Incorrect NAT occurs when returning packets to the client.
Quick Mode started by the VPN Gateway is incorrect, so client deletes the whole SA.
VPND daemon is listening on port 1701 on the first interface (eth0), which is internal. The issue is with a kernel table '
udp_response_nat', which is responsible for NATing the L2TP packets in case they are sent to an IP address, on which the VPND daemon is not listening.