system requirements

[Mathias Kölsch <matz@cs.ucsb.edu>]

Hi,

What are the system requirements for a debian-based router/firewall for
gigabit ethernet adapters?

Details: I need to put a subnet of about 20 machines, all gigabit
ethernet, including a gigabit switch, behind a fast but flexible
firewall. Debian seems to be a good choice for many reasons, however, I
have no experience on the demands of a high-throughput firewall on CPU,
buses, and the entire system. Can somebody confirm or crush my suspicion
that basically any reasonably fast (100+MHz) CPU with little (128MB)
memory is capable of handling the traffic organization between two
gigabit interfaces? And more generally, what pitfalls are there to be
avoided when choosing hardware for this purpose?
Pointers to performance measurements and other hard evidence are highly
appreciated!

Thanks a bunch,
Matz.