Is it possible to access the external IP or a server even if a router is present? Obviously more information will be needed, but not sure what you need to know...

Not sure exactly what your looking for here. Information is very very limited...

I'm starting to think maybe you are referring to some type of NAT/PAT box (ie. a $30 D-Link router from best buy)? If that’s the case, you can setup a DMZ. This will allow you to have unrestrictive access between a single server and the internet.

You could also do port forwarding. In which case you could have several servers, but they would not be able to run the same services. For instance, you could have a DNS server and foreword DNS services to its internal IP. Then you could have a web server and foreword services to another IP. But you couldn’t have 2 web servers (at least running on port 80 anyways).

Any more information would require additional information on your network topology...

Hostmonger