I start a container and share a port for UDP traffic as this:

docker run —rm -p 5060:5060/udp —name host1 -i -t ubuntu:14.04

Then in that container I wait for traffic with:

nc -u -l 5060

I then generate traffic from another machine:

nc -u <docker_host_ip> 5060

Then everything works fine and I can see that I receive the UDP traffic in the container.

But when I exit the container and do the same thing again, then I can no longer receive UDP traffic in the docker container.
If I wait for about 5 minutes before I start to send it will work though. I have also noticed that if the sender change the port it is binding to locally it will also work. So there seems to be some mapping that is not deleted when the docker container is removed.