CLI Reference Guide-R04

Chapter 16 | UniDirectional Link Detection Commands
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Example
Console(config)#udld recovery-interval 40
Console(config)#
udld aggressive This command sets UDLD to aggressive mode on an interface. Use the no form to
restore the default setting.
Syntax
[no] udld aggressive
Default Setting
Disabled
Command Mode
Interface Configuration (Ethernet Port)
Command Usage
UDLD can function in two modes: normal mode and aggressive mode.
◆ In normal mode, determination of link status at the end of the detection
process is always based on information received in UDLD messages: whether
that’s information about the exchange of proper neighbor identification or the
absence of such. Hence, albeit bound by a timer, normal mode determinations
are always based on gleaned information, and as such are “event-based.” If no
such information can be obtained (e.g., because of a bidirectional loss of
connectivity), UDLD follows a conservative approach to minimize false
positives during the detection process and deems a port to be in
“undetermined” state. In other words, normal mode will shut down a port only
if it can explicitly determine that the associated link is faulty for an extended
period of time.
◆ In aggressive mode, UDLD will also shut down a port if it loses bidirectional
connectivity with the neighbor for the same extended period of time (as that
mentioned above for normal mode) and subsequently fails repeated last-resort
attempts to re-establish communication with the other end of the link. This
mode of operation assumes that loss of communication with the neighbor is a
meaningful network event in itself, and a symptom of a serious connectivity
problem. Because this type of detection can be event-less, and lack of
information cannot always be associated to an actual malfunction of the link,
this mode is recommended only in certain scenarios (typically only on point-to-
point links where no communication failure between two neighbors is
admissible).