Basic Networkting Conceptes

8/18/2019 Basic Networkting Conceptes

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OSI Model & TCP/IP Protocols

Network Reference Model

A computer network connects two or more devices together to share informationand services. Multiple networks connected together form an internetwork.

Internetworking present challenges that interoperating between dierent typesproducts from dierent manufacturers requires consistent standards. Network reference models were developed to address these challenges. A networkreference model serves as a blueprint, detailing how communication betweennetwork devices should occur.

The two most recognied network reference models are!

The Open Systems Interconnection (OSI) model

The Department of Defense (DoD) model

"ithout the framework that network models provide, all network hardware andsoftware would have been proprietary. #rganiations would have been locked into asingle vendor$s equipment, and global networks like the Internet would have beenimpractical, if not impossible.

%etwork models are organied into layers, with each layer representing a speci&cnetworking function. These functions are controlled by protocols, which arerulesthat govern end'to'end communication between devices.

A network model is not a physical entity ( there is no #)I device. Manufacturers donot always strictly adhere to a reference model$s blueprint, and thus not everyprotocol &ts perfectly within a single layer. )ome protocols can function across

multiple layers.

The OSI Reference Model and Their Function

The Open Systems Interconnection (OSI) modelwas developed by theInternational Organization for Standardization (ISO), and formalied in *+-.It provided the &rst framework governing how information should be sent across anetwork.

The #)I reference model provides a number of bene&ts in understanding hownetworks function, by doing the following!

Reducing compleity! The #)I model breaks network communications

into smaller, simpler parts.

Standardizing interfaces! The #)I model standardies networkcomponents to allow multiple'vendor development and support.

"acilitating modular engineering! The #)I model allows dierent typesof network hardware and software to communicate with one another.


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#nsuring interopera$le tec%nology! The #)I model prevents changesin one layer from aecting the other layers, allowing for quicker development.

&ccelerating e'olution! The #)I model provides for eective updates andimprovements to individual components without aecting other componentsor having to rewrite the entire protocol.

Simplifying teac%ing and learning! The #)I model breaks networkcommunications into smaller components to make learning easier.

The #)I model consists of seven layers, each corresponding to a speci&c networkfunction!

"igure! #)I eference Model

OSI odel *%e +pper ayers (Software ayer)

The top three layers of the #)I model are often referred to as the upper layers.

Also called software layers!

/ayer'0 ' &pplication layer

/ayer'1 ' -resentation layer

/ayer'2 ' Session layer

3rotocols that operate at these layers manage application'level functions , and aregenerally implemented in software.


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The function of the upper layers of the #)I model can be di4cult to visualie. 5pperlayer protocols do not always &t perfectly within a layer, and often function acrossmultiple layers.

OSI odel *%e /ore ayers

The layer no fourth (*ransport ayer) is often referred to as core layer of OSImodel.

OSI odel *%e ower ayers

The bottom three layers of the #)I model are often referred to as the lower layers.Also called hardware layer!

/ayer'6 ( Network layer

/ayer'7 ( Dataink layer

/ayer'* ( -%ysical layer

3rotocols that operate at these layers control the end'to'end transport of databetween devices, and are implemented in both software and hardware.

TCP/IP Suite

The T839I3 suite:whose name is actually a combination of ;ust two individualprotocols, Transmission 8ontrol 3rotocol


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The T839I3 suite was developed at appro>imately the same time as the #)I model./ike the #)I model, the T839I3 suite is a means of organiing components in anorder that re?ects their functions in relation to one another. The components, orlayers, of the T839I3 stack are as follows!

&pplication layer! The application layer provides applications for &le

transfer, network troubleshooting, and Internet activities and supportsnetwork application programming interfaces imum transmission distances, physical connectors, and other similarattributes are de&ned by physical layer speci&cations.

( Data link layer: The data link layer defines how data is formatted for transmission and howaccess to the network is controlled.

TCP/IP Stack vs. the OSI Model@oth the #)I model and the T839I3 stack were developed, by dierent organiations,at appro>imately the same time as a means to organie and communicate thecomponents that guide the transmission of data. The layers of the T839I3 stackcorrespond to the layers of the #)I model!


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igure! #)I and T839I3 Model 8omparison

The T839I3 network access layer roughly corresponds to the #)I physical and

data link layers and is concerned primarily with interfacing with networkhardware and accessing the transmission media.

The T839I3 Internet layer corresponds closely to the network layer of the #)I

model and deals with the addressing of and routing between networkdevices.

The T839I3 transport layer, like the #)I transport layer, provides the means

for multiple host applications to access the network layer, either in a best'eort mode or through a reliable delivery mode.

The T839I3 application layer addresses applications that communicate with

the lower layers and corresponds to the separate application, presentation,and session layers of the #)I model. The additional layers of the #)I modelprovide some additional organiation of features related to applications.

What is protocol?

A protocol is a formal description of a set of rules and conventions that govern howdevices on a network communicate.


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Bave you wondered why dierent devices or application are able to send data toeach otherC or e>ample, you can send a message from your phone to your friendcomputer. The reason is because there devices or applications are using the sameprotocol.

"igure!Devices in %etwork

3rotocols are like the languages in human communication. 3eople who understandthe same languages are able to communicate to each other. )o it is the same as thedevices and applications. Devices and application with the same protocol are able tosend data to each other.

"igure! ules of Buman 8ommunication


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a!er "# $%%lication a!er

Applications provide the means for generating and receiving data that can be

transported on the network. Applications can be a client, a server or both a clientand server at the same time. #ne client application that we normally use is the

internet browser which is used to request and receive webpages from web server.

or web server, it has application that is used to store webpages, and upon request,

its will generate webpage data are sent to the internet browser.

igure! Application layer of both #)I and T839I3 Model

The Application layer is the top layer of both the #)I and T839I3 models. It is thelayer that provides the interface between the applications and networks. "ithoutthe application layer, data are not able to send through networks. or T839I3 model,application layers are usually referred to the combination of application,presentation and session layers of #)I Model.

There are many types of application protocol namely!

