Encrypted Data length in a CBC Block Cipher
What is the extra byte and what should it be?


That is due to the way padding is specified. The last byte is the padding length, from 0 to 255. That is the length of the padding without the length byte itself. So with "zero padding" there's still the padding length byte.


  The first section says the length is the sum of the block length, the contenct length, the MAC length and the padding length. So why in the example is the 8 byte block length ignored in the calculation?


The quote continues "this does not include the IV". That is because unlike the rest of the data, the IV is not encrypted.