-> cmb
Thank you for your statement. You are absolutely right that it is not the "finest" solution that WAN and LAN are on the same subnet but they are segregated via VLAN and not bridged. The WAN uses a gateway that`s why it has a static ip. This gateway is used by another network with the same subnet which is not connected to the first network with the same subnet. This needs to be changed but the reason was a connection of two networks that were not planned intentionally and the change has not been done yet.
In the "first" subnet with pfSense the IPSec clients are in the subnet 10.21.32.0/24, LAN is 10.21.30.0/24 (OpenVPN Clients in 10.21.31.0/24).
I changed the subnet for WAN (10.21.29.0/24) for testing on the weekend but the problem remains.
In the meantime I could figure out the problem. The problem only exists when MOBIKE is enabled (a new feature in 2.3 as far as I remember). If MOBIKE is disabled the DPD is sent via the WAN as intended. If MOBIKE is enabled the DPD is sent via LAN interface. So there could be a problem with the implementation of MOBIKE.