SF300 – switch loop ?

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    Ok – so we arranged for a new switch to be added to the stack tonight. Some background:

    We have 3 x SF300 switches – one is a 48port, there are two 24 ports.

    from the 48port (in layer 3 mode)

    GI1 is connected to a router
    GI2 is connected to switch2
    GI3 is connected to switch3
    GI4 is connected to an ADSL modem.

    there’s some vlanning, but it shouldn’t be related.

    So, tonight’s task was for someone to mount the new switch in the rack, screw it in and do nothing else.

    in the process of doing so, it seems some of the cables needed to be moved (it’s a bit of a rats nest) so a whole section was actually unplugged. After mounting the new switch and plugging all the cables back in, there was no comms.

    once we got it all sorted (unable to access the switches at all even when plugged directly into them with the trunk links broken down) by unplugging ALL the distribution layer cables, it all came back on.

    I got this from the log:

    15-Mar-2013 02:17:46 :%STP-W-PORTSTATUS: gi2: STP status Forwarding
    15-Mar-2013 02:17:31 :%STP-W-LOOPBACKDETRSLV: gi2: STP Loopback Detection resolved.

    So. have I missed something on my spanning tree configuration or other setting ?

    Surely it shouldn’t have shut down the whole network or caused a broadcast storm?

    What should I be checking?

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