Reference Guide

412 UDLD
Inconsistent UDLD Mode in Local and Neighboring Device
It is possible for the local device and its neighbor to be set to a different
UDLD mode (normal, aggressive). The UDLD mode is not contained in the
UDLD messages, so that the local device does not know the UDLD mode of
the neighbor and vice versa.
If the UDLD modes are different on the local and neighbor devices, the
devices act as follows:
• When the UDLD state of the link is bidirectional or unidirectional, both
devices shut down their ports.
• When the UDLD state of the port is undetermined, the side with the
normal UDLD mode merely issues a notification, while the side with the
aggressive UDLD mode shuts down the port.
If both devices are in normal mode, the port is not shut down when its state is
undetermined.
Reactivating a Shutdown Port
You can reactivate a port that was shut down by UDLD in one of the
following ways:
• Automatically —Configure the system to automatically reactivate ports
shut down by UDLD in the
Port Management > Error Recovery
Settings
page. In this case, when a port is shut down by UDLD, it is
automatically reactivated when the automatic recovery interval expires.
UDLD again begins running on the port. If the link is still unidirectional,
UDLD shuts it down again after the UDLD expiration time expires, for
instance.
•
Manually —Reactivate a port in the Port Management > Error Recovery
Settings
page.
Usage Guidelines
Dell does not recommend enabling UDLD on ports that are connected to
devices on which UDLD is not supported or disabled. Sending UDLD
packets on a port connected to a device that does not support UDLD simply
causes more traffic on the port without providing benefits.
In addition, take the following into consideration when configuring UDLD: