When users vpn in from external using a TCP based connection they drop after a couple of minutes. They don't have the same problem when using udp. The error message is 412 and it states.
Secure VPN connection terminated locally by the client.
Reason 412: The remote peer is no longer responding.
Below is what I see in the concentrator log when the connection is dropped.
IKE lost contact with remote peer, deleting connection (keepalive type: DPD)
Thanks