Connecting LANs, (network devices)

Backbone Networks, and Virtual LANs

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

CONNECTING DEVICESCONNECTING DEVICES

In this section, we divide connecting devices into five In this section, we divide connecting devices into five different categories based on the layer in which they different categories based on the layer in which they operate in a network.operate in a network.

Passive HubsActive HubsBridgesTwo-Layer SwitchesRoutersThree-Layer SwitchesGateways

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

15.2

Five categories of connecting devices

15.3

15.4

A repeater connecting two segments of a LAN

15.5

A repeater forwards every frame; it has no filtering capability.

Note

A repeater is a regenerator, not an amplifier.

A repeater connects segments of a LAN.

15.6

Function of a repeater

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

Designed to create two or more LAN segments, each of which is a separate collision domain

Bridges filter traffic by looking at MAC addresses.

A bridge has a table used in filtering decisions.

Note

A bridge does not change the physical (MAC) addresses in a frame.

Bridges

A Bridge has filtering capabilities. It can check the MAC address and decide which port should be forwarded or just dropped.

15.13

A bridge connecting two LANs

15.14

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 3

3. B send a frame to CNo 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.

15.17

LAN Switches

Switches Combine the connectivity of a hub with the traffic regulation of a bridge on each port

Routers connecting independent LANs and WANs

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.

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.

15.26

BACKBONE NETWORKSBACKBONE NETWORKS

A backbone network allows several LANs to be A backbone network allows several LANs to be connected. In a backbone network, no station is connected. In a backbone network, no station is directly connected to the backbone; the stations are directly connected to the backbone; the stations are part of a LAN, and the backbone connects the LANs. part of a LAN, and the backbone connects the LANs.

Bus BackboneStar BackboneConnecting Remote LANs

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

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 LANsVIRTUAL LANs

We can roughly define a We can roughly define a virtual local area networkvirtual local area network (VLAN) as a local area network configured by (VLAN) as a local area network configured by software, not by physical wiring.software, not by physical wiring.

MembershipConfigurationCommunication between SwitchesIEEE StandardAdvantages

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

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

VLANs create broadcast domains.

Note

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.

34