I've posted several questions on why my openvpn upload speed from my house runs at half the total bandwidth (paying for a 10mbps upload, every other service (http,ftp) maxes out this speed, but vpn transfers up max out at 4-5mbps??) but have gotten zero responses. I figured i'd try again.

I've started noticing a lot of this message:

replay-windows backtrack occurred [n]

where n is usually in the hundreds, but sometimes gets up into the thousands. i've looked this up and apparently it has something to do with dropped packets?

what exactly does this mean, is it related to the slowness, and how might I improve it?

Many people has complained similar issues. But I Guess, it has something to do with the latency or congestion of that particular connection to the VPN server. While every other services are working fine, then there must be a congestion at the vpn link. It can happen because of cpu load also. It is not always a problem with OpenVPN. You can, if possible, try the same link with other vpn, i.e. IPSEC and check.

There have been suggestions, since the problem is caused by using the UDP protocol, one can switch over to a TCP protocol instead. May be you can try to change the client configuration and see if it helps.

Here is an explanation to the error you are seeing:

http://openvpn.net/archive/openvpn-u.../msg00068.html
Here are some troubleshooting tips:

http://www.personalvpn.org/troubleshoot_openvpn.htm
http://support.real-time.com/open-so...vpn/index.html

Thanks!

thanks for the links. unfortunately these pages don't give any useful information on how to improve the speed, thought they do somewhat explain the reason behind these errors i'm getting.

my problem is that the speed is always slow, regardless if i am getting these messages or not. I can connect at my work or other places with a hardline ethernet directly into a router on a remote connection that gets >20mbps down, but I still only get 3-5mbps of actual sustained VPN transfer to the remote location. this makes any work with files larger than several megabytes essentially unusable - it feels like i'm on a dialup connection.

speedtest.net shows that I definitely have 50mbps down/10mbps up at the server.the specs of the server are:

Intel Core 2 Duo 2.4GHz
2GB RAM
Gigabit PCI-E intel ethernet adapter

well, kinda solved. just switched to using FTP over the openvpn and speeds are back to normal.... samba is slow I guess? over higher latency connections at least...

Psy, I ran into the same problem you did when using samba shares through openvpn. I was looking into transfer speeds through openvpn (UDP) and found cifs shares to only do a little over half the speed of nfs shares. I found SSH, FTP, and NFS to use the full speed of the link.

Likewise, I found an IPSEC VPN (OpenSWAN) to only transfer about half the speed of OpenVPN, even when using the same encryption algorithm. All of this was tested on an isolated LAN where other traffic and network delays were not an issue.

yeah, so i've seen. as well, i've recently figured out that some windows 7 machines (mainly laptops) have a power management setting that throttles down the CPU speed. i've recently turned this off and have seen restored consistency to openvpn using the full bandwidth available. on my win7 laptop the power setting is called "proccessor state power management" or something.