Domain Naming Issues

I have a domain name inside my network of xxx.net, I have a similiar name for a website of www.xxx.net outside my network on the internet.
When I am inside my network (xxx.net)I attempt to go to www.xxx.net and get the web page cannot be displayed error.
When I am outside my network I can go to www.xxx.net just fine. How can I get to www.xxx.net when inside my network of xxx.net?

Thank you!