[ovs-discuss] What is the role of ovsdb-server and vswitchd?

[Aishwarya]

Hi,

The instructions to start openvswitch say we need to run ovsdbserver
(listening on a unix socket in my case), and vswitchd subsequently. Now,
openvswitch is said to route packets in the kernel itself and not use
userspace. However, ovsdb-server and vswitchd are user processes. What is
the role of these actually when 2 vms are trying to send traffic via the
openvswitch? Lets say I configure the flow rules and then kill the vswitchd
process, the vms cannot communicate anymore. Why should this happen although
the kernel module is still loaded? How is the routing of the packet being
affected by these user level processes? I would assume that the database
server would be needed only to query something like port or flow
information. But it seems to be necessary while sending traffic too. Is this
because the switch on receiving traffic is querying the database to check
for the flows, before sending the traffic out? In that case, what does it
mean that openvswitch has High-performance forwarding using a Linux kernel
module (since it is using the user space program as well?)

Thanks,
Aish
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