H3C Technologies H3C WX5500E Series Access Controllers - Manual (Page 103)

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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.
Configuration restrictions and guidelines
• 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.
Configuration procedure
To enable loop guard:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter interface view or port
group view.
• Enter Layer 2 Ethernet interface view or
Layer 2 aggregate interface view:
interface interface-type interface-number
• Enter port group view:
port-group manual port-group-name
Use one of the commands.
3. Enable the loop guard
function for the ports.
stp loop-protection
By default, loop guard is
disabled.
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
device, the device will receive a large number of TC-BPDUs within a short time and be busy with flushing
forwarding address entries. This affects network stability.
With the TC-BPDU guard function, you can set the maximum number of immediate forwarding address
entry flushes that the device can perform every a specified period of time (10 seconds). For TC-BPDUs
received in excess of the limit, the device performs a forwarding address entry flush when the time period
expires. This prevents frequent flushing of forwarding address entries.
H3C does not recommend you disable this feature.
To enable TC-BPDU guard:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enable the TC-BPDU guard function. stp tc-protection enable
Optional.
By default, TC-BPDU guard is
enabled.