Cisco 350 Series Administration Manual page 224

Port Management
UDLD
Cisco 350, 350X and 550X Series Managed Switches, Firmware Release 2.4, ver 0.4
• Undetermined—The system cannot determine the state of the port, because one of the
following is occurring:
- The neighbor does not support UDLD.
or
- The local device does not receive traffic from the neighbor.
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 state of the port is determined to be bi-directional and the UDLD
information times out while the link on the port is still up, UDLD tries to re-establish
the state of the port.
• Aggressive
If the link state of the port is determined bi-directional and the UDLD information
times out, UDLD shuts down the port after an extended period of time, when it can
determine that the link is faulty. The port state for UDLD is marked as undetermined.
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.
• 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.
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