*= Byperte>t Transfer 3rotocol


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a!er # Presentation a!er

The 3resentation layer


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"igure! Data Transmission method

The session layer carries out the following tasks.

)tarts and ends a session across a network


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"igure! #)I Transport /ayer

The network layer routes information to its destination, but it cannot guarantee thatthe information arrives in correct order, free of errors, or even that it will arrive atall. The transport layer provides two protocols, 5D3 and T83, which providecommunication services directly to the application process on the host. The KbasicserviceL provided by the transport layer is session multiple>ing, which is performedby both 5D3 and T83. The Kpremium serviceL provided by the transport layer is

ensuring reliable delivery, which is performed only by T83.

The primary duty of the transport layer is the interconnection of applicationsessions to the network layer, which is provided by both 5D3 and T83. If T83 is used,the transport layer has the further responsibilities of establishing end'to'endoperations, segmentation, ?ow control, and applying reliability mechanisms

The *ransport layer (ayer2) does not actually send data, despite its name.Instead, this layer is responsible for the reliable transfer of data, by ensuring thatdata arrives at its destination error'free and in order.

The ma;or functions of Transport layer are given below!

Identifying Ser'ices ultipleing

Deultipleing

Segmentation

Se3uencing

Reassem$ling

#rror /orrection

"low control (or windowing)


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4u5ering

Service Identification

T83 and 5D3 ports identify services that run on a speci&c logical address.

#therwise, there would be no way to distinguish data destined for one service oranother on a device. or e>ample, port numbers allow both a web and email serverto operate simultaneously on the same address.

6ell7nown -orts"ell'known ports are assigned by the IA%A and are numbered 89:; and $elow.

These numbers are assigned to applications that are fundamental to the Internet.

Registered -ortsegistered ports are listed by IA%A and are numbered from 89:2 to 2


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-12 T83 )ecure )MT3


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or e>ample, you enter a 5/ for Oahoo into the address line in the Internet G>plorerwindow, and the Oahoo site corresponding to the 5/ appears. "ith the Oahoo siteopen, you can open the browser again in another window and type in another 5/ample, Hoogle=. Oou can open another browser window and type the 5/ for8isco.com and it will open. Three sites are open using only one I3 connection,because the session layer is sorting the separate requests based on the port

number.

Se*+entation

T83 takes data chunks from the application layers and prepares them for shipmentonto the network. Gach chunk is broken up into smaller segments which will &t thema>imum transmission unit pects the application process togive it data that will work.

Flow Control

If a sender transmits data faster than the receiver can receive it, the receiver willdrop the data, requiring it to be retransmitted. etransmission can waste time andnetwork resources, which are why most ?ow control methods try to ma>imie thetransfer rate while minimiing the requirements to retransmit.

In T83, basic ?ow control is implemented by acknowledgment by the receiver of thereceipt of dataP the sender waits for this acknowledgment before sending the ne>tpart. Bowever, if the round'trip time


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The T839I3 protocol suite incorporates two Transport layer protocols!

*ransmission /ontrol -rotocol (*/-) connection'oriented

+ser Datagram -rotocol (+D-) connectionless

"igure! T83 vs 5D3

The *ransport layer of the #)I model


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The 5D3 header length is always 1- bits. The &eld de&nitions in the 5D3 segment


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)equencing of data packets

Acknowledgement of receipt

Data'recovery features

*/- 1eader

The T83 header supplies information that is speci&c to the T83 protocol. This topicdescribes the components of the T83 header.

"igure! T83 Beader T83 segments are sent using I3 packets. The T83 header follows the I3 header,supplying information speci&c to the T83 protocol. This division of the headersallows host'level protocols other than T83 to e>ist.

*/- Segments #plained

Source -ort A *1'bit &eld that speci&es which port number the data

segment originated from on the source machine.

Destination -ort A *1'bit &eld that speci&es which port number the data

segment is destined for on the receiving machine.

Se3uence Num$er A 67'bit &eld that speci&es which sequence number

the particular segment of information is assigned. The sequence number is

used to number packets of information so that they may be counted on the

receiving side' guaranteeing a successful and complete delivery of

information.

&cknowledgment Num$er A 67 bit &eld that speci&es whether or not a

segment was received correctly. The acknowledgment number is always onehigher than the sequence number, since the receiving computer is e>pecting

the ne>t segment.

Data O5set A -'bit &eld that tells the receiving computer how long the

header is, and where the data actually begins.


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Reser'ed A 1'bit &eld that is reserved for future use. 8urrently this &eld is

represented as all eroes. In the future, it may be likely that T83 will make

use of this space for some reason or another.

+R? A *'bit control ?ag that stands for urgent. If the value is *, the

information is urgent and should be dealt with accordingly.

&/7 A *'bit control ?ag that, if set to *, indicates that the Acknowledgment

%umber &eld is signi&cant.

-S1 A *'bit control ?ag that stands for push. If set to *, all the information

sent so far is sent to the receiving application.

RS* *'bit control ?ag that stands for reset. If set to *, the connection is

reset.

S@N A *'bit control ?ag that stands for synchronie. If set to *, then a

sequence of numbers will be used to sort information packets. This also

marks the beginning of a connection.

"IN A *'bit control ?ag that stands for &nished. It also closes a connection,and indicates that there is no more data to be sent.

6indow A *1'bit &eld that is used for ?ow control. It indicates that a range

of sequence numbers past the last acknowledged sequence number do not

require further acknowledgment.

/%ecksum A *1'bit &eld that checks segment integrity. A calculation is

done on both the sending and receiving computer. This calculation is based

on the segment$s information, so we can use it to check and see if the packet

is indeed the same being received as it was sent.

+rgent -ointer A *1'bit &eld that indicates the beginning of urgent

information. )peci&cally, it points to a sequence number.

Options A &eld that may be used to set various optional settings.

-adding A spacer used to oset the #ptions &eld. )ince every row must

equal 67 bits, the 3adding &eld must add to the #ptions &eld to equal 67 bits.

)ince the #ptions &eld may vary, variable 3adding is needed.

Data The actual data being sent to the recipient computer.

