Can I stack 6248P switches by 10GB interfaces?

Hello all,

the question may look stupid, but I'm really got stuck and not stack :-)

I have two PowerConnect 6248P switches with the SFP+ interface cards, Dell's transmitters and fiber-optic cable, updated to the last firmware.

Both 10Gb links on switches are up and running, I can ping machines over that connection, but I can't stack the switches together. I wonder if it's possible at all?

Is stacking supported only with Dell's stacking module/cables only? Or may be I need to make a loop (with two fiber-optic cables), imitating stacking cables, to have stack running over 10Gb?

Does somebody successfully manage to stack switches over 10Gb interface?

In Stack Port summary I can select Stack Mode to Stack instead of Ethernet, but when I reboot switches it comes back to Ethernet.

Thanks in advance,

Nikolai