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CST Spanning Tree settings on Aruba 1930 switch in a switch tree of 2930M switches

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  • 1.  CST Spanning Tree settings on Aruba 1930 switch in a switch tree of 2930M switches

    Posted Aug 19, 2021 11:06 AM
    Hi all,
    we have recently installed 2 new Aruba 1930 switches (JL685A) into a network with many 2930M 24G / 2930M 48G / 3810M.
    I write this post to examine the 2 switches 1930 which from now I will call 1930sw01 and 1930sw02 and other 2 switches 2930M which from now I will call 2930Msw01 and 2930Msw02.
    1930sw01 is connected to 1930sw02 with a trunk (TRK1).
    1930sw01 is connected to 2930Msw01 with a second trunk (TRK2).
    1930sw02 is connected to 2930Msw02 with a second trunk (TRK2).
    2930Msw01 is connected to 2930Msw02 on 2 port 10G, A1 and A4.
    As you can understand, a loop is created that we manage and govern with the spanning tree.
    Now, I have a problem in my configuration.
    I want TRK1 (the link between the 2 1930s) to always remain in forwarding and that one of the 2 TRK2 (in 1930sw01 or 1930sw02) was put as alternate and therefore blocked.
    Unfortunately, exactly the opposite happens: if I connect all the network cables, TRK2 remains in forwarding both on 1930sw01 and on 1930sw02, while TRK1 becomes alternate / blocked on one of the 2 1930 switches (always 1930sw02).
    I have spanned tree enabled as MSTP on both of my 1930s.
    In CST configuration I tried to lower both the priority (from default 128 to 0 or 16 or 32) and the cost of the path (from 0 default or auto to 200 or 2000), but the result is always the same: TRK1 is always blocked.
    Why?
    Thanks in advance for the suggestions you can give me.
    Greetings

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    Alberto Crippa
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