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[QFX] Inconsistent packet drop stats seen after polling CoS-related SNMP OIDs

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Article ID: KB36576 KB Last Updated: 29 Mar 2021Version: 1.0
Summary:

On QFX platforms, polling class-of-service-related SNMP OIDs might cause the interface drop statistics to be inconsistent. This article indicates that the only way to recover from the state is to reboot the device.

Symptoms:

The following log messages will be seen when the issue is triggered:

Nov 19 07:00:07  switch kernel: et-0/0/33: invalid PFE PG counter pairs to copy, src 0xfffff8012285d720, dst 0
Nov 19 07:00:07  switch kernel: et-0/0/36: invalid PFE PG counter pairs to copy, src 0xfffff800076df570, dst 0
Nov 19 07:00:07  switch kernel: et-0/0/37: invalid PFE PG counter pairs to copy, src 0xfffff8012285d750, dst 0
Nov 19 07:00:07  switch kernel: et-0/0/40: invalid PFE PG counter pairs to copy, src 0xfffff800076df480, dst 0
Nov 19 07:00:07  switch kernel: et-0/0/44: invalid PFE PG counter pairs to copy, src 0xfffff800255374e0, dst 0
Nov 19 07:00:07  switch kernel: et-0/0/45: invalid PFE PG counter pairs to copy, src 0xfffff800076df420, dst 0
Nov 19 07:00:07  switch kernel: et-0/0/46: invalid PFE PG counter pairs to copy, src 0xfffff800076de390, dst 0
Nov 19 07:00:07  switch kernel: et-0/0/47: invalid PFE PG counter pairs to copy, src 0xfffff800076df210, dst 0
Nov 19 07:00:07  switch kernel: et-0/0/48: invalid PFE PG counter pairs to copy, src 0xfffff800076dff30, dst 0
Cause:

On QFX platforms, polling class of service-related SNMP OIDs might cause the interface drop statistics to be â€‹inconsistent. Here is an example of how the issue is triggered:

root@qfx> show interfaces queue xe-0/0/36:2 | match "Queue:|drop|SNMP" 
  Interface index: 652, SNMP ifIndex: 522  <-- interface snmp index number  
Queue: 0, Forwarding classes: best-effort <-- <Queue number 0 (best Effort)
  Queued:
    Tail-dropped packets : Not Available  
    RL-dropped packets   :                     0                     0 pps
    RL-dropped bytes     :                     0                     0 bps
    Total-dropped packets:            8306456612                 41574 pps   <-- packets

juniper@server1:~$ snmpwalk -v2c -c JUNIPER 10.85.150.190 1.3.6.1.4.1.2636.3.15.4.1.54.522  <-- This gives the drops for all queues.
iso.3.6.1.4.1.2636.3.15.4.1.54.522.0 = Counter64: 41574
iso.3.6.1.4.1.2636.3.15.4.1.54.522.1 = Counter64: 0
iso.3.6.1.4.1.2636.3.15.4.1.54.522.2 = Counter64: 0
iso.3.6.1.4.1.2636.3.15.4.1.54.522.3 = Counter64: 0
iso.3.6.1.4.1.2636.3.15.4.1.54.522.4 = Counter64: 0
iso.3.6.1.4.1.2636.3.15.4.1.54.522.5 = Counter64: 0
iso.3.6.1.4.1.2636.3.15.4.1.54.522.6 = Counter64: 0
iso.3.6.1.4.1.2636.3.15.4.1.54.522.7 = Counter64: 0

​root@qfx> show interfaces ae16 extensive | match "drop|last"
Mar 01 14:08:32
  Last flapped   : 2021-01-20 02:59:24 BOT (5w5d 11:09 ago)
  Statistics last cleared: 2021-02-27 12:25:44 BOT (2d 01:42 ago)
    Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0, Policed discards: 0, Resource errors: 0
    Carrier transitions: 0, Errors: 0, Drops: 5305587178, MTU errors: 0, Resource errors: 0
 
{master:0}
root@qfx> show interfaces ae16 extensive | match "drop|last"
Mar 01 14:08:34
  Last flapped   : 2021-01-20 02:59:24 BOT (5w5d 11:09 ago)
  Statistics last cleared: 2021-02-27 12:25:44 BOT (2d 01:42 ago)
    Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0, Policed discards: 0, Resource errors: 0
    Carrier transitions: 0, Errors: 0, Drops: 779501, MTU errors: 0, Resource errors: 0
 
{master:0}
root@qfx> show interfaces ae16 extensive | match "drop|last"
Mar 01 14:08:37
  Last flapped   : 2021-01-20 02:59:24 BOT (5w5d 11:09 ago)
  Statistics last cleared: 2021-02-27 12:25:44 BOT (2d 01:42 ago)
    Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0, Policed discards: 0, Resource errors: 0
    Carrier transitions: 0, Errors: 0, Drops: 13215, MTU errors: 0, Resource errors: 0
     
{master:0}
root@qfx> show interfaces ae16 extensive | match "drop|last"
Mar 01 14:08:42
  Last flapped   : 2021-01-20 02:59:24 BOT (5w5d 11:09 ago)
  Statistics last cleared: 2021-02-27 12:25:44 BOT (2d 01:42 ago)
    Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0, Policed discards: 0, Resource errors: 0
    Carrier transitions: 0, Errors: 0, Drops: 41574, MTU errors: 0, Resource errors: 0
Solution:

The issue is resolved in Junos OS releases 19.2R1-S4, 18.4R3-S1, 19.1R3-S1, 20.1R1, 20.2R1, 19.4R1-S2, 18.4R3-S2, 18.4R3-S5, 18.4R2-S4, 19.1R3-S3, 19.1R2-S1, 19.1R3-S2, 18.4R1-S7, 19.1R1-S5, 19.3R3, 19.4R2, 19.1R3, 19.2R2, and 19.3R2-S3 as detailed in PR1476829.

Meanwhile, the only way to recover from this state is to reboot the device after stopping all SNMP walks on CoS objects.

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