Refer to the exhibit.
What information can be derived from the output?
A.
Interfaces FastEthernet3/1 and FastEthernet3/2 are connected to devices that are
sending BPDUs with a superior root bridge parameter and no traffic is forwarded across the
ports. After the sending of BPDUs has stopped, the interfaces must be shut down
administratively, and brought back up, to resume normal operation.
B.
Devices connected to interfaces FastEthernet3/1 and FastEthernet3/2 are sending
BPDUs with a superior root bridge parameter, but traffic is still forwarded across the ports.
C.
Devices connected to interfaces FastEthernet3/1 and FastEthernet3/2 are sending
BPDUs with a superior root bridge parameter and no traffic is forwarded across the ports.
After the inaccurate BPDUs have been stopped, the interfaces automatically recover and
resume normal operation.
D.
Interfaces FastEthernet3/1 and FastEthernet3/2 are candidates for becoming the STP
root port, but neither can realize that role until BPDUs with a superior root bridge parameter
are no longer received on at least one of the interfaces.
Explanation:
Root guard is configured on a per-port basis. If a superior BPDU is received on the port, root
guard does not take the BPDU into account and so puts the port into a root-inconsistent
sate. When devices connected on FastEthernet3/1 and FastEthernet3/2 stops sending
superior BPDUs, the port will be unblocked again and will transition through STP states like
any other port.
Reference:
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800ae96b.shtml