Description

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.

Solution

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

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.