Chapter 15
| UniDirectional Link Detection Commands
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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.
Example
This example sets the message interval to 10 seconds.
Console(config)#udld message-interval 10
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 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,
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