Fortigate Firewall VLAN

[HS08]

Can we create a VLAN in fortigate firewall, let say VLAN 100 and assign VLAN 100 to port1 and port2?

[AEK]

You cannot create a VLAN interface without specifying the attached interface.

Also you can create the a VLAN 100 interface on port1, and another VLAN 100 interface on port2.

[Toshi_Esumi]

Depending on the model of your FGT(s), you can use either hardware switch, vlan switch, or software switch to bind port1 and port2 into one logical interface then assign a VLAN 100 subinterface on it. Be aware that once you bind them into one interface, you can't configure each of them separately. 
FGTs are not L2/L3 switch so VLAN operation is limited.

Toshi