This article explains the meaning and reason of Tail-dropped packets.

In this example, we are observing Tail-dropped packets in BE class and no explicit drop profile was used. By default, if you do not configure any drop profile, tail drop profile is in effect and functions as the primary mechanism for managing congestion. In the default tail drop profile, when the fill level is 0 percent, the drop probability is 0 percent. When the fill level is 100 percent, the drop probability is 100 percent.

Tail-dropped packets: —Number of packets dropped because the queue buffers were full.

The schedular configured for BE here. 

 schedulers {

    6PC_10PC_LOW {

      transmit-rate percent 6;

      buffer-size percent 20;

MX> show interfaces queue xe-0/0/2 | no-more | refresh 1

[2024/08/07 20:43:45]    Tail-dropped packets :              2489109                    0 pps

[2024/08/07 20:43:45]    RL-dropped packets  :                    0                    0 pps

[2024/08/07 20:43:45]    RL-dropped bytes    :                    0                    0 bps

[2024/08/07 20:43:45]    RED-dropped packets :                   13                    0 pps

[2024/08/07 20:43:45]     Low                :                   13                    0 pps

[2024/08/07 20:43:45]     Medium-low         :                    0                    0 pps

[2024/08/07 20:43:45]     Medium-high        :                    0                    0 pps

[2024/08/07 20:43:45]     High               :                    0                    0 pps

[2024/08/07 20:43:45]    RED-dropped bytes   :                15950                    0 bps

[2024/08/07 20:43:45]     Low                :                15950                    0 bps

[2024/08/07 20:43:46]     Medium-low         :                    0                    0 bps

[2024/08/07 20:43:46]     Medium-high        :                    0                    0 bps

[2024/08/07 20:43:46]     High               :                    0                    0 bps

We need to try to adjust transmit rate and buffer size to accommodate the traffic.

Please note: transmit/buffer size for all schedulers should not exceed 100 in total.