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virtio-win / kvm-guest-drivers-windows

Windows paravirtualized drivers for QEMU\KVM
https://www.linux-kvm.org/page/WindowsGuestDrivers
BSD 3-Clause "New" or "Revised" License
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Windows 2008r2 mtu 9000 issue. (Jumbo frames) #300

Closed jsm222 closed 3 years ago

jsm222 commented 6 years ago

Hi. In an openstack environment with physical mtu 9000: When netkvm gets mtu size from dhcp 9000, I have to manually set int.MTUSize in the advanced properties of the netKVM driver from 1500 to 9000 in order to make the net connection work. (shift-f10 during initial boot and devmgmt.msc in cmd...) It works out of the box on windows 2012r2.

The problem seems to also be described here: https://bugzilla.redhat.com/show_bug.cgi?id=1467797

Is it fixable in any way?

YanVugenfirer commented 6 years ago

Hi,

You can try setting EnablePMTUDiscovery in the registry (if it is not already set) https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/cc957539(v=technet.10) .

Best regards, Yan.

jsm222 commented 6 years ago

Thanks for your reply. As per this it is ON by default. (And it was not set e.g it did not exist) I do not have access to the OpenStack environment with jumbo frames before Monday. (But the windows system image was the same)

jsm222 commented 6 years ago

Well. I recreated the image and manually set init.MTUSize on the NIC device propeties before sysprep. A reg add database change of the setting during install in unattend.xml did not work..

sameehj commented 6 years ago

Is the device provided with the mtu parameter by Openstack? The virtio-net's host_mtu should be set to 9000 by OpenStack, please make sure that Openstack does that.

I have reread your first comment and now I understand that the issue with the Windows itself, so nevermind my comment. However I would suggest that you create a script that would apply the change to the registery key upon boot.

jsm222 commented 6 years ago

Openstack does not set host_mtu in my environment. Do you know a setting in queens/libvirt I could look for? It is not documented as a glance property..

I did try a script in unattend.xml with reg add and it did not work.. it set the mtu nic property correctly but it lost connection...

YanVugenfirer commented 3 years ago

Addressed by https://github.com/virtio-win/kvm-guest-drivers-windows/pull/495