CompTIA Network+ Certification Study Guide part 12 pps

ChApTEr 3 ExAM oBJECTIvES IN ThIS ChApTEr INTroduCTIoN A network is composed of many different devices; some perform a single function and others perform a variety of functions, from ro

ChApTEr 2: Network Media

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C Use 10BaseT cabling in each of the buildings, and connect the two buildings together using 10Base5 cabling

D Use 100BaseFX cabling in each of the buildings, and connect the two buildings together using 10BaseT cabling

Your network uses 100BaseFX so that data can be transferred at

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higher speeds and up to distances of 400 m During transmission, data can travel in both directions, but only in one direction at a given time Which of the following transmission methods is used?

A Simplex

B FireWire

C Half-Duplex

D Full Duplex Examine the illustration shown in Figure 2.13 Your network uses

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UTP cabling in a star topology Which of the following types of connectors is being used?

A RJ-45

B BNC

C ST

D SC

You are the Network

network looking to install a high-speed backbone You want to implement Gigabit Ethernet Which connectors could you use in such a network? (Choose one.)

FIGurE 2.13

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A RJ-11

B RG 58

C SC

D BNC

As a Network technician for 123 LLC, you are asked by your

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CIO about the access method of Gigabit Ethernet Which of the

following access methods does Gigabit Ethernet use?

A FDDI

C CSMA/CA

D Token passing

A new technician for 123 Corp plans out the maximum length of a

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Gigabit Ethernet segment using MMF optic cable is What is the

cor-rect distance? (Choose only one)

A 100 m

B 125 m

C 550 m

D 10 km

You are the network engineer assigned to implement a new

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100 Mbps network connection You need to select the correct

cabling, as well as the correct standard From the selections below,

choose which 100 Mbps networking standard makes use of only

two pairs of a Category 5 UTP cable

A 10BaseT

B 100BaseFL

C 100BaseTX

D 100BroadT4

You work as a network technician for 123 LLC You need to check

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the electrical signals being sent from the NIC port out on the cable

Which device would you use to complete this test? (Choose one.)

A A wire map

B A fox and hound

C A crossover cable

D A hardware loopback

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SElF TEST quICK ANSwEr KEy

B

1

A

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B

3

D

4

B

5

B

6

D

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C

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C

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A

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C

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B

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C

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C

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D

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ChApTEr 3

ExAM oBJECTIvES IN ThIS ChApTEr

INTroduCTIoN

A network is composed of many different devices; some perform a single

function and others perform a variety of functions, from routing data to

applying security filters As networking devices become more complex, they

also become more versatile, in that they may be able to perform multiple roles

that previously could only be carried out by individual devices Some network

devices are complex enough to warrant their own operating systems for

inten-sive and detailed configuration In some cases, these operating systems can

be switched out, substituted, or used to configure the device to perform roles

traditionally carried out by other devices For example, a Layer 3 switch might

be configured to combine both switching and routing functions This coming

together of technology within one device is called convergence.

In this chapter we will briefly discuss convergence, and we will look at the

most common network devices in use today on small and large networks,

including the Internet These devices range from the very simple (such as

an active hub, which simply repeats and sends out signals to all ports) to the

more complex devices, such as a firewall, which is responsible for controlling

traffic and applying security features

NETworK dEvICES

Network devices are components of a network that are required if the

network is to grow, function, or provide certain functionality There are a

number of devices that fall into this category, including routers, switches,

Network devices

ChApTEr 3: Network Devices

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and other devices that we’ve mentioned briefly in previous chapters These network devices provide functionality such as connectivity to physical media, security features, and the ability to connect to resources outside

of the local area network (LAN) Before we discuss the current state of networking and the available devices, let’s take a look at how the current devices evolved

historical Network devices

As we discussed in Chapter 1, networks have been around for decades, so

it follows that some devices have been around longer than others As we’ll see in the sections that follow, although some devices are as useful today as when they were initially introduced, others have become obsolete and are rarely used on today’s networks In discussing these devices, we’ll tell you about their purpose, features, and functions on a network

hEAd oF ThE ClASS…

oSI and Network devices

Network devices can be mapped to the Open Systems

Interconnect (OSI) networking model OSI is a group

of standards that provides a logical structure for

net-work operations and contains seven layers, which from

the highest to lowest are as follows: application,

pre-sentation, session, transport, network, data link, and

physical.

Network communication starts at the

applica-tion layer of the OSI model and works its way down

through the layers step by step to the physical layer The information then passes along the cable to the receiving computer, which starts the information at the physical layer From there it steps back up the OSI layers to the application layer where the receiving computer finalizes the processing and sends back an acknowledgement if needed Then the whole process starts over.

Table 3.1 shows the devices mapped to the OSI layers at which they operate.

