On Thu, 8 Aug 2019 at 10:08, Sven Vogel <S.Vogel@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 :-).



- Peter

Am 31.07.2019 um 15:50 schrieb Alvin Starr <alvin@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.