The two units in a failover configuration must have the same major (first number) and minor (second number) software version. However, you can use different versions of the software during an upgrade process; for example, you can upgrade one unit from Version 3.1(1) to Version 3.1(2) and have failover remain active. We recommend upgrading both units to the same version to ensure long-term compatibility.You need to disable configuration synchronization when upgrading a software image or changing the configuration on the active FWSM to verify that the configuration files are complete before the configuration is synchronized with the standby FWSM configuration.
