CCIE began in 1993, originally with a two-day lab, later changing to a one-day format. Fewer than 3% of Cisco-certified individuals attain CCIE certification and, on average, spend thousands of dollars and 18 months studying before passing. Many candidates build training labs at home using old equipment, then sell it to other candidates after passing. Alternatively, candidates may rent "rack time" online. The CCIE consists of a written exam and a "lab" exam (in each track). The written exam acts as a prerequisite of the lab exam and has a cost of $400 per attempt. The written exam consists of 100 questions that must be completed within 2 hours. Upon passing the written exam, the candidate has eighteen months to take the lab exam. The candidate has three years after passing the written exam to successfully complete the lab. The lab is an eight-hour, hands-on exam designed to demonstrate that the candidate knows Internetworking theory and demonstrates advanced hands-on mastery. Candidates that do not pass the CCIE lab in that interval must re-pass the written exam before again attempting the CCIE lab exam. The minimum waiting time between attempts is one month.