Hi,

Have you tried disabling the port and renabling it? It just is that one port that is having the spanning-tree issues right? If you switch it to a different port does it still do it? You may also want to update the firmware. http://www.dell.com/support/home/us/en/04/Drivers/DriversDetails?driverId=81TMJ&fileId=3681673153&osCode=NAA&productCode=networking-n1500-series&languageCode=en&categoryId=NI

Thank you for your help. The problem was on the Alcatel switch, it was configured with its own STP protocol