Correct Answer: A,B
Explanation/Reference:
Explanation:
STPDispute
Cisco switches has long time been implementing LoopGuard feature that allows for blocking the non- designated port when it loses the flow of STP BPDUs. This is helpful for detecting unidirectional link (normally on fiber optical links) and preventing Layer 2 loops that could go undetected by STP. Cisco's implementation of MSTP allows for detecting unidirection condition, by comparing the downstream port state reported in BPDUs. If the upstream switch sends superior root bridge information to the downstream bridge but receives the BPDUs with Designated bit set, the upstream switch concludes that the downstream does not hear its BPDU's. The upstream switch then blocks the downstream port and marks it as STP dispute link.
References: