Openvpn problem with file transfer



  • Hi

    I have configured OpenVpn site-to-site, tunnel is up and stable. I only have problem with transfering large files. I read that it could be mtu issue. I added to configuration:

    tun-mtu 1472;fragment 1400;mssfix

    Now I can ping with large packets but file transfering still won't work. It startded, copying then stop, then started again for a while.

    Please give me any clue where is a problem.


  • Rebel Alliance Global Moderator

    Problem in what that its slow?  Large files over wan with latency = slow ;)  What protocol are you using?  Ftp, Http, SMB? what?  What is your receive window?  How many datastreams are you using in the file copy?  What is the latency?

    What speeds are you seeing and what do you think you should see?  When you say you ping with large packets means what?  What did you do.. YOu do understand that fragmentation is normal and happens all the time..

    So top is ping no vpn, bottom is ping with vpn..  Notice the larger latency on it..  But still can ping at 1472 sized packets do not fragment set.




  • No, its not about speed. I cannot copy for example 100MB file through windows share, copying is started and for a while it is stuck and stop. I understand fragmentation, mtu and so on.

    For example I cannot do; ping host -l 1500, after changing mtu to 1472 its working but problem still have problem with file transfer.


  • Rebel Alliance Global Moderator

    You do undestand smb blows chunks over wan be it vpn or not..  Why don't you try say a sftp file copy or just plain http?

    As to ping host -l 1500 with do not fragment set would never work..  If you had anything that had issues with fragmentation that would fail anyway.  You would need to ping at 1472 to account for the overhead in a 1500 mtu.

    Why don't you just sniff the traffic and see what is happening.  You can sniff your openvpn interface on the client and then sniff traffic on the server at the same time and see what is going on..  Again smb over wan is going to be painful slow and problems.  Especially older versions.. They have suppose to have made some things better in 3.1.1 on windows 10 and server 2016 but have not had chance to play with it yet, etc.



  • hello zwierzu85

    how are you resolved this problem ?? I have a same problem and I can´t find a solution