Upgrading or downgrading the Arista Extensible Operating System (EOS) is accomplished by replacing the EOS image and reloading the switch. Depending on the switch model and the software change being made, it may be possible to minimize (or virtually eliminate) downtime and packet loss during an upgrade.There are two upgrade methods for the EOS:

Smart System Upgrade: SSU significantly decreases downtime and packet loss during upgrades. SSU is available on selected platforms, and is ideal for leaf switches and other non-redundant deployments.

Standard Upgrades and Downgrades: In those cases where an accelerated upgrade is not needed or not an option (such as for software downgrades and on unsupported platforms), performing a standard upgrade or downgrade using the steps described here will minimize downtime and packet loss.