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5-14
C
5: T
HAPTER
RANSPARENT
LAN 1
CBPDU
(root ID.cost.transmitter ID)
10.11.12
LAN 2
10.11.20
LAN 3
B
RIDGING
(R)
P1
10.0.10
Bridge A
P2
(B)
(R)
P1
Bridge C
10.11.29
P2
(D)
(R)
P1
10.12.81
Bridge F
P3
(D)
LAN 4
Figure 5-8 Spanning Tree Topology Calculated
Each bridge, except for the root bridge, must select a root port. To do this,
each bridge determines the most cost-effective path for packets to travel
from each of its ports to the root bridge. The cost depends on 1) the port's
path cost, and 2) the root path cost of the designated bridge for the LAN to
which this port is attached.
Root
Bridge
(D)
P1
Bridge B
P3
(D)
P2
(D)
(R)
P1
(D)
Bridge D
P3
P2
(B)
(B)
P2
(R)
P1
Bridge E
10.11.35
P2
(B)
(R) = Root Port
(D) = Designated Port
(B) = Backup Port
LAN 5
LAN 6
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