The problems in this appendix require you to convert dotted-decimal subnet masks to prefix format and vice versa. To do so, feel free to use the processes described in Chapter 14 of CCENT/CCNA ICND1 640-822 Official Cert Guide. (If you are reading this as a PDF that came with CCNA ICND2 640-816 Official Cert Guide, you will find a copy of the ICND1 book’s Chapter 14, “Converting Subnet Masks,” in the same location where you found this PDF.)
Many people use the information in Table E-1 when converting masks. The table lists the nine DDN mask values, the binary equivalent, and the number of binary 1s in the binary equivalent.