VPN Dial Up with FortiClient does not work on some devices

Question

Hi everyone,I am troubleshooting a persistent IPsec VPN issue on a specific Windows 11 workstation and looking for pointers on local OS interferences.Environment:Gateway: FortiGate 70G (Firmware v7.4.9).Protocol: IPsec Dial-up (IKEv1, Aggressive Mode).Failing Client: Windows 11 (FortiClient latest).The Issue: Phase 1 negotiation times out with "No response from the peer". The issue is strictly isolated to this specific PC.Troubleshooting & Isolation: I have confirmed the FortiGate configuration and Phase 1/2 proposals are correct by successfully connecting with other devices:Success: Another Windows 11 PC running FortiClient v6.0.0 connects immediately.Success: A MacOS device running FortiClient v7.4 connects immediately.Steps Taken:Verified local Firewall/AV allows the connection (tested with them disabled).Verified no ISP blocking (same behavior on different networks).Since it works on other clients, I have ruled out the FortiGate configuration.Has anyone encountered specific Windows 11 network stack issues or driver conflicts that would block IKE negotiation silently on one specific machine while others work fine?

vpolovnikov · Answer

Hey Lucas1,

Even though it seems like the issue is isolated to that specific device, capturing PCAP and IKE diagnostics as described in this article should move the needle forward a bit (community.fortinet.com/t5/FortiGate/Technical-Tip-How-to-troubleshoot-Intermittent-IPsec-Dial-up-VPN/ta-p/344361).

In addition, I'd also try not simply disabling local 3d party security solutions but deleting them altogether (sometimes, it helps). If nothing gets you any closer, I'd factory reset the laptop.

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