Reference Guide

410 UDLD
• Bidirectional —Traffic sent by a local device is known to be received by its
neighbor, and traffic from the neighbor is received by the local device.
•
Shutdown —The link is unidirectional. Traffic sent by a local device is
received by its neighbor, but traffic from the neighbor is not received by
the local device.
•
Undetermined —The system cannot determine the state of the port,
because of one of the following is occurring:
– The neighbor does not support UDLD.
or
– The neighbor does not receive traffic from the local device.
The UDLD action in this case depends on the UDLD mode of the device
as explained below.
UDLD supports the following modes of operation:
•Normal
– If the link is unidirectional, the port is shut down.
– If the link is undetermined, the port is not shut down. Its status is
changed to undetermined and a notification is sent.
• Aggressive
If the link is unidirectional or undetermined, the port is shut down.
UDLD is enabled on a port when one of the following occurs:
• The port is a fiber port and UDLD is enabled globally.
• The port is a copper port and you specifically enable UDLD on it.
How UDLD Works
When UDLD is enabled on a port, the following actions are performed:
• UDLD initiates the detection state on the port.
In this state, UDLD periodically sends messages on every active interface
to all neighbors. These messages contain the device ID of all known
neighbors. It sends these messages according to a user-defined message
time.