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Posting
Confirming what David has already posted, a loop depends on whether the two physical links between the stack and the downstream switch are two logical links or one logical link (port-channel/Etherchannel). The former will, by default, create a loop, the latter will not. The former will only transfer traffic on one link (the second is a redundant "spare") the latter can transfer data across both links. Failure of the fomer will likely cause a longer traffic interruption than the latter.
