Chapter 7: Spanning Tree Protocol (STP) 121
Section 7-2
As it might be expected, the links between the core and other switches are Gigabit
Ethernet. The uplinks from Catalyst A into the core, however, are Fast Ethernet.
When the root bridge is elected, Catalyst A wins based on its lower MAC address. (All
switches have their default bridge priorities of 32768.) Both of the uplink ports on switch
A become designated ports because it is now the root. The downlinks from C1 and C2 to
Catalyst A
Catalyst C1 Catalyst C2
19 19
4
32768: 00-01-42-3a-89-00
4
4
4
4
4
4
100FX 100FX
GigE
32768: 00-d0-00-74-60-00 32768: 00-d0-04-57-38-aa
Catalyst A
Catalyst C1
Catalyst C2
19 19
Root
Bridge
32768: 00-01-42-3a-89-00
4
4
44
4
4
100FX 100FX
32768:
00-d0-00-74-60-00
32768:
00-d0-04-57-38-aa
X
RP
GigE GigE
DP
DP
DP
RP
Figure 7-2 Network Diagram Demonstrating Poor STP Root Placement
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