Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureMedium
A network administrator needs to troubleshoot an intermittent connectivity issue between two switches. The issue randomly occurs and affects only a few devices. The administrator suspects a unidirectional link, where traffic flows in one direction but not the other. Which Cisco feature can help detect and prevent issues caused by such a link?
- ABPDU Guard
- BUDLD
- CLoop Guard
- DPort Security
Show answer & explanationAnswer & explanation
Correct answer: B. UDLD
Unidirectional Link Detection (UDLD) is a Cisco proprietary protocol that monitors the physical wiring of a link to detect if traffic is flowing in only one direction. If a unidirectional link is detected, UDLD can disable the port to prevent issues like Layer 2 loops or blackholing traffic.
Why the other options are wrong
- A. BPDU Guard prevents switches from being connected to access ports, protecting the spanning tree topology.
- C. Loop Guard prevents alternate or root ports from becoming designated ports, protecting against Layer 2 loops in specific STP scenarios.
- D. Port Security restricts devices that can connect to a port based on MAC addresses.
Unidirectional Link Detection (UDLD)
A Cisco proprietary protocol that monitors the physical integrity of a link to detect if traffic is flowing in only one direction, which can prevent Layer 2 issues.
- Detects unidirectional links.
- Operates at Layer 1/2.
- Can disable a port upon detection.
- Prevents issues like loops and traffic blackholes.
Memory trick: UDLD: Unidirectional Link Detector, sees if the road is one-way when it should be two.