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Datacenter Switching : Nexus ( FEX: Fabric Extenders )

December 31, 2019 ,
Today I am going to talk about the FEX that you generally heard when you are going to connect your datacenter servers in the Nexus Switching environment. It is called as Bridge Port Extension. It means there is a Parent Switch and the port of that parent switch get connected to FEX( that is another Switch) but act as the Interface card for the Parent switch.
  • Parent Switch :Nexus 5K or Nexus 7K
  • FEX:Nexus 2K ( Another Switch but interconnected with Parent Switch and controlled)
Nexus 7K or 5k is act as Parent Switch but Nexus 2K act as FEX for Parent Switch. So all the function of the Nexus 2K is controlled by the Parent Switch and that is Nexus 7K or 5K. Simply says that Nexus 2000 Series FEX behaves logically like Remote line cards for parent Nexus 5K  or 7K Nexus Switch.

Lets talk how we can connect the FEX with the parent switch in the datacenter environment.

Fig 1.1- FEX Connectivity

Let's talk about the basic Configurations to configure the FEX.

Step-1 :Enable the FEX feature

N5K-1(config)# feature fex

Step-2 :Create a FEX instance (Note: Its up to you to choose the FEX number, 100, in this example. FEX numbers can range from 100 to 199.)
N5k-1(config)#fex 100

Step-3 :Configure the interface(s) on the 5500 that will be used for connecting the FEX.

N5K-1(config)# int ethernet 1/1, ethernet 1/21
N5k-1(config-if)#switchport
N5k-1(config-if)#switchport mode fex-fabric
N5k-1(config-if)#channel-group 100

Step-4 :Create the port-channel and associate the FEX with it. (It’s always nice to keep the port-channel and FEX number the same if possible. It just makes it easier to know that FEX 100 is on port-channel 100, FEX 101 is on port-channel 101, and so on. Obviously, if those port-channels are already in use you wouldn’t be able to do that.)

N5k-1(config)#interface port-channel 100
N5k-1(config-if)#fex associate 100

Step-5 :Check to see if your FEX is online. It may take a minute for it to show up.

N5K-1# show fex
FEX             FEX                   FEX                 FEX
Number    Description    State              Model                 Serial
------------------------------------------------------------------------
100            FEX0100        Online   N2K-C2232PP-10GE   SSIXXXXXXXX
101            FEX0101        Online   N2K-C2248PP-1GE    SSIXXXXXXXX

If the FEX is running a different version of NX-OS than the 5505 it will download the matching image from the 5505. This process can take a few minutes. When you do a show FEX it will show “Image Download” under the “FEX State”.