Final answer:
UDLD (Unidirectional Link Detection) is the feature that detects unidirectional links and places the port into an error-disabled state to prevent network problems such as loops or traffic blackholes.
Step-by-step explanation:
The feature that detects unidirectional links and places the port into an error-disabled state is UDLD (Unidirectional Link Detection). UDLD is a Layer 2 protocol designed by Cisco to monitor the physical configuration of the cables and detect when a fiber or copper link is functioning in one direction only. When UDLD detects that the link is only receiving data but not able to transmit, it assumes there is a unidirectional link problem and disables the affected port to prevent any potential problems, such as loops or blackholing of traffic. Other features mentioned like BPDU Guard, Loop Guard, and Root Guard are also Cisco-specific features, but they serve different purposes in the network:
- BPDU Guard is used to protect the network from possible loops by shutting down ports that receive Bridge Protocol Data Unit (BPDU) packets on ports where they are not expected.
- Loop Guard provides additional protection against loops by checking for the absence of BPDUs on designated ports and blocking those ports if BPDUs are missing.
- Root Guard prevents a switch port from becoming a root port, ensuring the designated switch remains as the root switch in the network.