<div dir="ltr">It could be that too TBH I'm not sure :)</div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Sep 22, 2017 at 11:02 AM, Sławomir Kapłoński <span dir="ltr"><<a href="mailto:slawek@kaplonski.pl" target="_blank">slawek@kaplonski.pl</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Isn't OVS setting MTU automatically MTU for bridge as lowest value from ports connected to this bridge?<br>
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> Wiadomość napisana przez Miguel Angel Ajo Pelayo <<a href="mailto:majopela@redhat.com">majopela@redhat.com</a>> w dniu 22.09.2017, o godz. 10:32:<br>
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> I believe that one of the problems is that if you set a certain MTU in an OVS switch, new connected ports will be automatically assigned to such MTU the ovs-vswitchd daemon.<br>
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> On Wed, Sep 20, 2017 at 10:45 PM, Ian Wells <<a href="mailto:ijw.ubuntu@cack.org.uk">ijw.ubuntu@cack.org.uk</a>> wrote:<br>
> Since OVS is doing L2 forwarding, you should be fine setting the MTU to as high as you choose, which would probably be the segment_mtu in the config, since that's what it defines - the largest MTU that (from the Neutron API perspective) is usable and (from the OVS perspective) will be used in the system. A 1500MTU Neutron network will work fine over a 9000MTU OVS switch.<br>
><br>
> What won't work is sending a 1500MTU network to a 9000MTU router port. So if you're doing any L3 (where the packet arrives at an interface, rather than travels a segment) you need to consider those MTUs in light of the Neutron network they're attached to.<br>
> --<br>
> Ian.<br>
><br>
> On 20 September 2017 at 09:58, Ihar Hrachyshka <<a href="mailto:ihrachys@redhat.com">ihrachys@redhat.com</a>> wrote:<br>
> On Wed, Sep 20, 2017 at 9:33 AM, Ajay Kalambur (akalambu)<br>
> <<a href="mailto:akalambu@cisco.com">akalambu@cisco.com</a>> wrote:<br>
> > So I was forced to explicitly set the MTU on br-int<br>
> > ovs-vsctl set int br-int mtu_request=9000<br>
> ><br>
> ><br>
> > Without this the tap device added to br-int would get MTU 1500<br>
> ><br>
> > Would this be something the ovs l2 agent can handle since it creates the bridge?<br>
><br>
> Yes, I guess we could do that if it fixes your problem. The issue<br>
> stems from the fact that we use a single bridge for different networks<br>
> with different MTUs, and it does break some assumptions kernel folks<br>
> make about a switch (that all attached ports steer traffic in the same<br>
> l2 domain, which is not the case because of flows we set). You may<br>
> want to report a bug against Neutron and we can then see how to handle<br>
> that. I will probably not be as simple as setting the value to 9000<br>
> because different networks have different MTUs, and plugging those<br>
> mixed ports in the same bridge may trigger MTU updates on unrelated<br>
> tap devices. We will need to test how kernel behaves then.<br>
><br>
> Also, you may be interested in reviewing an old openvswitch-dev@<br>
> thread that I once started here:<br>
> <a href="https://mail.openvswitch.org/pipermail/ovs-dev/2016-June/316733.html" rel="noreferrer" target="_blank">https://mail.openvswitch.org/<wbr>pipermail/ovs-dev/2016-June/<wbr>316733.html</a><br>
> Sadly, I never followed up with a test scenario that wouldn't involve<br>
> OpenStack, for OVS folks to follow up on, so it never moved anywhere.<br>
><br>
> Cheers,<br>
> Ihar<br>
><br>
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</div></div>—<br>
Best regards<br>
Slawek Kaplonski<br>
<a href="mailto:slawek@kaplonski.pl">slawek@kaplonski.pl</a><br>
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