CCNP CIT Exam Cram 2 (Exam Cram 642-831)

Deal, Richard. CCNP BCMSN Exam Cram 2 , Que, 2003. ISBN: 0-7897-2991-1.

Cisco CCO: Troubleshooting STP, http://www.cisco.com/en/US/customer/tech/tk389/tk621/technologies_tech_note09186a0080136673.shtml