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.
You configure spanning-tree protocol loop protection to prevent selected interfaces from
interpreting the lack of received BPDUs as a “false positive” condition for making the
interface the designated port.
Related
Documentation
Configuring Loop Protection for a Spanning-Tree Instance Interface on page 428•
• Example: Enabling Loop Protection for Spanning-Tree Protocols on page 429
Loop Protection for a Spanning-Tree Instance Interface
By default, a spanning-tree protocol interface that stops receiving Bridge Protocol Data
Unit (BPDU) data frames will transition to the designated port (forwarding) state, creating
a potential loop. To prevent a spanning-tree instance interface from interpreting a lack
of received BPDUs as a “false positive” condition for assuming the designated port role,
you can configure one of the following loop protection options:
•
Configure the router to raise an alarm condition if the spanning-tree instance interface
has not received BPDUs during the timeout interval.
•
Configure the router to block the spanning-tree instance interface if the interface has
not received BPDUs during the timeout interval.
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.
Related
Documentation
Understanding Loop Protection for Spanning-Tree Instance Interfaces on page 426•
• Configuring Loop Protection for a Spanning-Tree Instance Interface on page 428
• Example: Enabling Loop Protection for Spanning-Tree Protocols on page 429
• bpdu-timeout-action on page 1452
• interface (Spanning Tree)
427Copyright © 2017, Juniper Networks, Inc.
Chapter 12: Configuring Layer 2 Control Protocol
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