Unidirectional Link Detection Configuration
This chapter shows a complete configuration to enable UDLD in a simple network topology.
Overview
The purpose of Unidirectional Link Detection protocol (UDLD) is to monitor the physical links and detect when a unidirectional link exists. Upon detection user can either block the port or notify the link status based on the network administrator's configuration.
UDLD works in two different modes:
• Normal mode
• Aggressive mode
Topology
Figure 16-4 shows the topology of the UDLD configuration.
Figure 16-4: UDLD Configuration
S1
#configure terminal | Enter configure mode |
(config)#udld enable | Enable UDLD globally |
(config)#udld message-time 7 | Configure message time for UDLD packets |
(config)#interface eth1 | Enter interface mode |
(config-if)#switchport | Configure the interface as switch port |
(config-if)#udld state enable | Enable UDLD on the interface |
(config-if)#udld mode normal | Configure udld mode as normal or aggressive |
(config-if)#commit | Commit config. |
(config-if)#exit | Exit from the interface mode |
S2
#configure terminal | Enter configure mode. |
(config)#udld enable | Enable UDLD globally. |
(config)#udld message-time 7 | Configure message time for UDLD packets |
(config)#interface eth2 | Enter interface mode |
(config-if)#switchport | Configure the interface as switch port. |
(config-if)#udld state enable | Enable UDLD on the interface. |
(config-if)#udld mode normal | Configure udld mode as normal or aggressive |
(config-if)#commit | Commit config. |
(config-if)#exit | Exit from the interface mode |
Validation
#show udld
UDLD : Enable
Message Interval(sec) : 7
Port UDLD Status Mode Link-Status
------------------------------------------------
Eth1 Enable Normal Bi-directional
Eth2 Disable Normal Unknown
Eth3 Disable Normal Unknown
Eth4 Disable Normal Unknown
Eth5 Disable Normal Unknown
Eth6 Disable Normal Unknown
Once the links is made Uni-directional, the output of the command Show udld is as follows:
#show udld
UDLD : Enable
Message Interval(sec) : 7
Port UDLD Status Mode Link-Status
------------------------------------------------
Eth1 Enable Normal Unidirectional
Eth2 Disable Normal Unknown
Eth3 Disable Normal Unknown
Eth4 Disable Normal Unknown
Eth5 Disable Normal Unknown
Eth6 Disable Normal Unknown
#sh running-config
udld Enable
udld message-time 7
#sh running-config in eth1
!
interface eth1
switchport
udld state Enable
!
#sh udld interface eth1
UDLD Status : Enable
UDLD Mode : Normal
Link-State : Unknown
For aggressive mode, udld output is as follows:
#show udld
UDLD : Enable
Message Interval(sec) : 7
Port UDLD Status Mode Link-Status
------------------------------------------------
eth1 Enable Aggressive Bi-Directional
#sh running config
udld Enable
udld message-time 7
#sh running-config in eth1
interface eth1
switchport
udld mode Aggressive
udld state Enable
Last modified date: 11-08-2023