Chapter3 Semster One -Discovery

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2007 Cisco Systems, Inc. All rights reserved. Cisco Public

ITE PC v4.0

Chapter 1 1

Connecting to the

Network

Networking for Home and Small Businesses

Chapter 3


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Chapter 1 2 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Objectives Explain the concept of networking and the benefits of

networks.

Explain the concept of communication protocols.

Explain how communication occurs across a localEthernet network.

Describe Access layer devices and communicationmethods on a local Ethernet network.

Describe Distribution layer devices andcommunication methods across networks.

Plan, implement, and verify a local network.


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Networking and Its Benefits Define the term network and identify various types of

networks


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Networks

Communication technology in the 1990s, and before,required separate, dedicated networks for voice, video andcomputer data communications.

Each of these networks required a different type of devicein order to access the network. Telephones, televisions,and computers used specific technologies and differentdedicated network structures, to communicate.

People can now watch live video broadcasts on their

computers, make a telephone call over the Internet, orsearch the Internet using a television. Converged networksmake this possible.


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Network Benefits

Networks range from simple networks consisting of twocomputers, to networks connecting millions of devices.Networks installed in small offices, or homes and homeoffices, are referred to as SOHO networks.

These enable sharing of resources, such as printers,

documents, pictures and music between a few localcomputers.

In business, large networks can be used to advertise andsell products, order supplies, and communicate with

customers. Networks allow for rapid communication such as email

and instant messaging, and provide consolidation,storage, and access to information on network servers.


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Networking and Its Benefits Describe the benefits of computer networking and list

examples of small, medium and large networks


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Networking and Its Benefits

Business and SOHO networks usually provide a sharedconnection to the Internet.

The Internet is considered a "network of networks"because it is literally made up of thousands of networks

that are connected to each other.

Here are other uses of a network and the Internet:

Sharing music and video files

Research and on-line learning

Chatting with friends

Planning vacations

Purchasing gifts and supplies


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Networking and Its Benefits Define the components of an Information network


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Network components

There are many components that can be part of anetwork, for example personal computers, servers,networking devices, and cabling.

These components can be grouped into four main

categories:

Hosts

Shared peripherals

Networking devicesNetworking media


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Network components

Hosts are devices that send and receivemessages directly across the network.

Shared peripherals are not directly connected to

the network, but instead are connected to hosts. The network devices, as well as networking

media, are used to interconnect hosts.


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Networking and Its Benefits Describe the Roles of computers on a network

Clients and servers


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Roles of computers on a network

All computers connected to a network that participate directlyin network communication are classified as hosts.

Hosts can send and receive messages on the network. Inmodern networks, computer hosts can act as a client, aserver, or both. Its the software installed on the computerthat determines which role the computer plays.

Servers are hosts that have software installed that enablethem to provide information, like email or web pages, to otherhosts on the network. (A single computer can run multiple

types of server software. ) Clients are computer hosts that have software installed that

enable them to request and display the information obtainedfrom the server. (A single computer can also run multipletypes of client software.)


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Peer-to-Peer network

Client and server software usually runs on separatecomputers, but it is also possible for one computer tocarry out both roles at the same time.

In small businesses and homes, many computers

function as the servers and clients on the network. Thistype of network is called a peer-to-peer network.

The simplest peer-to-peer network consists of twodirectly connected computers using a wired or

wireless connection.Multiple PCs can also be connected to create alarger peer-to-peer network but this requires a networkdevice, such as a hub, to interconnect the computers.


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Networking and Its Benefits Build computer peer-to-peer network and verify


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Network Topologies Differentiate between logical and physical topologies,

and explain how networks are represented graphically


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Network Topologies

Wired networks require lots of cabling and networkdevices to provide connectivity for all network hosts.

When networks are installed, a physical topology map iscreated to record where each host is located and how it is

connected to the network. The physical topology map also shows where the wiring is

installed and the locations of the networking devices thatconnect the hosts.

