Yes, that worked!
I'm unable to turn off tso on eth0 as can been seen in the output of ethtool -k eth0 :
tcp-segmentation-offload: off
tx-tcp-segmentation: off [fixed]
tx-tcp-ecn-segmentation: off [fixed]
tx-tcp-mangleid-segmentation: off [fixed]
tx-tcp6-segmentation: off [fixed]
But turning off gso and gro works:
root@telia:~# ethtool -K eth0 gso off gro off tso off
Cannot change tcp-segmentation-offload
root@telia:~# ethtool -k eth0
generic-segmentation-offload: off
generic-receive-offload: off
And speeds are normal:
[michael@linko ~]$ iperf3 -c bouygues.iperf.fr -6 -R -p 5207 -t 20
Connecting to host bouygues.iperf.fr, port 5207
Reverse mode, remote host bouygues.iperf.fr is sending
[ 5] local 2a01:79c:cebd:1e2c::a80 port 44030 connected to 2001:860:deff:1000::2 port 5207
[ ID] Interval Transfer Bitrate
[ 5] 0.00-1.00 sec 3.07 MBytes 25.8 Mbits/sec
[ 5] 1.00-2.00 sec 8.15 MBytes 68.4 Mbits/sec
[ 5] 2.00-3.00 sec 10.2 MBytes 85.2 Mbits/sec
[ 5] 3.00-4.00 sec 10.5 MBytes 87.8 Mbits/sec
[ 5] 4.00-5.00 sec 9.69 MBytes 81.3 Mbits/sec
[ 5] 5.00-6.00 sec 9.32 MBytes 78.2 Mbits/sec
[ 5] 6.00-7.00 sec 9.79 MBytes 82.1 Mbits/sec
[ 5] 7.00-8.00 sec 9.86 MBytes 82.7 Mbits/sec
[ 5] 8.00-9.00 sec 10.2 MBytes 85.8 Mbits/sec
[ 5] 9.00-10.00 sec 10.0 MBytes 84.0 Mbits/sec
[ 5] 10.00-11.00 sec 10.2 MBytes 85.8 Mbits/sec
[ 5] 11.00-12.00 sec 10.1 MBytes 84.9 Mbits/sec
[ 5] 12.00-13.00 sec 10.5 MBytes 88.1 Mbits/sec
[ 5] 13.00-14.00 sec 10.6 MBytes 89.0 Mbits/sec
[ 5] 14.00-15.00 sec 10.7 MBytes 90.1 Mbits/sec
[ 5] 15.00-16.00 sec 10.4 MBytes 87.1 Mbits/sec
[ 5] 16.00-17.00 sec 9.48 MBytes 79.6 Mbits/sec
[ 5] 17.00-18.00 sec 10.1 MBytes 84.6 Mbits/sec
[ 5] 18.00-19.00 sec 10.8 MBytes 90.4 Mbits/sec
[ 5] 19.00-20.00 sec 10.8 MBytes 90.4 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 196 MBytes 82.4 Mbits/sec 4 sender
[ 5] 0.00-20.00 sec 194 MBytes 81.6 Mbits/sec receiver
iperf Done.