Firewall: Front-End Back-End Scenario

Hey All

Can someone explain what a Front-End and Back-End scenario is in regards to a firewall? And how it works with  DMZ? There is all kinds of info out there but it mostly just jumps right into configuring and installation and doesn't really explain the terms.


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Well essentially a front end/back end configuration means your front end firewall will allow some traffic from the Internet back to hosts configured in the DMZ area between the two firewalls.  The back end firewall will stop all Internet traffic from reaching the LAN but could allow DMZ hosts to reach the LAN.  By having the two firewalls configured like that, you can be sure that no one from the Internet will have direct access to a LAN server.  The security policy configuration of each front end and back end firewall are relatively simple to configure.

Some people instead just go with a three pronged firewall approach with a single firewall unit with one interface connected to the external network, one connected to a DMZ network, and the other to the Internal LAN network.  Then you just build your security policies to allow internet traffic to reach the DMZ hosts but not the LAN and possibly allow DMZ hosts to reach LAN resources as needed.  Some people don't like the single firewall approach since it would be easier to make a mistake in the security policies to allow direct access to LAN resources from the Internet, or exploit a flaw in the firewall and bypass the security policies in place to get past the firewall onto the LAN.

Typically firewalls will be broken down into zones (External, Internal, DMZ zones) and the security policies dictate zone to zone traffic or host to host traffic between zones if you wanted to be very specific about who can talk to who.

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castellansolutionsAuthor Commented:
Thank you for that clear and easy to understand explanation. So I am clear:

1) The Front End Firewall protects the rest of the network from internet traffic, based on rules, but specifically traffic is sent to the DMZ from the Front-End Firewall?

2) The Bad-End Firewall accepts traffic from the DMZ (in this scenario)

So it would go Internet >> Front-End>> (DMZ) >> Back-End >> Services such as exchange?

Yep you essentially got it
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