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

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.. F

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

con-verted 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

Table 1-6 Binary and Decimal Equivalents of Hexadecimal Digits

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The best way to think about hexadecimal is to think of it as a shorthand way of read-ing binary It reduces an 8-bit number to just two hex digits This reduces the confu-sion 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

Four-Octet Dotted-Decimal Representation of a 32-Bit Binary Number

Currently, addresses assigned to computers on the Internet (IP addresses) are 32-bit binary numbers To make it easier to work with these addresses, the 32-bit binary number is broken into a series of decimal numbers To do this, split the binary number into four groups of eight binary digits Then convert each group of 8 bits (an octet) into its decimal equivalent Do this conversion exactly as was shown in the section,

“Binary-to-Decimal Conversion.”

When written, the complete decimal number is represented as four groups of decimal digits separated by periods, such as 10.15.129.201 This is called dotted-decimal nota-tion and provides a compact, easy-to-remember way of referring to 32-bit addresses This representation is used frequently later in this course, so be sure to understand it When converting to binary from dotted decimal, remember that each group of from one to three decimal digits represents a group of eight binary digits If the decimal number you are converting is less than 128, you need to add 0s to the left of the equiv-alent binary number until you have a total of 8 bits

For example, to convert the dotted-decimal value 10.15.129.201 to its binary equiva-lent, you should write the number as 00001010.00001111.10000001.11001001

Boolean Logic

Boolean logic is based on digital circuitry that accepts one or two incoming voltages and, based on these input voltages, generates an output voltage For the purpose of computers, the voltage difference is associated with two states, on and off These two states are in turn represented by a 1 or a 0, which are the two digits in the binary num-ber system

Hexadecimal Conversion

In this exercise, you practice converting hexadecimal values to decimal and binary values

Boolean logic is a binary logic that allows two numbers to be compared, and then a

choice based on those two numbers is generated These choices are the logical AND,

OR, and NOT With the exception of the NOT, Boolean operations have the same

func-tion They accept two numbers (1 or 0) and generate a result based on the logic rule

This section presents the operations, starting with the NOT operation The next

sec-tion provides an example of directly applying Boolean logic in networking—network

masking This example covers the AND operation

The NOT operation, as shown in Table 1-7, simply takes whatever value is presented

(0 or 1) and inverts it A 1 becomes a 0, and a 0 becomes a 1 Remember that the logic

gates are electronic devices built specifically for this purpose This is the logic rule that

they follow; whatever is input, the opposite is output

The AND operation, as shown in Table 1-8, takes two input values If both values are

1, the logic gate generates a 1 output; otherwise, it outputs a 0 There are four

combi-nations of input values Three combicombi-nations generate a 0, and one combination

gener-ates a 1 The AND operation is used extensively with IP addressing and subnet masks

The OR operation, as shown in Table 1-9, also takes two input values If one value is 1

or both values are 1, the output is 1 Just like the AND operation, there are four

com-binations of input values However, in an OR operation, three of the comcom-binations

generate a 1 output, and one combination generates a 0 output

The two networking operations that use Boolean logic are subnetwork masking and

wildcard masking Masking operations provide a way to filter addresses The addresses

identify the devices on the network Masking allows the addresses to be grouped or

controlled by other network operations

Table 1-7 NOT Operation

Table 1-8 AND Operation

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IP Addresses and Subnet Masks

The 32-bit binary addresses used on the Internet are called Internet Protocol (IP)

addresses This section covers the relationship between IP addresses and network masks You learn more about IP addresses in Chapter 7

When IP addresses are assigned to computers, some of the bits on the left side of the

32 bit IP number are used to represent a network The number of bits designated depends

on the address class The bits left over in the 32-bit IP address identify a particular computer on the network A computer is called a host So a computer’s IP address usually consists of a network portion and a host portion that represents a particular computer on a particular network

For the computer to know how the 32-bit IP address has been split, a second 32-bit number called a subnetwork maskis used This mask is a guide that indicates how the

IP address should be interpreted by identifying how many of the bits identify the com-puter’s network The network mask sequentially fills in the 1s from the left side of the mask A subnetwork mask is always all 1s until the network address is identified Then

it is all 0s from there to the mask’s rightmost bit The bits in the IP address that are 0 identify the computer (host) on that network Some examples of subnet masks follow Example 1:

11111111.00000000.00000000.00000000 written in dotted decimal is 255.0.0.0 Example 2:

11111111.11111111.00000000.00000000 written in dotted decimal is 255.255.0.0

In the first example, the first 8 bits from the left are the network address, and the last

24 bits are the host address In the second example, the first 16 bits are the network address, and the last 16 bits are the host address

Converting the IP address 10.34.23.134 to binary results in the following:

