Create README.md

Author: jishi

README.md

@@ -893,3 +893,22 @@ DOCKER
 -----
 
 Docker usage is maintained by [Chris Nesbitt-Smith](https://github.com/chrisns) at [chrisns/docker-node-sonos-http-api](https://github.com/chrisns/docker-node-sonos-http-api)
+
+## FIREWALL
+
+If you are running this in an environment where you manually have to unblock traffic to and from the machine, the following traffic needs to be allowed:
+
+### Incoming
+TCP, port 3500 (Sonos events)
+UDP, port 1905 (Sonos initial discovery)
+TCP, port 5005 (if using the default api port)
+TCP, port 5006 (if using https support, optional)
+
+### Outgoing
+TCP, port 1400 (Sonos control commands)
+UDP, port 1900 (Sonos initial discovery)
+TCP, whatever port used for webhooks (optional)
+
+The UDP traffic is a mixture of multicast (outgoing), broadcast (outgoing) and unicast (incoming). The multicast address is 239.255.255.250, the broadcast is 255.255.255.255 and the unicast is from the Sonos players.
+
+If port 3500 is occupied while trying to bind it, it will try using 3501, 3502, 3503 etc. You would need to adjust your firewall rules accordingly, if running multiple instances of this software, or any other software utilizing these ports.