In this tutorial we’ll be going over FEX configuration for ACI switches using the APIC GUI.

Refer to the below document which overviews the ACI supported FEX models:
https://www.cisco.com/c/dam/en/us/td/docs/switches/datacenter/nexus9000/hw/interoperability/fexmatrix/fextables.html#9300ACI

Prerequisites:
* Fabric discovery completed
* Have a general understanding of ACI Access Policies

My Setup:
* Running ACI version 4.0(3d)
* Topology: Leaf-101 eth1/5 and eth1/6 connected to FEX with eth1/11 on the FEX connected to downstream server:

Before we get started in the actual configuration, below is a high level overview of the Access Policy objects and object names we’ll be using:

The first step in configuring a FEX connected to your leaf switch is to configure a Leaf Profile. To configure a Leaf Profile navigate to the following APIC web GUI path:
Fabric -> Access Policies -> Switches -> Leaf Switches -> Profiles

Right click Profiles and select Create Leaf Profile

From here we’ll assign a name to our Leaf Profile as well as select the leaves we want to be associated to our Leaf Profile. For our purposes we’ll name our Leaf Profile Leaf-101-LeafProf since we’re only configuring a FEX connected to Leaf-101:

Click Next and Finish to skip the interface Associations, we’ll come back to this later. Our next step is to create the Leaf Interface Profile.

We can create the Leaf Interface Profile directly from the Leaf Profile page by clicking the + sign in the Associated Interface Selector Profiles region:

Or we can navigate to the following APIC web GUI path:
Fabric -> Access Policies -> Interfaces -> Leaf Interfaces -> Profiles

Right click Profiles and select Create Leaf Interface Profile

For our purposes we’re going to name our Leaf Interface Profile Leaf-101-to-FEX-IntProf:

The next step is to create a Leaf Interface Selector to signify that a particular leaf interface is connected to a FEX.

We can create the Leaf Interface Selector directly from the Create Leaf Interface Profile window by clicking the + sign:

Or you can navigate to the following APIC web GUI path:
Fabric -> Access Policies -> Interfaces -> Leaf Interfaces -> Profiles -> YOUR_LEAF_PROFILE_HERE

Right click YOUR_LEAF_PROFILE_HERE and select Create Access Port Selector

From here we’ll assign a Name, Interface ID, FEX Profile, FEX ID, and mark the leaf interface as connected to a FEX. For our configuration we’ll name our Leaf Interface Selector Leaf-101-to-FEX-199-IntSelect, use eth1/5-6 as our Interface ID, assign a FEX ID of 199, and create a new FEX Profile:

You can create the FEX Profile directly from the Create Access Port Selector window:

Or you can navigate to the following APIC web GUI path:
Fabric -> Access Policies -> Interfaces -> Leaf Interfaces -> Profiles

Right click Profiles and select Create FEX Profile

In our FEX Profile we’ll define a Name and FEX Access Interface Selector, used for the FEX interface to our downstream server (eth1/11). For our purposes we’ll name our FEX Profile FEX-199-FEXProf:

From here we’ll assign a name to our FEX Access Interface Selector of FEX-199-IntSelect, assign the eth1/11 downstream interface to our server, and create/associate our Interface Policy Group for port-channel, virtual port-channel, or individual access port configuration down to our endpoint(s):

 

This concludes all the necessary FEX configuration.

To verify that the FEX is seen by the leaf switch you can run the “show fex detail” command on your leaf switch connected to your FEX, and can also run the “show port-channel extended” command to verify that the automatically created port-channel between the leaf and FEX is formed. A port-channel between a leaf switch and FEX is automatically created even if using a single interface between your leaf and FEX.