Using IPFire 2.17 Core 89 as the IPsec-server, Windows 7 shows the error message "Error 809: The network connection between your computer and the VPN could not be established because the remote server is not responding.". when trying to connect.
From the logs:
charon: 15[NET] sending packet: from <ipsec-ip>[500] to <client-ip>[500] (337 bytes)
charon: 11[JOB] deleting half open IKE_SA after timeout