Co+%arison of TCP versus ,-P

*/- +D-

Transmission 8ontrol 3rotocol 5ser Datagram 3rotocol

8onnection'oriented 8onnection'less oriented


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Huaranteed Delivery %o Huaranteed Delivery

)ends Acknowledgments Does not send Acknowledgments

eliable, but slower 5nreliable, but faster

)egments and )equences Data Does %#T segment9sequence data

low 8ontrol %o low 8ontrol

3erforms 88 on data 3erforms 88 on data

3rotocol %o is 1 3rotocol %o is *0

Gg! BTT3, T3, )MT3 Gg! D%), DB83, TT3

The Network a!er

The Network layer (ayer;) controls internetwork communication, and has two

key responsibilities!

ogical addressing ( provides a unique address that identi&es both

the host, and the network that host e>ists on. Routing ( determines the best path to a particular destination

network, and then routes data accordingly.

3rotocols implemented at the %etwork9Internet layer include!

Internet 3rotocol version -


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The second'lowest layer


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a!er 1# Ph!sical a!er

The lowest layer of the #)I eference Model is layer *, the physical layerP it iscommonly abbreviated K3BOL. The physical layer is special compared to the otherlayers of the model, because it is the only one where data is physically moved

across the network interface. All of the other layers perform useful functions tocreate messages to be sent, but they must all be transmitted down the protocolstack to the physical layer, where they are actually sent out over the network

"igure! #)I 3hysical /ayer-%ysical ayer "unctions

The following are the main responsibilities of the physical layer in the #)I eferenceModel!

o DeAnition of 1ardware SpeciAcations! The details of operation of cables,connectors, wireless radio transceivers, network interface cards and otherhardware devices are generally a function of the physical layer


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igure! 8ommunication 3rocess in #)I Model

"igure! 8ommunication 3rocess in T839I3 Model


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2thernet Technolo*!

Introduction

In todayQs business world, reliable and e4cient access to information has becomean important asset in the quest to achieve a competitive advantage. ile cabinetsand mountains of papers have given way to computers that store and manageinformation electronically.

8omputer networking technologies are the glue that binds these elements together.%etworking allows one computer to send information to and receive informationfrom another. "e can classify network technologies as belonging to one of two basicgroups. /ocal area network


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"igure! )mall Token ing %etwork

edia &/et%od

Signal-ropagation

et%od

Speed

*opologies

aimum/onnecti

ons

*wistedpair

Tokenpassing

orwarded fromdevice to device


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"igure! iber Distributed Data Interface pensive than twisted'pair cable. @ecause most iber Distributed

Data Interface


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et%od -ropagationet%od

ed es /onnections

"i$eroptic

Tokenpassing

orwarded fromdevice to device am, but you should be aware of

the basics. G>pect to see limited information on iber optics, DDI, and token

passing, but study more for the E7.6 standards and how Token ing networks work.

2thernet Technolo*!

#t%ernet is a family of technologies that provides data'link and physicalspeci&cations for controlling access to a shared network medium. It has emerged asthe dominant technology used in /A% networking.

Gthernet was originally developed by Fero> in the *+0Es, and operated at 7.+-Mbps. The technology was standardied as #t%ernet Bersion 8 by a consortium of threecompanies ' DG8, Intel, and Fero>, collectively referred to as DIC and furtherre&ned as #t%ernet II in *+7.

In the mid *+Es, the Institute of #lectrical and #lectronic #ngineers(I###)published a formal standard for Gthernet, de&ned as the I### =9:.; standards. Theoriginal E7.6 Gthernet operated at *EMbps, and successfully supplanted competing/A% technologies, such as Token ing.

Gthernet has several bene&ts over other /A% technologies! )imple to install and manage

Ine>pensive

le>ible and scalable

Gasy to interoperate between vendors

5p until two years ago, Gthernet networks were the most common networks on the

planet. "ith the boom of the Internet, other network types have grown rapidly, but

Gthernet still remains the easiest and most cost'eective networking topology.

Gthernet is usually installed as a bus or star architecture. The bus architecture is the

easiest to set up, as the wire runs from computer to computer and is terminated at

each end. The star architecture requires more cable and more work, but is easier totroubleshoot. If a break occurs in the cable of a bus architecture, the network fails. If

a break occurs in the cable of a star architecture, only the network segment that

contains that break fails.

Gthernet is a passive network. All network tra4c is delivered node'to'node. That

means the computers themselves transfer all the data, not hubs or routers. They

are also called 8)MA98D networks, or 8arrier )ense Multiple Access with 8ollision


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Detection. That means that two nodes cannot transmit at the same time. If two

nodes transmit data at the same time, the data collides and fails to transfer.

Therefore, Gthernet networks require the node to check for network activity before

sending data.

"igure! #t%ernet *ec%nology

I222 340 Standards

Standard Description

=9:.9 )G8'IGGG )tandards for /ocal and Metropolitan Area%etworks! #verview S Architecture

=9:.8 Bigh /evel Interface


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=9:.8> @roadband "ireless Access isting technologies. This layer provides versatility inservices to thenetwork layer protocols that are above it, while communicatingeectively with the variety ofMA8 and /ayer * technologies below it. The //8, as asublayer, participates in theencapsulation process.

An //8 header tells the data link layer what to do with a packet when it receives aframe. ore>ample, a host receives a frame and then looks in the frame header tounderstand that thepacket is destined for the I3 protocol at the network layer.

&/ Su$layer

The MA8 sublayer deals with physical media access. The IGGG E7.6 MA8speci&cation de&nes MA8 addresses, which uniquely identify multiple devices at thedata link layer. The MA8 sublayer maintains a table of MA8 addresses


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The Role of CSM$/C- in 2thernet

Gthernet signals are transmitted to every host connected to the /A%, using a specialset of rules to determine which station can KtalkL at any particular time. This topicdescribes that set of rules.

"igure!8arrier )ense Multiple Access 8ollision Detection


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use. If it is, the8)MA98D stations wait. If the network is not in use, the stationstransmit. A collision occurswhen two stations listen for network tra4c, hear none,and transmit simultaneously


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"igure! MA8 Address adecimal format that is actually burned intothe %I8. This address is referred to as the MA8 address and it is e>pressed as groupsof he>adecimal digits that are organied in pairs or quads, such as the following!

