We just an HP C-class blade chassis which included two GbE2c network modules.  These modules are Nortel switches running AlteonOS that connect the blades to the rest of your network.  When I turned these guys up the other day, every VLAN stopped working, so I ran down to the data center and unplugged the uplink.  I called HP and soon found out that the GbE2c doesn’t play nice with Cisco switches out-of-the-box.  Since we have a Cisco network (not now, I guess), we can into some problems.