Fabric upgrades are simple because the APIC allows you to manage upgrades for the entire fabric from a single dashboard (centrally). The Cisco APIC acts as the repository of the image and as the booting server. Leaf switches and spine switches have in-band connectivity to the Cisco APIC, and when upgrading, the switches download the firmware from the Cisco APIC. To complete an upgrade successfully, you must have connectivity from the leaf switches and spine switches that you are upgrading to the Cisco APIC. To maintain connectivity, you should define a minimum of two maintenance groups and upgrade one group at a time. Wait until the first group has successfully completed the upgrade before upgrading the second group.

At a high level, the steps to upgrade or downgrade the Cisco ACI fabric are as follows. (The procedure for upgrading and downgrading are the same unless stated otherwise in the release notes of a specific release.)

Ensure that you have the required CIMC version required for the Cisco APIC upgrade.

Download the Cisco ACI controller image (the Cisco APIC image) into the repository.

Download the Cisco ACI switch image into the repository.

Upgrade the cluster of the Cisco APICs.

Verify that the fabric is operational and the APIC cluster is “fully fit” before proceeding.

Divide the switches into multiple groups, and upgrade the switches by group, verifying that the fabric is operational between switch group upgrades. For example, assume that you divided the switches into two groups—East and West. You could then go through the following upgrade process:

Upgrade the East group of switches.

Verify that the fabric is operational.

 Upgrade the West group of switches.

 Verify that the fabric is operational.