FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
In IPsec VPN network, all tunnels go down and are recovered after few minutes automatically.

This article describes this feature.

By default, dynamic interface is created when an IPsec is established.

When tunnel goes down, deleting the corresponding interface is very slow in the kernel and IPsec process has to wait for significant time.
If a number of tunnel goes down, IPsec process (iked) becomes stuck in D state and then, other tunnels are down by dpd timeout.

'set net-device', new route-based IPsec logic was introduced in 5.6.3 not to create an interface when tunnel is brought up and it is well explained in the KB article but its major impact is overlooked.

Even though the change is simple,  that option has caused major outages in a number of large IPsec VPN network.

Related Articles

Technical Tip: 'set net-device' new route-based IPsec logic