title: Exposed port shows as filtered when using nmap
body: <p>I have a container with EXPOSE 27017 in Dockerfile, public ip and published port 27017. There is related info from <code>ice inspect</code> output:</p>
  
  <pre><code>...
  "PortBindings": {
      "27017/tcp": [
          {
              "HostPort": "27017"
          }
      ]
  },
  ...
  "NetworkSettings": {
      "Bridge": "",
      "Gateway": "",
      "IpAddress": "172.31.0.16",
      "IpPrefixLen": 0,
      "PortMapping": null,
      "Ports": {
          "27017/tcp": [
              {
                  "HostIp": "134.168.18.146",
                  "HostPort": "27017"
              }
          ]
      },
      "PublicIpAddress": "134.168.18.146"
  },
  </code></pre>
  
  <p>Still, i can't connect to database using public ip, and <code>nmap</code> shows port 27017 as filtered.</p>
  
  <p>Is there additional steps to expose container's port?</p>