00001010.00100010.00010111.10000110

Table 1-9 OR Operation

To determine the network portion of the IP address, compare the subnet mask bits

to all 32 bits of the IP address 1 bit at a time, using the AND process, and record the

result The combination of a 0 IP address bit and a 0 mask bit is a 0 The combination

of a 0 and a 1 is a 0 The combination of a 1 and a 1 is a 1 To better demonstrate,

consider the following examples:

Example 1: Using the first mask (255.0.0.0):

00001010.00100010.00010111.10000110: IP address 11111111.00000000.00000000.00000000: network mask 00001010.00000000.00000000.00000000 is the network part of the address

In dotted-decimal format, 10.0.0.0 is the network portion of the IP address

Example 2: Using the second mask (255.255.0.0):

00001010.00100010.00010111.10000110: IP address 11111111.11111111.00000000.00000000: network mask 00001010.00100010.00000000.00000000 is the network part of the address

In dotted-decimal format, 10.34.0.0 is the network portion of the IP address

The importance of subnetwork masking will become much clearer as you work more

with IP addresses For now, it is only important that you understand the concept of the

network mask

Summary

In this chapter, you learned the following key points:

■ Computers are vital components of every network The more you know about

computers, the easier it is to understand networks

■ Knowing how a computer functions makes it easier to understand networks

■ TCP/IP is the protocol of the Internet

■ The ping command is a simple way of testing connectivity.

■ Software allows the user to interface with the hardware In networking, web

browsers and e-mail are the most commonly used software programs

■ Troubleshooting PCs is a necessary skill when working on networks

■ It is important to be familiar with the components of a computer and to

under-stand the functions of a NIC It is also important to be able to install a NIC

■ Bits are binary digits 8 bits equals 1 byte

34 Chapter 1: Introduction to Networking

■ Computers can recognize and process data only by using the binary number sys-tem The binary number system is made up of 0s and 1s

■ The hexadecimal number system is used frequently at higher levels of computa-tion The hexadecimal number system uses 16 symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,

A, B, C, D, E, and F

■ Boolean logic is a binary logic that allows two numbers to be compared An operation is created based on the two numbers Three common Boolean logic operators are NOT, AND, and OR

■ IP addresses are the 32-bit binary addresses used on the Internet

To supplement all you’ve learned in this chapter, refer to the chapter-specific Videos, PhotoZooms, and e-Lab Activities on the CD-ROM accompanying this book

Key Terms

American Standard Code for Information Interchange (ASCII) The most commonly

used code for representing alphanumeric data in a computer Uses binary digits (bits)

to represent the symbols typed on the keyboard

application Interprets the data and displays the information in a comprehensible

format as the last part of an Internet connection Applications work with protocols

to send and receive data across the Internet

backplane A large circuit board that contains sockets for expansion cards

binary A number system characterized by 1s and 0s (1 = on, and 0 = off)

bit The smallest unit of data in a computer A bit equals 1 or 0 It is the binary

for-mat in which data is processed, stored, and transmitted by computers In a computer,

bits are represented by on/off switches or the presence or absence of electrical charges,

light pulses, or radio waves

Boolean logic In computer operation with binary values, Boolean logic can describe

electromagnetically charged memory locations or circuit states that are either charged

(1 or true) or not charged (0 or false) The computer can use an AND gate or an OR

gate operation to obtain a result that can be used for further processing

bus A collection of circuits through which data is transmitted from one part of a

computer to another

byte A unit of measure that describes the size of a data file, the amount of space on

a disk or another storage medium, or the amount of data being sent over a network

1 byte equals 8 bits of data

CD-ROM drive An optical drive that can read information from a CD-ROM

central processing unit (CPU) The computer’s “brain,” where most of the

calcula-tions take place

dotted-decimal notation A syntactic representation for a 32-bit integer that consists

of four 8-bit numbers written in base 10 with periods (dots) separating them Used to

represent IP addresses on the Internet, as in 192.67.67.20

expansion slot An opening in a computer, usually on the motherboard, where an

expansion card can be inserted to add new capabilities to the computer

File Transfer Protocol (FTP) An application protocol, part of the TCP/IP protocol

suite, used to transfer files between network hosts

floppy disk drive Reads and writes to floppy disks

36 Chapter 1: Introduction to Networking

GB (gigabyte) Approximately 1 billion bytes Sometimes called a “gig.” Hard drive capacity on most PCs is typically measured in GB

Gbps (gigabits per second) One billion bits per second A standard measurement of the amount of data transferred over a network connection 10G or 10 Gigabit Ethernet operates at 10 Gbps

hard disk drive Reads and writes data on a hard disk The primary storage device in the computer

hyperlink A computer program command that points to other HTML files on a web server or other places on the same documents Provides shortcuts to other web pages and files

