[CentOS] More about firewalling

Hi All,

So before when I used PIX's for my employer, our traffic was statically routed to one IP and then the firewall decided if allowed/ denied and passed it on or dropped it.

I have a Comcast business circuit with 13 IP's. The gateway device they provide is a 'pass through' device. They sent traffic for all 13 IP's my way. It just allows traffic through. So if I put in a device to firewall (like Ipcop or Vyatta or something) in front, say it has 3 NICS, how do I do that?

If the Firewall has IP A and Traffic for IP B comes in how would IP A answer and decide if the traffic to IP B belonged? Without statically routing I am confused on how to accomplish this?

How fast does this device need to be?

Best, -Jason