Introduction to Internetworking - Module 1

To understand the role that computers play in a networking system, consider the Internet. Internet connections are essential for businesses and education. Careful planning is required to build a network that will connect to the Internet. Even for an individual personal computer (PC) to connect to the Internet, some planning and decisions are required. Computer resources must be considered for Internet connection. This includes the type of device that connects the PC to the Internet, such as a network interface card (NIC) or modem. Protocols, or rules, must be configured before a computer can connect to the Internet. Proper selection of a Web browser is also important.

This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams.  

Students who complete this lesson should be able to perform the following tasks:

• Understand the physical connections needed for a computer to connect to the Internet
• Recognize the components of a computer
• Install and troubleshoot NICs and modems
• Configure the set of protocols needed for Internet connection
• Use basic procedures to test an Internet connection
• Demonstrate a basic ability to use Web browsers and plug-ins

 1.1  Connecting to the Internet  

  1.1.1  Requirements for Internet connection   

 

This page will describe the physical and logical requirements for an Internet connection.

The Internet is the largest data network on earth. The Internet consists of many large and small networks that are interconnected. Individual computers are the sources and destinations of information through the Internet. Connection to the Internet can be broken down into the physical connection, the logical connection, and applications.

A physical connection is made by connecting an adapter card, such as a modem or a NIC, from a PC to a network. The physical connection is used to transfer signals between PCs within the local-area network (LAN) and to remote devices on the Internet.

The logical connection uses standards called protocols. A protocol is a formal description of a set of rules and conventions that govern how devices on a network communicate. Connections to the Internet may use multiple protocols. The Transmission Control Protocol/Internet Protocol (TCP/IP) suite is the primary set of protocols used on the Internet. The TCP/IP suite works together to transmit and receive data, or information.

The last part of the connection are the applications, or software programs, that interpret and display data in an understandable form. Applications work with protocols to send and receive data across the Internet. A Web browser displays HTML as a Web page. Examples of Web browsers include Internet Explorer and Netscape. File Transfer Protocol (FTP) is used to download files and programs from the Internet. Web browsers also use proprietary plug-in applications to display special data types such as movies or flash animations.

This is an introductory view of the Internet, and it may seem to be a simplistic process. As the topic is explored in greater depth, students will learn that data transmission across the Internet is a complicated task.

The next page will describe some PC components.

  1.1  Connecting to the Internet 

  1.1.2  PC basics 

  

Computers are important building blocks in a network. Therefore, students must be able to identify the major components of a PC. Many networking devices are special purpose computers, with many of the same components as general purpose PCs.

A computer must work properly before it can be used to access information such as Web-based content. This will require students to troubleshoot basic hardware and software problems. Therefore, students must be familiar with the following small, discreet PC components:

Students should also be familiar with the following PC subsystems:

