfdf2c00b      0t0  UDP [::1]:9000

# Send a UDP packet and see it's received
$ echo -n "mark" | nc -vvu localhost 9000
Connection to localhost 9000 port [udp/cslistener] succeeded!

# Try to send another packet which doesn't get received

# Check lsof and see there is now a socket between 9000 and an ephemeral port (presumably from the first packet sent)
$ lsof -Pni :9000
COMMAND   PID        USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
nc      59231 markneedham    5u  IPv6 0xd2ab0eedfdf2c00b      0t0  UDP [::1]:9000->[::1]:60845

# Start nc server, wait 1s for read
nc -kluvw 1 localhost 9000

# send packet
echo -n "mark" | nc -vvuw1 localhost 9000