Udld (Interface Configuration) - Cisco Catalyst 2950 Command Reference Manual

Chapter 2 Cisco IOS Commands

udld (interface configuration)

Use the udld interface configuration command to enable UniDirectional Link Detection (UDLD) on an
individual interface or to prevent a fiber-optic interface from being enabled by the udld global
configuration command. Use the no form of this command to return to the udld global configuration
command setting or disable UDLD if entered on a nonfiber-optic port.
Syntax Description
aggressive
disable
enable
Defaults On fiber-optic interfaces, UDLD is not enabled, in aggressive mode, or disabled. For this reason,
fiber-optic interfaces enable UDLD according to the state of the udld enable or udld aggressive global
configuration command.
On nonfiber-optic interfaces, UDLD is disabled.
Command Modes
Interface configuration
Command History Release
12.0(5.2)WC(1)
12.1(6)EA2
Usage Guidelines
UDLD is supported on fiber- and copper-based Ethernet ports.
A UDLD-capable port cannot detect a unidirectional link if it is connected to a UDLD-incapable port of
another switch.
This setting overrides the global UDLD configuration on the switch.
In normal mode, if UDLD is in the advertisement or in the detection phase and all the neighbor cache
entries are aged out, UDLD restarts the link-up sequence to resynchronize with any potentially
out-of-sync neighbors.
If you enable aggressive mode, when all the neighbors of a port have aged out either in the advertisement
or in the detection phase, UDLD restarts the link-up sequence to resynchronize with any potentially
out-of-sync neighbor. UDLD shuts down the port if, after the fast train of messages, the link state is still
undetermined. Use aggressive mode on point-to-point links where no failure between two neighbors is
allowed. In this situation, UDLD probe packets can be considered as a heart beat whose presence
guarantees the health of the link. Conversely, the loss of the heart beat means that the link must be shut
down if it is not possible to re-establish a bidirectional link.
78-11381-05
udld {aggressive | enable | disable}
no udld {aggressive | enable | disable}
Enable UDLD in aggressive mode on the specified interface.
Disable UDLD on the specified interface. This keyword applies only to
fiber-optic interfaces.
Enable UDLD in normal mode on the specified interface.
Modification
This command was first introduced.
The aggressive keyword was added.
Catalyst 2950 Desktop Switch Command Reference
udld (interface configuration)
2-313