In TelePresence campus networks, a link can transmit in one direction only, causing a lengthy delay in fault detection and, thus, excessive packet loss.
UniDirectional Link Detection (UDLD) protocol is a Layer 2 protocol that uses a keepalive to test that the switch-to-switch links connect and operate correctly. Enabling UDLD is a prime example of how to implement a defense-in-depth approach to failure detection and recovery mechanisms because UDLD (a L2 protocol) acts as a backup to the native Layer 1 unidirectional link detection capabilities provided by IEEE 802.3z (Gigabit Ethernet) and 802.3ae (Ten Gigabit Ethernet) standards.
The UDLD protocol allows devices connected through fiber-optic or copper Ethernet cables connected to LAN ports to monitor the physical configuration of the cables and detect when a unidirectional link exists. When a unidirectional link is detected, UDLD shuts down the affected LAN port and triggers an alert. Unidirectional links, such as shown in Figure 1, can cause a variety of problems, including spanning tree topology loops.
You can configure UDLD to be globally enabled on all fiber ports by entering the following command:
Switch(config)# udld enable
Additionally, you can enable UDLD on individual LAN ports in interface mode by entering the following commands:
Switch(config)# interface GigabitEthernet8/1 Switch(config-if)# udld port
Interface configurations override global settings for UDLD.
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