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Port Status and Configuration

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 10-19 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.

Trunk

ProCurve

Switch

Link Failure

Third Party

Switch

ProCurve

Switch

Figure 10-19. 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 uni-

direction 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

10-24

HP ProCurve Management And Configuration Guide

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