Switching

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  • 1.  BPDU hanadling on a port with rstp disabled (per port)

    Posted 01-16-2020 13:17

    Hi,

     

    Lets assume that a switch has RSTP globally enabled, but on some ports it has RSTP disabled (set protocols rstp interface <name> disable).

    What happens when it receives a RSTP BPDU on one of the ports with rstp disabled? Does it forward them to all the rest of the “rstp disabled” ports? Drops them? Floods to ALL ports?

     

    Regards,

    Pawel



  • 2.  RE: BPDU hanadling on a port with rstp disabled (per port)
    Best Answer

     
    Posted 01-16-2020 13:35

    In general, it should flood.  This is the "standard (?)" behavior I have experienced with most switches.  I do not believe this an formal RFC type document for how to handle this, and do believe not covered under 802.1D or w.

     

    Some recent testing of QFX5100/5110 for an PVST situation we found that QFX5100/5110 drops -  the 'standard' BPDU packet always; enabled or disabled never floods.  So depending on the product this might change.  Unfortunately to know for sure, you probably have to run a local test on the product you want to use, with what ever code release you are using.

     

    Good Luck



  • 3.  RE: BPDU hanadling on a port with rstp disabled (per port)

     
    Posted 01-16-2020 19:52

    Hi Gentleman,

     

    If the device receives a BPDU packet, BPDU will be flooded to the same segment only if you don't have anything configured for STP or any of its variations/flavors.



  • 4.  RE: BPDU hanadling on a port with rstp disabled (per port)

     
    Posted 01-16-2020 19:28

    I believe if the port is not enabled for rstp then the bpdu frame will be treated as any other multicast frame and would be flooded to other ports. This is similar to a bpdu frame received which the switch doesnt recognize so it will flood. However the behavior may vary across different juniper platforms as suggested by rccpgm in the last reply.



  • 5.  RE: BPDU hanadling on a port with rstp disabled (per port)

     
    Posted 01-16-2020 19:40

    Greetings pmazurkiewicz,

     

    If you have RSTP configured but disabled on some ports as you described, It will prevent the RSTP BPDU from the peer device on the configured interface and also never transits such RSTP BPDU to the peer device. However, other BPDU's from STP, MSTP, or VSTP enabled device, will not be prevented by the above configuration, if you want to prevent those BPDU's you will have to use this configuration as well "set ethernet-switching-options bpdu-block interface ge-x/x/x drop"

     

    For more information, refer to the following link:

    http://www.juniper.net/techpubs/en_US/junos12.2/topics/task/configuration/spanning-trees-bpdu-block-cli.html#bpdu-block-drop

     

     

    If this solves your problem, please mark this post as "Accepted Solution" so we can help others too.
    If you consider that my input was helpful, giving me a kudos would make my day:)