I am configuring a Linux router with iptables. I want to write acceptance tests for the configuration that assert things like:
traffic from some guy on the internet is not forwarded, and
TCP to port 80 on the webserver in the DMZ from hosts on the corporate LAN is forwarded.
An ancient FAQ alludes to a iptables -C option which allows one to ask something like, "given a packet from X, to Y, on port Z, would it be accepted or dropped?" Although the FAQ suggests it works like this, for iptables (but maybe not ipchains as it uses in the examples) the -C option seems to not simulate a test packet running through all the rules, but rather checks for the existence for an exactly matching rule. This has little value as a test. I want to assert that the rules have the desired effect, not just that they exist.
I've considered creating yet more test VMs and a virtual network, then probing with tools like nmap for effects. However, I'm avoiding this solution due to the complexity of creating all those additional virtual machines, which is really quite a heavy way to generate some test traffic. It would also be nice to have an automated testing methodology which can also work on a real server in production.
How else might I solve this problem? Is there some mechanism I might use to generate or simulate arbitrary traffic, then know if it was (or would be) dropped or accepted by iptables?
