Firewall for network without NAT

[Robert Kropiewnicki <phantomnj@gmail.com>]

Hello all,

I am in the process of learning iptables.  Progress is slow but
steady, however there is one thing that continues to vex me and it may
simply be a problem of terminology with regards to finding help.

I'm looking to eventually replace a couple of firewall machines with
Linux boxes running iptables.  For one of the firewalls, the network
it protects consists of machines that all have real-world IP
addresses.  Given the nature of the network and its usage, I am cannot
institute NAT on the network.

Unfortunately, the difficulty I'm running into is that every tutorial
I can find has focused on using NAT.

Can someone guide me to the specific rules I need, whether by posting
them here or pointing me to a tutorial, in order to provide firewall
services for a network consisting purely of publicly addressable IP's?

Regards,
Robert Kropiewnicki