Spanning Tree Example

Spanning Tree Example
In Figure 15.6, the three switches all have the same priority of 32768. However, notice the MAC
address of each switch. By looking at the priority and MAC addresses of each switch, you
should be able to determine the root bridge.
Because 2950A has the lowest MAC address and all three switches use the default priority,
2950A will be the root bridge.
To determine the root ports on switches 2950B and 2950C, you need to look at the cost of
the link connecting the switches. Because the connection from both switches to the root switch
is from port 0 using a 100Mbps link, that has the best cost and both switches’ root port will then
be port 0.
Use the bridge ID to determine the designated ports on the switches. The root bridge always
has all ports as designated. However, because both 2950B and 2950C have the same cost to the
root bridge and because switch 2950B has the lowest bridge ID, the designated port will be on
switch 2950B. Because 2950B has been determined to have the designated port, switch 2950C
will put port 1 in blocking state to stop any network loop from occurring.