3Com S7906E Configuration Manual page 50

When a loop is detected on an access port, the device operates on the port according to the
pre-configured loopback detection actions, sends trap messages and log information to the terminal,
and deletes the corresponding MAC address forwarding entry.
When a loop is detected on a trunk port or a hybrid port, the device sends trap messages and log
information to the terminal. If loopback detection control is also enabled on the port, the device operates
on the port according to the pre-configured loopback detection actions, sends trap messages and log
information to the terminals, and deletes the corresponding MAC address forwarding entry.
Follow these steps to configure loopback detection:
To do...
Enter system view
Enable global loopback
detection
Configure the interval for port
loopback detection
Enter
Ethernet port
Enter
view
Ethernet port
view or port
Enter port
group view
group view
Enable loopback detection on a
port
Enable loopback detection
control on a trunk port or a
hybrid port
Enable loopback detection in all
the VLANs to which trunk or
hybrid ports belong
Specify actions to be taken on a
port when a loop is detected on
it
Loopback detection on a given port is enabled only after the loopback-detection enable
command has been configured in both system view and the port view of the port.
Loopback detection on all ports will be disabled after you configure the undo loopback-detection
enable command in system view.
For loopback detection actions to take effect on a trunk or hybrid port, you need to configure the
loopback-detection control enable command in the port view of the port.
Use the command...
system-view
loopback-detection enable
loopback-detection
interval-time time
interface interface-type
interface-number
port-group manual
port-group-name
loopback-detection enable
loopback-detection control
enable
loopback-detection per-vlan
enable
loopback-detection action
{ shutdown | semi-block |
no-learning }
1-10
Remarks
—
Required
Disabled by default
Optional
30 seconds by default
Use either command
Configurations made in
Ethernet port view takes effect
on the current port only;
configurations made in port
group view takes effect on all
ports in the port group
Required
Disabled by default
Optional
Disabled by default
Optional
Enabled only in the default
VLAN(s) with trunk port or
hybrid ports
Optional
By default, the port does not
specify loopback detection
actions.