Pretty simple setup.  2 MS425 switches flexible stacked (only one stack port used).  2 MS355 physically stacked.  We've created crossed switch aggregate ports on both stacks.  When we connect one link, everything is fine.  As soon as we connect the second link, everything blows up and both links go down.  Of course the event log is useless.  All I see is STP port changes, but no explanations.  Besides, it's an aggregate, so STP should be disabled automatically on the individual links.  We've removed all other links, so there are no physical loops. ... View more