[ovs-discuss] Incorrect packet statistics when mirroring vlans

Shweta Seth (shwseth) shwseth at cisco.com
Thu Dec 13 21:30:09 UTC 2018


When mirroring packets between two VLANs, we have observed that the OVS
mirror packet transmit statistics as displayed by the "ovs-vsctl list
mirror show tx packets" command is not correct.

We have configured OVS mirror to mirror all the packets
transmited/received on two VLANS (21 and 22) to a VM virtual NIC
connected to VLAN 30.  We have confirmed that this mirror works both by
looking at the OVS mirror statistics and by dumping the packets within
the mirror destination VM. We are using the following command to
configure this mirroring:

$ ovs-vsctl -- set bridge pm-br mirrors=@m -- --id=@m create mirror
name=36 select_all=true select-vlan=21,22 output-vlan=30

But when we transmit packets on a VLAN that is not configured for
mirroring (e.g VLAN 10) on the same bridge we see that the OVS mirror
statistics still go up. We expected that as this VLAN is not configured
for mirroring, the mirror packet statistics will not go up.

This issue was not seen in OVS version 2.3.2 and before but seen with
2.5.2 and after.

Is this a known issue? Any help in debugging this will be appreciated.
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