If you take HCIE, you should prepare for three exams: written test+experiment+interview. There are many resources available on Datacom, and the theoretical part is not difficult. As long as you have a good class, it is not a problem to have a question bank exam, but you should carefully prepare for the experiment and interview, because you have to do 8 hours in a row during the experiment exam, and you usually have to do more real experiments and tests. The questions asked in the interview are random and comprehensive, but there is also a question bank. Just find an experienced engineer or lecturer to practice more. It usually takes about seven months to prepare for a short period of five months and a long period of two years.