99!99!9c!2;!:e!9= or 9999!9c2;!:e9=


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Gach device on a /A% must have a unique MA8 address to participate in thenetwork. The MA8 address identi&es the location of a speci&c computer on a /A%.5nlike other kinds of addresses used in networks, the MA8 address should notbechanged unless there is some speci&c need.

Trans+ission Media

S*- and +*-! Similarities

@oth )T3 and 5T3 cables consist of two wires. #ne wire carries an electrical signal.

The other wire is grounded and helps minimie noise. or both )T3 and 5T3, a group

of more than one pairs is often collected into a single cable. Gight'strand and 72'

strand cables are common in communications wiring.

/%aracteristics of +*-

5nshielded twisted pair cable uses an insulator to protect twisted pairs. Although

the protective covering is helpful, it doesnQt qualify as a shield against interference

in the same way as the metallic covering found on )T3 cable. 5T3 cable is generally

cheaper and its transmission speed is faster than that of )T3.

"igure! 5T3 and )T3 8able

/%aracteristics of S*-

)hielded twisted pair cable adds multiple layers of protection from interference. A

metallic shield covers each pair of cables in a given connection. Gach pair of cables

is then placed inside another metallic shield. An additional grounded wire is also

often added to improve the eects of shielding. Although these multiple layers of

protection can greatly bene&t signal clarity, improper grounding of the shields can


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cause the shields to actually pick up unwanted signals and make clarity issues

worse. Installation of )T3 cables requires greater technical knowledge, and the

technology is more e>pensive than 5T3.

The more common transmission media are twisted pair and &ber optics. 8ategories

de&ned under twisted pair support transmission over various distances and datarates. The most common 5T3 cable in the enterprise network are 8ategory 2,

8ategory 2e, 8ategory 1, 8ategory 1a and 8ategory 0, which supports *E Mbps to

*E Hbps rates.

"igure! Gthernet 8able

#t%ernet o'er *wisted-air /a$ling

Gthernet technology standards are the responsibility of the IGGG E7.6 working

group. This group is responsible for evaluating and eventually approving Gthernet

speci&cations as new Gthernet technologies are developed such as Higabit and

*EHigabit Gthernet. Although this group de&nes the standards for Gthernet, it looks

to other established standards organiations to de&ne the speci&cations for physical

cabling and connectors. These organiations include the American %ational

)tandards Institute


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• 8ategory 7

• 8ategory 6

• 8ategory 2

• 8ategory 2e

• 8ategory 1

• 8ategory 1a

• 8ategory 0

/ategory 8

8AT *, or 8ategory *, cable is best suited for telephone communications. It is not

suitable for data transmission or Gthernet data work usage. It is mostly used for on'

premises wiring.

/ategory :

8ategory 7, or 8AT 7, cables are capable of data transmission of up to - Mbps. It is a

/evel 7 cable and was used on A8net and token ring networks sometime ago. /ike

8AT *, 8AT 7 is not suitable for Gthernet data work usage.

/at ; /a$le

8ategory 6 8able, or 8at 6, is an older iteration of Gthernet cables that is limited to

*E Mbps


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8at 2 was the widely used successor to 8at 6 cable. 8at 2 allows for *E9*EE Mbps.

Gthernet connections. The way the cable was wrapped changed from 8at 6 to 8at 2

to not allow as many twists per foot. This reduced the amount of interference.

8ategory 2 is capable of handling transmissions up to *EE MB

/at 0e /a$le

8at 2e is an enhanced version of 8at 2 cabling. 8at 2e will allow for *E9*EE9*,EEE

Mbps. Gthernet connections. Higabit Gthernet


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/at ;Data networks utiliing frequencies up to *1 MB, popular for *EMbit9s Gthernet networks

/at 2 3rovides performance of up to 7E MB, frequently used on *1Mbit9s token ring networks

/at 03rovides performance of up to *EE MB, frequently used on *EEMbit9s Gthernet networksP may be unsuitable for *EEE@A)G'Tgigabit Gthernet

/at 0e3rovides performance of up to *EE MB, frequently used forboth *EE Mbit9s and *EEE@A)G'T gigabit ethernet networks

/at >3rovides performance of up to 72E MB a uture speci&cation for *E Hbit9s applications

/at Designed for transmission at frequencies up to 1EE MB. uturespeci&cation for *E Hbit9s applications

*a$le! 5nshielded Twisted 3air tra pairs. The e>tra pairs are either

unused, con&gured to carry telephone signals, or used to supply power to remote

network devices using 3ower over Gthernet. Dierent grades are available, such as

8at 2 which is used for *E9*EEMb Gthernet connections, and 8at 2e, which can

also handle Higabit Gthernet speeds. Oou can &nd the grade by looking at theprinted markings on the cable, with most cables conforming to the 8at 2e

speci&cation.

Strai*ht6thru7 Crossover7 and Rollover Ca5les

http://en.wikipedia.org/wiki/Category_3_cablehttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Category_4_cablehttp://en.wikipedia.org/wiki/Token_ringhttp://en.wikipedia.org/wiki/Category_5_cablehttp://en.wikipedia.org/wiki/Category_5_cable#Category_5ehttp://en.wikipedia.org/wiki/Category_6_cablehttp://en.wikipedia.org/wiki/Category_6_cable#Category_6ahttp://en.wikipedia.org/wiki/Category_7_cablehttp://en.wikipedia.org/wiki/Category_3_cablehttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Category_4_cablehttp://en.wikipedia.org/wiki/Token_ringhttp://en.wikipedia.org/wiki/Category_5_cablehttp://en.wikipedia.org/wiki/Category_5_cable#Category_5ehttp://en.wikipedia.org/wiki/Category_6_cablehttp://en.wikipedia.org/wiki/Category_6_cable#Category_6ahttp://en.wikipedia.org/wiki/Category_7_cable


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There are several IGGG E7.6 standards that de&ne Gthernet transfer over 8ategory

2


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*. 8onnecting a router to a hub7. 8onnecting a router to a )witch6. 8onnecting a computer to a switch-. 8onnecting a computer to a hub

2. 8onnecting a )witch to hub

6it% 0>=&!

