User's Manual

User’s Manual of SGS-5240 Series Managed Switch
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4.2.19 UDLD
The switch can be configured to detect general loopback conditions caused by hardware problems or faulty protocol settings.
When enabled, a control frame is transmitted on the participating ports, and the switch monitors inbound traffic to see if the
frame is looped back.
4.2.19.1 Global Configuration
Switch Management > UDLD > Global Configuration page is used to configure the Unidirectional Link Detection message probe
interval, detection interval, and recovery interval.
◆ Message Interval – Configures the message interval between UDLD probe messages for ports in the advertisement phase
and determined to be bidirectional. (Range: 7-90 seconds; Default: 15 seconds)
UDLD probe messages are sent after linkup or detection phases. During the detection phase, messages are exchanged at the
maximum rate of one per second. After that, if the protocol reaches a stable state and determines that the link is bidirectional,
the message interval is increased to a configurable value based on a curve known as M1(t), a time-based function described in
RFC 5171.
If the link is deemed anything other than bidirectional at the end of the detection phase, this curve becomes a flat line with a
fixed value of Mfast (7 seconds).
If the link is instead deemed bidirectional, the curve will use Mfast for the first four subsequent message transmissions and then
transition to an Mslow value for all other steady-state transmissions. Mslow is the value configured by this command.
◆ Detection Interval – Sets the amount of time the switch remains in detection state after discovering a neighbor. (Range: 5-255
seconds; Default: 5 seconds)
When a neighbor device is discovered by UDLD, the switch enters “detection state” and remains in this state for specified
detection-interval. After the detection-interval expires, the switch tries to decide whether or the link is unidirectional based on the
information collected during the “detection state.”
◆ Recovery Status – Configures the switch to automatically recover from UDLD disabled port state after a period specified by
the Recovery Interval. (Default: Disabled)
When automatic recovery state is changed, any ports shut down by UDLD will be reset.
◆ Recovery Interval – Specifies the period after which to automatically recover from UDLD disabled port state. (Range:
30-86400 seconds; Default: 7 seconds)
When the recovery interval is changed, any ports shut down by UDLD will be reset.