VSYSs communicate with each other through virtual interfaces.

A virtual interface is a logical interface automatically created for a VSYS upon its creation, which is used by the VSYS to communicate with other VSYSs. The link layer and protocol layer of a virtual interface always remain up. To enable communication between VSYSs through a virtual interface, you must set an IP address for the virtual interface and add it to a security zone so that it can operate properly.

Virtual interface names are defined in vsysif+interface number format. The public system's virtual interface name is vsysif0. The vsysif interface numbers for other VSYSs start at 1 and are automatically assigned based on the system's usage of interface numbers.

The following figure shows that virtual interfaces of the public system and VSYSs are connected through virtual links. If the public system and VSYSs are treated as independent devices and virtual interfaces are used for communication between them, you can add the virtual interfaces to security zones and configure routes and policies to enable communication between the public system and each VSYS and between VSYSs.