Connection aborted during data transfer to FileServer via IPSec tunnel

Hello everybody,
For some time now we have had the problem that the connection or the upload is interrupted immediately after the first 256 resp. 512 KB during a data upload via an IPSec tunnel to a remote Windows network share. The tunnel itself remains. A download of data or work via RDP (Server 2008 R2) is also easily possible.

IPFire is used on both sides. The networks are net-to-net coupled via IPSec tunnel.
The problem only occurs with an IPFire version> Core 126. The whole thing was tested until the current version Core 138, unfortunately without success (each same configuration as in the working constellation under Core 125).

On the client side Win7 and Ubuntu clients are operated. On the server side, a Server 2008 R2 is used.

Who has a hint why that could be?
Many thanks for your help.


Hello Mike,

this sounds like an MTU problem somewhere between the two VPN peers. Hard to debug, but quite likely.

The MTU Size was 1500 on both sides. Changing the size to 1492 showed no effect. The transfer brakes after 768 kb. A rollback to IPFire Core 125 with the same configuration/settings works without problems.
Both firewalls are operated behind each one AVM Fritzbox 7490.

Oh yeah those are brilliant to lose packets randomly.

Can you try to collect a packet trace with tcpdump and did you try tracepath?