-in 8 6%iteEOrange

-in : Orange 6%ite

-in ; 6%iteE?reen

3in - ( @lue9"hite

-in 0 6%iteE4lue

3in 1 ( Hreen9"hite

3in 0 ( "hite9@rown

3in ( @rown9"hite

6it% 0>=4!

3in * ( "hite9Hreen

3in 7 ( Hreen9"hite

3in 6 ( "hite9#range

3in - ( @lue9"hite

3in 2 ( "hite9@lue

3in 1 ( #range9"hite


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"igure! )traight'Through 8able 8olor 8ode

The above e>ample of a straight'thru pinout is using the 21A921@ standards but

we could have ;ust as easily used the 21A921@ standards on both ends. Actuallymost of the industry uses 21@ although the military uses 21A. It doesn$t matter

as long as both ends have the same pinout. Oou could even make your own color

order if you choose but this is certainly not recommended.

Most networking equipment nowadays support automatic medium'dependent

interface crossover cept that they have

pairs of wires that crisscross. This allows for two devices to communicate at the

same time. 5nlike straight'through cables, we use crossover cables to connect

likedevices


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*. 8onnecting a computer to a router7. 8onnecting a computer to a computer6. 8onnecting a router to a router-. 8onnecting a switch to a switch

2. 8onnecting a hub to a hub

A cross over cable is con&gured with - of the wires in the same order on each end.

The other four wires are crossed


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"igure! 8ross 8able 8olor 8ode


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"igure! 8at2 8able Termination

Rollover ca5le

ollover cables, like other cabling types, got their name from how they are wired.ollover cables essentially have one end of the cable wired e>actly opposite fromthe other. This essentially Krolls overLthe wires' but why would we need to do such a thingC ollover cables, also called

Oost cables, usually connect a device to a router or switch$s console port. This allowsa programmer to make a connection to the router or switch, and program it as

needed.

"igure! ollover 8able 8olor 8ode

Fi5er O%tic Ca5lin*iber #ptics, also called optical &bers, are microscopic strands of very pure glass

with about the same diameter of a human hair. Thousands of these optical &bers are

arranged in bundles in optical cables and are used to transmit light signals over

long distances. The bundles are protected by a ;acket, which is the cableQs outer

covering.

The single optical &ber consists of the core which is the thin glass center of the &ber

where the light travels, the outer optical material that surrounds the core and

re?ects the light back into it is the cladding, and the plastic coating that protects

the &ber from moisture and damage is the buer coating.

)ingle'mode and multi'mode are the two types of optical &bers. The single'mode,

used for long distances, has small cores and transmits infrared laser light. The


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multi'mode, normally used for short distances, has large cores and transmits

infrared light.

"igure! #ptical iber 8ore and 8lading


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"igure! )ingle mode vs Multimode iber

• If the diameter of the core of the &ber is large enough so that there are manypaths that light can take through the &ber, the &ber is called KmultimodeL&ber.

• )ingle'mode &ber has a much smaller core that only allows light rays to travelalong one mode inside the &ber.

"igure! Multimode vs )ingle Mode 8ore Diameter

Trans+ittin*/Receivin* -evices


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"igure! #ptical iber Transmission system

"igure! #ptical iber 8onnector

Power over 2thernet Po2

-ower o'er #t%ernet (-o#) allows both data and power to be sent across thesame twisted'pair cable, eliminating the need to provide separate powerconnections. This is especially useful in areas where installing separate power mightbe e>pensive or di4cult.

3oG can be used to power many devices, including!

Joice over I3


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referred to as p%antom power. Higabit Gthernet requires the phantom powermethod, as it uses all eight wires in a twisted'pair cable.

The device that providespower is referred to as the -ower Source #3uipment(-S#). 3oG can be supplied using an eternal power inFector,though eachpowered device requires a separate power in;ector.

More commonly, an =9:.;afcompliant network switc% is used to providepowerto many devices simultaneously. The power supplies in the switchmust be largeenough to support both the switch itself, and the devices it ispowering.

"igure! 3ower over Gthernet G>ample

2thernet $N Se*+ents

)egment length is an important consideration when using Gthernet technology in a/A%. This topic describes segments and their limitations.

"igure! )egment

A segment is a network connection made by a single unbroken network cable.Gthernet cables and segments can span only a limited physical distance, beyondwhich transmissions will become degraded because of line noise, reduced signalstrength, and failure to follow the 8arrier )ense Multiple Access with 8ollisionDetection imum segment length.


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Any device that operates at /ayer * of the #pen )ystems Interconnection tend segments. This topic describeshow adding repeaters or hubs can overcome the distance limitation in an Gthernet/A%.

"igure! /A% G>tended with Bub

A repeater is a physical'layer device that takes a signal from a device on thenetwork and actsas an ampli&er. Adding repeaters to a network e>tends thesegments of the network so data can be communicated successfully over longerdistances. There are, however, limits on the numberof repeaters that can be addedto a network.

A hub, which also operates at the physical layer, is similar to a repeater. "hen ahub receives atransmission signal, it ampli&es the signal and retransmits it. 5nlike arepeater, however, a hubcan have multiple ports to connect to a number of networkdevicesP therefore, a hub retransmitsthe signal to every port to which a workstationor server is connected. Bubs do not read any of the data passing through them, and

they are not aware of the source or destination of the frame.Gssentially, a hubsimply receives incoming bits, ampli&es the electrical signal, and transmitsthesebits through all of its ports to the other devices on the network.

A hub e>tends, but does not terminate, an Gthernet /A%. The bandwidth limitationof a shared technology remains. Although each device has its own cable thatconnects into the hub, all users of a given Gthernet segment compete for the sameamount of bandwidth.

Collision -o+ains


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"igure! 8ollision Domain

In e>panding an Gthernet /A% to accommodate more users with more bandwidthrequirements, you can create separate physical network segments, called collision

domains, so collisions are limited to a domain rather than the entire network. Thistopic describes collision domains.

