If a switch receives a superior BPDU and goes directly into a blocked state, what mecanism
must be in use?
A.
Etherchannel guard
B.
root guard
C.
loop guard
D.
BPDU guard
Explanation:
The key here is the word ‘switch’. The entire switch goes into a blocked state, meaning that it
can’t participate in STP, it is blocked. Root guard basically puts the port in a listening state
rather than forwarding, still allowing the device to participate in STP.
BPDUGuard goes to errdisabled, root guard goes to blocked. B is true.
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Megatron is correct on this one.
“When you enable BPDU guard on the switch, spanning tree shuts down PortFast-configured interfaces that receive BPDUs instead of putting them into the spanning tree blocking state.”
Ref:
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4000/8-2glx/configuration/guide/stp_enha.html
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root guard goes to “root-inconstant” state, which is basically a listening state. The “switch” does not go into a blocking state, its a port. This question is asked at least 3 times in this version. I agree that root guard is the most correct answer simply because a portfast port will never have a “superior” BPDU. It will be errdisabled after the first.
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