Good tutorial on iptables

OfWolfAndMan

So I just installed free radius on my Centos install to allow authentication for my routers and a few other network devices. I went through the tutorial (Pretty straightforward), yet I couldn't get it to work! 30 minutes later, it totally went over my head that it's a rule in the firewall (I did an iptables --flush since that's the only command I know for iptables). Boom! RADIUS worked. This happened when I tried getting the SDN controller Opendaylight to talk to my virtual network before as well. Does anyone have some good documentation to teach me iptables? I know LX-102 may teach me a bit, but I think it'd be useful to learn in more depth.

OfWolfAndMan

This is the best I could find to meet my needs:

HowTos/Network/IPTables - CentOS Wiki