This chapter describes configuring Uni-Directional Link Detection (UDLD). UDLD monitors a link
between two BigIron RX devices and provides a fast detection of link failures. UDLD 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 20

shows an example.

FIGURE 20

UDLD example

Ports enabled for UDLD exchange proprietary health-check packets once every 500 ms (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, UDLD will be kept in a
suspended state until it receives the first keep-alive message from the other end. In this
suspended state, UDLD will continue to send the keep-alive message but will not bring the port
down after maximum number of retries is done and no keep-alive message is received from the
other end. The UDLD will transition from this suspended state to active state after it receives the

Without link keepalive, the ports remain
enabled. Traffic continues to be load balanced to the
ports connected to the failed link.

When link keepalive is enabled, the feature
brings down the ports connected
to the failed link.