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Best
    Li Tianqing



At 2014-10-27 17:42:41, "Ihar Hrachyshka" <ihrachys at redhat.com> wrote:
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>On 27/10/14 02:18, Li Tianqing wrote:
>> Hello, 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.
>
>There is a neutron spec currently in discussion for Kilo to finally
>fix MTU issues due to tunneling, that also tries to propagate MTU

>inside instances: https://review.openstack.org/#/c/105989/


The problem is i do not know why the vm with 1500 mtu can not send large file? 
I found the packet send out all with DF, and is it because the DF set default by linux cause the packet
be dropped? And the application do not handle the return back icmp packet with the smaller mtu?


>
>/Ihar
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