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Re: [Xen-devel] [PATCH] set mtu from bridge also on vif interface

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] set mtu from bridge also on vif interface
From: Olaf Hering <olaf@xxxxxxxxx>
Date: Mon, 7 Feb 2011 10:25:24 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Mon, Feb 07, Ian Campbell wrote:

> On Sun, 2011-02-06 at 13:41 +0000, Olaf Hering wrote:
> > Apply mtu size from bridge interface also in vif interface.
> > This depends on a kernel change which allows arbitrary mtu sizes until
> > the frontend driver has connected to the backend driver. Without this
> > kernel change, the vif mtu size will be limited to 1500 even with this
> > change to the vif-bridge script.
> > 
> > Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
> In my experience the bridge will only allow it's MTU to be set to the
> minimum of all the ports (or 1500ish if there are no ports) and will
> reset to the new minimum when you add a new port.
> So does this patch do anything in the absence of the ability to
> configure the MTU of a VIF from the toolstack?

This depends if the bridge interface is part of the Xen toolstack
configuration or if the bridge is part of the system configuration. In
my setup the bridge is part of the system configuration and gets its mtu
from the config of the physical interface, eth0 in my case. So br0 has
mtu of 9000 already when vif-bridge runs.

With this change, the vif interfaces follow the system configuration.


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