Need a little help studying for certification exams? You can find a treasure trove of free study guides for Cisco, Linux, Microsoft and Unix certifications at the Global Document Database.

IT professional Clayton Dukes built and maintained his Global Document Database as a labor of love. Once you create a user account, you can access nearly everything at no charge. A download section provides even more resources, and you can use the forums to exchange study tips with your peers.

You'll find a special area of study guides for Cisco Certified Network Associate (CCNA), Cisco Certified Network Professional (CCNP), Cisco Certified Design Associate (CCDA), Cisco Certified Design Professional (CCDP), and Cisco Certified Internetwork Expert (CCIE). These resources include design and implementation guides for the Open Shortest Path First protocol, SNA over frame, and setting up Border Gateway Protocol with your ISP.

There's another section dedicated to security topics such as Cisco PIX firewall basics, Cisco Secure Integrated Firewall, IP Security and secure management of routers.

Global Document Database also offers the "The Ultimate CCIE Study Guide v.3.0". The 150-page book covers all the topics Cisco outlines in its blueprint for CCIE, along with 175 practice questions for the written exam.

If you like what you see, there's a form you can use to make a donation to a "tip jar" to support the site.