I have installed and configured OpenVPN on my server. It uses TUN interface and allows many clients connecting to it at the same time. I will post config below. Actually there are 2 clients connecting. One of them is configured on router powered by OpenWrt, however I have also tried native OpenVPN client on Gentoo Linux and Windows 7 behind that router. All of them working correctly. Internet is that location is based on ADSL2+.
Second client has 2 internet connections: UMTS and ETTH. When it connects to server using UMTS, everything is working correctly, but slow
When it connects via ETTH, client successfully establishes VPN connection. Ping is working between server and client. But when he tries to access any resources on the server through VPN, it fails sometimes, depending on data. If it is small website - it loads correctly and fast. But when trying to download 4MB file, it stucks everytime on 16,996KB. After longer while transfer interrupts.
This client uses Windows XP, however we also tried booting Ubuntu Live and the conclusion is that OS makes no difference.
I have already spent 3 days investigating this issue. Previously I have been using TAP interface, but finally migrated to TUN and it makes no difference. Tcpdump showed me that bigger websites got truncated and there are many duplicated packets sent from server to client.
tls-auth /path/to/tls.key 0
server 172.18.0.0 255.255.255.0
keepalive 30 120
Affected client config:
tls-auth tls.key 1
keepalive 30 120
Do you have any ideas what might be wrong? What else can I check and what server configration might help?
I already tried playing with tun-mtu and mssfix options on both side, lowering MTU even to 1400 but it didn't help.
Thank you in advace for help!