Dell PowerEdge FX2: CMC Configuration Gotchya

Back in September I wrote an introductory post (If you haven’t read that post click here) on the DELL PowerEdge FX2 HCI hardware and why we had selected it for our VSAN Management platform. After a busy two months consisting of a VMworld, vForumAU and VeeamOn it’s finally time to put start working towards putting these babies into production.

I’m hoping to do a series of posts around the FX2s and VSAN and thought I would kick things off with the short but very important public service announcement around the default configuration behavior of the Chassis Management Controller network port settings and how if you don’t RTFM you could be left with an angry network guy beating down at your door!

CAUTION: Connecting the STK/Gb2 port to the management network will have unpredictable results if the CMC setting is not changed from default Stacking to Redundant, to implement NIC failover. In the default Stacking mode, cabling the Gb1 and STK/Gb2 ports to the same network (broadcast domain) can cause a broadcast storm. A broadcast storm can also occur if the CMC setting is changed to Redundant mode, but the cabling is daisy chained between chassis in the Stacking mode. Ensure that the cabling model matches the CMC setting for the intended usage.

That warning should be one of the first things you read as you go through the CMC for PowerEdge FX2 User Guide but just in case you don’t read that and are looking to take advantage of the redundant NIC feature the CMC offers similar to that found in the DELL M1000e Chassis you need to Network -> General Settings and change the default radio option shown below from Stacking to Redundant.

If this isn’t done and you do attempt to set up redundant management ports in the stacking option you will more than likely as the caution suggests impact your network due to the switches grinding to a halt under the stress of the broadcast storm…and in turn have some not to happy networking admins coming after you once they work out whats going on.

The diagram above, pulled from the online documentation shows you what not to do if Management Port 2 is configured in stacking Mode. Stacking mode is used to daisy chain a number of FX2 Chassis for single access management if required. I would have thought that having the least dangerous option set as default was the way to go but it is certainly a case of be aware that some assumptions can lead to major headaches…so a final reminder to RTFM just in case…and be aware of this default behavior in the FX2 CMCs.