My problem started out as poor bandwidth between a 64 bit Win 7 Home OpenVPN server in location A (Northern Europe) and a Win 7 or Linux Client in location B (Southern Europe).
Location A has FTTC 70Mbps/20Mbps
Location B has FTTH 60Mbps/10Mbps
Both connections work well up to their expected limits, except when connecting machines at each location directly to each other (e.g. first openVPN running with server at Location A and client at Location B, typically seeing around 2 - 4 Mbps maximum down speed to the client and 5 - 6 Mbps up speed from the client through the tunnel).
Now I have tried TCP iperf between the two locations with both Win7 and linux at location B and Win7 at location A. In both directions I'm seeing only around 5 Mbps in either direction give or take .5 Mbps. When transferring data from Location A to Location B I'm expecting to see something much closer to the upload limit of the FTTC connection at location A (20 Mbps).
Trying speedtest.net from Location B picking a speedtest.net server at Location A sees the full bandwidth of the FTTH connection up and down at Location B, and similarly, trying speedtest.net from Location A picking a speedtest.net server at Location B sees the full bandwidth of the FTTC connection up and down at location A.
Any ideas what might be causing the problem or what would be the best next steps to further pin down the problem?