In addition to the physical topology map, it is sometimesnecessary to also have a logical view of the networktopology. A logical topology map groups hosts by howthey use the network, no matter where they are physically

located.


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Communication Protocols Explain the concept of communication in terms of

source, destination and channel


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Communication Concept

The primary purpose of any network is to provide amethod to communicate information.

All communication begins with a message, orinformation, that must be sent from one individual or

device to another.

All communication methods have three elements incommon.

The first of these elements is the messagesource, or sender. Message sources are people, orelectronic devices, that need to communicate amessage to other individuals or devices.


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The second element of communication is thedestination, or receiver, of the message. Thedestination receives the message and interprets it.

A third element, called a channel, provides the

pathway over which the message can travel fromsource to destination.

In any conversation between two people, there aremany rules, or protocols, that the two must follow inorder for the message to be successfully deliveredand understood.


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Among the protocols for successful humancommunication are:

Identification of sender and receiver

Agreed-upon medium or channel (face-to-face,

telephone, letter, photograph)

Appropriate communication mode (spoken,written, illustrated, interactive or one-way)

Common languageGrammar and sentence structure

Speed and timing of delivery


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Communication Protocols Explain the need for rules and protocols in order for

communication to occur


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Communication Protocols

Protocols are specific to the characteristics of the source,channel and destination of the message.

Protocols define the details of how the message istransmitted, and delivered. This includes issues of:

Message format

Message size

Timing

Encapsulation

Encoding

Standard message pattern


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Explain the concept of encoding in relation to humancommunication


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Message Encoding

One of the first steps to sending a message isencoding it. Written words, pictures, and spokenlanguages each use a unique set of codes,sounds, gestures, and/or symbols to represent the

thoughts being shared. Encoding is the process of converting thoughts into

the language, symbols, or sounds, fortransmission.

Decoding reverses this process in order to interpretthe thought.


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Message Encoding

Encoding also occurs in computer communication.Encoding between hosts must be in an appropriateform for the medium.

Messages sent across the network are first

converted into bits by the sending host. Each bit isencoded into a pattern of sounds, light waves, orelectrical impulses depending on the networkmedia over which the bits are transmitted.

The destination host receives and decodes thesignals in order to interpret the message.


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Message Formatting When a message is sent from source to destination,

it must use a specific format or structure.

Message formats depend on the type of messageand the channel that is used to deliver the message.

The process of placing one message format (theletter) inside another message format (theenvelope) is called encapsulation.

De-encapsulation occurs when the process isreversed by the recipient and the letter is removedfrom the envelope.


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Message Formatting

Each computer message is encapsulated in aspecific format, called a frame, before it is sent overthe network.

A frame acts like an envelope; it provides theaddress of the intended destination and the addressof the source host.


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Explain the concept of message formatting andencapsulation


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Explain that messages have size restrictions dependingon the channel used


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Message size

An individual conversation may be made up of manysmaller sentences to ensure that each part of themessage is received and understood.

Likewise, when a long message is sent from onehost to another over a network, it is necessary tobreak the message into smaller pieces.

The rules that govern the size of the pieces, or

frames, communicated across the network are verystrict. They can also be different, depending on thechannel used. Frames that are too long or too shortare not delivered.


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Timing and Access methods

Explain the concept of timing and access methods inrelation to human communication

Access Method

Access Method determines when someone isable to send a message. These timing rules arebased on the environment.

Therefore , it is necessary for computers todefine an access method. Hosts on a networkneed an access method to know when to beginsending messages and how to respond whenerrors occur.


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Timing and Access methods

Flow Control

Timing also effects how much information can besent and the speed that it can be delivered.

In network communication, a sending host can

transmit messages at a faster rate than thedestination host can receive and process. Sourceand destination hosts use flow control to negotiatecorrect timing for successful communication.

