tailieunhanh - CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 7

Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 7 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | B Page 29 Tuesday May 20 2003 2 53 PM Bits Bytes and Measurement Terms 29 Table 1-6 Binary and Decimal Equivalents of Hexadecimal Digits Binary Hexadecimal Decimal 0000 0 0 0001 1 1 0010 2 2 0011 3 3 0100 4 4 0101 5 5 0110 6 6 0111 7 7 1000 8 8 1001 9 9 1010 A 10 1011 B 11 1100 C 12 1101 D 13 1110 E 14 1111 F 15 To convert from hexadecimal to binary convert every hex digit into 4 bits. For example to convert hex AC 0xAC to binary you first convert hex A which is 1010 binary and then you convert hex C which is 1100 binary. So hex AC is 10101100 in binary. Notice that all possible combinations of four binary digits have only one hexadecimal symbol whereas two symbols are required for decimal. The reason why hex is used is that two hexadecimal digits can efficiently represent any combination of eight binary digits as opposed to decimal which would require up to four digits . In allowing two decimal digits to represent 4 bits using decimal could also cause confusion in reading a value. For example the eight bit binary number 01110011 would be 115 if converted to decimal digits. Does this represent 11-5 or 1-15 If 11-5 is used the binary number would be 10110101 which is not the number originally converted. Using hexadecimal the conversion is 1F which always converts back to 00011111. I Page 30 Tuesday May 20 2003 2 53 PM 30 Chapter 1 Introduction to Networking The best way to think about hexadecimal is to think of it as a shorthand way of reading binary. It reduces an 8-bit number to just two hex digits. This reduces the confusion of reading long strings of binary numbers and the amount of space it takes to write them. Remember that hexadecimal is sometimes abbreviated as 0x so hex 5D might be written as 0x5D. To convert from hex to binary simply expand each hex digit into its 4-bit binary equivalent. Hexadecimal Conversion In this exercise you practice converting hexadecimal values to decimal and binary values. Four-Octet Dotted-Decimal .