There are two types of Cisco FEXs or Fabric Extenders in the Cisco UCS world:
* Blade Chassis FEX
* Rack Mount FEX
Now, we are going to take a look at each of them.
Blade Chassis Cisco FEX : If you are using blade servers, you must have FEXes in the back of it to provide connectivity to the Cisco UCS system. The FEXes are connected to the Fabric Interconnects. There are two FEX slots in the Blade Chassis, one for A side connectivity and one for B side connectivity. FEX A connects to Fabric Interconnect A, and FEX B connects to Fabric Interconnect B.
The Fabric Interconnects are not cross connected, like your instinct may tell you to do. Failure of a FEX or Fabric Interconnect is handled at the software layer, by either the software running on your blades, or by UCS Manager, it is your choice!
Rack Mount Cisco FEX : This operates with a similar principle as the Blade Chassis FEX, except it is mounted in a rack. The purpose of this is to add more ports to your Fabric Interconnect so you can take advantage of the Cisco UCS’s full potential. 54 ports can get eaten up pretty quickly, and this is Cisco’s answer to that problem.
