[ovs-discuss] Use of ovs-vsctl with ovs-dpctl questions

Justin Pettit jpettit at nicira.com
Mon Nov 9 18:07:55 UTC 2009

On Nov 9, 2009, at 9:12 AM, John Galgay wrote:

> 1.  What are the modes in which ovs-vsctl (switch) and ovs-dpctl  
> work together .. or separately.  And how do they relate to loading  
> the openvswitch_mod.ko and brcompat_mod.ko modules?

I need to put up a better diagram of how all the components work, but  
for now I can point you to a paper that we wrote:


Sections 3 and 4 describe the architecture of Open vSwitch.  If you  
look at Figure 2, ovs-dpctl controls the Fast Path and ovs-vsctl  
configures the Slow Path.  In general, you'll probably want to use ovs- 
vsctl to handle configuration.  ovs-dpctl is mostly useful for  
debugging purposes.  Since the datapath is essentially a cache for the  
traffic that is occurring on the network, you can use the "ovs-dpctl  
dump-flows" command to see what traffic is being processed and what  
actions are occurring currently.

Neither of those commands will load the kernel modules.

> 2.  Can I -or- Must I use the switch functions of ovs-vsctl in  
> conjunction with the datapath functions of ovs-dpctl ... or are they  
> exclusive from each other.  In other words, can I get the benefits  
> of the vswitch for bridging/switching and still define strict  
> datapaths between ports on the switch?

They are essentially unrelated.  I think your best bet may be to use  
ovs-ofctl to setup static rules defining how traffic should move.  For  
example, you could define that port 1's traffic is sent to port 2 and  
vice versa.  Once you define those rules, the traffic that matches  
them won't be switched according to a MAC table.

> 3.  Are the ovs-dpctl capabilities tied to openflow?  If not, cool.   
> If so, can I use the openflow capabilities for datapaths without an  
> openflow controller?

In Open vSwitch, the datapath (which ovs-dpctl controls) is just a  
simple, fast forwarding table.  ovs-vswitchd (or ofproto) contain an  
OpenFlow module, which they then translate on-demand into datapath  

Once again, you may want to look at ovs-ofctl, which sends OpenFlow  

> 4.  What are the best options regarding openflow controllers today?

The only one that I know of is NOX, which is available at  
noxrepo.org.  This is also a project hosted by Nicira.

> 5.  Can an openflow controller also manage real 10G switches in the  
> network (such as Arista with its EOS)?

The last I heard, Arista was reworking their OpenFlow port, so I don't  
think it's publicly available.  You can buy OpenFlow "real" switches  
from NEC and Toroki.  Most of the OpenFlow switches I know are 1G  
switches that may support 10G uplinks.  I know of some organizations  
doing 10G ports, but I don't know when they will be available.


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