Customer copied the config from MX where no issues were seen & in PTX they are observing RED-dropped packets in Bronze scheduler or queue 0, but no such issue with Silver with similar config.
set class-of-service drop-profiles Bronze-H interpolate fill-level 0 set class-of-service drop-profiles Bronze-H interpolate fill-level 100 set class-of-service drop-profiles Bronze-H interpolate drop-probability 0 set class-of-service drop-profiles Bronze-H interpolate drop-probability 100 set class-of-service drop-profiles Silver-H interpolate fill-level 90 set class-of-service drop-profiles Silver-H interpolate fill-level 100 set class-of-service drop-profiles Silver-H interpolate drop-probability 10 set class-of-service drop-profiles Silver-H interpolate drop-probability 100 root@Router> show interfaces queue et-0/0/0 forwarding-class Bronze Physical interface: et-0/0/0, up, Physical link is Up Interface index: 1252, SNMP ifIndex: 544 Description: Router-et-0/1/0 Forwarding classes: 16 supported, 5 in use Egress queues: 8 supported, 5 in use Queue: 0, Forwarding classes: Bronze Queued: Packets : 273404 405 pps Bytes : 34446360 407904 bps Transmitted: Packets : 272768 404 pps Bytes : 34368768 406984 bps Tail-dropped packets : 0 0 pps Tail-dropped bytes : 0 0 bps RED-dropped packets : 636 1 pps RED-dropped bytes : 77592 920 bps root@Router> show interfaces queue et-0/0/0 forwarding-class Silver Physical interface: et-0/0/0, up, Physical link is Up Interface index: 1252, SNMP ifIndex: 544 Description: MX-1-et-0/1/0 Forwarding classes: 16 supported, 5 in use Egress queues: 8 supported, 5 in use Queue: 2, Forwarding classes: Silver Queued: Packets : 0 0 pps Bytes : 0 0 bps Transmitted: Packets : 0 0 pps Bytes : 0 0 bps Tail-dropped packets : 0 0 pps Tail-dropped bytes : 0 0 bps RED-dropped packets : 0 0 pps RED-dropped bytes : 0 0 bps
The probability of dropping packet rises from Zero itself which means even with slight fill in queue there is a valid drop probability.
PTX has line function in (ASIC) for drop profile, for configs starting from (0,0) some drops will be seen as that is the correct behavior. A line from coordinates (0,0) (100,100) will have a slope of 45 degrees. Any increase in fill level will cause drop probability to increase. So at 3-4% fill level drop probability of 4% is expected.
MX has steps and line function is not available in ASIC, so first step takes time to rise drop probability (i.e product limitation)
So config should be adjust in PTX, if you need different behaviour. Start from fill level say for example 4-5 %.
On MX platforms, the configured fill-level value represents the point at which the first drop probability step becomes active, not necessarily the exact point where drops will always start occurring.
So with "set class-of-service drop-profiles Bronze-H interpolate fill-level 5", the drop probability does not increase linearly from 0–5% like on PTX.
Instead, due to the ASIC implementation on MX, drops may not be observed immediately at exactly 5% queue fill. The first drop behavior depends on the internal step-based implementation in the ASIC.
In contrast, PTX uses a line-function based implementation, where drop probability starts increasing progressively from the configured point.
Hence the suggestion is to have higher non-zero interpolate fill-level on PTX.
Therefore, on MX, the configured fill-level should be treated as the trigger point for the first drop profile step rather than an exact deterministic drop point.
