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We are running Ocata and our MTU is not set to 1450.. since out
external provider is not running on a 9000.<br>
<br>
<br>
Remo <br>
<br>
<div class="moz-cite-prefix">On 9/14/17 11:10 AM, John Petrini
wrote:<br>
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<div
style="margin:0px;padding:0px;display:block;width:100%;height:auto">Hi
List, <br>
<br>
We are running Mitaka and having an MTU issue. Instances
that we launch on our provider network use Jumbo Frames
(9000 MTU). There is a Layer2 link between the OpenStack
switches and our Core. This link uses and MTU of 1500. <br>
<br>
Up until recently this MTU mismatch has not been an issue
because none of our systems are sending large enough
packets to cause a problem. Recently we've begun
implementing a SIP device that sends very large packets,
sometimes even over 9000 bytes and requires fragmentation.<br>
<br>
What we found in our troubleshooting is that when large
packets originate from our network to an instance in
OpenStack they are being fragmented (as expected). Once
these packets reach the qbrXXXXXXXX-XX port iptables
defragments the packet and forwards it to the tap
interface unfragmented. If we set the MTU on the tap
interface to 1500 it will refragment the packet before
forwarding it to the instance. <br>
<br>
A similar issue happens the other direction. Large packets
originating from the OpenStack instance are fragmented (we
set the mtu of the interface in the instance to 1500 so
this is expected) but again once the packets reach the
qbr-XXXXXXXX-XX interface iptables defragments them again.
If we set the MTU of the qvbXXXXXXXX-XX to 1500 the packet
is refragmented. <br>
<br>
So long story short if we set the instance MTU to 1500 and
the qbrXXXXXXXX-XX and qvbXXXXXXXX-XX ports on the compute
node to 1500 MTU the packets remain fragmented and are
able to traverse the network. <br>
<br>
So the question becomes can we modify the default MTU of
our provider networks so that the instances created on
this network receive a 1500 MTU from DHCP and the ports on
the compute node are also configured to a 1500 MTU? <br>
<br>
I've been looking at the following neutron config option
in /etc/neutron/plugins/ml2/ml2_conf.ini: <br>
<br>
physical_network_mtus =physnet1:9000,providernet:9000 <br>
<br>
Documentation on this setting is not very clear. Will
adjusting this to 1500 for providernet accomplish what we
need? <br>
<br>
Thank You, <br>
<br>
John Petrini<br>
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