Networking Devices 21

8/6/2019 Networking Devices 21

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Network Devices


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Ethernet - Architecture


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What are internetworking

devices?

Internetworking devices are

products used to connect networks As computer networks grow in size

and complexity, so do the

internetworking devices used toconnect them.


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The purposes of having

devices First, they allow a greater number of nodes

to be connected to the network.

Second, they extend the distance over which

a network can extend.

Third, they localize traffic on the network.

Fourth, they can merge existing networks.

Fifth, they isolate network problems so that

they can be diagnosed more easily.


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What internetworking devices operate at

the physical layer (layer 1) of the OSImodel?

A repeater can provide a simple solution if either

of these two problems exists.

When signals first leave a transmitting station,they are clean and easily recognizable

However, the longer the cable length, the weaker

and more deteriorated the signals become as they

pass along the networking media.


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What is the disadvantage associated with

using a repeater?

it can't filter network traffic. Data,

sometimes referred to as bits, arriving at

one port of a repeater gets sent out on all

other ports

data gets passed along by a repeater to all

other LAN segments of a networkregardless of whether it needs to go there or

no


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What problem could occur as a result of

too much traffic on a network?

if segments of a network are only connected

by non-filtering devices such as repeaters,

this can result in more than one user trying

to send data on the network at the same time

If more than one node attempts to transmit

at the same time, a collision will occur.

When a collision occurs, the data from each

device impact and are damaged


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Hub Multi-port repeaters are often called hubs

Hubs are very common internetworking

devices

Generally speaking, the term hub is used

instead of repeater when referring to the

device that serves as the center of a star

topology network.


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Hubs Intelligent hubs have console ports, to allow

monitoring of the hubs status and port activity.

Passive hubs just repeat any incoming signals to

every port available, therefore does not act as a line

repeater. Passive hubs just split signals to multiple ports but

do not regenerate the signals, which means that

they do not extend a cables length. They only allow

two or more hosts to connect to the same cable

segment.

Active hubs regenerate signals.

Hubs utilise star topology.


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Advantages As an active hubs regenerate signals, it

increases the distance that can be spanned by

the LAN (up to 100 meters per segment). Hubs can also be connected locally to a

maximum of two other hubs, therebyincreasing the number of devices that can beattached to the LAN.

Active hubs are usually used againstattenuation, which is a decrease in thestrength of the signal over distance.


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Disadvantages

Bandwidth is shared by all hosts i.e. 10Mbs

shared by 25 ports/users.

Can create bottlenecks when used with

switches.

Have no layer 3 switching capability.

Most Hubs are unable to utilise VLANS.


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What internetworking device can be

used to filter traffic on the network?

One way to solve the problems of too much

traffic on a network and too many collisions

is to use an internetworking device called a

bridge.

A bridge eliminates unnecessary traffic and

minimizes the chances of collisionsoccurring on a network by dividing it into

segments


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Bridges

A network bridge connects multiple network segments at

the data link layer (layer 2) of the OSI model.

Bridges are similar to repeaters or network hubs, devices that

connect network segments at the physical layer

However a bridge works by using bridging where trafficfrom one network is managed rather than simply rebroadcast

to adjacent network segments

In Ethernet networks, the term "bridge" formally means a

device that behaves according to theIEEE

802.1D standard -this is most often referred to as a network switch in

marketing literature.


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At what layer of the OSI model

do bridges operate? Because bridges operate at the data link layer, layer 2,they are not required to examine upper-layer

information.

A bridge works at the data-link (physical network) level of a

network, copying a data frame from one network to the next

network along the communications path.


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How are bridge data-

forwarding decisions limited?

Although bridges use tables todetermine whether or not toforward data to other segmentsof the network, the types of

comparisons and decisions theymake are relatively low level,simple ones


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What types of network traffic

problems is a bridge incapableof solving?

Bridges work best where traffic from one

segment of a network to other segments is

not too great.

However, when traffic between network

segments becomes too heavy, the bridge canbecome a bottleneck and actually slow

down communication


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Transparent and Source Route

BridgingTransparent Bridging

This method uses a forwardingdatabase to send frames acrossnetwork segments. The

forwarding database is initiallyempty and entries in the databaseare built as the bridge receivesframes. If an address entry is notfound in the forwardingdatabase, the frame isrebroadcast to all ports of thebridge, forwarding the frame toall segments except the sourceaddress.

Also known as adaptive bridges.

Route Source Bridging

With source route bridging twoframe types are used in order tofind the route to the destination

network segment. Single-Route(SR) frames comprise most of thenetwork traffic and have setdestinations, while All-Route(AR) frames are used tofind routes. Bridges send ARframes by broadcasting on allnetwork branches; each step ofthe followed route is registeredby the bridge performing it.


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ADVANTAGES

Self configuring

Primitive bridges are often inexpensive

Reduce size of collision domain

Transparent to protocols above the MAC layer

Allows the introduction of management -performance information and access control

LANs interconnected are separate and physicalconstraints such as number of stations,repeaters and segment length don't apply


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How many addressing schemes

are there in networking?

One of the addressing schemes is the

MAC address

The second addressing scheme in

networking makes use of what is calledthe IP address


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How do IP addresses differ

from MAC addresses? Like MAC addresses, every IP address is

unique. No two IP addresses are ever alike.

However, while MAC addresses are

physical addresses that are actually hard-

coded into the NIC card and occur at the

data link layer IP addresses are implemented in software

and occur at the network layer of the OSI

model.


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Switches

A switch is a multi-port bridge.

It operates at OSI data link layer 2.

It stores MAC addresses in an internal lookup table.

Temporary switched paths are created between the

frames source destination.

Some Switches have limited layer 3 IP routing

capabilities. Switches can be configured to use VLANS.

Switches support spanning tree protocol to create

resilient networks.


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What are routers?

Routers are another type of internetworking

device.

These devices pass data packets between

networks based on network protocol or

layer 3 information.

Routers have the ability to make intelligentdecisions as to the best path for delivery of

data on the network.


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Routers Routers are OSI network layer 3 devices

Using interface modules can connect different layer

2 technologies e.g. Ethernet, FDDI, token ring etc

Routers have the capability to interconnect network

segments or entire networks (WANS/MANS).

These devices examine incoming packets to

determine the destination address of the data. It

then examines its internal routing table to choose

the best path for the packet through the network,

and switches them to the proper outgoing port.


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What network problems can

routers help resolve?

The problem of excessive broadcast traffic

can be solved by using a router

Routers are able to do this, because they do

not forward broadcast frames unlessspecifically told to do so


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How do routers differ from

bridges?

First, bridging occurs at the data link layer

or layer 2,while routing occurs at thenetwork layer or layer 3 of the OSI model.

Second, bridges use physical orMAC

addresses to make data forwarding

decisions. Routers use a different

addressing scheme that occurs at layer three

Networking Devices 21

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