The Article provides on details to be checked when there are queue drops seen for queue 0[Best effort quque] and workaround

• On Junos QFX5200 & QFX5210 platforms, traffic drop might be seen on interface queue where microburst traffic is present and lag interfaces are used with member interfaces located on the same pipe in PFE
• The interface will show drops on the output errors
• The "show interfaces <interface-name> extensive " output will show drops under "queue 0 " when checked under "Egress queues" section
• Traffic drops will be seen and customer will see impact

labroot@jtac-QFX5200> show interfaces et-0/0/0 extensive | no-more 

Physical interface: et-0/0/0, Enabled, Physical link is Up

 Interface index: 700, SNMP ifIndex: 536, Generation: 191

 Description: jtac-QFX5200

 Link-level type: Ethernet, MTU: 9114, LAN-PHY mode, Speed: 100Gbps, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled, Flow control: Disabled, Media type: Fiber

 Device flags  : Present Running

 Interface flags: SNMP-Traps Internal: 0x4000

 Link flags   : None

 CoS queues   : 10 supported, 10 maximum usable queues

 Hold-times   : Up 0 ms, Down 0 ms

 Current address: 18:0a:bc:91:ae:11, Hardware address: 18:0a:bc:91:ae:11

 Last flapped  : 2025-03-28 17:39:58 UTC (1w0d 11:13 ago)

 Statistics last cleared: 2023-11-17 03:46:57 UTC (72w1d 01:06 ago)

 Traffic statistics:

  Input bytes :   4367709757537480      164746176 bps

  Output bytes :   1930874248800314      174672296 bps

  Input packets:    2681393340642        21974 pps

  Output packets:    1297087574153        22935 pps

  IPv6 transit statistics:

  Input bytes :          0

  Output bytes :          0

  Input packets:          0

  Output packets:          0

 Input errors:

  Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 0, L3 incompletes: 0, L2 channel errors: 0, L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 0

 Output errors:

  Carrier transitions: 154, Errors: 0, Drops: 858580, Collisions: 0, Aged packets: 0, FIFO errors: 0, HS link CRC errors: 0, MTU errors: 0, Resource errors: 0

 Egress queues: 10 supported, 5 in use

 Queue counters:    Queued packets Transmitted packets   Dropped packets

  0           1297043747378    1297042888798        858580. >>>>>>>>>>>>>>>>Drop seen on Queue0

  3                 0           0           0

  4                 53           53           0

  7              44725539        44725539            0

  8                 8           8           0

 Queue number:     Mapped forwarding classes

  0          best-effort

  3          fcoe

  4          no-loss

  7          network-control

  8          mcast

 Active alarms : None

• In deployments where micro burst traffic is present and lag interfaces are used with member interfaces located on same pipe in the PFE then traffic drop might be seen on interface queue.
• On Junos QFX5200 & QFX5210 platforms interfaces within PFE are mapped to pipe [0-4]. Each pipe is then allocated a fixed amount of shared buffer for ingress and egress traffic.
• If the ingress and egress ports are on same pipe then buffer is not efficiently utilised hence queue drops might be seen.

Please use below command to check queue drops:

#show interfaces queue <interface>