[AnyShadow]

Most of my clients have Zyxel routers (really a ADSL modem/router combination) and have only Network Address Translation to shield them from the Internet

I have already installed ZoneAlarm on all client PCs, but am more concerned about protecting their file servers.

Can I put hardware firewalls behind these routers without any problems? Or, do I have to replace the Zyxel modem/routers with ADSL modems?

Just to be clear, I'm talking about several clients, each at different locations, and each with their own ADSL connection.

Also, which hardware firewalls do you recommend for small businesses?

 

[JohnWill]

There's no reason you can't use a software or hardware firewall to protect the servers.

 

[AnyShadow]

I have gone with the Modem->Hardware Firewall approach.

Overall speed seems a little better, and router configuration (to properly let the hardware firewall handle VPN) became more trouble than it was worth.

 

[Monstrous Mi]

You can put a firewall anywhere with only rare exceptions of it causing problems. In industry, the common practice is to have a firewall after a router.

If you really want help you should upload a network diagram so we can see where the router, file servers, and clients are located.