Response Timeout

Hosts on the network have rules that specify howlong to wait for responses and what action to takeif a response timeout occurs.


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Explain standard message patterns in relation tohuman communication

Unicast

Multicast

Broadcast


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Message Patterns

A one-to-one message pattern is referred to as aunicast, meaning that there is only a single destinationfor the message.

When a host needs to send messages using a one-to-

many pattern, it is referred to as a multicast. Multicastingis the delivery of the same message to a group of hostdestinations simultaneously.

If all hosts on the network need to receive the messageat the same time, a broadcast is used. Broadcastingrepresents a one-to-all message pattern.

Additionally, hosts have requirements for acknowledgedversus unacknowledged messages.


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Relate human communications concepts of messages,unit sizes, timing, encapsulation, encoding andstandard message patterns to the term protocol .


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Protocols and Importance

All communication, both human and computer, isgoverned by pre-established rules, or protocols.These protocols are determined by the characteristicsof the source, channel and destination.

Protocols are especially important on a local network.In a wired environment, a local network is defined asan area where all hosts must "speak the samelanguage" or in computer terms "share a common

protocol".


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Protocols and Importance

The most common set of protocols used on localwired networks is Ethernet.

The Ethernet protocol defines many aspects ofcommunication over the local network, including:

message format, message size, timing, encoding,and message patterns.


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Importance of standardization

In the early days of networking, each vendor used their

own, proprietary methods of interconnecting networkdevices and networking protocols. Equipment from onevendor could not communicate with equipment fromanother.

Standards are beneficial to networking in many ways:

Facilitate design

Simplify product development

Promote competitionProvide consistent interconnections

Facilitate training

Provide more vendor choices for customers


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Protocols

There is no official local networking standard protocol,but over time, one technology, Ethernet, has becomemore common than the others. It has become a defacto standard.

The committee responsible for the Ethernet standardsis 802.3.

Since the creation of Ethernet in 1973, standards have

evolved for specifying faster and more flexible versionsof the technology. This ability for Ethernet to improveover time is one of the main reasons that it hasbecome so popular.


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Communication Across a Local EthernetNetwork

Physical addressing identifies Source, Destination andChannel on an Ethernet Network


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Physical Addressing

All communication requires a way to identify thesource and destination.

On Ethernet networks, a method exists for identifyingsource and destination hosts. Each host connected

to an Ethernet network is assigned a physicaladdress which serves to identify the host on thenetwork.

Every Ethernet network interface has a physicaladdress assigned to it when it is manufactured. Thisaddress is known as the Media Access Control(MAC) Address. The MAC address identifies eachsource and destination host on the network.


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Describe some of the basic characteristics of Ethernetfor communicating across the channel


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Ethernet Communication

The Ethernet protocol standards define many aspectsof network communication including frame format,frame size, timing and encoding.

When messages are sent between hosts on an

Ethernet network, the hosts format the messages intothe frame layout that is specified by the standards.

Frames are also referred to as Protocol Data Units(PDUs).


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Ethernet Communication

The format for Ethernet frames specifies the location ofthe destination and source MAC addresses, andadditional information including:

Preamble for sequencing and timing

Start of frame delimiter

Length and type of frame

Frame check sequence to detect transmission

errors.


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Describe the need for a hierarchical design in anEthernet Network


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Ethernet Network hierarchical design

On an Ethernet network, the host MAC address issimilar to a person's name.

A MAC address indicates the individual identityof a specific host, but it does not indicate where

on the network the host is located. If all hosts on the Internet (over 400 million of them)

were each identified by only their unique MACaddress, imagine how difficult it would be to locate

a single one.


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Ethernet Network hierarchical design

Ethernet technology generates a large amount ofbroadcast traffic in order for hosts to communicate.

Broadcasts are sent to all hosts within a singlenetwork

Broadcasts consume bandwidth and slow networkperformance. Imagine what would happen if themillions of hosts attached to the Internet were all inone Ethernet network and were using broadcasts!

