Loop Protection for a Spanning-Tree Instance Interface
You can prevent a spanning-tree instance interface from interpreting a lack of received BPDUs as a “false positive” condition for making the interface the designated port.
To configure a spanning-tree instance interface to participate in loop protection, include the bpdu-timeout-action statement with either the block or alarm option for the STP interface.
You can include this statement at the following hierarchy levels:
- [edit protocols rstp]
- [edit protocols mstp]
- [edit protocols vstp]
- [edit routing-instances routing-instance-name protocols rstp]
- [edit routing-instances routing-instance-name protocols mstp]
- [edit routing-instances routing-instance-name protocols vstp]
 | Note: Spanning-tree instance interface loop protection is enabled for all spanning-tree instances on the interface, but blocks or alarms only those instances that stop receiving BPDUs. |
We recommend you configure loop protection only on non-designated interfaces such as the root or alternate interfaces. Otherwise, if you configure loop protection on both sides of a designated link, then certain STP configuration events (such as setting the root bridge priority to an inferior value in a topology with many loops) can cause both interfaces to transition to blocking mode.
