This is a good book for review purposes, but must be read carefully. Since the information is so condensed, it is very easy to pass over errors in information. For example, an as yet unmentioned error in the book is as follows: On page 31 (TCP/IP) the discussion is on subnet masking. In point number 4 it reads that a NETWORK address of all ones or zeroes is not allowed, which is true, but what is really being referenced in this example is a Class C address with a subnet mask of 255.255.255.224 which creates blocks of 32 possible addresses per subnet - 2. This means that a HOST address of X.X.X.32 is not allowed because a HOST address cannot be all ones or zeroes. This took me some time to figure out. If the host address is 32 with a subnet mask of 224, that means that all 5 bits of the host address are zero, which is illegal.