Cisco 350 Series Administration Manual page 223

10
UDLD
176
This section describes how the Unidirectional Link Detection (UDLD) feature.
It covers the following topics:
• UDLD Overview
• UDLD Global Settings
• UDLD Interface Settings
• UDLD Neighbors
UDLD Overview
UDLD is a Layer 2-protocol that enables devices connected through fiber-optic or twisted-pair
Ethernet cables to detect unidirectional links. A unidirectional link occurs whenever traffic
from a neighboring device is received by the local device, but traffic from the local device is
not received by the neighbor.
The purpose of UDLD is to detect ports on which the neighbor does not receive traffic from
the local device (unidirectional link) and to shut down those ports.
All connected devices must support UDLD for the protocol to successfully detect
unidirectional links. If only the local device supports UDLD, it is not possible for the device to
detect the status of the link. In this case, the status of the link is set to undetermined. The user
can configure whether ports in the undetermined state are shut down or not.
UDLD States and Modes
Under the UDLD protocol, ports are assigned the following states:
• Detection—System is attempting to determine whether the link is bidirectional or
unidirectional. This is a temporary state.
• 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.
Cisco 350, 350X and 550X Series Managed Switches, Firmware Release 2.4, ver 0.4
Port Management
UDLD