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Spanning tree root bridge issue

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  • 1.  Spanning tree root bridge issue

    Posted Feb 23, 2015 09:36 AM

    Hi.

     

    We have a network with a core layer switch 5406 and access switches.

    Spanning tree root guard protection is in place on the links from Core to access.

    However at some point I get this messsage in one of the access switches:

    I 02/19/15 15:38:58 00839 stp: CST Root changed from 4096: a01d48-80cc00 to
                32768: (this device)
    I 02/19/15 15:38:58 00839 stp: IST Root changed from 4096: a01d48-80cc00 to
                32768: (this device)
    I 02/19/15 15:38:58 00077 ports: port 52 is now off-line

     

    And at the same time on the Core:
    Feb 19 15:39:52 192.168.200.254 00077 ports:  port B13 is now off-line
    Feb 19 15:39:59 192.168.200.254 00435 ports:  port B13 is Blocked by STP
    Feb 19 15:40:00 192.168.200.254 00076 ports:  port B13 is now on-line
    Feb 19 15:40:17 192.168.200.254 00077 ports:  port B13 is now off-line
    Feb 19 15:40:20 192.168.200.254 00435 ports:  port B13 is Blocked by STP
    Feb 19 15:40:20 192.168.200.254 00076 ports:  port B13 is now on-line

     

    After a while the logs on the access switch:

    I 02/19/15 15:39:00 00435 ports: port 52 is Blocked by STP
    I 02/19/15 15:39:01 00839 stp: CST Root changed from 32768: (this device) to
                4096: a01d48-80cc00
    I 02/19/15 15:39:01 00839 stp: IST Root changed from 32768: (this device) to
                4096: a01d48-80cc00
    I 02/19/15 15:39:01 00076 ports: port 52 is now on-line

     

     

    Any ideas what sould possibly casue this since the root guard command is on place?

     

     

    Regards,

    Dimitra K.



  • 2.  RE: Spanning tree root bridge issue

    Posted Feb 23, 2015 05:10 PM

    I would be looking at the connection between the two ports - it looks like it might be flapping.



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