H3C S5120-EI Series Operation Manual page 113

To do...
Enter port group
view
Enable the root guard function for
the port(s)
Among loop guard, root guard and edge port settings, only one function (whichever is configured the
earliest) can take effect on a port at the same time.
Enabling Loop guard
By keeping receiving BPDUs from the upstream device, a device can maintain the state of the root port
and blocked ports. However, due to link congestion or unidirectional link failures, these ports may fail to
receive BPDUs from the upstream devices. In this case, the downstream device will reselect the port
roles: Those ports in forwarding state that failed to receive upstream BPDUs will become designated
ports, and the blocked ports will transition to the forwarding state, resulting in loops in the switched
network. The loop guard function can suppress the occurrence of such loops.
If a loop guard–enabled port fails to receive BPDUs from the upstream device, and if the port takes part
in STP calculation, all the instances on the port, no matter what roles the port plays, will be set to, and
stay in, the Discarding state.
Make this configuration on the root port or an alternate port of a device.
Follow these steps to enable loop guard:
To do...
Enter system view
Enter Ethernet
interface view, or
Enter
Layer 2
interface view
aggregate
or port group
interface view
view
Enter port group
view
Enable the loop guard function for
the ports
Among loop guard, root guard and edge port settings, only one function (whichever is configured the
earliest) can take effect on a port at the same time.
Use the command...
port-group manual
port-group-name
stp root-protection
Use the command...
system-view
interface interface-type
interface-number
port-group manual
port-group-name
stp loop-protection
1-36
Remarks
Required
Disabled by default
Remarks
—
Required
Use either command.
Required
Disabled by default