Switches that have a DB-9 connection for console (e.g. X250), require a serial cable or a serial to USB adapter. A rollover cable can not be used to connect to an Ethernet port.
Note that the purple DB-9 to RJ-45 adapter shipped with EXOS switches with RJ-45 console ports requires a straight-through Ethernet cable to be used. A rollover or crossover cable should not be used with this adapter.