In general, if you are supporting a dynamic IP client end, you will have to use Aggressive mode Phase1, so make sure that mode is set for dynamic clients. The first trouble shooting step is to verify your parameters are all correct and matching.įor Phase1, is the end gateway dynamic or static? Fortigate to Fortigate can use both Main and Aggressive modes for dynamic connections, but many other brands can not. Then IKE takes over in Phase2 to negotiate the shared key with periodic key rotation as well as dealing with NAT-T (NAT tunnelling), and all the other 'higher-end' parameters. Phase1 is the basic setup and getting the two ends talking. In IKE/IPSec, there are two phases to establish the tunnel. Here are some basic steps to troubleshoot VPNs for FortiGate. I'll show you a method that can be used to initiate traffic from that network as well. The network admin typically doesn't have direct access on the computers on either side of the VPN in order to initiate that traffic. One problem in particular that has always bugged me is that you need access to the end machines involved to initiate traffic across the link. Most of the real debugging happens inside the CLI.

The GUI offers not much help, it is either UP or Down. The IKE protocol is 'chatty', and negotiates back and forth between the two ends for several rounds. Debugging what is going wrong with a VPN setup is difficult.

Fortigate debug ipsec