ch5 NetworkDevices

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Connecting LANs, (network

devices)Backbone Networks,

and Virtual LANs

Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display. 1


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CONNECTING DEVICESCONNECTING DEVICES

In this section, we divide connecting devices into fiveIn this section, we divide connecting devices into five

different categories based on the layer in which theydifferent categories based on the layer in which they

operate in a network.operate in a network.

Passive Hubs

Active Hubs

BridgesTwo-Layer Switches

Routers

Three-Layer Switches

Gateways

Topics discussed in this section:To

pics discussed in this section:

15.2


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Five categories of connecting devices

15.


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15.!

A repeater connecting two segments of a LA


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15.5

A re"eater #orwards ever$ #ra%e&it 'as no #iltering ca"abilit$.

ote

A re"eater is a regenerator,not an a%"li#ier.

A re"eater connects seg%ents o# a LAN.


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15.

Function of a repeater


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Repeaters

A re"eater solves t'e "roble% o# too %an$ nodes and

not enoug' cable& cleans, a%"li#ies, and resends a

signal t'at is weakened b$ long cable lengt'.


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Hu

b Multi-port repeater to construct astar topology.

15.


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Hubs

*egenerate and

re"eat signals

+sed as network

concentration

"oints

ulti"ort re"eater

Beco%ing obsolete


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Hubs


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Bridges: Layer 2


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Bridges

-esigned to create two or %ore LAN seg%ents, eac' o#

w'ic' is a se"arate collision do%ain

Bridges #ilter tra##icb$ looking at AC

addresses.


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A bridge 'as a table used in

#iltering decisions.

ote

A bridge does not c'ange t'e "'$sical

(AC) addresses in a #ra%e.

Bridges

A Bridge 'as #iltering ca"abilities. t can c'eck

t'e AC address and decide w'ic' "ort s'ould

be #orwarded or /ust dro""ed.

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A bridge connecting two LAs

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A learning bridge and the process of learning

1. A send a frame to DThe table is blank,

frame floods the net,

learned A to port 1 for

future usage.

2. E send a frame to AForward the frame only

to port 1 learned E to

port !

!. " send a frame to #

$o entry of #, floods

the net and add one

more entry, " to port 2

%. The learning &ontinues.

15.15


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Switches: Layer 2

A 0witc' is a ulti"ort Bridge


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Switche

sTwo-layer switch, betterperor!ance, !ulti-port bridge."llocate a uni#ue port to each

station, no collision.Three layer switch, aster and !ore

sophisticated router. "llow aster

table loo$up and orwarding.

15.


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L"% Switches

0witc'es Co%bine t'e

connectivit$ o# a 'ubwit' t'e tra##ic

regulation o# a bridge

on eac' "ort


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!outers connecting independent LAs and "As

*outer

Three layer de'i&e, route pa&kets based on ()address. #onne&t *A$s and +A$s. outing tables

,whi&h normally dynami& and updated using routing

proto&ols, are used for making de&isions about route.

15.1


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&onnection Media ' (T)*!ple!entation

+*"'T*" species an R-/ connector or

unshielded twisted-pair 0(T)1 cable. The lettersR stand or registered ac$, and the nu!ber /

reers to a specic wiring se#uence.The R-/connector and ac$ are the !ost co!!on


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"ttach the R-/


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Straight-Through &ables

Maintain the pin connection allthe way through the cable.

3ire connected to pin 4 is thesa!e on both ends.

(sed to connect such de5ices as)&s or routers to other de5icessuch as hubs or switches. 06nele5eldi7erent.1


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&rosso5er &able

&ross the critical pair to properlyalign, trans!it, and recei5e signalson de5ices with li$e connections.

)in 4 connected to pin 8, pin 2connected to pin 9.

(sed to connect si!ilarde5ices:

switch to switch, switch to hub, hubto hub, router to router, )& to )&.


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Rollo5er &ables 0Cisco consolecable )

connect a co!puter ter!inal to a

routers console port. This cable istypically ;at and has a light blue color.

The console port allows !onitoring

and conguration o a &isco hub,switch, or router.


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15.2

BACKBONE NETWORKSBACKBONE NETWORKS

A backbone network allows several LAs to beA backbone network allows several LAs to be

connected. In a backbone network, no station isconnected. In a backbone network, no station is

directly connected to the backbone# the stations aredirectly connected to the backbone# the stations are

part of a LA, and the backbone connects the LAs.part of a LA, and the backbone connects the LAs.

Bus BackboneStar Backbone

Connecting Remote LAs

Topics discussed in this section:Topics discussed in this section:


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n a bus backbone, t'e to"olog$

o# t'e backbone is a bus.

15.2


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n a star backbone, t'e to"olog$ o# t'e

backbone is a star&

t'e backbone is /ust one switc'.

15.2


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VIRTUAL LANsVIRTUAL LANs

"e can roughly define a"e can roughly define a virtual local area networkvirtual local area network

$%LA& as a local area network configured by$%LA& as a local area network configured by

software, not by physical wiring.software, not by physical wiring.

!embershi"Con#iguration

Communication between Switches

$%%% Standard

Advantages

Topics discussed in this section:Topics discussed in this section:

15.2


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A switch connecting three LAs

15.3


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A switch using %LA software

15.1


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&igure '()'* Two switches in a backbone using %LA software

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VLANs create broadcast do%ains.

ote

15.


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3hat are the benets o a

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