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buffer-partition (Egress)


Hierarchy Level


The egress shared buffer pool is divided into three partitions. Each partition reserves a percentage of the available shared buffer pool for a type of traffic, so that the switch provides enough resources to support a mix of best-effort, lossless, and multicast traffic (multicast also includes broadcast and destination lookup fail traffic). To better support the mix of traffic on your network, you can optimize the allocation of egress shared buffers to different types of traffic by fine-tuning the shared buffer partitions.

The percentages you configure for the three egress shared buffer partitions must total exactly 100 percent. If the total of the three shared buffer percentages is not 100 percent, the system returns a commit error and does not commit the configuration. You can configure any partition to 0 (zero) percent as long as the allocation to other partitions totals 100 percent.

This is a global allocation that applies to all ports. All ports on the switch receive the same allocation of egress shared buffers.

If you do not configure buffer partitions, the switch uses the default partitioning.


Changing the buffer configuration is a disruptive event. Traffic stops on all ports until buffer reprogramming is complete.


The default egress buffer partition shown in Table 1 supports networks with a balanced mix of best-effort, multicast, and lossless traffic. It is the recommended configuration if you are using the default configuration with two lossless forwarding classes.

Table 1: Default Egress Shared Buffer Partitioning

Lossless Partition

Lossy Partition

Multicast Partition




The sum of the default percentages configured for each partition is 100 percent. The sum of the partition percentages must always total 100 percent.


dynamic-threshold value

Threshold for maximum buffer share for a queue at the egress buffer partition.


Shared buffer space reserved for all lossless egress traffic.


Shared buffer space for best-effort unicast egress traffic.


Shared buffer space reserved for all multicast (including broadcast and destination lookup fail) egress traffic.

percent percent

The percentage of buffer space to allocate to the specified buffer partition (lossless, lossy, or multicast buffers). The sum of the percentages for the three buffer partitions must total 100 percent.

Required Privilege Level

interfaces—To view this statement in the configuration.interface-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 12.3.

dynamic-threshold option introduced in Junos OS Release 19.1R1 for the QFX Series.

dynamic-threshold option introduced in Junos OS Evolved Release 19.4R1 for the QFX Series.