Support Support Downloads Knowledge Base Juniper Support Portal Community

Knowledge Base

Search our Knowledge Base sites to find answers to your questions.

Ask All Knowledge Base Sites All Knowledge Base Sites JunosE Defect (KA)Knowledge BaseSecurity AdvisoriesTechnical BulletinsTechnotes Sign in to display secure content and recently viewed articles

xSTP Protocol Data Unit flooding on EX and QFX devices



Article ID: KB35928 KB Last Updated: 15 Jun 2020Version: 1.0

This article explains the default behavior on EX2300, EX3400, EX4600, QFX5k series devices w.r.t xSTP BPDU (Bridge Protocol Data Unit) flooding, and provides a workaround to prevent it.


In the above-mentioned products, the default behavior of a switch is to address incoming xSTP BPDUs in the following way (when xSTP is not configured).

When a switch receives an incoming xSTP BPDU, it is sent to the PFE host path where it is re-inserted over the VLAN. This, in turn, may affect the link bandwidth as XSTP BPDU is flooded.

In order to prevent this from happening, no-mstp-flooding, no-vstp-flooding and no-stp-flooding have been introduced. By enabling these knobs under "switch-options", the packets are dropped at the PFE host path and never flooded/re-injected to the VLANs. 

CLI commands:
user@host# set switch-options no-mstp-flooding
user@host# set switch-options no-vstp-flooding
user@host# set switch-options no-stp-flooding


  1. Please verify the version on which you are trying to run the command. All three knobs are available for use in 15.1X53-D56 and 17.3 release onwards.  
  2. no-mstp-flooding, no-vstp-flooding and no-stp-flooding are hidden knobs and do not auto-populate on pressing the Tab key or the Space bar. You will have to type the command completely.
  3. This is not advised to be added to the configuration when xSTP is running on the setup since it prevents flooding of BPDUs to the VLANs.
Comment on this article > Affected Products Browse the Knowledge Base for more articles related to these product categories. Select a category to begin.

Getting Up and Running with Junos

Getting Up and Running with Junos Security Alerts and Vulnerabilities Product Alerts and Software Release Notices Problem Report (PR) Search Tool EOL Notices and Bulletins JTAC User Guide Customer Care User Guide Pathfinder SRX High Availability Configurator SRX VPN Configurator Training Courses and Videos End User Licence Agreement Global Search