L2TP VPN in iOS issue. No data transferring.

RouterOS General
1

Hi,

I am using RouterOS 6.37.1 (stable) on the VPN server.

When my client from UAE uses L2TP VPN on iOS 11 via WiFi everything works for him.
When he uses 4G mobile data nothing opens. Just no Internet.

What could be the problem ?

2

Is that your only client or do you have more?
L2TP/IPsec only works when there is a single client per IP address.
On 4G there will normally be a NAT between you and the client, and when another client is behind the same NAT, it will fail.

Also, it will likely fail when there is double-NAT. You can work around that problem by:

  • noting the parameters for the dynamic IPsec peer created by configuring the L2TP server with IPsec secret
  • remove the IPsec secret from the L2TP server
  • manually create the IPsec peer as it was before but set “generate policy” to “port override” instead of “port strict”.

It may be that you can do the same by updating to the current version and check that exchange mode “main l2tp” is
active instead of “main”. I am not sure that this fixes it.