openssh-based file transfers (e.g. rsync, scp, ...) are running 40 (!!) times faster via IPv4 than IPv6

[Philipp Marek]

> Unfortunately the traceroute(6) results are both more or less random.
> Sometimes traceroute "hangs" a while, wherever,
> sometimes traceroute6. Sometimes traceroute is faster, sometimes
> traceroute6. Not reliable.
That might just as well be DNS issue; the reported latency
values are the interesting data.


> Your MTU question, tried as adviced:
> 
> Maximum size for IPv4 is 1466, and max size for IPv6 is 1444.
> Exceeding these values leads to a "ping: local error:
> Message too long, mtu=1492" in both cases.
Hmmm, the IPv6 header is 20 bytes longer than IPv4 -- so there
are still 2 bytes missing.

Please try to set the MTU manually smaller, eg. to 1400,
and test once more.