[ovs-discuss] [OVN] Can flow table work when OVN controller lost connection to OVN Database

Numan Siddique numans at ovn.org
Tue Oct 13 12:39:47 UTC 2020

On Tue, Oct 13, 2020 at 5:21 PM James Guo <guoyongxhzhf at 163.com> wrote:
> I am not sure whether flowtable of vm continue to work when OVN controller lost connection to OVN Database
> If flowtable continue to work, can flowtable work after vm restart?

What do you mean by flowtable continue to work ? If you mean that the
VM's datapath is not disrupted and it can continue to send and receive
traffic, then yes, it will work.

I did some testing and I can see that the traffic for the VM will
continue to work as long as ovn-controller has claimed the logical
port of the VM.

When the VM restarts and if the corresponding ovs interface is deleted
and readded again, then I am certain that the traffic for that VM will
be broken
after that. That is because, when the interface is deleted,
ovn-controller will release the interface and delete all the flows for
that VM interface and when
it see the interface back, it will not reprogram the flows because it
doesn't have connectivity to Southbound database.


> according to http://www.openvswitch.org//support/dist-docs-2.5/ovn-architecture.7.html section Life Cycle of a VIF, it looks that flowtable will not work after vm power off
> Thanks for your reply
> section Life Cycle of a VIF:
> 11.On every hypervisor, ovn-controller notices the empty  Chassis column  in the Binding table’s row for the logical port.  This means that ovn-controller no longer knows the  physical  location of  the logical port, so each instance updates its OpenFlow table to reflect that.
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