HA unsupported between different FortiGate 90G and 91G series hardware generations

Because of significant differences in interface naming conventions between Generation 1 and Generation 2 FortiGate 90G and 91G series devices, the high availability (HA) feature is not supported between Generation 1 and Generation 2 of the same devices.

For example, for a Generation 1 FortiGate 91G device, the following output is observed:

FortiGate-91-Gen1 # get hardware status
Model name: FortiGate-91G
ASIC version: SOC5
CPU: ARMv8
Number of CPUs: 8
RAM: 7547 MB
EMMC: 9982 MB(MLC) /dev/mmcblk0
Hard disk: 114473 MB /dev/nvme0n1
USB Flash: not available
Network Card chipset: FortiASIC NP7LITE Adapter (rev.)
Hardware Board ID: 002

For a Generation 2 FortiGate 91G device, the following output is observed:

FortiGate-91G-Gen2 # get hardware status
Model name: FortiGate-91G
ASIC version: SOC5
CPU: ARMv8
Number of CPUs: 8
RAM: 7547 MB
EMMC: 9982 MB(MLC) /dev/mmcblk0
Hard disk: 114473 MB /dev/nvme0n1
USB Flash: 58991 MB
Network Card chipset: FortiASIC NP7LITE Adapter (rev.)
Hardware Board ID: 003

Observe the Generation differences are reflected in the differences in Hardware Board ID.

In this example, for the Generation 1 FortiGate 91G, the WAN interfaces are wan1 and wan2, respectively. However, for the Generation 2 FortiGate 91G, the WAN interfaces are x1 and x2, respectively. Therefore, because of the differences in interface names, HA cannot be formed between these Generation 1 and Generation 2 devices.