Network Security Admin looking for advice.

First study for the CCNA(Prerequisite to CISSP), buy some good simulators. You may find the CCNA harder than subsequent Cisco tests.

A less expensive path to get a thorough understanding of Firewalling and advanced TCP/IP(with a vendor neutral stance) is to set up a FreeBSD Firewall. I like how easy it is to log events, and the syntax is simple yet powerful(arguably more so than Linux's IPchains). It may or may not do much for your career path but given that it is free to download and there is a ton of free documentation plus most IT folks have access to an outdated machine it will give you a chance to set up a cheap lab, and if you don?t spend too much time trying to configure a Desktop Environment it will get you familiar with entering commands at a command line, something that you?ll be seeing a lot of in your future career.