Hardware Firewall in a webhosting cluster... What do you do?

[pgentoo]

Hey guys,

I'm looking at scaling out my hosting environment from a single server to at least seperate boxes for iSCSI Fileserver, Mail (eventually multiple), DB (eventually clustered), Secondary DNS, and Web (eventually multiple web boxes). I am also going to setup some boxes to host Xen based VPS's for clients.

I was thinking that I should probably setup a single (or 2 failover boxes) gateway/firewall in my rack so I can have a central place to enforce firewall rules, do bandwidth throttling (especially for the VPS's), traffic accounting (cacti?), etc.

I'm just curious what the rest of you do in production environments for this.

Please describe yoru configuration (or your dream configuration) if you have a few mintes.

Thanks!