It is better to divide larger networks into smaller,more manageable pieces and one way to dividelarger networks is to use a hierarchical designmodel.


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Hierarchical design

Hierarchical design is used to group devices intomultiple networks organized in a layered approach, thisallows local traffic to remain local. Only traffic that isdestined for other networks is moved to a higher layer.

It provides increased efficiency, optimization offunction, and increased speed.

The hierarchical design has three basic layers:

Access Layer - to provide connections to hosts in a localEthernet network.

Distribution Layer - to interconnect the smaller local networks.

Core Layer - a high-speed connection between distributionlayer devices.


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Explain the purpose of a logical network address as thelocation of a host on a Network (source anddestination)


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Logical addressing With the hierarchical design, there is a need for a logical

addressing scheme that can identify the location of a host.

This is the Internet Protocol (IP) addressing scheme.

On a host, the MAC address does not change; it is

physically assigned to the host NIC and is known as thephysical address. The physical address remains the sameregardless of where the host is placed on the network.

The IP address is similar to the address of a person. It isknown as a logical address because it is assignedlogically based on where the host is located. The IPaddress, or network address, is assigned to each host bya network administrator based on the local network.


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IP addresses

IP addresses contain two parts.

One part identifies the local network. Thenetwork portion of the IP address will be thesame for all hosts connected to the same localnetwork.

The second part of the IP address identifies theindividual host. Within the same local network, thehost portion of the IP address is unique to eachhost.


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Access Layer Devices and CommunicationMethods

Describe the Purpose of the Access Layer and how itis used within an Ethernet Network


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Access Layer

IP traffic is managed based on the characteristics anddevices associated with each of the three layers:Access, Distribution and Core. The IP address is usedto determine if traffic should remain local or be movedup through the layers of the hierarchical network.

Access Layer

The Access Layer provides a connection point for enduser devices to the network and allows multiple hosts to

connect to other hosts through a network device, usuallya hub or switch.

The Access Layer is the most basic level of the network.It is the part of the network in which people gain access toother hosts and to shared files and printers


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Describe the function of a Hub and how it operateswithin an Ethernet Network


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Function of Hubs

A hub is one type of networking device that is installedat the Access Layer of an Ethernet network.

Hubs are simple multiple port devices that are used toconnect hosts to the network. They do not have the

necessary electronics to decode the messages sentbetween hosts on the network, therefore they cannotdetermine which host should get any particularmessage.

A hub simply accepts electronic signals from one portand regenerates (or repeats) the same message out allof the other ports.


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Function of Hubs

A NIC on a host accepts messages only addressed to thecorrect MAC address. Hosts ignore messages that are notaddressed to them.

Only one message can be sent through an Ethernet hub at

a time. It is possible for two or more hosts to attempt tosend a message at the same time, if this happens, theelectronic signals that make up the messages collide witheach other at the hub.

A collision causes the messages to become garbled andunreadable by the hosts. The area of the network where ahost can receive a garbled message resulting from acollision is known as a collision domain.

It is necessary to limit the size of a collision domain.


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Describe the function of switches and how they areused in an Ethernet network


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Function of switches

An Ethernet switch is a device that is used at theAccess Layer. A switch connects multiple hosts to thenetwork, but unlike a hub, a switch can forward amessage to a specific host.

When a host sends a message to another host on theswitch, the switch accepts and decodes the frames toread the physical (MAC) address portion of themessage.

A table in the switch, called a MAC address table,contains a list of all of the active ports and the hostMAC addresses that are attached to them. When amessage is sent between hosts, the switch checks to

see if the destination MAC address is in the table.


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Function of switches

The MAC address table is dynamically updatedeach time a new source MAC address is read bythe switch. In this way, a switch quickly learns theMAC addresses of all attached hosts.

