for the purpose of a redundency, incase the primary ISP goes down the backup kicks in.
Can this be done with the basic license (max 3 vlans) or you need to have the security plus license. (20 vlans)
Currently not using the 3rd vlan (dmz)
With the base license you do get 3 zone (2 regular zones and 1 restricted zone). But with the restricted zone you can only talk to one vlan either inside or outside. For redundancy to work when one ISP goes down you would want the 3-rd zone to talk to the inside and outside.
With the Base license, the third VLAN must be configured with the no forward interface command to restrict this VLAN from initiating contact to one other VLAN.
So, you need security plus license so, you will not have this restriction.
You would need the security plus license.