H3C S3100 Series Command Manual

1-21
Use the undo loopback-detection control enable command to disable the loopback port control
function on the trunk or hybrid port.
The loopback port control function works in conjunction with the loopback detection function (refer to
loopback-detection enable). If a loop is found on a VLAN of the trunk or hybrid port:
z With the function enabled on the trunk or hybrid port, the system will set the port to the block state
(ports in this state cannot forward data packets), send log and trap messages to the terminal, and
remove the corresponding MAC forwarding entry. After the loop is removed, the port will
automatically resume the normal forwarding state.
z With the function disabled on the trunk or hybrid port, the system will only send log and trap
messages to the terminal, and the port is still in the normal forwarding state.
By default, the loopback port control function is enabled on ports if the device boots with the default
configuration file (config.def); if the device boots with null configuration, this function is disabled.
Note that this command is invalid for an access port.
Related command: loopback-detection enable.
Example
# Enable the loopback port control function on Ethernet 1/0/1.
<Sysname> system-view
System View: return to User View with Ctrl+Z.
[Sysname] interface ethernet 1/0/1
[Sysname-Ethernet1/0/1] port link-type trunk
[Sysname-Ethernet1/0/1] loopback-detection control enable
loopback-detection enable
Syntax
loopback-detection enable
undo loopback-detection enable
View
System view or Ethernet port view
Parameter
None
Description
Use the loopback-detection enable command to enable the loopback detection function on the
current port to detect whether an external loopback occurs on the port.
Use the undo loopback-detection enable command to disable the loopback detection function on the
port.
1) If a loop is found on an access port, the system will set the port to the block state (ports in this state
cannot forward data packets), send log and trap messages to the terminal, and remove the
corresponding MAC forwarding entry.
z If you have enabled the loopback port auto-shutdown function (with the loopback-detection
shutdown enable
command) on the access port, the system will shut down the port, and send log
and trap messages to the terminal. After the loop is removed, you need to use the undo shutdown
command to bring up the port.

H3C S3100 Series Specifications

General

Brand	H3C
Model	S3100 Series
Category	Switch
Language	English