Port Management
UDLD
157 Cisco Sx350, SG350X, SG350XG, Sx550X & SG550XG Series Managed Switches, Firmware Release 2.2.5.x
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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.
• UDLD receives UDLD messages from neighboring devices. It caches these messages
until the expiration time (3 times message time) has passed. If a new message is
received before the expiration time, the information in that message replaces the
previous one.
• When the expiration time expires, the device does the following with the information
received:
- If the neighbor message contains the local device ID—The link status of the port
is set to bidirectional.
- If the neighbor message does not contain the local device ID—The link status of
the port is set to unidirectional, and the port is shut down.
• If UDLD messages are not received from a neighboring device during the expiration
time frame, the link status of the port is sent to undetermined and the following occurs:
- Device is in normal UDLD mode: A notification is issued.
- Device is in aggressive UDLD mode. The port is shut down.
While the interface is in the bidirectional or the undetermined state, the device periodically
sends a message each message time seconds. The above steps are performed over and over.
A port that was shut down can be reactivated manually in the Error Recovery Settings page.
For more information, see Reactivating a Shutdown Port.
If an interface is down and UDLD is enabled, the device removes all neighbor information and
sends at least one ULDL message to the neighbors informing them that the port is down. When
the port is brought up, the UDLD state is changed to Detection.
UDLD Not Supported or is Disabled on a Neighbor
If UDLD is not supported or disabled on a neighbor, then no UDLD messages are received
from that neighbor. In this case, the device cannot determine whether the link is unidirectional
or bidirectional. The status of the interface is then set to undetermined.
Reactivating a Shutdown Port
You can reactivate a port that was shut down by UDLD in one of the following ways:
• Automatically—You can configure the system to automatically reactivate ports shut
down by UDLD in the Error Recovery Settings page. In this case, when a port is shut
down by UDLD, it is automatically reactivated when the automatic recovery interval
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