I believe we need to emit ICMP / need to frag messages to have proper
support
on different MTUs (on router sides), I wonder how does it work the other way
around (when external net is 1500, and internal net is 1500-geneve
overhead).

Is there any way to match packet_size > X on a flow?

How could we implement this?



On Wed, Jul 11, 2018 at 1:01 PM Daniel Alvarez Sanchez <dalva...@redhat.com>
wrote:

> On Wed, Jul 11, 2018 at 12:55 PM Daniel Alvarez Sanchez <
> dalva...@redhat.com> wrote:
>
>> Hi all,
>>
>> Miguel Angel Ajo and I have been trying to setup Jumbo frames in
>> OpenStack using OVN as a backend.
>>
>> The external network has an MTU of 1900 while we have created two tenant
>> networks (Logical Switches) with an MTU of 8942.
>>
>
> s/1900/1500
>
>>
>> When pinging from one instance in one of the networks to the other
>> instance on the other network, the routing takes place locally and
>> everything is fine. We can ping with -s 3000 and with tcpdump we verify
>> that the packets are not fragmented at all.
>>
>> However, when trying to reach the external network, we see that the
>> packets are not tried to be fragmented and the traffic doesn't go through.
>>
>> In the ML2/OVS case (reference implementation for OpenStack networking),
>> this works as we're seeing the following when attempting to reach a network
>> with a lower MTU:
>>
>
> Just to clarify, in the reference implementation (ML2/OVS) the routing
> takes place with iptables rules so we assume that it's the kernel
> processing those ICMP packets.
>
>>
>> 10:38:03.807695 IP 192.168.20.14 > dell-virt-lab-01.mgmt.com: ICMP echo
>> request, id 30977, seq 0, length 3008
>>
>> 10:38:03.807723 IP overcloud-controller-0 > 192.168.20.14: ICMP
>> dell-virt-lab-01.mgmt.com unreachable - need to frag (mtu 1500), length
>> 556
>>
>> As you can see, the router (overcloud-controller-0) is responding to the
>> instance with an ICMP need to frag and after this, subsequent packets are
>> going fragmented (while replies are not):
>>
>> 0:38:34.630437 IP 192.168.20.14 > dell-virt-lab-01.mgmt.com: ICMP echo
>> request, id 31233, seq 0, length 1480
>>
>> 10:38:34.630458 IP 192.168.20.14 > dell-virt-lab-01.mgmt.com: icmp
>>
>> 10:38:34.630462 IP 192.168.20.14 > dell-virt-lab-01.mgmt.com: icmp
>>
>> 10:38:34.631334 IP dell-virt-lab-01.mgmt.com > 192.168.20.14: ICMP echo
>> reply, id 31233, seq 0, length 3008
>>
>>
>>
>> Are we missing some configuration or we lack support for this in OVN?
>>
>> Any pointers are highly appreciated :)
>>
>>
>> Thanks a lot.
>>
>> Daniel Alvarez
>>
>>
>
> _______________________________________________
> discuss mailing list
> disc...@openvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
>
_______________________________________________
discuss mailing list
disc...@openvswitch.org
https://mail.openvswitch.org/mailman/listinfo/ovs-discuss

Reply via email to