Table 3.1 Mapping of Network Devices to the OSI Model

oSI layer devices

Application Gateway Presentation Gateway Session Gateway Transport Gateway Network Router, multilayer or Layer 3 switches, gateway Data Link NIC, bridge, Layer 2 switches, access point, gateway Physical Hub, MAU, repeater, gateway

Network Devices 101

Hubs

Although hubs have been around since the early days of networking, they

continue to be one of the most commonly used connection-based

net-work components Especially now that home netnet-works are growing and

more small office home offices (SOHOs) are emerging, hubs are

becom-ing a common household item Some homes are even built with a plan

for a centralized wiring system, Internet access, routers, and hubs all

included

Hubs are predecessors of switches, which we’ll discuss later in this

chapter, and are central locations for connecting network cabling

Multi-ple cables connect into the hub, providing a method for data to be passed

from one cable to another This is also why switches are sometimes

referred to as switching hubs, though that terminology is not commonly

used today

As we discussed in Chapter 1, a star topology uses a hub to connect

workstations, servers, and other devices As shown in Figure 3.1, you can

easily remember the layout of a hub if you think of a wheel and picture

how the spokes go to the hub of the wheel Each spoke is a connection and

the hub of the wheel is the hub of the network where all the cables come

together Because all of the connections concentrate in the center, the hub

is also called a concentrator.

Each of the cables that extends to the hub from computers and other

network devices is plugged into its own port on the hub The port

pro-vides an interface between the cable and the hub For example, because

star topologies may use unshielded twisted-pair (UTP) cable, UTP is

a common cable type that is used with hubs The RJ-45 connector of

the cable is plugged into a port on

the hub When data is sent from

a computer, it is carried along the

cable to the port that the RJ-45

connector is plugged into The hub

then takes this data and passes it to

the other ports, allowing the data

to travel along the other cables to

workstations and devices that are

attached to it The number of ports

on a hub will vary, but generally

four or more are provided Many

hubs provide 24 or 28 ports and

can be attached together (or more

commonly referred to as uplinked FIGurE 3.1 Hubs Are Used in Star Topologies.

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or cascaded together) to provide connectivity to even more computers or network devices There are rules, of course; when working with hubs, you should always apply the 5-4-3 rule, which states that you can only con-nect a total of 5 segments linked together via 4 hubs and only 3 of those segments can be populated with network hosts such as PCs or printers Breaking rules of this kind could lead to a degradation of performance and possible problems

The two main types of hubs are passive and active A switching hub is

actually a type of switch that behaves like a hub

Passive hubs

In discussing hubs to this point, we have essentially been talking about pas-sive hubs A paspas-sive hub provides basic features of moving data from one port to another Its function is simply to receive data from one port of the hub and send it out to the other ports For example, an 8-port hub receives data from port 3 and then resends that data to ports 1, 2, 4, 5, 6, 7, and 8

It is as simple as that

A passive hub contains no power source or electrical components There

is no signal processing It simply attaches the ports internally and enables communication to flow through the network

Active hubs

An active hub provides the same functionality that a passive hub does, with

an additional feature Active hubs repeat (regenerate) the data while resend-ing it to all of its ports By usresend-ing active hubs you can increase the length of your network beyond regular cable length limits For example, UTP Category

5 cabling can be run a maximum of 100 m With an active hub, you can run Category 5 UTP 100 m on each side of the hub so that your cable now runs

a length of 200 m in total

Exam warning

Hubs broadcast traffic on every single port Because hubs only operate at the physi-cal layer, they are deemed unintelligent A hub is simple by design; a signal comes in from a connected PC, and the hub just sends that signal out to every port that it knows For example, suppose an 8-port hub has eight PCs attached If PC 1 sends an e-mail

to PC 2, that transmission will go to all the eight PCs The data, of course, will get to its destination, but all six of the uninvolved PCs are interrupted because each has to examine the data to determine if it is the recipient This process takes time, and if you multiply this over the traffic of a normal large-scale enterprise network, it’s easy to see why hubs are typically limited to small networks.

