I agree with iolair---CCNA Security, but you may want to consider CompTIA Security+ before that, to get a decent foundation of network security topics. The Cisco Security track covers a lot that is necessary knowledge for networking, so just the Security direction will enable you to be very knowledgeable in networking, and even at a greater level in some topics (VPNs, access-lists, CBAc/FIREWALL FEATURE SETS IN ROUTERS, CRYPTO, just turned off CAPS...ewps..., IPS, and packet details/breakdowns, as well as going into some detail about routing/routing protocols, and switching (a lot).
One thing at a time, though! Other very interesting certs (IMHO), which I plan on pursuing (AFTER passing the CCIE Sec lab!) are Ethical Hacker and CISSP.
Good luck! Networking/IT/IS Security Professionals are always in demand in the marketplace, and that demand grows progressively, directly proportional to advancement in existing and new IT/IS/Networking technologies---one reason in particular is that whenever an improvement of an existing technology, or especially the establishment of new technologies, there's always some 15 year-old reclusive, always-stays-inside, easily-sunburned, small-animal-injuring deathly-afraid-of-bugs-yet-collects-them-in-an-OCD-nerdy-way, glue-eating, 82-pounds-soaking-wet, will-never-graduate-from-virgin-status, lack-of-bass-in-the-voice, mom's-clothes-wearing, dilusional-about-social-status, klutz, point-and-click-wannabe-programmer, Yahoo-chatroom-booter, hopefully-will-never-reproduce, human-gene-pool-embarrassment, future-Darwin-Awards-candidate script-kiddie little $h1T from Switzerland or China that finds some vulnerability, exploits it, and does something (that severely lacks creativity) to thousands of systems around the world, hoping to get a girlfriend (with whom he would be clueless as to what to do, especially if she had little-to-no clothes on). Poor kid...
So, I guess you see how passionate (or obsessive, both of which are good qualities in this case

)I am about security.
Good luck in your endeavors, home-slice.
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