You can have more than one http servers in your box, and 80 is the default port number for the service. http://yourdomain/ == http://yourdomain:80/ If you have the second http server, then you need to use different port number, say 8888, to distinguash it from the first one. BTSync has a http server in itself, and it uses port 8888. This is nothing to do with the external accessibility. So what you have to do is to close port 8888 at your router / firewall.