How does it learn the addresses? A switch buildsthe MAC address table by examining the sourceMAC address of each frame that is sent betweenhosts. When a new host sends a message or

responds to a flooded message, the switchimmediately learns its MAC address and the port towhich it is connected.


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Broadcast Domains and broadcasts using hubs andswitches


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Broadcast Messaging

When hosts are connected using either a hub or aswitch, a single local network is created. Within thelocal network it is often necessary for one host to beable to send messages to all the other hosts at thesame time.

This can be done using a message known as abroadcast.

Remember a message can only contain onedestination MAC address. So, how is it possible for a

host to contact every other host on the local networkwithout sending out a separate message to eachindividual MAC?


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Broadcast Messaging

To solve this problem, broadcast messages are sent toa unique MAC address that is recognized by all hosts.This broadcast MAC address is actually a 48-bitaddress made up of all ones.

The broadcast MAC address in hexadecimal notation isFFFF.FFFF.FFFF. Each F in the hexadecimal notationrepresents four ones in the binary address.

When a host sends a broadcast message, hubs andswitches forward the message to every connected host

within the same local network. For this reason, a localnetwork is also referred to as a broadcast domain.


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MAC and IP addresses

On a local Ethernet network, a NIC only accepts aframe if the destination address is either the broadcastMAC address, or corresponds to the MAC address ofthe NIC, yet most network applications, however, relyon the logical destination IP address to identify the

location of the servers and clients.

If a sending host only has the logical IP address of thedestination host? How does the sending host determinewhat destination MAC address to place within theframe?

The sending host can use an IP protocol called addressresolution protocol (ARP) to discover the MAC address

of any host on the same local network


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Address Resolution Protocol (ARP)

ARP uses a three step process to discover andstore the MAC address of a host on the localnetwork

1. The sending host creates and sends a frame

addressed to a broadcast MAC address.Contained in the frame is a message with the IPaddress of the intended destination host.

2. Each host on the network receives the broadcast

frame and compares the IP address inside themessage with its configured IP address. Thehost with the matching IP address sends itsMAC address back to the original sending host.


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Address Resolution Protocol (ARP)

3. The sending host receives the message andstores the MAC address and IP addressinformation in a table called an ARP table.

Once the sending host has the MAC address of the

destination host in its ARP table, it can send framesdirectly to the destination without doing an ARPrequest.


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Distribution Layer Devices andCommunication Methods

Describe the reasons for expanding your network with adistribution layer


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Distribution Layer

It is often necessary to divide one local network intomultiple Access Layer networks as the network grows.There are many ways to divide networks based ondifferent criteria, including:

Physical location

Logical function

Security requirements

Application requirements

The Distribution Layer connects these independentlocal networks and controls the traffic flowing betweenthem, therefore, It is responsible for ensuring thattraffic between hosts on the local network stays local.


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Describe the function of routers and how they are usedin the network


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Routers

A router is a networking device that connects a local

network to other local networks.

Routers, like switches, are able to decode and read themessages that are sent to them. Unlike switches, whichonly decode (unencapsulate) the frame containing theMAC address information, routers decode the packetthat is encapsulated within the frame.

The packet format contains the IP addresses of the

destination and source hosts, as well as the messagedata being sent between them. The router reads thenetwork portion of the destination IP address and usesit to find which one of the attached networks is the bestway to forward the message to the destination.


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Routers How does the router determine what path to send the

message to get to the destination network?Each port, or interface, on a router connects to adifferent local network. Every router contains a table ofall locally-connected networks and the interfaces thatconnect to them called a Routing table. It containsinformation about the routes, or paths, that the routeruses to reach other remote networks that are not locallyattached.

When a router receives a frame, it decodes the frame

to get to the packet containing the destination IPaddress. It matches the address of the destination to allof the networks that are contained in the routing table.

The process of forwarding the packets toward theirdestination network is called routing.


