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Gigabit Ethernet Switch User's Guide
On the Bridge Level
♦ Root Bridge The switch with the lowest Bridge Identifier
is the Root Bridge. Naturally, you will want the Root Bridge
to be the best switch among the switches in the loop to
ensure the highest network performance and reliability.
♦ Bridge Identifier This is the combination of the Bridge
Priority (a parameter that you can set) and the MAC address
of the switch. Example: 4 00 80 C8 00 01 00, where 4 is the
Bridge Priority. A lower Bridge Identifier results in a higher
priority for the switch, and thus increases it probably of
being selected as the Root Bridge.
♦ Designated Bridge From each LAN segment, the attached
Bridge that has the lowest Root Path Cost to the Root Bridge
is the Designated Bridge. It forwards data packets for that
LAN segment. In cases where all Switches have the same
Root Path Cost, the switch with the lowest Bridge Identifier
becomes the Designated Bridge.
♦ Root Path Cost The Root Path Cost of a switch is the sum
of the Path Cost of the Root Port and the Root Path Costs of
all the switches that the packet goes through. The Root Path
Cost of the Root Bridge is zero.
♦ Bridge Priority This is a parameter that users can set.
The smaller the number you set, the higher the Bridge
Priority is. The higher the Bridge Priority, the better the
chance the Switch will be selected as the Root Bridge.
On the Port Level
♦ Root Port Each switch has a Root Port. This is the port
that has the lowest Path Cost to the Root Bridge. In case
there are several such ports, then the one with the lowest
Port Identifier is the Root Port.
24
Switch Management
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