Site to site IPSec VPN Tunnel failure on restart

#1 First it would be important to understand _why_ the VPN goes down.

The tunnel goes down because there' s a monkey at the controls pressing reset. Why it won' t come up on command until the monkey fixes it by hand is the problem. The real problem is that I have tunnels with real peers that won' t come up several times per week. After manually fixing only able to see one debug log at a time I bought another Fortigate for home so I could see both debug logs and verify that this isn' t a multi vendor problem. There are several distinct problems but the major one I' ve reduced down to this simple demonstration between two Fortigate so others can easily replicate the problem. Why my peers drop the tunnels without notification my logs don' t explain. They won' t admit to or fix anything so they just keeps going down. The Pix 501 that the Fortigate replaced handled whatever problem it is just fine.

#2 I don' t understand why DPD is not a solution. DPD IMHO always is the choice for proper VPN handling. Despite #1, half-dead VPNs are a common problem if not using DPD.

Have you watched the debug logs? DPD spams the other router and the debug logs every 10-60 seconds. That would be fine for VPN where the DPD traffic would be dwarfed by the real traffic but my traffic is tiny files a couple of times per day. DPD would account for more than 99.9% of the traffic. Some of my peers do not support DPD and the tunnels won' t work at all if I enable DPD. All other brands I' ve tested recover from a stuck SA without so much as a second try and I' m steadily obtaining more to test. My peers, none of which use Fortigate, think DPD is not needed since none have enabled it. The Cisco Pix 501 that I replaced only produced stuck SA when I made changes and no tunnel had DPD. Why does Fortigate require DPD just to have tunnels that work? DPD is for quickly diverting continuous use high priority traffic down an alternate tunnel when the main tunnel goes down. DPD is not for coaxing functional tunnels from a defective IPSec implementation.

#3 I' d upgrade to MR7_recent patch. (patch2 looks rather old)

I have many Fortigate routers with FortiOS versions spanning several years including some very new ones. The behavior is identical. If Fortinet thought there was a problem it would have been fixed by now so they must think it' s not a problem.

So why are these not acceptable solutions?

All tunnels failed regularly when I copied the settings over from the Pix. I reviewed documentation and obtained correct keylife from peer admin and this improved many tunnels. I studied the debug logs recorded over several days and discovered that the keylife that they see is not always correct. A tunnel with a Netscreen was supposed to have a 3600 second phase 2 but I noticed in the logs that it was expiring every 3300 seconds. Odd corrections like these made more tunnels reliable. Then I discovered the auto connect options and almost all tunnels were completely reliable. No matter how well I correct the mismatches and how many options I turn on a few tunnels still fail. More options only made them fail less often. With all the options turned on the tunnels fail no less than once per week. Some days I get many calls. The Pix had rock solid tunnels with outrageous keylife mismatches and no special settings. The Fortigate does not even when the keylife is carefully tuned and the settings are maxed out.

Also, what does your debug vpn shows? When the connection is down?

The router reboots without notifying the other router that the tunnels are going down. The non rebooted router has an active phase 1 and phase 2. When the rebooted router recovers the non rebooted router continues to send traffic through the orphaned phase 2 SA for the remainder of its life. I can bring down the phase 2 but it won' t come back up. The non rebooted sends phase 2 initiations through the orphaned phase 1 for the remainder of its life. diagnose vpn tunnel flush brings down all phase 2 but does not bring down phase 1. Since Fortinet doesn' t give us observation and control of phase 1 I must edit the phase 1 to destroy all of phase 1 and phase 2 SA. Then the tunnels will come up on request.