User’s Guide
FUJITSU PSWITCH
December/2018
79
The LLDP component transmit and receive functions can be enabled/disabled
separately per physical port. By default, both transmit and receive functions are
disabled on all ports.
Both local and remote data may be displayed by the user interface and retrieved
using SNMP as defined in the LLDP MIB definitions.
3.1.2.13.
UDLD (Unidirectional Link Detection)
The UDLD feature detects unidirectional links to physical ports. UDLD must be
enabled on the both sides of the link in order to detect a unidirectional link. The
UDLD protocol operates by exchanging packets containing information about
neighboring devices. The purpose of the UDLD feature is to detect and avoid
unidirectional links. A unidirectional link is a forwarding anomaly in a Layer 2
communication channel in which a bidirectional link stops passing traffic in one
direction.
3.1.2.13.1.
UDLD Modes
The UDLD supports two modes: normal and aggressive.
In normal mode, a port's state is classified as undetermined if an anomaly exists.
An anomaly might be the absence of its own information in received UDLD
messages or the failure to receive UDLD messages. An undetermined state has no
effect on the operation of the port. The port is not disabled and continues
operating.
When operating in UDLD normal mode, a port will be put into a disabled state
(D-Disable) only in the following situations:
The UDLD PDU received from a partner does not have its own details (echo).
When there is a loopback, and information sent out on a port is received back
exactly as it was sent.
When operating in UDLD aggressive mode, a port is put into a disabled state for
the same reasons that it occurs in normal mode. Additionally, a port in UDLD
aggressive mode can be disabled if the port does not receive any UDLD echo
packets even after bidirectional connection was established. If a bidirectional link
is established, and packets suddenly stop coming from partner device, the UDLD
aggressive-mode port assumes that link has become unidirectional.
