If you kept the default ports during installation, those are the only two that need to be open. They can be blocked at several points, once at the router, next at the computer itself. Though making sure the ports are not blocked by a fire wall may not be sufficient. Web proxies and virus checkers can also prevent communication between client and server. From version 18 on forward we use the http protocol and this is a bit more aggressively examined by virus checkers. Web proxy servers can redirect or block communication they are not configured for.
Additionally, you still need to be able to access your BIM Manager via the Internet. A private IP address will not do. Using only a public IP address will present more challenges and should be considered only when you are testing. You should use a Fully Qualified Domain Name to connect to your BIM manager. This means that you really should be using a DNS server on your local network and that you have registered your domain with the Internet Registrar.
Hope that helps,
Graphisoft Technical Support