If a switch port goes directly into a blocked state only when a superior BPDU is received, what
mechanism must be in use?
A.
STP BPDU guard
B.
loop guard
C.
STP Root guard
D.
EtherChannel guard
Explanation:
Root guard allows the device to participate in STP as long as the device does not try to
become the root. If root guard blocks the port, subsequent recovery is automatic. Recovery
occurs as soon as the offending device ceases to send superior BPDUs.
Source: http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-treeprotocol/10588-74.html
Correct
https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10588-74.html
Root guard uses blocking, BPDU guard uses err-disabled
From that link.
“If the bridge receives superior STP Bridge Protocol Data Units (BPDUs) on a root guard-enabled port, root guard moves this port to a root-inconsistent STP state. This root-inconsistent state is effectively equal to a listening state.”
I agree that root guard is the most correct answer, and at least this version of the question talks about a port and not the switch. “superior BPDU ” is the key I believe. It indicates that some BPDU was accepted, and BPDU guard would not accept any.