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Catalyst 3500XL switches always connect at half duplex. When hardset to full duplex, the connection does not come up and shows the error message %GIGASTACK-1-NO_LOOP_DETECT


Core issue

The %GIGASTACK-1-NO_LOOP_DETECT message indicates the link neighbor of link [dec] of  GigaStack GBIC in [chars] did not respond to the loop detection request. If loop  topology is deployed, make sure all switches in the stack are running the latest  software. 

This message means that no acknowledgement for the loop-detection request is  received from one of the links on a GigaStack GBIC module. Either the  neighboring switch does not support the GigaStack GBIC loop-breaking algorithm,  or the link between the two GigaStack GBIC modules is broken. In this  condition, a GigaStack loop topology is not automatically detected, and the  connectivity between switches in the stack can be lost. [dec] is the link  number, and [chars] is the slot number.


If a loop topology is used with the GigaStack GBIC module, ensure that the  latest software is running on all switches in the stack. Check the GigaStack  GBIC modules involved to ensure that they are functioning. 

Gigastack can work only in half duplex. For more information, refer to the Features section of Catalyst GigaStack GBIC.