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Step Command Remarks
1. Enter system view.
system-view
N/A
2. Enter Layer 2 Ethernet
interface view.
interface
interface-type
interface-number
N/A
3. Enable BPDU drop on the
interface.
bpdu-drop any
By default, BPDU drop is
disabled.
Enabling PVST BPDU guard
An MSTP-enabled device forwards PVST BPDUs as data traffic because it cannot recognize PVST
BPDUs. If a PVST-enabled device in another independent network receives the PVST BPDUs, a
PVST calculation error might occur. To avoid PVST calculation errors, enable PVST BPDU guard on
the MSTP-enabled device. The device shuts down a port if the port receives PVST BPDUs.
To enable PVST BPDU guard:
Step Command Remarks
1. Enter system view.
system-view
N/A
2. Enable PVST BPDU guard.
stp pvst-bpdu-protection
By default, PVST BPDU guard is
disabled.
About dispute guard
Dispute guard is enabled by default. You do not need to manually configure this feature.
Dispute guard can be triggered by unidirectional link failures. If an upstream port receives inferior
BPDUs from a downstream designated port in forwarding or learning state because of a
unidirectional link failure, a loop appears. Dispute guard blocks the upstream designated port to
prevent the loop.
As shown in Figure 42, in norm
al conditions, the spanning tree calculation result is as follows:
• Device A is the root bridge, and Port A1 is a designated port.
• Port B1 is blocked.
When the link between Port A1 and Port B1 fails in the direction of Port A1 to Port B1 and becomes
unidirectional, the following events occur:
1. Port A1 can only receive BPDUs and cannot send BPDUs to Port B1.
2. Port B1 does not receive BPDUs from Port A1 for a certain period of time.
3. Device B determines itself as the root bridge.
4. Port B1 sends its BPDUs to Port A1.
5. Port A1 determines the received BPDUs are inferior to its own BPDUs. A dispute is detected.
6. Dispute guard is triggered and blocks Port A1 to prevent a loop.
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