Configuring Uni-Directional Link Detection (Udld); Configuration Considerations - HP ProCurve 9304M Installation And Configuration Manual

Chapter 9

Configuring Uni-Directional Link Detection (UDLD)

Uni-directional Link Detection (UDLD) monitors a link between two HP devices and brings the ports on both ends
of the link down if the link goes down at any point between the two devices. This feature is useful for links that are
individual ports and for trunk links. Figure 9.1 shows an example.
Figure 9.1 UDLD example
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Normally, an HP device load balances traffic across the ports in a trunk group. In this example, each HP device
load balances traffic across two ports. Without the UDLD feature, a link failure on a link that is not directly
attached to one of the HP devices is undetected by the HP devices. As a result, the HP devices continue to send
traffic on the ports connected to the failed link.
When UDLD is enabled on the trunk ports on each HP device, the devices detect the failed link, disable the ports
connected to the failed link, and use the remaining ports in the trunk group to forward the traffic.
Ports enabled for UDLD exchange proprietary health-check packets once every second (the keepalive interval). If
a port does not receive a health-check packet from the port at the other end of the link within the keepalive
interval, the port waits for two more intervals. If the port still does not receive a health-check packet after waiting
for three intervals, the port concludes that the link has failed and takes the port down.

Configuration Considerations

• The feature is supported only on Ethernet ports.
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