Routing rules on router are used to configure Private VLAN on dedicated server. These routers are used to connect your dedicated servers to the internet. Dedicated switch is required to configure private VLAN for more than one server LAN on using a patch file instead on using only 2 servers.
Clients who require very high security consider Private VLAN as private VLAN offers a highly secured environment. You can allow public access to the servers you want to i.e. you can allow public access to the front web servers and you can disable the public access to the servers where you have your mission critical data like the database servers and the servers you wish to disable the public access. These kind of adjustments can be done for the clients who have heavy traffic on their websites and forums. In this kind of adjustment only dedicated web servers are allowed to communicate with database servers on private LAN and the remote access to the database server is completely disabled for others.
If all this is done properly, nothing can go wrong on the web servers as no one will be able to access your database servers. Also, the web servers will only allow the http traffic. Make sure that the server with less open ports will make it more secure.