• Transistor – Device that amplifies a signal or opens and closes a circuit.
• Integrated circuit – Device made of semiconductor material that contains many transistors and performs a specific task.
• Resistor – An electrical component that limits or regulates the flow of electrical current in an electronic circuit.
• Capacitor – Electronic component that stores energy in the form of an electrostatic field that consists of two conducting metal plates separated by an insulating material.
• Connector – The part of a cable that plugs into a port or interface.
• Light emitting diode (LED) – Semiconductor device that emits light when a current passes through it.
• Printed circuit board (PCB) – A circuit board which has conducting tracks superimposed, or printed, on one or both sides. It may also contain internal signal layers and power and ground planes. Microprocessors, chips and integrated circuits and other electronic components are mounted on the PCB.
• CD-ROM drive – A device that can read information from a CD-ROM.
• Central processing unit (CPU) – The part of a computer that controls the operation of all the other parts. It gets instructions from memory and decodes them. It performs math and logic operations, and translates and executes instructions. 
• Floppy disk drive – A computer drive that reads and writes data to a 3.5-inch, circular piece of metal-coated plastic disk. A standard floppy disk can store approximately 1 MB of information. 
• Hard disk drive – A computer storage device that uses a set of rotating, magnetically coated disks called platters to store data or programs. Hard drives come in different storage capacity sizes.
• Microprocessor – A microprocessor is a processor which consists of a purpose-designed silicon chip and is physically very small. The microprocessor utilizes Very Large-Scale Integration (VLSI) circuit technology to integrate computer memory, logic, and control on a single chip. A microprocessor contains a CPU.
• Motherboard – The main printed circuit board in a computer. The motherboard contains the bus, the microprocessor, and integrated circuits used for controlling any built-in peripherals such as the keyboard, text and graphics display, serial ports and parallel ports, joystick, and mouse interfaces. 
• Bus – A collection of wires on the motherboard through which data and timing signals are transmitted from one part of a computer to another.
• Random-access memory (RAM) – Also known as read-write memory because new data can be written to it and stored data can be read from it. RAM requires electrical power to maintain data storage. If a computer is turned off or loses power all data stored in RAM is lost.
• Read-only memory (ROM) – Computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read.
• System unit – The main part of a PC, which includes the chassis, microprocessor, main memory, bus, and ports. The system unit does not include the keyboard, monitor, or any external devices connected to the computer.
• Expansion slot – A socket on the motherboard where a circuit board can be inserted to add new capabilities to the computer. Figure  shows Peripheral Component Interconnect (PCI) and Accelerated Graphics Port (AGP) expansion slots. PCI is a fast connection for boards such as NICs, internal modems, and video cards. The AGP port provides a high bandwidth connection between the graphics device and the system memory. AGP provides a fast connection for 3-D graphics on computer systems.
• Power supply – The component that supplies power to a computer.

The following backplane components are also important:

• Backplane – A backplane is an electronic circuit board containing circuitry and sockets into which additional electronic devices on other circuit boards or cards can be plugged; in a computer, generally synonymous with or part of the motherboard.
• Network interface card (NIC) – An expansion board inserted into a computer so that the computer can be connected to a network.
• Video card – A board that plugs into a PC to give it display capabilities.
• Audio card – An expansion board that enables a computer to manipulate and output sounds.
• Parallel port – An interface capable of transferring more than one bit simultaneously that is used to connect external devices such as printers.
• Serial port – An interface that can be used for serial communication in which only one bit is transmitted at a time.
• Mouse port – A port used to connect a mouse to a PC.
• USB port – A Universal Serial Bus connector. A USB port connects devices such as a mouse or printer to the computer quickly and easily.
• Firewire – A serial bus interface standard offering high-speed communications and isochronous real-time data services.
• Power cord – A cord used to connect an electrical device to an electrical outlet that provides power to the device.

Think of the internal components of a PC as a network of devices that are all attached to the system bus.

The Lab Activity will help students find and identify the physical components of a PC.

The next page will provide more information about NICs.

  1.1  Connecting to the Internet  

  1.1.3  Network interface card    

 

This page will explain what a NIC is and how it works. Students will also learn how to select the best NIC for a PC.

A NIC, or LAN adapter, provides network communication capabilities to and from a PC. On desktop computer systems, it is a printed circuit board that resides in a slot on the motherboard and provides an interface connection to the network media.  On laptop computer systems, it is commonly integrated into the laptop or available on a small, credit card-sized PCMCIA card.  PCMCIA stands for Personal Computer Memory Card International Association. PCMCIA cards are also known as PC cards. The type of NIC must match the media and protocol used on the local network.

The NIC uses an interrupt request (IRQ), an input/output (I/O) address, and upper memory space to work with the operating system. An IRQ value is an assigned location where the computer can expect a particular device to interrupt it when the device sends the computer signals about its operation. For example, when a printer has finished printing, it sends an interrupt signal to the computer. The signal momentarily interrupts the computer so that it can decide what processing to do next. Since multiple signals to the computer on the same interrupt line might not be understood by the computer, a unique value must be specified for each device and its path to the computer. Prior to Plug-and Play (PnP) devices, users often had to set IRQ values manually, or be aware of them, when adding a new device to a computer.

These considerations are important in the selection of a NIC:

• Protocols – Ethernet, Token Ring, or FDDI
• Types of media – Twisted-pair, coaxial, wireless, or fiber-optic
• Type of system bus – PCI or ISA

Students can use the Interactive Media Activity to view a NIC.

The next page will explain how NICs and modems are installed.

