Cisco 550X Série Guide De Démarrage Rapide page 17

No IP route:
If the switch and your computer are in different IP subnets, you need
one or more routers to route the packets between the two subnets.
Unusually long access time:
Due to the standard spanning tree loop detection logic, adding new
connections may take 30 to 60 seconds for the affected interfaces
and/or LAN to become operational.
Cisco 550X Series Stackable Managed Switches Quick Start Guide 17