I've got 4 Force10 switches on a client's network. The first 3 (F10-0,1,2) are all running SFTOS (old version of FTOS) while the fourth (F10-3) is a POE switch running FTOS.
In FTOS, a given port must be either layer2 or layer3, which means you cannot assign an IP address to the port you want to use as the switches uplink. In my case, the network looks like this.

Firewall > F10-2 p48
                  F10-2 p47 > F10-1 p48
                              p46 > F10-0 p48
                                         F10-0 p47 > F10-3 p48
                                         F10-0 p05 > F10-3 p01

F10-3 p01 has an IP (so it's in layer3 mode), and is used for management, while F1-3 p48 is used as a layer2 switchport (uplink).

The problem is that when both F10-3 p01 and p48 are enabled and connected to F10-0 (p05 and p47), the entire network goes sideways and all switches crap out until we unplug either F10-0 p05 or p47. This suggests to me, that we have a routing loop, but that doesn't make any sense as F10-3 p01 isn't switching in layer2, and F10-3 p48 doesn't have an IP (so not in layer 3).

The problem has to be that p01 and p48 can't both be plugged in at the same time, but I don't understand why.

Anyone have any theories?