  1.1  Connecting to the Internet  

  1.1.4  NIC and modem installation

 

This page will explain how an adapter card, which can be a modem or a NIC, provides Internet connectivity. Students will also learn how to install a modem or a NIC.

A modem, or modulator-demodulator, is a device that provides the computer with connectivity to a telephone line. A modem converts data from a digital signal to an analog signal that is compatible with a standard phone line. The modem at the receiving end demodulates the signal, which converts it back to digital. Modems may be installed internally  or attached externally to the computer using a phone line.

A NIC must be installed for each device on a network. A NIC provides a network interface for each host. Different types of NICs are used for various device configurations. Notebook computers may have a built-in interface or use a PCMCIA card. Figure  shows PCMCIA wired, wireless network cards, and a Universal Serial Bus (USB) Ethernet adapter. Desktop systems may use an internal network adapter , called a NIC, or an external network adapter  that connects to the network through a USB port.

Situations that require NIC installation include the following:

• Installation of a NIC on a PC that does not already have one
• Replacement of a malfunctioning or damaged NIC
• Upgrade from a 10-Mbps NIC to a 10/100/1000-Mbps NIC
• Change to a different type of NIC, such as wireless
• Installation of a secondary, or backup, NIC for network security reasons

To perform the installation of a NIC or modem the following resources may be required:

• Knowledge of how the adapter, jumpers, and plug-and-play software are configured
• Availability of diagnostic tools
• Ability to resolve hardware resource conflicts

The next page will describe the history of network connectivity.

  1.1  Connecting to the Internet  

  1.1.5  Overview of high-speed and dial-up connectivity    

 

This page will explain how modem connectivity has evolved into high-speed services.

In the early 1960s, modems were introduced to connect dumb terminals to a central computer. Many companies used to rent computer time since it was too expensive to own an on-site system. The connection rate was very slow. It was 300 bits per second (bps), which is about 30 characters per second.

As PCs became more affordable in the 1970s, bulletin board systems (BBSs) appeared. These BBSs allowed users to connect and post or read messages on a discussion board. The 300-bps speed was acceptable since it was faster than the speed at which most people could read or type. In the early 1980s, use of bulletin boards increased exponentially and the 300 bps speed quickly became too slow for the transfer of large files and graphics. In the 1990s, modems could operate at 9600 bps. By 1998, they reached the current standard of 56,000 bps, or 56 kbps.

Soon the high-speed services used in the corporate environment such as Digital Subscriber Line (DSL) and cable modem access moved to the consumer market. These services no longer required expensive equipment or a second phone line. These are "always on" services that provide instant access and do not require a connection to be established for each session. This provides more reliability and flexibility and has simplified Internet connection sharing in small office and home networks.

The next page will introduce an important set of network protocols.

  1.1  Connecting to the Internet 

  1.1.6  TCP/IP description and configuration 

 

This page will introduce the Transmission Control Protocol/Internet Protocol (TCP/IP).

TCP/IP is a set of protocols or rules that have been developed to allow computers to share resources across a network. The operating system tools must be used to configure TCP/IP on a workstation. The process is very similar for Windows or Mac operating systems.

The Lab Activity will teach students how to obtain basic TCP/IP configuration information.

The next page will introduce the ping command.

  1.1  Connecting to the Internet 

  1.1.7  Testing connectivity with ping 

 

 

This page will explain how the ping command is used to test network connectivity.

Ping is a basic program that verifies a particular IP address exists and can accept requests. The computer acronym ping stands for Packet Internet or Inter-Network Groper. The name was contrived to match the submariners' term for the sound of a returned sonar pulse from an underwater object.

The ping command works by sending special Internet Protocol (IP) packets, called Internet Control Message Protocol (ICMP) Echo Request datagrams, to a specified destination. Each packet sent is a request for a reply. The output response for a ping contains the success ratio and round-trip time to the destination.  From this information, it is possible to determine if there is connectivity to a destination. The ping command is used to test the NIC transmit and receive function, the TCP/IP configuration, and network connectivity. The following types of ping commands can be issued:

                                    

• ping 127.0.0.1 – This is a unique ping and is called an internal loopback test. It is used to verify the TCP/IP network configuration. 
• ping IP address of host computer – A ping to a host PC verifies the TCP/IP address configuration for the local host and connectivity to the host.
• ping default-gateway IP address – A ping to the default gateway indicates if the router that connects the local network to other networks can be reached.
• ping remote destination IP address – A ping to a remote destination verifies connectivity to a remote host.

