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Re: [Xen-users] domU ignores MTU

  • To: Xen Users <xen-users@xxxxxxxxxxxxxxxxxxx>
  • From: Christoph Fritsche <chr.fr@xxxxxxx>
  • Date: Mon, 12 May 2008 05:05:26 +0200
  • Delivery-date: Sun, 11 May 2008 20:04:37 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>

On 2008-05-12 03:48, Todd Deshane wrote:
>> Is there a way, other than ifconfig, to set the MTU, or force Xen not to
>> send juboframes?
> Have you looked here:
> http://xen.markmail.org/search/?q=jumbo%20frame
> Cheers,
> Todd
Hi Todd,

I used google and stumbled across several of these posts. Most of them
talk about how to enable jubo frames and whether Xen is capable of it.
My problem is quite the opposite. I do not want jumbo frames and have
them not fitting through the wire.

As far as I have read the MTU is set on the device. So it is done in the
domU, plain old 1500 bytes. I checked the vif settings in dom0 and there
it reads again 1500 bytes. The path is set to 1500 bytes. I read that
the bridge will use the lowest MTU of the enslaved devices (1500 bytes).

When capturing with tcpdump, regular Ethernet frames consist of 1514
bytes and some contain *1962* bytes. Those big ones get lost.

How to get Xen to stick to the MTU?

Kind regards,

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