Hypertext Markup Language (HTML) A simple hypertext document-formatting lan-guage that uses tags to indicate how a given part of a document should be interpreted

by a viewing application, such as a web browser

Internet The largest global internetwork, connecting tens of thousands of networks worldwide and having a culture that focuses on research and standardization based on real-life use

Internet Protocol (IP) A network layer protocol in the TCP/IP protocol suite offering

a connectionless internetwork service

Kb (kilobit) Approximately 1000 bits

KB (kilobyte) Approximately 1000 bytes (1024 bytes exactly)

kbps (kilobits per second) One thousand bits per second A standard measurement of the amount of data transferred over a network connection

kBps (kilobytes per second) One thousand bytes per second A standard measurement

of the amount of data transferred over a network connection

keyboard port Connects a keyboard to a PC

logical connection Uses standards called protocols

Mb (megabit) Approximately 1 million bits

MB (megabyte) Approximately 1 million bytes (1,048,576 bytes exactly) A megabyte

is sometimes called a “meg.” The amount of RAM in most PCs is typically measured

in MB Large files are typically some number of MB in size

Mbps (megabits per second) One million bits per second A standard measurement

of the amount of data transferred over a network connection Basic Ethernet operates

at 10 Mbps

MBps (megabytes per second) One million bytes per second A standard

measure-ment of the amount of data transferred over a network connection

Media Access Control (MAC) address A standardized data link layer address that is

required for every port of devices that connect to a LAN Other devices in the network

use these addresses to locate specific ports in the network and to create and update

routing tables and data structures MAC addresses are 6 bytes long and are controlled

by the IEEE

memory chips RAM chips on memory cards plug into the motherboard

microprocessor A silicon chip that contains a CPU

modem A device that converts digital and analog signals At the source, a modem

converts digital signals to a form suitable for transmission over analog communication

facilities At the destination, the analog signals are returned to their digital form

motherboard A computer’s main circuit board

mouse port Connects a mouse to a PC

network interface card (NIC) A printed circuit board that provides network

commu-nication capabilities to and from a PC

network interface card (NIC) A printed circuit board that provides network

commu-nication capabilities to and from a PC

octet Eight bits In networking, the term octet often is used (rather than byte)

because some machine architectures employ bytes that are not 8 bits long

parallel port An interface that can transfer more than 1 bit simultaneously It

con-nects external devices, such as printers

Personal Computer Memory Card International Association (PCMCIA) An

organi-zation that has developed a standard for small credit card-sized devices called

PCM-CIA cards (or PC cards) Originally designed to add memory to portable computers,

the PCMCIA standard has been expanded several times and is now suitable for many

types of devices

physical connection A connection to a network that is made by connecting a

special-ized expansion card, such as a modem or NIC, from a PC with a cable to a network

ping Stands for Packet Internet Groper Often used in IP networks to test the

reach-ability of a network device

plug-in Software or a program that can easily be installed and used as part of a web

browser

38 Chapter 1: Introduction to Networking

power cord Connects an electrical device to an electrical outlet to provide power to the device

power supply Supplies power to a computer

printed circuit board (PCB) A thin plate on which chips (integrated circuits) and other electronic components are placed

protocol A formal description of a set of rules and conventions that govern how devices on a network exchange information

random-access memory (RAM) Also known as read-write memory Can have new data written to it as well as stored data read from it

read-only memory (ROM) A type of computer memory in which data has been prerecorded

serial port Can be used for serial communication in which only 1 bit is transmitted

at a time

sound card An expansion board that handles all sound functions

subnetwork In IP networks, a network that shares a particular subnet address Sub-networks are Sub-networks arbitrarily segmented by a network administrator to provide a multilevel, hierarchical routing structure while shielding from the addressing complex-ity of attached networks Sometimes called a subnet

subnetwork mask A 32-bit address mask used in IP to indicate the bits of an IP address that are being used for the subnet address

system unit The main component of a PC system

TB (terabyte) Approximately 1 trillion bytes Hard drive capacity on some high-end computers is measured in TB

Tbps (terabits per second) One trillion bits per second A standard measurement

of the amount of data transferred over a network connection Some high-speed core Internet routers and switches operate at more than Tbps

Transmission Control Protocol/Internet Protocol (TCP/IP) A common name for the suite of protocols developed by the U.S DoD in the 1970s to support the construction

of worldwide internetworks TCP and IP are the two best-known protocols in the suite

universal serial bus (USB) port Lets peripheral devices such as mice, modems, keyboards, scanners, and printers be plugged in and unplugged without resetting the system

video card A board that plugs into a PC to give it display capabilities