The chapter on subnetting should be considered criminal. Wrong address ranges are used to demonstrate subnet masking which would leave a newcommer to subnetting completely confused. If you can catch the errors you know enough about subnetting to answer the subnetting questions in the exam. I will credit the book though for forcing me to go to more athoritatize sources to fully understand sub and super-netting. After the subnetting fiasco I didn't trust the rest of the book so I can't comment on the other subjects. I spite of this book I was able to score 965 on the TCP/IP test.