Listen 80
ServerName www.example.com
DocumentRoot /www/example.com

NameVirtualHost 172.20.30.40

<VirtualHost 172.20.30.40 172.20.30.50>
DocumentRoot /www/example.org
ServerName www.example.org
# ...
</VirtualHost>

<VirtualHost 172.20.30.40>
DocumentRoot /www/example.net
ServerName www.example.net
ServerAlias *.example.net
# ...
</VirtualHost>