OcNOS DC : Layer 2 Guide : Layer 2 Configuration : Unidirectional Link Detection Configuration
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 19-33 shows the topology of the UDLD configuration.
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