[Openstack] Directional network performance issues with Neutron + OpenvSwitch

Darragh O'Reilly dara2002-openstack at yahoo.com
Fri Oct 25 09:15:47 UTC 2013

Hi Thiago,

you have configured DHCP to push out a MTU of 1400. Can you confirm that the 1400 MTU is actually getting out to the instances by running 'ip link' on them?

There is an open problem where the veth used to connect the OVS and Linux bridges causes a performance drop on some kernels - https://bugs.launchpad.net/nova-project/+bug/1223267 .  If you are using the LibvirtHybridOVSBridgeDriver VIF driver, can you try changing to LibvirtOpenVswitchDriver and repeat the iperf test between instances on different compute-nodes.

What NICs (maker+model) are you using? You could try disabling any off-load functionality - 'ethtool -k <iface-used-for-gre>'.

What kernal are you using: 'uname -a'?

Re, Darragh.

> Hi Daniel,

> I followed that page, my Instances MTU is lowered by DHCP Agent but, same
> result: poor network performance (internal between Instances and when
> trying to reach the Internet).
> No matter if I use "dnsmasq_config_file=/etc/neutron/dnsmasq-neutron.conf +
> "dhcp-option-force=26,1400"" for my Neutron DHCP agent, or not (i.e. MTU =
> 1500), the result is almost the same.
> I'll try VXLAN (or just VLANs) this weekend to see if I can get better
> results...
> Thanks!
> Thiago

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