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[QFX] Incorrect port rate counters during port mirroring

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Article ID: KB35613 KB Last Updated: 06 May 2020Version: 1.0
Summary:

In QFX5200, with port mirroring using 100G interface, although it mirrors all traffic to the egress interface properly, the display 'show interfaces et-x/x/x' shows incorrect pps counters.

Symptoms:

In a QFX5200 device, port mirroring with ingress port as et-0/0/1 and egress port to be et-0/0/0 was configured. When checking the pps using 'show interface extensive', the pps on both interfaces do not match.

Ingress shows ~50G traffic coming in, but egress shows only ~15G. However, all traffic is reaching the mirrored port.

Topology:

Ixia ------ et-0/0/1 QFX5200  et-0/0/0 ------------ ixia
root@switch> show configuration interfaces et-0/0/0
unit 0 {
    family ethernet-switching;
}

{master:0}
root@switch> show configuration interfaces et-0/0/1   
unit 0 {
    family ethernet-switching {
        interface-mode trunk;
        vlan {
            members V107;
        }
    }
}


Basic IPv4 unicast packets are being sent:

---(refreshed at 2019-03-13 11:09:30 PDT)---
   Input  packets:          60069379586             51140907 pps  <-- Ingress pps
   Output packets:                    0                    0 pps
     Input  packets:                    0                    0 pps
     Output packets:                    0                    0 pps


---(refreshed at 2019-03-13 11:09:31 PDT)---
   Input  packets:                    0                    0 pps
   Output packets:          60068961177             14669967 pps  <-- egress pps
     Input  packets:                    0                    0 pps
     Output packets:                    0                    0 pps

Ideally, the egress pps and ingress pps should match.

After stopping the traffic:
root@switch> show interfaces et-0/0/1 extensive | match pps               
   Input  packets:          60146448396                    0 pps
   Output packets:                    0                    0 pps
     Input  packets:                  0                    0 pps
     Output packets:                  0                    0 pps

{master:0}
root@switch> show interfaces et-0/0/0 extensive | match pps   
   Input  packets:                    0                    0 pps
   Output packets:          60146448396                    0 pps
     Input  packets:                  0                    0 pps
     Output packets:                  0                    0 pps

All packets at ingress and egress of these ports match. It is only the pps that has the issue.
Cause:

Interface statistics are not read properly from the hardware at regular intervals by the PFE. This is a display issue.

Solution:

There is no configuration issue to correct. To avoid this issue, lock the values when reading in the hardware so that it is displayed properly.

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