FortiClient IPSec VPN disconnects after around 20 seconds

Hi together,

acutally I am dealing on the following issue:

We tried to setup a remote IPSec VPN as SSL-VPN wont't be supported in the future.

The connection establishes, routes are configured on the client correctly. There are also packets sent from the client to the company network (packet counter is increasing) but no packets are received (packet counter is staying at 0).

On the Fortigate (acutally only a 40F for testing) the packets are shown in the capture and (e.g. a ping) also reaching the destination. The destination (e.g. DNS-Server) responds successfully and Fortigate sends the packet back into the tunnel (the packet capture shows this). But the packets are not received by the client.

After arount 20 seconds (+/- 5 seconds) the FortiClient ends the connection. But I think it is not really ending it, only killing it, as the connection stays in status "up" on the Forit for a while then.

Forti 40F has 7.4.7, Forticlient has Version 7.4.0.1658.

Config of Forti:

config vpn ipsec phase1-interface     edit "vpn.remote"         set type dynamic         set interface "wan"         set ip-version 6         set keylife 14400         set mode aggressive         set peertype one         set net-device disable         set mode-cfg enable         set ipv4-dns-server1 192.168.10.31         set proposal aes256-sha512         set dpd on-idle         set dhgrp 21         set xauthtype auto         set nattraversal forced         set peerid "vpn.remote"         set assign-ip-from name         set ipv4-name "N_VPN-Remote"         set psksecret ENC "THISISVERYSECRET"     next end config vpn ipsec phase2-interface     edit "vpn.remote"         set phase1name "vpn.remote"         set proposal aes256-sha512         set dhgrp 21         set keylifeseconds 7200     next end  config firewall policy     edit 6         set name "Remote-VPN"         set uuid 9a18dc24-4de5-51ef-100b-bd5e9bd00d97         set srcintf "vpn.remote"         set dstintf "IoT" "LAN" "VPN"         set action accept         set srcaddr "N_VPN-Remote"         set dstaddr "all"         set schedule "always"         set service "ALL"         set logtraffic all         set groups "VPN-Users"     next end

The Forticlient is configured accordingly (otherwise there won't be established a connection AFAIK).

We also tried with "set authusrgrp GROUPNAME" but also this won't work.

Hope you can maybe help me.

Thanks!

Ketanest