HP 6120XG ProCurve Series 6120 Blade Switches Management and Configuration Gui - Page 246

Port Status and Configuration Uni-Directional Link Detection (UDLD) Uni-Directional Link Detection (UDLD) Uni-directional Link Detection (UDLD) monitors a link between two ProCurve switches and blocks the ports on both ends of the link if the link fails at any point between the two devices. This feature is particularly useful for detecting failures in fiber links and trunks. Figure 10-21 shows an example. Scenario 1 (No UDLD): Without UDLD, the switch ports remain enabled despite the link failure. Traffic continues to be load-balanced to the ports connected to the failed link. Scenario 2 (UDLD-enabled): When UDLD is enabled, the feature blocks the ports connected to the failed link. Fiber Third Party Switch ProCurve Switch ProCurve Switch Trunk Link Failure Third Party Switch Third Party Switch ProCurve Switch Figure 10-21. UDLD Example In this example, each ProCurve switch load balances traffic across two ports in a trunk group. Without the UDLD feature, a link failure on a link that is not directly attached to one of the ProCurve switches remains undetected. As a result, each switch continue to send traffic on the ports connected to the failed link. When UDLD is enabled on the trunk ports on each ProCurve switch, the switches detect the failed link, block the ports connected to the failed link, and use the remaining ports in the trunk group to forward the traffic. Similarly, UDLD is effective for monitoring fiber optic links that use two unidirection fibers to transmit and receive packets. Without UDLD, if a fiber breaks in one direction, a fiber port may assume the link is still good (because the other direction is operating normally) and continue to send traffic on the 10-31