Students will use the ping and tracert commands in the Lab Activity.

The next page will discuss Web browsers.

  1.1  Connecting to the Internet 

  1.1.8  Web browser and plug-ins 

 

This page will explain what a Web browser is and how it performs the following functions:

• Contacts a Web server
• Requests information
• Receives information
• Displays the results on the screen

A Web browser is software that interprets HTML, which is one of the languages used to code Web page content. Some new technologies use other markup languages with more advanced features. HTML, which is the most common markup language, can display graphics or play sound, movies, and other multimedia files. Hyperlinks that are embedded in a Web page provide a quick link to another location on the same page or a different Internet address.

Two of the most popular Web browsers are Internet Explorer (IE) and Netscape Communicator. These browsers perform the same tasks. However, there are differences between them. Some websites may not support the use of one of these browsers. It is a good idea to have both programs installed.

Here are some features of Netscape Navigator:

• Was the first popular browser
• Uses less disk space
• Displays HTML files
• Performs e-mail and file transfers

Here are some features of IE:

• Is powerfully integrated with other Microsoft products
• Uses more disk space
• Displays HTML files
• Performs e-mail and file transfers

There are also many special, or proprietary, file types that standard Web browsers are not able to display. To view these files the browser must be configured to use the plug-in applications. These applications work with the browser to launch the programs required to view special files:

• Flash – Plays multimedia files created by Macromedia Flash
• Quicktime – Plays video files created by Apple
• Real Player – Plays audio files

Use the following procedure to install the Flash plug-in:

• Go to the Macromedia website.
• Download the latest flash player installer file.
• Run and install the plug-in in Netscape or IE.
• Access the Cisco Academy website to verify the installation and proper operation.

Computers also perform many other useful tasks. Many employees use a set of applications in the form of an office suite such as Microsoft Office. Office applications typically include the following:

• Spreadsheet software contains tables that consist of columns and rows and it is often used with formulas to process and analyze data.
• Modern word processors allow users to create documents that include graphics and richly formatted text.
• Database management software is used to store, maintain, organize, sort, and filter records. A record is a collection of information identified by some common theme such as customer name.
• Presentation software is used to design and develop presentations to deliver at meetings, classes, or sales presentations.
• A personal information manager includes an e-mail utility, contact lists, a calendar, and a to-do list.

Office applications are now a part of daily work, as typewriters were before PCs.

The Lab Activity will help students understand how a Web browser works.

The next page will discuss the troubleshooting process.

  1.1  Connecting to the Internet 

  1.1.9  Troubleshooting Internet connection problems 

  

The Lab Activity on this page will show students how to troubleshoot hardware, software, and network configuration problems. The goal is to locate and repair the problems in a set amount of time to gain access to the curriculum. This lab will demonstrate how complex it is to configure Internet access. This includes the processes and procedures used to troubleshoot computer hardware, software, and network systems.

This page concludes this lesson. The next lesson will discuss computer number systems. The first page will describe the binary system.

  1.2  Network Math  

  1.2.1  Binary presentation of data    

 

This page will explain how computers use the binary number system to represent data.

Computers work with and store data using electronic switches that are either ON or OFF. Computers can only understand and use data that is in this two-state or binary format. The 1s and 0s are used to represent the two possible states of an electronic component in a computer. 1 is represented by an ON state, and 0 is represented by an OFF state. They are referred to as binary digits or bits.

American Standard Code for Information Interchange (ASCII) is the code that is most commonly used to represent alpha-numeric data in a computer.  ASCII uses binary digits to represent the symbols typed on the keyboard. When computers send ON or OFF states over a network, electrical, light, or radio waves are used to represent the 1s and 0s. Notice that each character is represented by a unique pattern of eight binary digits.

Because computers are designed to work with ON/OFF switches, binary digits and binary numbers are natural to them. Humans use the decimal number system, which is relatively simple when compared to the long series of 1s and 0s used by computers. So the computer binary numbers need to be converted to decimal numbers.

