ASA prerequisites for high availability
In order for two ASA devices to operate in a high availability arrangement (either active/active or active/standby) there are some prerequisites that must be fulfilled as far as licensing and software versions go.
For failover to operate, ASA devices don’t need to have the same license on each unit. However there are limitations as to what licenses should exist on both devices. These limitations are described clearly in the Cisco documentation linked at the end of this note.
In addition, the software version used in each ASA has some limitations. Both ASAs must have the same major (first number) and minor (second number) software version. So HA can be deployed on two ASAs with version numbers 8.4.1(11) and 8.4.3, but not on two ASAs with version numbers 8.4.1 and 8.6. This information can also be seen in the same Cisco document.