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Chapter 15Connecting LANs,

Backbone Networks,and Virtual LANs

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15-1 CONNECTING DEVICES15-1 CONNECTING 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 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:

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Figure 15.1 Five categories of connecting devices

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Figure 15.  A repeater connecting two segments of a LA 

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A repeater connects seg!ents o" a LAN.

 ote

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A repeater "orwards e$er% "ra!e&

it has no "iltering capabilit%.

 ote

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A repeater is a regenerator,

not an a!pli"ier.

 ote

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Figure 15.! Function of a repeater 

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Figure 15."  A hierarchy of hubs

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A bridge has a table used in

"iltering decisions.

 ote

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Figure 15.5  A bridge connecting two LAs

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A bridge does not change the ph%sical

+AC- addresses in a "ra!e.

 ote

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Figure 15.#  A learning bridge and the process of learning 

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Figure 15.$  Loop problem in a learning bridge

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Figure 15.%  A system of connected LAs and its graph representation

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Figure 15.& Finding the shortest paths and the spanningtree in a system of bridges

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Figure 15.1' Forwarding and blocking ports after using spanningtree algorithm

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Figure 15.11  !outers connecting independent LAs and "As