Cisco Catalyst 2960 Series User Manual

Event-Driven Detection and Echoing
UDLD relies on echoing as its detection operation. Whenever a UDLD device learns about a new neighbor
or receives a resynchronization request from an out-of-sync neighbor, it restarts the detection window on its
side of the connection and sends echo messages in reply. Because this behavior is the same on all UDLD
neighbors, the sender of the echoes expects to receive an echo in reply.
If the detection window ends and no valid reply message is received, the link might shut down, depending on
the UDLD mode. When UDLD is in normal mode, the link might be considered undetermined and might not
be shut down. When UDLD is in aggressive mode, the link is considered unidirectional, and the port is disabled.
Related Topics
Enabling UDLD Globally , on page 399
Enabling UDLD on an Interface , on page 400
UDLD Reset Options
If an interface becomes disabled by UDLD, you can use one of the following options to reset UDLD:
•
The udld reset interface configuration command.
•
The shutdown interface configuration command followed by the no shutdown interface configuration
command restarts the disabled port.
•
The no udld {aggressive | enable} global configuration command followed by the udld {aggressive |
enable} global configuration command reenables the disabled ports.
•
The no udld port interface configuration command followed by the udld port [aggressive] interface
configuration command reenables the disabled fiber-optic port.
•
The errdisable recovery cause udld global configuration command enables the timer to automatically
recover from the UDLD error-disabled state, and the errdisable recovery interval interval global
configuration command specifies the time to recover from the UDLD error-disabled state.
Related Topics
Enabling UDLD Globally , on page 399
Enabling UDLD on an Interface , on page 400
Default UDLD Configuration
Table 42: Default UDLD Configuration
Default SettingFeature
Globally disabledUDLD global enable state
Disabled on all Ethernet fiber-optic portsUDLD per-port enable state for fiber-optic media
Disabled on all Ethernet 10/100 and 1000BASE-TX
ports
UDLD per-port enable state for twisted-pair (copper)
media
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
398
Information About UDLD

Cisco Catalyst 2960 Series Specifications

General

Layer	Layer 2
Power over Ethernet (PoE)	Available on some models
RAM	128 MB
Flash Memory	32 MB
MAC Address Table Size	8000
Operating Temperature	0°C to 45°C (32 to 113°F)
Ports	24 or 48 x 10/100/1000