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Re: [Xen-users] Setting vifX.Y's MTU automatically in Xen 3

On 04/15/2011 06:12 AM, Pasi Kärkkäinen wrote:
> On Wed, Apr 13, 2011 at 07:33:49AM -0400, Digimer wrote:
>> Hi all,
>>   I've got Xen 3.0 (stock as available on CentOS 5.6). I'm trying to use
>> jumbo frames, but when Xen creates vifX.Y interfaces, it uses 1500. This
>> brings the xenbrX bridges down to 1500, and effectively messes up
>> anything thinking that it can use the larger packet size.
>>   So how can I make sure that all vifX.Y interfaces created by Xen are
>> set to a given MTU? I've grepped the files under /etc/xen, but haven't
>> seen a specific place to set it.
>> Thanks!
> I think first I'd try to modify vif-bridge script and make sure
> MTU of the vif is adjusted before attaching to the bridge.
> Verify you get that working, and then let's figure out what's the best way..
> -- Pasi

This fails. I tried adding to 'vif-bridge':

case "$command" in
        setup_bridge_port "$vif"
        ifconfig $vif mtu 9000
        add_to_bridge "$bridge" "$vif"

Alternatively, I tried adding to 'xen-network-common.sh':

add_to_bridge () {
    local bridge=$1
    local dev=$2

    # Don't add $dev to $bridge if it's already on a bridge.
    if [ -e "/sys/class/net/${bridge}/brif/${dev}" ]; then
        ip link set ${dev} up || true
    ifconfig ${dev} mtu 9000
    brctl addif ${bridge} ${dev}
    ip link set ${dev} up

Both cases caused the start of the domU to fail, complaining that the
scripts failed.


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