Right now, we test neutron under havana release. We configured
network_device_mtu=1450 in neutron.conf,
After create vm, we found the vm interface's mtu is 1500, the ping, ssh, is
ok. But if we scp large file between vms
then scp display 'stalled'. And iperf is also can not completed.
If we configured vm's mtu to 1450, then iperf, scp all is ok.
If we iperf with -M 1300, then the iperf is ok too.
The vms path mtu discovery is set by default. I do not know why the vm whose
mtu is 1500 can not send large file.
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