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Hi Sanna Kor,
To resolve this, you must enable native IKEv2 fragmentation, which fragments the payload within the IKEv2 protocol itself before it hits the network layer, ensuring all packets remain small enough to traverse the cellular network unmodified.
Because IKEv2 fragmentation is a negotiated protocol feature, you must apply this registry fix to both your Windows VPN server and your Windows client machines. Open the Registry Editor on both systems and navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PolicyAgent. Create a new DWORD (32-bit) Value named EnableIKEv2Fragmentation and set its value data to 1. After configuring the registry on both ends, open the services.msc console and restart the IPsec Policy Agent service, or reboot the machines, to apply the new configuration. Once the services reload, your VPN will successfully negotiate fragmentation and connect seamlessly over cellular networks.
Hope this answer has brought you some useful information. If it did, please hit “accept answer”. Should you have any questions, feel free to leave a comment.
VPHAN