OverviewWhen upgrading firmware from version 6.4.x to 7, there have been some changes made with acceleration which could cause incompatibility. So, if upgrading devices in stages, it's possible there could be issues with accelerated traffic if the devices are running different firmware versions.
CauseVarious changes to WAN memory, communities, and TCP options have been made in 6.4.3, 6.4.0, and 6.4.4. Any versions earlier than this will not have the changes which will be necessary to run acceleration properly with version 7 devices.
ResolutionPlease be aware that version 6.4.4 or newer should be compatible with any version of 7. It would be best to make sure that all devices are running at least version 6.4.4 before upgrading them to version 7 in stages.