Refer to the exhibit.
All switches have default bridge priorities, and originate BPDUs with MAC addresses as indicated.
The numbers shown are STP link metrics. Which two ports are in blocking state after STP converges?
(Choose two.)
A.
the port on switch SWD that connects to switch SWE
B.
the port on switch SWF that connects to switch SWG
C.
the port on switch SWD that connects to switch SWC
D.
the port on switch SWB that connects to switch SWD
A non-root port is either a Designated port or Blocking port. If the switch’s MAC address is lower than the remote-switch, then it becomes the DE port and the remote-switch’s port is blocking. If the switch’s MAC is higher than the remote-switch’s MAC, then it’s port blocks and the other switch’s port becomes DE.
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D is wrong. The port on switch D would block due to the higher MAC and the port of switch B would be designated due to the lower MAC.
Where there is a shared link between switches then ignoring the case where there is a root port on the segment the lower priority will be designated and the higher priority will be blocking.
C is correct but no others are because all the other ports they offer as blocking are the lower priority ones on the segment hence would be designated port.
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D is correct.
All switches have equal priority hence MAC addresses (last digit) influence Bridge ID.
(1) SWA will become root (lowest digit – 0)
(2) SWD and SWC will set the root port in direction of SWA (because of lowest cost).
(3) On segment SWB-SWD the SWD port will become designated because of lowest cost.
(4) The SWB switch will choose root path over SWC because costs over SWC and SWD are equal and SWC has lower MAC.
(5) The port on SWB to SWD will not be designated because of (3) and will not be root port because of (4). Hence it will be blocked.
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