We are running Ocata and our MTU is not set to 1450.. since out external provider is not running on a 9000.
Remo On 9/14/17 11:10 AM, John Petrini wrote: > Hi List, > > 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. > > 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. > > 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. > > 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. > > 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. > > 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? > > I've been looking at the following neutron config option in > /etc/neutron/plugins/ml2/ml2_conf.ini: > > physical_network_mtus =physnet1:9000,providernet:9000 > > Documentation on this setting is not very clear. Will adjusting this > to 1500 for providernet accomplish what we need? > > Thank You, > > John Petrini > > > > _______________________________________________ > Mailing list: http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack > Post to : openstack@lists.openstack.org > Unsubscribe : http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack
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