root@Router:pfe> show cda class-of-service buffer-manager wred-prf-sw-table chip 0
WRED Profile Software Table on Chip 0 : | | Curve IDs | WRED| Ref | LossPrio| LossPrio| LossPrio| LossPrio| Prof| Cnt | 0 | 1 | 2 | 3 | ECN Type ----|-------|---------|---------|---------|---------|----------------- 1 | 469 | 0 | 0 | 0 | 0 | Mark-Disable 2 | 2 | 2 | 0 | 0 | 1 | Mark-Disable 3 | 2 | 5 | 0 | 4 | 3 | Mark-Disable
root@Router:pfe> show cda class-of-service buffer-manager wred-prf-hw-table chip 0 index 2 Wred Profile Information for Index 2 on Chip 0: ------|-------------------------------------------------------------------|---------------------------------------------------------------------| Index| Hardware Data | Decoded | | | Drop Profile | ECN | DCTCP | | | | Start | End | DP|ECN|MaxP Rise|Prob 2pt5|Qmax Frac|PFC|Drop Cpbl|Mark Style|Unrated|Frac| OffsetP |MaxP Rise| MinProb | Fill | Prob | Fill | Prob | --|---|---------|---------|---------|---|---------|----------|-------|----|---------|---------|---------|---------|---------|---------|---------| 0| 0| 64| 0| 63| 0| 0| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 100.000%| 100.000%| 0| 1| 64| 0| 63| 0| 1| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 100.000%| 100.000%| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 1| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 2| 0| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 2| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 3| 0| 64| 0| 31| 0| 0| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 50.000%| 100.000%| 3| 1| 64| 0| 31| 0| 1| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 50.000%| 100.000%| 4| 0| 64| 0| 63| 0| 0| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 100.000%| 100.000%| 4| 1| 64| 0| 63| 0| 1| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 100.000%| 100.000%| 5| 0| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 5| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 6| 0| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 6| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 7| 0| 64| 0| 31| 0| 0| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 50.000%| 100.000%| 7| 1| 64| 0| 31| 0| 1| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 50.000%| 100.000%| ------|-------------------------------------------------------------------|---------------------------------------------------------------------| Changing set class-of-service drop-profiles Bronze-H interpolate fill-level 0 set class-of-service drop-profiles Bronze-H interpolate fill-level 100 set class-of-service drop-profiles Bronze-H interpolate drop-probability 0 set class-of-service drop-profiles Bronze-H interpolate drop-probability 100 to set class-of-service drop-profiles Bronze-H interpolate fill-level 90 set class-of-service drop-profiles Bronze-H interpolate fill-level 100 set class-of-service drop-profiles Bronze-H interpolate drop-probability 0 set class-of-service drop-profiles Bronze-H interpolate drop-probability 100 root@Router:pfe> show cda class-of-service buffer-manager wred-prf-hw-table chip 0 index 2 Wred Profile Information for Index 2 on Chip 0: ------|-------------------------------------------------------------------|---------------------------------------------------------------------| Index| Hardware Data | Decoded | | | Drop Profile | ECN | DCTCP | | | | Start | End | DP|ECN|MaxP Rise|Prob 2pt5|Qmax Frac|PFC|Drop Cpbl|Mark Style|Unrated|Frac| OffsetP |MaxP Rise| MinProb | Fill | Prob | Fill | Prob | --|---|---------|---------|---------|---|---------|----------|-------|----|---------|---------|---------|---------|---------|---------|---------| 0| 0| 168| 127| 63| 0| 0| 0| 0| 0| 3.968750| 4.967431| 0.000000| 79.895%| 0.000%| 100.000%| 99.868%| 0| 1| 168| 127| 63| 0| 1| 0| 0| 0| 3.968750| 4.967431| 0.000000| 79.895%| 0.000%| 100.000%| 99.868%| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 1| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 2| 0| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 2| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 3| 0| 64| 0| 31| 0| 0| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 50.000%| 100.000%| 3| 1| 64| 0| 31| 0| 1| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 50.000%| 100.000%| 4| 0| 168| 127| 63| 0| 0| 0| 0| 0| 3.968750| 4.967431| 0.000000| 79.895%| 0.000%| 100.000%| 99.868%| 4| 1| 168| 127| 63| 0| 1| 0| 0| 0| 3.968750| 4.967431| 0.000000| 79.895%| 0.000%| 100.000%| 99.868%| 5| 0| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 5| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 6| 0| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 6| 1| 0| 0| 0| 0| 0| 0| 0| 0| 0.000000| 0.000000| 0.000000| 0.000%| 0.000%| 1.562%| 0.000%| 7| 0| 64| 0| 31| 0| 0| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 50.000%| 100.000%| 7| 1| 64| 0| 31| 0| 1| 0| 0| 0| 0.000000| 1.000000| 0.000000| 0.000%| 0.000%| 50.000%| 100.000%| ------|-------------------------------------------------------------------|---------------------------------------------------------------------|