Routing TCP/IP, Volume I (CCIE Professional Development)

Working with Hexadecimal Numbers

Writing out binary octets isn't much fun. For people who must work with such numbers frequently, a briefer notation is welcome. One possible notation is to have a single character for every possible octet. However, there are 2⁸ = 256 different combinations of eight bits, so a single-character representation of all octets would require 256 digits, or a base 256 numbering system.

Life is much easier if an octet is viewed as two groups of four bits. For instance, 11010011 can be viewed as 1101 and 0011. There are 2⁴ = 16 possible combinations of four bits, so with a base 16, or hexadecimal, numbering system, an octet can be represented with two digits. (The root hex means “six,” and deci means “ten.”) Table A.1 ...