Two cool articles up on Linuxjournal.com regarding IPTables, the built-in firewall for Linux. I've struggled to learn how IPTables works (especially after using the excellent OpenBSD pf firewall) but these videos really explain IPTables well:
I would encourage you to watch both videos if you use Linux, especially if your system is exposed to the Internet (not behind a home router).
Finally, after 6 long months of studying for this thing! It was tough and I thought that I had bombed it halfway through. I'll keep it short: know all the objectives and you'll pass.
Next up is the CCDP ARCH exam. I've passed the CCNP routing and switching exams which are prerequisites for the CCDP so I figured why not just take one more exam and add another certification to my belt? After that's done I'll take the MPLS exam and have the CCIP certification. I think I'll take a break after that...