Running a Reverse Proxy in Apache
The company also has a couple of application servers which have
private IP addresses and unregistered DNS entries, and are inside the
firewall. The application servers are visible within the network -
including the webserver, as "internal1.example.com" and
"internal2.example.com", But because they have no public DNS entries,
anyone looking at internal1.example.com from outside the company
network will
get a "no such host" error.