title: Cannot open UDP ports for docker containers in GNS3 for inter-container port access
body: <p>I have a gns3 ubuntu 16.04 machine appliance that I installed from GNS3 market place. I am trying to simulate DDoS amplification attack in GNS3 (version 2.1.21). Part of it, I want to open UDP ports vulnerable to amplification (such as NTP : 123, DNS : 53, CHARGEN : 19....).</p>
  
  <p>I tried to use <code>iptables</code> command to switch open the ports, but this is not available on ubuntu containers in GNS3. I then tried to create my own docker image with ubuntu 16.04 and use <code>EXPOSE 123/udp</code> in the DockerFile. I build the docker image and import in GNS3. Still all ports on container remains closed.</p>
  
  <p>Nmap scan on the container gives me <code>All 1000 scanned ports are closed</code>. How do I open udp ports on my ubuntu containers so I can send udp traffic from one container to other ?</p>
  
  <p><img src="https://i.stack.imgur.com/HpjWV.png" alt="GNS3 with ubuntu 16.04 docker container"></p>