Sometimes binary numbers are converted to hexadecimal numbers. This reduces a long string of binary digits to a few hexadecimal characters. It is easier to remember and to work with hexadecimal numbers.

The next page will discuss bits and bytes.

  1.2  Network Math 

   1.2.2  Bits and bytes 

  

This page will explain what bits and bytes are.

A binary 0 might be represented by 0 volts of electricity.

A binary 1 might be represented by +5 volts of electricity.

Computers are designed to use groupings of eight bits. This grouping of eight bits is referred to as a byte.  In a computer, one byte represents a single addressable storage location. These storage locations represent a value or single character of data, such as an ASCII code. The total number of combinations of the eight switches being turned on and off is 256. The value range of a byte is from 0 to 255. So a byte is an important concept to understand when working with computers and networks.

The next page will describe the Base 10 number system.

  1.2  Network Math 

  1.2.3  Base 10 number system 

  

Numbering systems consist of symbols and rules for their use. This page will discuss the most commonly used number system, which is decimal, or Base 10.

Base 10 uses the ten symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. These symbols, can be combined to represent all possible numeric values.

The decimal number system is based on powers of 10. Each column position of a value, from right to left, is multiplied by the base number 10 raised to a power, which is the exponent. The power that 10 is raised to depends on its position to the left of the decimal point. When a decimal number is read from right to left, the first or rightmost position represents 100, which equals 1. The second position represents 101, which equals 10. The third position represents 102, which equals 100. The seventh position to the left represents 106, which equals 1,000,000. This is true no matter how many columns the number has.

Here is an example:

2134 = (2x103) + (1x102) + (3x101) + (4x100)

This review of the decimal system will help students understand the Base 2 and Base 16 number systems. These systems use the same methods as the decimal system.

The next page will describe the Base 2 number system.

  1.2  Network Math 

  1.2.4  Base 2 number system 

 

This page will discuss the number system that computers use to recognize and process data, which is binary, or Base 2.

The binary system uses only two symbols, which are 0 and 1. The position of each digit from right to left in a binary number represents the base number 2 raised to a power or exponent. These place values are, from right to left, 20, 21, 22, 23, 24, 25, 26, and 27, or 1, 2, 4, 8, 16, 32, 64, and 128 respectively.

Here is an example:

101102 = (1 x 24 = 16) + (0 x 23 = 0) + (1 x 22 = 4) + (1 x 21 = 2) + (0 x 20 = 0) = 22 (16 + 0 + 4 + 2 + 0)

This example shows that the binary number 10110 is equal to the decimal number 22.

The next page will explain the conversion of decimal numbers to binary numbers.

  1.2  Network Math 

  1.2.5  Converting decimal numbers to 8-bit binary numbers 

 

 

This page will teach students how to convert decimal numbers to binary numbers.

There are several ways to convert decimal numbers to binary numbers. The flowchart in Figure  describes one method. This method is one of several methods that can be used. It is best to select one method and practice with it until it always produces the correct answer.

Conversion exercise:

Use the example below to convert the decimal number 168 to a binary number:

• 128 is less than 168 so the left most bit in the binary number is a 1. 168 - 128 = 40.
• 64 is not less than or equal to 40 so the second bit from the left is a 0.
• 32 is less than 40 so the third bit from the left is a 1. 40 - 32 = 8.
• 16 is not less than or equal to 8 so the fourth bit from the left is a 0.
• 8 is equal to 8 so the fifth bit from the left is a 1. 8 - 8 = 0. Therefore, the bits to the right are all 0.

This example shows that the decimal number 168 is equal to the binary number 10101000.

The number converter activity in Figure  will allow students to practice decimal to binary conversions.

In the Lab Activity, students will practice the conversion of decimal numbers to binary numbers.

The next page will discuss the conversion of binary numbers to decimal numbers.

  1.2  Network Math 

  1.2.6  Converting 8-bit binary numbers to decimal numbers 

  

This page will teach students how to convert binary numbers to decimal numbers.

There are two basic ways to convert binary numbers to decimal numbers. The flowchart in Figure  shows one example.

Students can also multipy each binary digit by the base number of 2 raised to the exponent of its position.

Here is an example:

Convert the binary number 01110000 to a decimal number.