In traditional Gthernet segments, the network devices compete for the samebandwidth, withonly one device being able to transmit data at a time. The networksegments that share the samebandwidth are known as collision domains, becausewhen two or more devices within thatsegment try to communicate at the sametime, collisions may occur.

It is possible, however, to use other network devices operating at /ayer 7 and aboveof the #)Imodel to divide a network into segments and reduce the number of devices that are competingfor bandwidth. Gach new segment, then, results in a new

collision domain. More bandwidth isavailable to the devices on a segment, andcollisions in one collision domain do not interferewith the working of the othersegments.

The broadcast domain is another key concept. The &ltering of frames based on theirMediaAccess 8ontrol tend to &lteringbroadcastframes. @y their very nature, broadcast frames mustbe forwardedPtherefore, a collection o&nterconnected switches forms a single broadcast domain. Ittakes a /ayer 6 entity, such as arouter, to terminate a /ayer 7 broadcast domain.

IP $ddressin* and Su5nettin*

Introduction

There are various aspects to I3 addressing, including calculations for constructingan I3 address, classes of I3 addresses designated for speci&c routing purposes, andpublic versus private I3 addresses. There are also two dierent types of I3addresses! I3 version -


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currently the most common, but the *7'bit I3v1 address is also in use, and willprobably become the more common address type over time. This lesson describes67'bit I3v- addressing, e>cept where I3v1 is e>plicitly identi&ed.

An I3 address is a numeric identi&er assigned to each machine on an I3 network. Itdesignates the speci&c location of a device on the network.

Ter+inolo*!

• 4it A bit is one digit, either a * or a E.

• 4yte A byte is bits.

• Octet An octet, made up of bits, is ;ust an ordinary 'bit binary number.

• Network address This is the designation used in routing to send packetsto a remote network ' for e>ample, *E.E.E.E, *07.*1.E.E, and *+7.*1.*.E.

• 4roadcast address The address used by applications and hosts to sendinformation to all nodes on a network is called the broadcast address.G>amples include 722.722.722.722, which is all networks, all nodesP*07.*1.722.722, which is all subnets and hosts on network *07.*1.E.EP and*E.722.722.722, which broadcasts to all subnets and hosts on network*E.E.E.E.

An I3 address consists of 67 bits of information. These bits are divided into foursections, referred to as octets or bytes, each containing * byte


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I3F was predominantly used on%ovell networks, but is mostly deprecated. I- is themost widely'usedlogical address today.

Internet Protocol IP

I- was developed by the Department of Defense =. This guide willconcentrate on I3v-, and I3v1 will be covered e>tensively in a separate guide.

igure! I-'2 1eader

IP $ddressin* Rules

It is a 67 bit dotted decimal number with - octets, each octet of bits.

It is divided into two portions, %etwork and host portion

I3 addresses must be unique in a network

67 bits divided into - octets

Gach octet has a decimal value range of E to 722.

The network portion cannot be all E$s nor all *$s

The &rst octet cannot be *70


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The original designers of T839I3 de&ned an I3 address as a 67'bit number and

this system, now named Internet 3rotocol Jersion - ample!

80=.=9.8>2.;An I3 address is separated into four octets!

"irst Octet Second Octet *%ird Octet "ourt% Octet *2 .E .*1- .6

Gach octet is bits long, resulting in a ;:$it I- address. A computerunderstandsan I3 address in its binary formP the above address in binarywould look as follows!

"irst Octet Second Octet *%ird Octet "ourt% Octet

*EE****E .E*E*EEEE .*E*EE*EE .

EEEEEE**

IP $ddress Classes

To accommodate dierent sies of networks and aid in classifying them, I3addresses are divided into categories called classes. This topic describes the I3address classes and the structure of the I3 addresses within them.

Assigning I3 addresses to classes is known as classfull addressing. The classes weredeterminedduring the early days of the Internet by the Internet Assigned %umbers

Authority


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*a$le! %etwork 3art and Bost 3art of I3v-

Class $ IP addresses

The 8lass A address uses only the &rst octet (= $its) of the ;:$it number toindicate thenetwork address. The remaining three octets of the ;:$it number areused for host addresses.The &rst bit of a /lass & address is always G9.H )ince the&rst bit is a E, the lowest number that can be represented is 99999999 ample of a /lass & address!Address! 1-.67.72-.*EE)ubnet Mask! 722.E.E.E

Class 8 IP addresses

The 8lass @ address uses two of the four octets (8> $its) to indicate the networkaddress. Theremaining two octets specify host addresses. The &rst 7 bits of the &rstoctet of a /lass 4address are always binary *E. )tarting the &rst octet with binary*E ensures that the /lass 4space is separated from the upper levels of the 8lass Aspace. The remaining 1 bits in the &rstoctet may be populated with either *s or Es.

Therefore, the lowest number that can be represented with a 8lass @ address is89999999


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)ubnet Mask! 722.722.722.E

Class - IP addresses

/lass D I3 addresses are known as multicast I3 addresses. Multicasting is atechnique developed to send packets from one device to many other devices,

without any unnecessary packet duplication. In multicasting, one packet is sentfrom a source and is replicated as needed in the network to reach as many end'users as necessary. Oou cannot assign these I3 addresses to your devices.

our left most bits of the left most octet of a /lass D network is reserved as8889. The other 7 bits are used to identify the group of computers the multicastmessage is intended for.

The minimum possible value for the left most octet in binaries is 88899999imum possible value for the leftmost octetis 88898888 ample, the I3address 8:.8>.9.9 is a network address, while 8.88.9 would be a /lass /network. A router uses the network I3 address when it searches its I3 route table forthe destination network location. The decimal numbers that &ll the &rst two octetsin a /lass 4 network address are assigned. The last two octets contain Es becausethose *1 bits are for host numbers and are used for devices that are attached to thenetwork. In the I3 address 8:.8>.9.9, the &rst two octets are reserved for the

network addressP it is never used as an address for any device that is attached to it.An e>ample of an I3 address for a device on the 8:.8>.9.9 network would be8:.8>.8>.8. In this e>ample, 8:.8> is the network address portion and 8>.8 isthe host address portion.

