Which switch would STP choose to become the root bridge in the selection process?
A.
32768: 11-22-33-44-55-66
B.
32768: 22-33-44-55-66-77
C.
32769: 11-22-33-44-55-65
D.
32769: 22-33-44-55-66-78
Explanation:
The root bridge of the spanning tree is the bridge with the smallest (lowest) bridge ID. Each
bridge has a configurable priority number and a MAC Address; the bridge ID contains both
numbers combined together – Bridge priority + MAC (32768.0200.0000.1111). The Bridge
priority default is 32768 and can only be configured in multiples of 4096(Spanning tree uses
the 12 bits extended system ID). To compare two bridge IDs, the priority is compared first,
as if looking at a real number anything less than 32768…will become the target of being the
root. If two bridges have equal priority then the MAC addresses are compared; for example,
if switches A (MAC=0200.0000.1111) and B (MAC=0200.0000.2222) both have a priority of
32768 then switch A will be selected as the root bridge.
In this case, 32768: 11-22-33-44-55-66 would be the bridge because it has a lower priority
and MAC address.
My opinion is answer A & B are invalid
Bridge ID should be Bridge Priority + System ID Extension (32768 + VLAN 1) + MAC address.
C) 32769: 11-22-33-44-55-65 should be the correct answer
Reference: http://www.firewall.cx/networking-topics/protocols/spanning-tree-protocol/1054-spanning-tree-protocol-root-bridge-election.html
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I don’t aggree with you.
The default port of priority is 32768 on all switches. The lower port number wins.
In this case the lowest MAC address wins, it makes the correct answer “A”.
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The default value of priority is 32768 on all switches. The lower priority number wins.
In this case the lowest MAC address wins, it makes the correct answer “A”.
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