Default Udld Configuration; Configuring Udld On The Switch - Cisco 4500M Software Manual

Default UDLD Configuration

The switch periodically transmits UDLD packets to neighbor devices on interfaces with UDLD enabled.
If the packets are echoed back within a specific time frame and they are lacking a specific
acknowledgment (echo), the link is flagged as unidirectional and the interface is shut down. Devices on
both ends of the link must support UDLD in order for the protocol to successfully identify and disable
unidirectional links.
By default, UDLD is locally disabled on copper interfaces to avoid sending unnecessary control traffic
Note
on this type of media, since it is often used for access interfaces.
Figure 21-1
from Switch A on the interface. However, Switch A does not receive traffic from Switch B on the same
interface. UDLD detects the problem and disables the interface.
Figure 21-1 Unidirectional Link
TX
TX
Default UDLD Configuration
Table 21-1
Table 21-1 UDLD Default Configuration
Feature
UDLD global enable state
UDLD per-interface enable state for fiber-optic media
UDLD per-interface enable state for twisted-pair (copper) media Disabled on all Ethernet 10/100 and 1000BaseTX

Configuring UDLD on the Switch

The following sections describe how to configure UDLD:
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Software Configuration Guide—Release 12.2(25)EW
21-2
shows an example of a unidirectional link condition. Switch B successfully receives traffic
Switch A
RX
RX
Switch B
shows the UDLD default configuration.
Enabling UDLD Globally, page 21-3
Enabling UDLD on Individual Interfaces, page 21-3
Disabling UDLD on Nonfiber-Optic Interfaces, page 21-3
Disabling UDLD on Fiber-Optic Interfaces, page 21-4
Resetting Disabled Interfaces, page 21-4
Default Status
Globally disabled
Enabled on all Ethernet fiber-optic interfaces
interfaces
Chapter 21 Configuring UDLD
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