Private vs Pu5lic $ddresses


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The rapid growth of the Internet resulted in a shortage of I3v- addresses.Inresponse, the powers that be designated a speci&c subset of the I3v- addressspace to be pri'ate, to temporarily alleviate this problem.A pu$lic address can be routed on the Internet. Thus, devices that should beInternet accessible


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A local loopback address is used to let the system send a message to itself fortesting. A typical local loopback I3 address is 8:.9.9.8.

$uto confi*uration IP $ddresses

"hen neither a statically nor a dynamically con&gured I3 address is found on

startup, thosehosts supporting I3v- link'local addresses will generate an address inthe8> pre&> range. This address can be used only for local networkconnectivity andoperates with many caveats, one of which is that it will not berouted. Oou will mostly see thisaddress as a failure condition when a 38 fails toobtain an address via DB83.

Network I-

The network portion of an I3 address is also referred to as the network ID, which isimportantbecause most hosts on a network can directly communicate only withdevices in the samenetwork. If the hosts need to communicate with devices thathave interfaces assigned to someother network ID, there must be a network devicethat can route data between the networks.This is true even when the devices sharethe same physical media segment.A network ID enables a router to put a packetonto the appropriate network segment. The hostID helps the router deliver the/ayer 7 frame encapsulating the packet to a speci&c host on thenetwork. As aresult, the I3 address is mapped to the correct MA8 address, which is needed bythe/ayer 7 process on the router to address the frame.

9ost I-

Gach class of a network allows a &>ed number of hosts. In a /lass & network, the&rst octet isassigned to the network, leaving the last three octets to be assigned tohosts. The &rst hostaddress in each network imum number of hosts in a /lass 4network is :8> :, or>0,0;2.In a /lass / network, the &rst three octets areassigned to the network. This leaves the &naloctet to be assigned to hosts, so thema>imum number of hosts is := :, or :02.

:hat is Su5net Mask;

An I3 address has two components, the network part and the host part. eally, I3address is a combination of I3 address and )ubnet mask and the purpose of subnet

mask is to identify which part of an I3 address is the network part and which part isthe host part. )ubnet mask is also a 67 bit number where all the bits of the networkpart are represented as * and all the bits of the host part are represented as E.

If we take an e>ample for a /lass / network, 8=.89.9, the address part andthe subnet mask can be represented as below!

/omponent 4inary Decimal

http://www.omnisecu.com/tcpip/internet-layer-ip-addresses.htmhttp://www.omnisecu.com/tcpip/internet-layer-ip-addresses.htm


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Address 3art **EEEEEE.*E*E*EEE.EEEE*E*E.EEEEEEEE

*+7.*1.*E.E

)ubnet Mask ********.********.********.EEEEEEE 722.722.722.E

*a$le! )ubnet Mask G>ample

or a /lass / I3 address, the &rst three octets are used to represent the %etworkpart and the last octet is used to represent the host part. rom the above table, wecan see all * in the network part and all E in the host part. "hen this subnetmask is converted to a decimal, it will become 722.7222.722.E.

,nderstandin* :ild Card Masks

A wild card mask matc%es actly how a wild card mask works and how we can use it.

*%e Rules

)o there are two basic rules of a wild card mask.

• E'bit U match• *'bit U ignore

*%e *arget

"hat can wild card masks targetC

• A single host


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*argeting an #ntire Network

To target an entire network means that every bit within the %GT"# portion of theI3 address must match. All others we can ignore. )o for a 8lass'8 network


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If you look here the bit we want to match on is the 76rd bit. The subnet mask for a

slash 76 is 722.722.72-.E. "e then subtract it from 722.722.722.722 to get our

wild card which is E.E.*.722.

I- /lass Default Su$net ask Default wildcardask

8lass A 722.E.E.E E.722.722.722

8lass @ 722.722.E.E E.E.722.722

8lass 8 722.722.722.E E.E.E.722

*a$le! Default)ubnet MaskS "ildcard Mask /ist

The 8oolean $N- O%eration

Heorge @oole, a mathematician who lived in the *EEs, created a branch of mathematics that came to be called @oolean math after its creator. @oolean mathhas many applications in computing theory. In fact, you can &nd subnet numbers

given an I3 address and subnet mask using a @oolean A%D.

A @oolean A%D is a math operation performed on a pair of one'digit binarynumbers. The result is another one'digit binary number. The actual math is evensimpler than those &rst two sentencesR The following list shows the four possibleinputs to a @oolean A%D, and the result!

• E A%D E yields a E

• E A%D * yields a E

• * A%D E yields a E

• * A%D * yields a *

Oou can perform a @oolean A%D on longer binary numbers, but you are really ;ustperforming an A%D on each pair of numbers. or instance, if you wanted to A%Dtogether two four'digit numbers, E**E and EE**, you would perform an A%D on the&rst digit of each number and write down the answer. Then you would perform anA%D on the second digit of each number, and so on, through the four digits.


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0 1 1 0

(ANDing)

0 0 1 1

-----------

0 0 1 0

"hen you @oolean A%D together two longer binary numbers, you perform what iscalled a bitwise @oolean A%D. This term simply means that you do what the

previous e>ample shows! Oou A%D together the &rst digits from each of the two

original numbers, and then the second digits, and then the third, and so on, until

each pair of single'digit binary numbers has been A%Ded.

I3 subnetting math frequently uses a @oolean A%D between two 67'bit binary

numbers. The actual operation works ;ust like the ne>t e>ample!

:hat is -efault *atewa!;

It$s the Gntry and G>it point of the network.a. It$s the /A%9Gthernet I3 address of a router.b. I3 address and the default gateway should be in the same network.c. The default gateway is used only to communicate with other9foreign.

