I came across a problem recently while attempting to transfer a largish (23mb) file from my web server to my file server via my OpenVPN tunnel.

The tunnel has been working perfectly since it was first established. SSH and small file copies went fine. But this copy would get to 2,112kb and then stall. No matter how many times I attempted it. I attempted the same transfer using the public interwebs (I was scp'ing so it was encrypted anyway) and this worked perfectly, so there was obviously a problem with the OpenVPN tunnel.