Configuring Uni-Directional Link Detection (Udld) - Dell PowerConnect B-RX Configuration Manual

Configuring Uni-Directional Link Detection (UDLD)

This chapter describes configuring Uni-Directional Link Detection.Uni-directional Link Detection
(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
FIGURE 20
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
first keep-alive message from the other end. In the active state, UDLD peers will continue to
exchange keep alive messages periodically and if there are keep-alive messages are missed for
certain number of times from the other end, UDLD will bring down the logical port. The UDLD will
then transition from active to suspended state.
Everytime UDLD is enabled on a port, the port will be transitioned into the suspended state to
detect if the other end (peer) supports UDLD. This include the case where:
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BigIron RX Series Configuration Guide
53-1002253-01
shows an example.
UDLD example
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.
User enables UDLD on a port
A port that has UDLD enabled coming back up after an system reboot
Port was brought down by UDLD after uni-directional link was detected and now the problem is
fixed.
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