I have seen this topic as a difficult one so I wanted to write a little about it to explain the proper way to cable up a Cisco UCS Chassis to a Cisco 6120XP Fabric Interconnect. The Fabric Interconnect it crucial when setting up an Cisco UCS Chassis as it is what controls the chassis allows for proper failover and also acts as your connection back to the network and your fiber channel SAN.
There is no real secret when wiring up a Single UCS Chassis with a single 6120xp Fabric Interconnect, you simply plug it in and go. You do however need to make sure that the ports on the 6120XP Fabric Interconnect are set to “Server Mode” or else the connections will not work.
It is a completely different story when you are wiring up multiple UCS Chassis with multiple 6120 Fabric Interconnects. The first thing to remember is from the old Ghost Busters movie and “Don’t cross the streams”. What this means is that each of your UCS Chassis should have two IO Modules in the back and what you NEVER want to do is connect one IO Module to different Fabric Interconnects. So just to say again 1 IO module should only connect to 1 6120xp Fabric Interconnect. This is very important because if you wire this up incorrectly your UCS chassis will not see the 6120XP Fabric Interconnect and you will not have connectivity to your SAN or Network.