Cisco APIC Installation and ACI Upgrade and Downgrade Guide

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Cisco APIC Installation and ACI Upgrade and Downgrade Guide

How ACI switch upgrades and downgrades work

Updated: July 12, 2026

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Describes the sequence of events that occur when performing an upgrade or downgrade of an ACI switch node in the fabric.

When performing an upgrade or downgrade of an ACI switch node, there is a certain sequence of events that occur to the device(s) being upgraded or downgraded. Most of these events happen in the background, so it's important to understand what you should expect to see when you trigger an upgrade of an ACI switch node.

Summary

The key components involved in the ACI switch upgrade and downgrade process are:

  • APIC: Pushes the image to the switch and manages the upgrade process

  • Switch filesystem and bootflash: Provides storage space for image extraction

  • BIOS and EPLD images: May require updates during the upgrade process

  • SSD firmware: Automatically upgraded if necessary (starting with release 2.1(4))

Workflow

These stages describe how ACI switch upgrades and downgrades work:

  1. The APIC pushes the image to the switch and prepares the system for upgrade.
    • The image is pushed from the APIC to the switch.
    • The filesystem and bootflash of the switch is checked to ensure that there is enough space to extract the image.
  2. The system extracts the image and updates the boot partitions.
    • The image is extracted, and the primary grub partition is updated to the target version. The older version is moved into the recovery partition.
  3. The system upgrades firmware components if applicable.
    • The BIOS and EPLD images are upgraded if applicable.
  4. The switch performs a clean reload and rejoins the fabric with the new software version.
    • The switch will do a clean reload, and will re-join the ACI fabric running the newer version of software.
    Starting with release 2.1(4), support was added for the third-party Micron Solid State Drive (SSD) firmware auto update. As part of the standard Cisco APIC software upgrade process, the switches will reboot when they upgrade. During that boot-time process, the system will also check the current SSD firmware and will automatically perform an upgrade to the SSD firmware, if necessary. If the system performs an SSD firmware upgrade, the switches will then go through another clean reboot afterward.