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Packet Loss Priority and Drop Profiles on vMX

vMX handles packet priorities within a queue by assigning a threshold to each loss priority within a queue and dropping new packets of that loss priority level when the queue depth exceeds the threshold. When the queue becomes oversubscribed, packets of lower priority are dropped to ensure that there is room in the queue for packets of higher priority.

Packet loss priority has four loss priority levels:

  • low

  • medium-low

  • medium-high

  • high

vMX supports three thresholds so the medium-low and medium-high loss priority levels are grouped together. vMX maps the packet loss priority to tricolor marking as follows:

Packet Loss Priority










vMX drop profiles define the threshold within a queue for a given loss priority as the fill level value associated with the drop probability of 100 percent. If you do not specify a drop probability of 100 percent in the drop profile, the threshold defaults to 100 percent. All other fill level values are ignored. These drop profiles can be referenced by the scheduler to evaluate packets with different loss priority settings.

You can set packet loss priority for packets using behavior aggregate (BA) classifiers, firewall filters, or firewall policers.


vMX has the following limitations for supporting drop profiles and packet loss priority:

  • If you do not apply drop profiles to the queue, then packets are tail dropped.

  • The show interface queue command does not display separate drop rates for the medium-high PLP and medium-low PLP because they both map to yellow. All yellow drop rates appear as medium-high drops.