If a switch receives a superior BPDU and goes directly into a blocked state, what mechanism
must be in use?
A.
BPDU guard
B.
portfast
C.
EherCahannel guard
D.
loop 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.
This same question is asked with rootguard as one of the options. BPDU guard would put a port into errdisable state
“PortFast BPDU guard prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port. 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.May 6, 2007”
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The explanation about root guard is correct also however, in that only the port is put into the root-inconsistent state rather than blocking. Neither answer has the “switch” put into a blocking state, but “superior BPDU” implies that some BPDU was accepted. BPDU guard would not accept any BPDU, because hosts on a port with portfast enabled have no business issuing any.
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Root guard
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