[ovs-discuss] OVN - VLAN packet duplicate processing on egress pipeline

[Mark Michelson]

On 07/23/2018 08:03 AM, Anil Venkata wrote:
> Packets destined for VLAN remote logical ports are sent out through 
> physical table 65 rather than physical table 32 (Geneve remote logical 
> ports are sent through table 32). I found below description in ovn 
> architecture documentation.
> 
> http://www.openvswitch.org//support/dist-docs/ovn-architecture.7.html
> 
> A  special  case  is  that  when a localnet port exists on the
> datapath, remote port is connected by switching to the  local‐
> net  port.  In this case, instead of adding a flow in table 32
> to reach the remote port, a flow  is  added  in  table  33  to
> switch  the logical outport to the localnet port, and resubmit
> to table 33 as if it were unicasted to a logical port  on  the
> local hypervisor.
> 
> 
> Any reason for this decision. Because of this, packet is redundantly 
> processed in logical switch's egress pipeline on both local and remote 
> hypervisors.

Keep in mind that from OVN's perspective, a localnet port represents a 
local exit from the logical switch. It doesn't know if the packet will 
end up back in br-int again on another hypervisor. It would be equally 
valid for the packet to be modified by a separate OVS switch and sent 
out of the underlay network entirely once it has gone out the localnet 
port. Thus if it does not go through the egress pipeline of the local 
hypervisor, there is the chance that it will not go through the egress 
pipeline of the logical switch at all.

There are potential ways that we could get around this redundant 
processing. However, before suggesting anything concrete or actually 
proposing that anything actually should be done, I'll echo Russell's 
question about whether this is actually causing a noticeable problem.

> 
> Thanks
> Anil
> 
>    
> 
> 
> 
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