Troubleshooting Tip: How to fix 'phase1 negotiation failed due to time up' error during to the FortiClient IPSEC VPN + Certificate Authentication

[volkanavsar]

Description	This article describes how to fix issues that may arise during an IPsec VPN connection with certificate authentication due to lower MTU settings or fragmentation.
Scope	FortiClient IPSEC VPN.
Solution	To ascertain if the issue pertains to 'Phase 1 negotiation failed due to timeout', verify the logs: Diagnostic_Result\FCDiagData\general\logs\trace\FortiIKE_1_error   To fix the issue: Log in to the EMS and configure the assigned 'Remote Access Profile' as demonstrated below: To incorporate the following script, modify the profile XML accordingly: <ipsecvpn>    <connections>       <connection>          <name>your IPsec VPN</name>             <ike_settings>                  <enable_ike_fragmentation>1</enable_ike_fragmentation> <ipsecvpn>    <options>       <mtu_size>1500</mtu_size> Related documents:  IKE fragmentation example IPsec VPN These changes may address the issue of 'Phase 1 negotiation failed due to timeout' during the IPsec VPN connection.