During the dual-machine hot standby system version upgrade process, which of the following sequences should be followed for the backup machine upgrade steps? 1. Shutdown the heartbeat interface of…

During the dual-machine hot standby system version upgrade process, which of the following sequences should be followed for the backup machine upgrade steps? 1. Shutdown the heartbeat interface of the standby machine; 2. Undo shutdown the heartbeat interface of the standby machine; 3. Upgrade the system software version of the backup machine; 4. Undo shutdown the business interface of the standby machine; 5. Verify the upgrade results of the standby machine; 6. Save configuration; 7. Wait for the active and standby firewalls to synchronize session tables and other entries; 8. Shutdown the business interface of the standby machine;