NOTE:

Work from right to left. Remember that anything raised to the 0 power is 1.

0 x 20 = 0 

0 x 21 = 0 

0 x 22 = 0 

0 x 23 = 0 

1 x 24 = 16

1 x 25 = 32

1 x 26 = 64

0 x 27 = 0  

__________

 = 112

The Lab Activity will let students practice the conversion of binary numbers to decimal numbers.

The next page will discuss dotted decimal notations.

  1.2  Network Math 

  1.2.7  Four-octet dotted decimal representation of 32-bit binary numbers 

  

This page will explain how binary numbers are represented in dotted decimal notation.

Currently, addresses assigned to computers on the Internet 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. First the binary number is split into four groups of eight binary digits. Then each group of eight bits, or octet, is converted into its decimal equivalent. This conversion can be performed as shown on the previous page.

When written, the complete binary number is represented as four groups of decimal digits separated by periods. This is called dotted decimal notation and provides a compact and easy way to refer to 32-bit addresses. This representation is used frequently later in this course, so it is necessary to understand it. For dotted decimal to binary conversions, remember that each group of one to three decimal digits represents a group of eight binary digits. If the decimal number that is being converted is less than 128, zeros will be needed to be added to the left of the equivalent binary number until there are a total of eight bits.

Try the following conversions for practice:

Convert 200.114.6.51 to its 32-bit binary equivalent.

Convert 10000000 01011101 00001111 10101010 to its dotted decimal equivalent.

The next page will introduce the hexadecimal number system.

  1.2  Network Math 

  1.2.8  Hexadecimal 

 

This page will teach students about the hexadecimal number system. Students will also learn how hexadecimal is used to represent binary and decimal numbers.

The hexadecimal or Base 16 number system is commonly used to represent binary numbers in a more readable form.  Computers perform computations in binary. However, there are several instances when the binary output of a computer is expressed in hexadecimal to make it easier to read.

The configuration register in Cisco routers often requires hexadecimal to binary and binary to hexadecimal conversions. Cisco routers have a configuration register that is 16 bits long. The 16-bit binary number can be represented as a four-digit hexadecimal number. For example, 0010000100000010 in binary equals 2102 in hexadecimal. A hexadecimal number is often indicated with a 0x. For example, the hexadecimal number 2102 would be written as 0x2102.

Like the binary and decimal systems, the hexadecimal system is based on the use of symbols, powers, and positions.  The symbols that hexadecimal uses are the digits 0 through 9 and the letters A through F.

All combinations of four binary digits can be represented with one hexadecimal symbol. These values require one or two decimal symbols. Two hexadecimal digits can efficiently represent any combination of eight binary digits. The decimal representation of an eight-bit binary number will require either two or three decimal digits. Since one hexadecimal digit always represents four binary digits, hexadecimal symbols are easier to use than decimal symbols when working with large binary numbers. Using hexadecimal representation also reduces the confusion of reading long strings of binary numbers and the amount of space it takes to write binary numbers. Remember that 0x may be used to indicate a hexadecimal value. The hexadecimal number 5D might be written as 0x5D.

To convert to binary, simply expand each hexadecimal digit into its four-bit binary equivalent. 

The Lab Activity will teach students how to convert hexadecimal numbers into decimal and binary values.

The next page will discuss Boolean logic.

  1.2  Network Math 

  1.2.9  Boolean or binary logic 

 

This page will introduce Boolean logic and explain how it is used.

Boolean logic is based on digital circuitry that accepts one or two incoming voltages.  Based on the input voltages, output voltage is generated. For computers the voltage difference is represented as an ON or OFF state. These two states are associated with a binary 1 or 0.

Boolean logic is a binary logic that allows two numbers to be compared and makes a choice based on the numbers. These choices are the logical AND, OR, and NOT. With the exception of the NOT, Boolean operations have the same function. They accept two numbers, which are 1 and 0, and generate a result based on the logic rule.

The NOT operation takes the value that is presented 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. The logic rule that they follow is whatever the input is, the output is the opposite.

The AND operation compares two input values. If both values are 1, the logic gate generates a 1 as the output.  Otherwise it outputs a 0. There are four combinations of input values. Three of these combinations generate a 0, and one combination generates a 1.

