Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureMedium
A network administrator is troubleshooting an intermittent connectivity issue between two Cisco Catalyst switches. The issue manifests as periods of packet loss and flapping links, specifically on fiber optic connections. Both switches report 'UDLD_DISABLED' messages. Which feature should the administrator enable to detect and prevent such issues on these links?
- AStorm Control
- BUnidirectional Link Detection (UDLD)
- CPort Security
- DBPDU Guard
Show answer & explanationAnswer & explanation
Correct answer: B. Unidirectional Link Detection (UDLD)
Unidirectional Link Detection (UDLD) is designed to detect and disable unidirectional links, which can cause issues like spanning-tree loops and black-holing of traffic, especially on fiber optic connections where one-way communication might occur without a link-down event.
Why the other options are wrong
- A. Storm Control prevents excessive broadcast, multicast, or unknown unicast traffic from overwhelming the switch, unrelated to unidirectional links.
- C. Port Security restricts MAC addresses on a port to prevent unauthorized access, not to detect unidirectional links.
- D. BPDU Guard shuts down a port if it receives a BPDU, preventing unauthorized devices from participating in STP, not for detecting unidirectional links.
Unidirectional Link Detection (UDLD)
A Layer 2 protocol that monitors the physical integrity of a link to detect if traffic is flowing in only one direction, which can lead to network issues like loops or black holes.
- Prevents issues caused by one-way communication on a link.
- Operates in normal or aggressive mode.
- Typically used on fiber optic links.
Memory trick: UDLD Uncovers Unidirectional Disasters