Example for Configuring LBDT to Detect Loops on the Downstream Network

Networking Requirements

As shown in Figure 1, a new department of an enterprise connects to aggregation switch Switch, and this department belongs to VLAN 100. Loops may occur due to incorrect connections or configurations. As a result, communication on the Switch and uplink network may be affected.

It is required that the Switch should detect loops on the new network to prevent the impact of loops on the Switch and connected network.

Figure 1 Networking for configuring LBDT to detect loops on the downstream network

Configuration Roadmap

The new department network has only VLAN 100, so configure LBDT on the Switch to detect loops. The configuration roadmap is as follows:

Enable LBDT on the GE0/0/1 of the Switch to detect loops in a specified VLAN so that loops on the downstream network can be detected.
Set LBDT parameters so that the Switch can immediately shut down GE0/0/1 after a loop is detected. This prevents the impact of the loop on the Switch and connected network.

Configure interfaces on other switching interfaces as trunk or hybrid interfaces and configure these interfaces to allow packets from VLANs to pass through to ensure Layer 2 connectivity on the new network and between the new network and the Switch.

Procedure

Enable LBDT on the interface.

<HUAWEI> system-view
[HUAWEI] sysname Switch
[Switch] interface gigabitethernet 0/0/1
[Switch-GigabitEthernet0/0/1] loopback-detect enable
[Switch-GigabitEthernet0/0/1] quit

Specify the VLAN ID of LBDT packets.

[Switch] vlan 100
[Switch-vlan100] quit
[Switch] interface gigabitethernet 0/0/1
[Switch-GigabitEthernet0/0/1] port link-type hybrid
[Switch-GigabitEthernet0/0/1] port hybrid tagged vlan 100
[Switch-GigabitEthernet0/0/1] loopback-detect packet vlan 100
[Switch-GigabitEthernet0/0/1] quit

Configure LBDT parameters.

# Set the interval for sending LBDT packets.

[Switch] loopback-detect packet-interval 10

# Configure an action taken after a loop is detected.

[Switch] interface gigabitethernet 0/0/1
[Switch-GigabitEthernet0/0/1] loopback-detect action shutdown
[Switch-GigabitEthernet0/0/1] quit

Verify the configuration.

Run the display loopback-detect command to check the LBDT configuration.

[Switch] display loopback-detect                                              
Loopback-detect sending-packet interval: 10

(A): Auto Loopback-detect                                                                                                           
-----------------------------------------------------------------                                                                   
Interface                     RecoverTime  Action     Status                                                                        
-----------------------------------------------------------------
GigabitEthernet0/0/1          30           shutdown   NORMAL
-----------------------------------------------------------------

The preceding command output shows that the LBDT configuration is successful.

Construct loops on the downstream network and run the display loopback-detect command to check whether GE0/0/1 is shut down.

[Switch] display loopback-detect 
Loopback-detect sending-packet interval: 10                                     
                                                                                
(A): Auto Loopback-detect                                                                                                           
-----------------------------------------------------------------                                                                   
Interface                     RecoverTime  Action     Status                                                                        
-----------------------------------------------------------------
GigabitEthernet0/0/1          30           shutdown   SHUTDOWN
-----------------------------------------------------------------

The preceding command output shows that GE0/0/1 is shut down.

Configuration Files

Switch configuration file

#
sysname Switch
#
vlan batch 100
#
loopback-detect packet-interval 10
#
interface GigabitEthernet0/0/1
 port link-type hybrid
 port hybrid tagged vlan 100
 loopback-detect packet vlan 100
 loopback-detect enable
#
return