The OR operation also takes two input values.  If at least one of the input values is 1, the output value is 1. Again there are four combinations of input values. Three combinations generate a 1 and the fourth generates a 0.

The two networking operations that use Boolean logic are subnetwork and wildcard masking. The masking operations are used to filter addresses. The addresses identify the devices on the network and can be grouped together or controlled by other network operations. These functions will be explained in depth later in the curriculum.

The next page will explain how network masks are used.

  1.2  Network Math 

  1.2.10  IP addresses and network masks

 

This page will explain the relationship between IP addresses and network masks.

When IP addresses are assigned to computers, some of the bits on the left side of the 32-bit IP number 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 referred to as a host. The IP address of a computer consists of a network and a host part.

To inform a computer how the 32-bit IP address has been split, a second 32-bit number called a subnetwork mask is used. This mask is a guide that determines how the IP address is interpreted. It indicates how many of the bits are used to identify the network of the computer. The subnetwork mask sequentially fills in the 1s from the left side of the mask. A subnet mask will always be all 1s until the network address is identified and then it will be all 0s to the end of the mask. The bits in the subnet mask that are 0 identify the computer or host.

Some examples of subnet masks are as follows:

11111111000000000000000000000000 written in dotted decimal as 255.0.0.0

11111111111111110000000000000000 written in dotted decimal as 255.255.0.0

In the first example, the first eight bits from the left represent the network portion of the address, and the last 24 bits represent the host portion of the address. In the second example the first 16 bits represent the network portion of the address, and the last 16 bits represent the host portion of the address.

The IP address 10.34.23.134 in binary form is 00001010.00100010.00010111.10000110.

A Boolean AND of the IP address 10.34.23.134 and the subnet mask 255.0.0.0 produces the network address of this host:

00001010.00100010.00010111.10000110 

11111111.00000000.00000000.00000000 

00001010.00000000.00000000.00000000

The dotted decimal conversion is 10.0.0.0 which is the network portion of the IP address when the 255.0.0.0 mask is used.

A Boolean AND of the IP address 10.34.23.134 and the subnet mask 255.255.0.0 produces the network address of this host:

00001010.00100010.00010111.10000110 

11111111.11111111.00000000.00000000 

00001010.00100010.00000000.00000000

The dotted decimal conversion is 10.34.0.0 which is the network portion of the IP address when the 255.255.0.0 mask is used.

This is a brief illustration of the effect that a network mask has on an IP address. The importance of masking will become much clearer as more work with IP addresses is done. For right now it is only important that the concept of the mask is understood.

This page concludes this lesson. The next page will summarize the main points from the module.

Summary

Decimal representation of IP addresses and network masksThis page summarizes the topics discussed in this module.

A connection to a computer network can be broken down into the physical connection, the logical connection, and the applications that interpret the data and display the information. Establishment and maintenance of the physical connection requires knowledge of PC components and peripherals. Connectivity to the Internet requires an adapter card, which may be a modem or a network interface card (NIC).

In the early 1960s modems were introduced to provide connectivity to a central computer. Today, access methods have progressed to services that provide constant, high-speed access.

The logical connection uses standards called protocols. The Transmission Control Protocol/Internet Protocol (TCP/IP) suite is the primary group of protocols used on the Internet. TCP/IP can be configured on a workstation using operating system tools. The ping utility can be used to test connectivity.

A web browser is software that is installed on the PC to gain access to the Internet and local web pages. Occasionally a browser may require plug-in applications. These applications work in conjunction with the browser to launch the program required to view special or proprietary files.

Computers recognize and process data using the binary, or Base 2, numbering system. Often the binary output of a computer is expressed in hexadecimal to make it easier to read. The ablility to convert decimal numbers to binary numbers is valuable when converting dotted decimal IP addresses to machine-readable binary format. Conversion of hexadecimal numbers to binary, and binary numbers to hexadecimal, is a common task when dealing with the configuration register in Cisco routers.

Boolean logic is a binary logic that allows two numbers to be compared and a choice generated based on the two numbers. Two networking operations that use Boolean logic are subnetting and wildcard masking.

The 32-bit binary addresses used on the Internet are referred to as Internet Protocol (IP) addresses.