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Configuring UDLD
How to Configure UDLD
If you enable aggressive mode when all the neighbors of a port have aged out either in the advertisement or in the
detection phase, UDLD restarts the link-up sequence to resynchronize with any potentially out-of-sync neighbor. UDLD
shuts down the port if, after the fast train of messages, the link state is still undetermined.
Figure 71 UDLD Detection of a Unidirectional Link
Default UDLD Settings
How to Configure UDLD
Enabling UDLD Globally
Follow these steps to enable UDLD in the aggressive or normal mode and to set the configurable message timer on all
fiber-optic ports on the switch:
TX
TX
RX
RX
Switch A
Switch B
Switch B successfully
receives traffic from
Switch A on this port.
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However, Switch A does not receive traffic
from Switch B on the same port. If UDLD
is in aggressive mode, it detects the
problem and disables the port. If UDLD is
in normal mode, the logical link is
considered undetermined, and UDLD
does not disable the interface.
Feature Default Setting
UDLD global enable state Globally disabled
UDLD per-port enable state for fiber-optic media Disabled on all Ethernet fiber-optic ports
UDLD per-port enable state for twisted-pair (copper) media Disabled on all Ethernet 10/100 and 1000BASE-TX ports
UDLD aggressive mode Disabled
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