3Com 3C17205-US - Corp SUPERSTACK 3 SWITCH 4400..., Руководство по внедрению

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How STP Works 53
Figure 12 Port costs in a network
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Bridge A has the lowest Bridge Identifier in the network, and has
therefore been selected as the Root Bridge.
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Because Bridge A is the Root Bridge, it is also the Designated Bridge
for LAN segment 1. Port 1 on Bridge A is therefore selected as the
Designated Bridge Port for LAN Segment 1.
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Port 1 of Bridges B, C, X and Y have been defined as Root Ports
because they are the nearest to the Root Bridge and therefore have
the most efficient path.
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Bridges B and X offer the same Root Path Cost for LAN segment 2,
however, Bridge B has been selected as the Designated Bridge for the
segment because it has a lower Bridge Identifier. Port 2 on Bridge B is
therefore selected as the Designated Bridge Port for LAN Segment 2.