H3C S5120-SI series Configuration Manual page 96

To do...
Enter interface view or port
group view
Enable the root guard function
for the port(s)
NOTE:
You cannot configure root guard and loop guard on a port at the same time.
Enabling loop guard
By continuing to receive BPDUs from the upstream device, a device can maintain the state of the root port
and blocked ports. However, link congestion or unidirectional link failures might cause these ports to fail
to receive BPDUs from the upstream devices. The 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.
The initial state of a loop guard-enabled port is discarding in every MSTI. When the port receives BPDUs,
its state transitions normally. Otherwise, it stays in the discarding state to prevent temporary loops.
Configure loop guard on the root port and alternate ports of a device.
Follow these steps to enable loop guard:
To do...
Enter system view
Enter interface view or port
group view
Enable the loop guard function
for the ports
NOTE:
Do not enable loop guard on a port that connects user terminals. Otherwise, the port will stay in the
•
discarding state in all MSTIs because it cannot receive BPDUs.
• You cannot configure edge port settings and loop guard, or configure root guard and loop guard on a
port at the same time.
Enabling TC-BPDU guard
When a device receives topology change (TC) BPDUs (the BPDUs that notify devices of topology
changes), the device flushes the forwarding address entries. If someone forges TC-BPDUs to attack the
Use the command...
•
Enter Ethernet interface view or Layer 2
aggregate interface view:
interface interface-type interface-number
•
Enter port group view:
port-group manual port-group-name
stp root-protection
Use the command...
system-view
•
Enter Ethernet interface view or Layer 2
aggregate interface view:
interface interface-type interface-number
•
Enter port group view:
port-group manual port-group-name
stp loop-protection
85
Remarks
Required
Use one of the commands.
Required
By default, root guard is
disabled.
Remarks
—
Required
Use one of the commands.
Required
By default, loop guard is
disabled.