[libvirt-users] OVS / KVM / libvirt / MTU

[Sven Vogel]

Hi Peter,

Maybe my English it not good enough. I would understand the highest but not the smallest. You know? :)

You mean if any VM has 2000 set and another will set 3000 we get 3000 for all on the bridge? What I don’t understand is if the bridgec already has 9000 set as MTU they will be shrined down?!?

For me I think it lags of some functionality.


__

Sven Vogel
Teamlead Platform

EWERK DIGITAL GmbH
Brühl 24, D-04109 Leipzig
P +49 341 42649 - 11
F +49 341 42649 - 18
S.Vogel at ewerk.com
www.ewerk.com

Geschäftsführer:
Dr. Erik Wende, Hendrik Schubert, Frank Richter
Registergericht: Leipzig HRB 17023

Zertifiziert nach:
ISO/IEC 27001:2013
DIN EN ISO 9001:2015
DIN ISO/IEC 20000-1:2011

ISAE 3402 Typ II Assessed

EWERK-Blog<https://blog.ewerk.com/> | LinkedIn<https://www.linkedin.com/company/ewerk-group> | Xing<https://www.xing.com/company/ewerk> | Twitter<https://twitter.com/EWERK_Group> | Facebook<https://de-de.facebook.com/EWERK.IT/>

Mit Handelsregistereintragung vom 09.07.2019 ist die EWERK RZ GmbH auf die EWERK IT GmbH verschmolzen und firmiert nun gemeinsam unter dem Namen: EWERK DIGITAL GmbH, für weitere Informationen klicken Sie hier<https://www.ewerk.com/ewerkdigital>.

Auskünfte und Angebote per Mail sind freibleibend und unverbindlich.

Disclaimer Privacy:
Der Inhalt dieser E-Mail (einschließlich etwaiger beigefügter Dateien) ist vertraulich und nur für den Empfänger bestimmt. Sollten Sie nicht der bestimmungsgemäße Empfänger sein, ist Ihnen jegliche Offenlegung, Vervielfältigung, Weitergabe oder Nutzung des Inhalts untersagt. Bitte informieren Sie in diesem Fall unverzüglich den Absender und löschen Sie die E-Mail (einschließlich etwaiger beigefügter Dateien) von Ihrem System. Vielen Dank.

The contents of this e-mail (including any attachments) are confidential and may be legally privileged. If you are not the intended recipient of this e-mail, any disclosure, copying, distribution or use of its contents is strictly prohibited, and you should please notify the sender immediately and then delete it (including any attachments) from your system. Thank you.

Am 08.08.2019 um 11:43 schrieb Peter Crowther <peter.crowther at melandra.com<mailto:peter.crowther at melandra.com>>:

On Thu, 8 Aug 2019 at 10:08, Sven Vogel <S.Vogel at ewerk.com<mailto:S.Vogel at ewerk.com>> wrote:
The question for me is why they use the smallest?

Because otherwise some frames won't get through because the interface can't receive them, and the job of network equipment is to enable and maintain communication :-).

Cheers

Sven

- Peter

[...]

Am 31.07.2019 um 15:50 schrieb Alvin Starr <alvin at netvel.net<mailto:alvin at netvel.net>>:

In general if no MTU is set on interface creation the default value is 1500.

On OVS the bridge MTU is automatically set to the smallest port MTU. So you just have to set the MTU of each port of the bridge.

Take a look at: https://bugzilla.redhat.com/show_bug.cgi?id=1160897
It is a bit of a pain to read but seems to confirm the statement about the OVS MTU value being set by the MTU of the ports.

I have been using OVS with Xen and a few years ago I had to wrap my head around this problem.
Once you start setting the MTU to something other than 1500 you will find you need to set ALL the MTU values of ALL your interfaces.
Otherwise some inherited default will bite you.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/libvirt-users/attachments/20190809/869a8a7d/attachment.htm>