VirtualHost Examples: Serving the same content on different IP addresses (such as an internal and external address)

This document attempts to answer the commonly-asked questions about setting up virtual hosts.

These scenarios are those involving multiple web sites running on a single server, via name-based or IP-based virtual hosts.

The server machine has two IP addresses (192.168.1.1 and 172.20.30.40). The machine is sitting between an internal (intranet) network and an external (internet) network. Outside of the network, the name server.example.com resolves to the external address (172.20.30.40), but inside the network, that same name resolves to the internal address (192.168.1.1).

The server can be made to respond to internal and external requests with the same content, with just one VirtualHost section.

##############################################
Server configuration

NameVirtualHost 192.168.1.1
NameVirtualHost 172.20.30.40

<VirtualHost 192.168.1.1 172.20.30.40>
DocumentRoot /www/server1
ServerName server.example.com
ServerAlias server
</VirtualHost>

##############################################

Now requests from both networks will be served from the same VirtualHost.

Note: 
On the internal network, one can just use the name server rather than the fully qualified host name server.example.com.
Note also that, in the above example, you can replace the list of IP addresses with *, which will cause the server to respond the same on all addresses.