:hat is CI-R;

/lassless InterDomain Routing


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967 722.722.722.722 E.E.E.E *

96* 722.722.722.72- E.E.E.* 7

96E 722.722.722.727 E.E.E.6 -

97+ 722.722.722.7- E.E.E.0

97 722.722.722.7-E E.E.E.*2 *1

970 722.722.722.77- E.E.E.6* 67

971 722.722.722.*+7 E.E.E.16 1-

970 722.722.722.*7 E.E.E.*70 *7

97- 722.722.722.E E.E.E.722 721

976 722.722.72-.E E.E.*.722 2*7

977 722.722.727.E E.E.6.722 *,E7-

97* 722.722.7-.E E.E.0.722 7,E-

97E 722.722.7-E.E E.E.*2.722 -,E+1

9*+ 722.722.77-.E E.E.6*.722 ,*+7

9* 722.722.*+7.E E.E.16.722 *1,6-

9*0 722.722.*7.E E.E.*70.722 67,01


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97 722.E.E.E 16.722.722.722

*,E06,0-*,7-

9* 722.E.E.E *70.722.722.722 7,*-0,-6,1-

9E E.E.E.E 722.722.722.722

-,7+-,+10,7+1

*a$le! I3v- 8ID %otation Table

The &gure shows the usage of 8ID ( multiple routes to multiple 8lass 8 networksare grouped into a single route, which can reduces the sie of I)3 7, I)3 6, and I)3 -routing tables.

"igure!8lassless Inter'Domain outing


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( 8ID is an e>tension to J/)M and route summariation. It is also referred toas preA routing.

Su5nettin*

• It is the process of breaking down an I3 network into smaller sub'networkscalled subnets.

• It is essentially the modi&cation of a single I3 network to create two or morelogically visible sub'networks.

• It changes the subnet mask of the local network number to produce an evennumber of smaller network numbers, each with a corresponding range of I3addresses.

Review of IPv(

The table below summaries the possible network numbers, the total number of each type, and the number of hosts in each 8lass A, @, and 8 network.

Default su$net mask Range

/lass & 722.E.E.E


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GE8:J equals G8888 8888.8888 EEEE.EEEE EEEE.EEEE EEEEV 'W *7 bits are

turned on


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K)ubnettingL means we $orrow some $its from t%e 1ost part to add to t%eNetwork part. This allows us to have more networks than using the default subnetmask. or e>ample, we can borrow some bits in the ne>t octet to make the address**.*.E.* belong to a dierent network from **.E.E.*.

9ow to su5net;Do you remember that I said Kin the subnet mask, bit * represents for %etwork partwhile bit E presents for Bost partLC "ell, this also means that we can specify howmany bits we want to borrow by changing how many bit E to bit * in the subnetmask.

/et$s come back to our e>ample with the I3 **.E.E.*, we will write all numbers inbinary form to reveal what a computer really sees in an I3 address.

%ow you can clearly see that the subnet mask will decide which is the %etwork part,which is the Bost part. @y borrowing bits, our subnet mask will be like this!

After changing the second octet of the subnet mask from all KEV to all K*V, the%etwork part is now e>tended. %ow we can create new networks by changingnumber in the &rst or second octet. This greatly increases the number of networks

we can create. "ith this new subnet mask, I3 **.*.E.* is in dierent network from I3**.E.E.* because K*V in the second octet now belongs to the %etwork part.

)o, in conclusion we KsubnetL by borrowing bit KEV in the Bost portion andconverting them to bit K*V. The number of borrowed bits is depended on how manynetworks we need.


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%ote! A rule of borrowing bits is we can only borrow bit E from the left to the rightwithout skipping any bit E. or e>ample, you can borrow like this! K**** ****. **EEEEEE.EEEE EEEE.EEEE EEEEV but not this! K**** ****. *E*E EEEE.EEEE EEEE.EEEEEEEEV. In general, ;ust make sure all your bit K*Vs are successive on the left and allyour bit KEVs are successive on the right.

Calculate how +an! networks and hosts6%er6su5net

In our e>ample, you may raise a question! Kwhen we borrow bits, how many sub'networks and how many hosts per sub'network do it createCL

%ote! rom now, we will call sub'networks KsubnetsL. This term is very popular soyou should be familiar with it.

9ow +an! new su5nets;

@ecause we can change any bit in the second octet to create a new subnet, each bitcan be KEV or K*V so with this subnet mask ample, we borrow bits so we will have 7n U 7 U 721 subnetsR

9ow +an! hosts %er su5net;

The number of hosts per subnet is depended on the Bost part, which is indicated bythe KEV part of the subnet mask. )o suppose k is the number of bits KEV in thesubnet mask. The formula to calculate the number of hosts is 7k. @ut notice thatwith each subnet, there are two addresses we can$t assign for hosts because theyare used for network address S broadcast address. Thus we must subtract the resultto 7. Therefore the formula should be!

The number of hosts per subnet U 7k ( 7

In our e>ample, the number of bit KEV in the subnet mask 722.722.E.E


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3ic. *' )ubnet 8alculation Aid.

This tool is useful before you remember all the weights from left to right and right to

left.

3ic. 7 ' G>ample of )ubnet @inary'to'Decimal 8onversion.

Kuestion 8

Hiven the pre&> *+7.*1.*.E97-, what should be the length of subnet mask allowing

up to + subnetsC

&nswer 8


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The address belongs to the class 8 and uses its default network mask. That leaves

us with bits to play with


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Kuestion ;

Hiven the pre&> *07.*1.E.E9*0, how many subnets can you createC

&nswer;

This is a bit tricky isnQt itC In order to answer this question, you donQt need any

calculator, paper or pen. Oou must trust the rule 7 in lesson 7+. The address and its

network mask = converted into binary look like presented below!

3ic. ' The %umber of )ubnets for *07.*1.E.E9*0

As you see the number of bits we have e>tended the class @ address is! 8. )o, the

number of subnets we can create with it is! : su$nets, since this subnet bit can be

either * or E.

3ic. + ' Nuestions 6 Answer

Kuestion 2

"hat length of network mask would be the most optimal for routerQs point'to'point

connectionC

http://ciscoiseasy.blogspot.com/2010/11/lesson-29-ipv4-subnetting-rules.htmlhttp://ciscoiseasy.blogspot.com/2010/11/lesson-29-ipv4-subnetting-rules.html


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&nswer 2

The key to this question is to understand that point'to'point connection needs only

7 host addresses


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Documents

Basic Networkting Conceptes