Network Devices 103

An active hub has a power source and built-in repeaters to boost the

signal There are extra electronics built into an active hub that allow for

signal regeneration, which is how the incoming data on one port is repeated

to the other ports Because the signal is repeated in this way to the other

ports, an active hub is also called a multiport repeater.

switching hubs

Although active and passive hubs will pass data to every other port on the

hub, a switching hub will only send data to its intended port Switching hubs

are also referred to as intelligent hubs, as they can determine which port will

get the data to its proper destination The fact is, however, that even though

it is referred to as a switching hub, these are the features of another device

called a switch (which we’ll discuss later in this chapter) Although this term

may be used in the real world to refer to a switch, for the Network+ exam

it’s best to keep the components separate in your mind A switch is a switch,

and a hub is a hub

Repeaters

A repeater is a device that is rarely seen on networks today, as its features are

typically incorporated into other devices, such as active and switching hubs

The repeater will take a signal that may be weakening and regenerate it to its

original strength In doing so, it actually recreates the signal, making it the

same strength that it was when it left the sending workstation

To help you understand a repeater, imagine that you are with a friend and

both of you are standing at opposite ends of a street If you shouted

some-thing to your friend, the sound would fade over a distance If someone stood

between the two of you, however, and repeated your message, then it would

be repeated strong and loud, allowing your friend to hear it A repeater works

Test day Tip

The Network+ exam includes questions that deal with active hubs Passive hubs

aren’t covered on the current version of the exam This information is included for

completeness.

Exam warning

Hubs operate at the physical layer of the OSI model (also known as Layer 1) Hubs are

designed to simply forward data from one port of the hub to another, so they don’t use

upper-layer protocols such as Internet Protocol (IP), Internetwork Packet Exchange (IPX),

or Media Access Control (MAC) addressing to ensure that the data reaches its intended

destination.

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in a similar fashion by repeating the data so it’s in its original, strong form preventing corruption as it weakens over distance

Historically, repeaters were first created to fix a problem Cables had length limitations, which were solved by connecting a repeater to two cable segments to extend the range beyond the regular distance limit Repeaters were commonly used on Ethernet networks, such as those using UTP or coaxial cable, and provided networks with the ability to extend cable seg-ments 10BaseT limitations are 100 m or approximately 328 feet Thickwire (also known as 10Base5 or Thicknet) can normally transmit a distance of

500 m, whereas thinwire (also known as 10Base2 or Thinnet) can normally transmit a distance of 185 m By putting a repeater between these segments, the distance that data can travel can be doubled Remember, when using repeaters, greater lengths of cabling were allowed when planning a cabling scheme

Bridges

A bridge is a network connectivity device that connects two different net-works and makes them appear to be one network It can connect two differ-ent LANs, or allow a larger LAN to be segmdiffer-ented into two smaller halves The bridge filters local traffic between the two networks and copies all other traffic to the other side of the bridge

Bridges are intelligent devices and have the ability to forward packets

of data based on MAC addresses A bridge can look at a packet of data and determine the source and destination involved in the transfer of packets It will read the specific physical address of a packet on one network segment and then decide to filter out the packet or forward it to another segment

A bridge is another device that has largely become a thing of the past Although bridges were a common component of older networks, their fea-tures are now typically incorporated into switches One benefit of a switch over a bridge is that a bridge only has two ports typically, one for each seg-ment that it is connecting Switches may have many ports, and as we’ve already seen, incorporate features that were previously found in other devices, such as hubs

Note

Unlike previous versions of the Network+ exam, repeaters are no longer directly tested

on the exam The function of a repeater is to regenerate data so that it can be passed further than the maximum distance of a cable segment The ability to regenerate data and perform this function is now found incorporated in other network devices, such as hubs and switches.

Network Devices 105

Network segmentation

A bridge is a simple way to accomplish network segmentation Placing a

bridge between two different segments of the network decreases the amount

of traffic on each of the local networks Although this does accomplish

network segmentation, most network administrators opt to use routers or

switches, which are discussed later in the chapter

Bridges segment the network by MAC addresses When one of the

work-stations connected to one network has to transmit a packet, the packet is

copied across the bridge as long as the packet’s destination is not on its

origi-nating network segment A bridge uses a bridging table to calculate which

MAC addresses are on which network The MAC address uniquely identifies

computers and other devices on a network, just as the full address of your

house uniquely identifies its location

Multistation Access Units

Multistation access units (also known as MAUs or MSAUs) are used to

connect workstations on a Token Ring network Sometimes, an MAU is

referred to as a hub on the Network+ exam, but it shouldn’t be confused

with the active and passive hubs we discussed earlier, which are used on

Ethernet networks The features of an MAU are different from those of a

standard hub

An MAU typically has eight or more ports that provide connections

for workstations and other network devices on a Token Ring network It

is also generally nonpowered, although some have been produced that are

powered with lights to indicate connectivity and activity An MAU is not

something you will commonly find on newer networks simply because

newer networks generally are installed as Ethernet, more typically Fast

Ethernet or Gigabit Ethernet MAUs are used with Token Ring networks,

which are present in today’s environments, but are not as prevalent as

Ethernet

Test day Tip

The Network+ exam frequently uses the term bridging and does refer to the actual

device quite often Make sure that you understand the concepts of bridging that it will

connect up to two different network segments.

Exam warning

Bridges operate at the data link layer of the OSI model and use physical addressing to

join several networks into a single network efficiently.