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Explain the concept of the default gateway


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Default Gateway The method that a host uses to send messages to a

destination on a remote network differs from the way ahost sends messages on the same local network. Whena host needs to send a message to another host locatedon the same network, it will forward the message

directly. When a host needs to send a message to a remote

network, it must use the router. The host includes the IPaddress of the destination host within the packet just likebefore. However, when it encapsulates the packet into aframe, it uses the MAC address of the router as thedestination for the frame. In this way, the router willreceive and accept the frame based on the MACaddress.


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Default Gateway How does the source host determine the MAC address of the

router?

A host is given the IP address of the router throughthe default gateway address configured in its TCP/IPsettings.

The default gateway address is the address of therouter interface connected to the same local networkas the source host. All hosts on the local network usethe default gateway address to send messages to therouter. Once the host knows the default gateway IPaddress, it can use ARP to determine the MACaddress. The MAC address of the router is thenplaced in the frame, destined for another network.


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Describe how the router keeps tract of multiplenetworks using routing and ARP tables


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Routing and ARP tables

Routers move information between local and remotenetworks, therefore, routers must use both ARP androuting tables to store information.

Routing tables are not concerned with the addressesof individual hosts therefore they contain theaddresses of networks and the best path to reachthose networks.

Entries can be made to the routing table in two ways:dynamically updated by information received fromother routers in the network, or manually entered by anetwork administrator.


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Routing and ARP tables

A router forwards a frame to one of two places: adirectly connected network containing the actualdestination host, or to another router on the path toreach the destination host. When a router

encapsulates the frame to forward it out of an Ethernetinterface, it must include a destination MAC address.

Routers obtain MAC addresses from ARP tables.

Each router interface is part of the local network towhich it is attached and maintains its own ARP tablefor that network. The ARP tables contain the MACaddresses and IP addresses of all of the individualhosts on that network.


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Define the term local area network (LAN)


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Local Area Network (LAN)

The term Local Area Network (LAN) refers to a localnetwork, or a group of interconnected local networksthat are under the same administrative control.

LANs typically use Ethernet or wireless protocols, and

they support high data rates. The term Intranet is often used to refer to a private

LAN that belongs to an organization, and is designedto be accessible only by the organization's members,

employees, or others with authorization.


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Differentiate between implications of adding hosts toMy local network vs. adding to a remote network


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Hosts on a local or Remote network

Placing all hosts on a single local network allows them

to be seen by all other hosts. This is because there isone broadcast domain and hosts use ARP to find eachother.

In a simple network design it may be beneficial to keepall hosts within a single local network. However, asnetworks grow in size, increased traffic will decreasenetwork performance and speed. In this case, it may bebeneficial to move some hosts onto a remote network.

Placing additional hosts on a remote network willdecrease the impact of traffic demands. However, hostson one network will not be able to communicate withhosts on the other without the use of routing.


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Learn to Use Packet Tracer


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Plan, Implement and Verify a Local Network

Plan and document the building of a small home orsmall business Ethernet network


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Build a virtual model of their small home or smallbusiness network


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Describe the features of multifunction devices and howthey are used in the network


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Connect and properly document the network installation


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Perform simple workgroup tasks in order to shareresources


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Sharing Resources One of the most common purposes of networking is to share

resources such as files and printers.

By default, Windows XP uses a process known as Simple FileSharing. With Simple File Sharing, specific users and groups cannotbe prevented from accessing shared files.

Simple File Sharing can be disabled so that more specific securityaccess levels can be assigned. When this is done, the followingpermissions are available to assign to resources:

Full Control

Modify

Read & ExecuteList Folder Contents

Read

Write


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Summary Information networks carry data using hosts as clients,

servers, or both.

All computer communication involves a source,destination, and channel.

Rules called protocols govern computercommunications.

Larger networks are divided into smaller, moremanageable ones using a layered hierarchical design.

Each network host needs both a physical MAC addressand a logical IP address.

Good network design requires a network plan.


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Chapter3 Semster One -Discovery