[ovs-discuss] Deleting and re-creating mirror with different configuration does not work

[Ben Pfaff]

On Fri, Apr 08, 2016 at 09:43:09AM +0200, Vasileios Kotronis wrote:
> I have an issue with port mirroring on ovs. I am trying to reload a mirror configuration on-the-fly, using an internal bridge port as the target mirror out port. There is no error that makes ovs complain, but the behavior of the mirror is not the intended one.
> 
> Here are the steps I followed:
> 
> 1) First, I clear the bridge’s mirrors:
> 
> ovs-vsctl clear Bridge my_br mirrors
> 
> 2) Afterwards, I create a new mirror from eth1 to the mirror out port (the latter port is an internal port used for this purpose):
> 
> ovs-vsctl -- set Bridge my_br mirrors=@m1 -- --id=@eth1 get Port eth1 -- --id=@mir0 get Port mir0 -- --id=@m1 create Mirror name=port_mirror1 select-dst-port=@eth1 select-src-port=@eth1 output-port=@mir0
> 
> 3) Using tcpdump on eth1 and mir0 and comparing their outputs I see that the mirror works correctly.
> Till now, all good.
> 
> 4) Next, I am changing the configuration of the mirror since I want, on-the-fly, to monitor a different interface with the same mirror out target.
> 
> 5) I am clearing the old configuration:
> 
> ovs-vsctl clear Bridge my_br mirrors
> 
> 6) I am creating the new mirror from eth2 to the mirror out port:
> 
> ovs-vsctl -- set Bridge my_br mirrors=@m1 -- --id=@eth2 get Port eth2 -- --id=@mir0 get Port mir0 -- --id=@m1 create Mirror name=port_mirror1 select-dst-port=@eth2 select-src-port=@eth2 output-port=@mir0
> 
> 7) Using tcpdump on eth2 and mir0 and comparing their outputs I see that the mirror DOES NOT work correctly.
> 
> That is, I still see traffic from the old mirrored interface (eth1), which should not be there after clearing the mirror. 
> Also, after such a process, it may happen that I see only the correct arp and ipv6 traffic on mir0, but no ipv4 traffic, or the traffic may be mixed
> with the old interface traffic which should not happen.
> 
> It is hard to understand if this is an ovs bug or whether I am doing sth totally wrong. 

This is quite strange.  It tends to indicate that Open vSwitch has
somehow retained the old configuration.  Please try restarting
ovs-vwitchd at this point.  If that makes a difference, then it is
almost certainly an OVS bug.  If the behavior of the previous
configuration persists, however, then it's probably something else.

> Moreover, I would like to ask if you are aware of any side-effects of
> using port mirroring on interfaces that are bonded, since I also tried
> another mirror creation on such an interface and I could only see arp
> and ipv6 traffic, no ipv4 packets. This did not have to do anything
> with changing the mirror configuration, but is related to the port
> mirroring problems with OVS.

Do you mean mirroring with a bond as a source or as a destination?  Both
of them should work, but we have not tested either one very much.

My recollection is that mirroring to an SLB bond will not work well; I
believe that this is documented.