What is InterVlan 

InterVLAN is a feature of Fortigate firewalls that allows communication between devices on different VLANs. VLANs are virtual LANs, which are used to segment a network into smaller, more manageable pieces.

By default, devices on different VLANs cannot communicate with each other, even if they are connected to the same physical network. InterVLAN routing is necessary to allow devices on different VLANs to communicate with each other.

Fortigate firewalls support InterVLAN routing by configuring VLAN interfaces and routing policies. A VLAN interface is a logical interface that is associated with a specific VLAN, and routing policies are used to allow or deny traffic between different VLANs.

For example, if you have a Fortigate firewall and you want to allow communication between devices on VLAN 10 and VLAN 20, you would need to create VLAN interfaces for VLAN 10 and VLAN 20 and then create a routing policy that allows traffic between those two interfaces.

InterVLAN routing is an important feature of Fortigate firewalls in modern network environments where VLANs are commonly used to segment networks for security, performance, or management reasons.