Download 5). Network Devices and VLAN

Connecting LANs, (network
devices)
Backbone Networks,
and Virtual LANs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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CONNECTING DEVICES
In this section, we divide connecting devices into five
different categories based on the layer in which they
operate in a network.
Topics discussed in this section:
Passive Hubs
Active Hubs
Bridges
Two-Layer Switches
Routers
Three-Layer Switches
Gateways
15.2
Five categories of connecting devices
15.3
A repeater connecting two segments of a LAN
15.4
Note
A repeater connects segments of a LAN.
A repeater forwards every frame;
it has no filtering capability.
A repeater is a regenerator,
not an amplifier.
15.5
Function of a repeater
15.6
Repeaters
A repeater solves the problem of too many nodes and
not enough cable; cleans, amplifies, and resends a
signal that is weakened by long cable length.
Hub

Multi-port repeater to construct a star
topology.
15.8
Hubs
• Regenerate and
repeat signals
• Used as network
concentration
points
• Multiport repeater
• Becoming obsolete
Hubs
Bridges: Layer 2
Bridges
Bridges filter traffic
by looking at MAC
addresses.
Designed to create two or more LAN segments, each of
which is a separate collision domain
Bridges
A Bridge has filtering capabilities. It can check
the MAC address and decide which port should
be forwarded or just dropped.
Note
A bridge has a table used in
filtering decisions.
A bridge does not change the physical
(MAC) addresses in a frame.
15.13
A bridge connecting two LANs
15.14
A learning bridge and the process of learning
1. A send a frame to D
The table is blank, frame
floods the net, learned A
to port 1 for future usage.
2. E send a frame to A
Forward the frame only to
port 1; learned E to port 3
3. B send a frame to C
No entry of C, floods the
net and add one more
entry, B to port 2
4. The learning continues.
15.15
Switches: Layer 2
A Switch is a Multiport Bridge
Switches


Two-layer switch, better performance,
multi-port bridge. Allocate a unique port to
each station, no collision.
Three layer switch, faster and more
sophisticated router. Allow faster table
lookup and forwarding.
15.1
7
LAN Switches
Switches Combine the
connectivity of a hub
with the traffic
regulation of a bridge
on each port
Router
Three layer device, route packets based on IP
address. Connect LANs and WANs. Routing tables
,which normally dynamic and updated using routing
protocols, are used for making decisions about route.
Routers connecting independent LANs and WANs
15.19
Connection Media / UTP Implementation
EIA/TIA specifies an RJ-45 connector for
unshielded twisted-pair (UTP) cable. The letters RJ
stand for registered jack, and the number 45
refers to a specific wiring sequence. The RJ-45

connector and jack are the most common
Attach the RJ-45
Straight-Through Cables



Maintain the pin connection all the
way through the cable.
Wire connected to pin 1 is the same
on both ends.
Used to connect such devices as PCs
or routers to other devices such as
hubs or switches. (One level
different.)
Crossover Cable



Cross the critical pair to properly align,
transmit, and receive signals on devices
with like connections.
Pin 1 connected to pin 3, pin 2
connected to pin 6.
Used to connect similar devices: switch
to switch, switch to hub, hub to hub,
router to router, PC to PC.
Rollover Cables (Cisco console cable )
connect a computer terminal to a
router's console port. This cable is
typically flat and has a light blue color.
 The console port allows monitoring and
configuration of a Cisco hub, switch, or
router.

BACKBONE NETWORKS
A backbone network allows several LANs to be
connected. In a backbone network, no station is
directly connected to the backbone; the stations are
part of a LAN, and the backbone connects the LANs.
Topics discussed in this section:
Bus Backbone
Star Backbone
Connecting Remote LANs
15.26
In a bus backbone, the topology
of the backbone is a bus.
15.27
In a star backbone, the topology of the
backbone is a star;
the backbone is just one switch.
15.28
VIRTUAL LANs
We can roughly define a virtual local area network
(VLAN) as a local area network configured by
software, not by physical wiring.
Topics discussed in this section:
Membership
Configuration
Communication between Switches
IEEE Standard
Advantages
15.29
A switch connecting three LANs
15.30
A switch using VLAN software
15.31
Figure 15.17 Two switches in a backbone using VLAN software
15.32
Note
VLANs create broadcast domains.
15.33
What are the benefits of a VLAN?



A VALN saves company time and money because
reconfiguration is done through software. Physical
reconfiguration is not necessary.
A VLAN provides extra security for a network. Members
of a VLAN can send broadcast messages with the
assurance that users in other groups will not receive
these messages.
A VLAN reduces network traffic. A VLAN creates virtual
workgroups. Each workgroup member can send
broadcast messages to others in the workgroup. This
eliminates the need for multicasting and all the overhead
messages associated with it.
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