What is the Virtual Wire Pair ?

What is the virtual wire?

A virtual wire logically binds two Ethernet interfaces together, allowing for all traffic to pass between the interfaces, or just traffic with selected VLAN tags (no other switching or routing services are available).

A virtual wire pair consists of two interfaces that do not have IP addressing and are treated like a transparent mode VDOM. All traffic received by one interface in the virtual wire pair can only be forwarded to the other interface, provided a virtual wire pair firewall policy allows this traffic. Traffic from other interfaces cannot be routed to the interfaces in a virtual wire pair. Redundant and 802.3ad aggregate (LACP) interfaces can be included in a virtual wire pair. 

Example

In this example, a virtual wire pair (port2 and port3) makes it easier to protect a web server that is behind a FortiGate operating as an Internal Segmentation Firewall (ISFW). Users on the internal network access the web server through the ISFW over the virtual wire pair.