Huawei Quidway S8500 Series Command Manual page 841

Command Manual – STP
Quidway S8500 Series Routing Switches
Description
Use the stp interface loop-protection command to enable loop protection on the
switch in system view.
Use the undo stp interface loop-protection command to restore the default loop
protection state.
When port roles change, you can use the stp interface loop-protection command to
change port state from forwarding state to discarding state, thus avoiding port
loopback.
Use the undo stp interface loop-protection command to restore the default running
state of loop protection in system view.
The root port and other blocked ports maintain their state according to the BPDUs sent
by uplink switch. Due to link congestion or unidirectional link failure, these ports may be
unable to receive BPDUs and the switch will select root port again. In this case, the
former root port will turn into the specified port and the former blocked ports will change
to the forwarding state, and link loop appears.
The loop protection function can inhibit the generation of loop. After it is enabled, the
root port role will change according to the uplink port state. The blocked port will
maintain in discarding state and do not forward packets, thus avoiding link loop.
By default, loop protection is disabled.
Caution:
If the equipment connected to the port of the switch cannot send STP packets to the
switch, do not configure the loop-protection command; otherwise the port will be
congested for a long time.
Related command: stp loop-protection.
Note:
For a loopback port, if the port participates in STP calculation, it must be specified port
regardless of internal loop or external loop. However, the port is always set to be in
discarding state on all instances.
Example
# Enable loop protection on the Ethernet2/1/1.
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Chapter 1 MSTP Configuration Commands