# Using Packet Prioritization on a Traffic Shaping Rule

## Overview

Traffic priority is a way of ensuring that specific applications or subnets are guaranteed a certain amount of the uplink bandwidth at all times. Traffic priorities only come into play when the network is using all of the pre-configured bandwidth on the uplink. Take note that this bandwidth can change when link aggregation is enabled because the uplink changes per stream based upon the ratio specified.

## Traffic Queues

Specifying a traffic shaping rule as High, Normal, Low guarantees a certain fraction of the uplink to each priority level. The ratios are as follows:

- High 4/7
- Normal 2/7
- Low 1/7

By default, all traffic is marked as having a Normal priority level. Traffic shaping rules that are marked at the same priority level share the same fraction of their respective levels. For instance, if there are 5 traffic shaping rules marked as High priority on a 10Mbps pipe each rule would have access to ~1.1Mbps.

Each traffic rule supersedes each rule below it and the rules below it must strictly adhere to their fractional bandwidth limits. For instance, if there is a high traffic shaping rule but no low traffic shaping rules configured then the high priority traffic would have access to 5/7 of the available bandwidth on the uplink and normal traffic would have 2/7s. Additionally, if there are no high priority traffic shaping rules then normal priority traffic gets 6/7 of the bandwidth and low priority gets 1/7 of the uplink's bandwidth.

## Low-Latency Queue

Finally, in addition to the above configurable priorities, there is an additional low-latency queue priority which is not user configurable. This queue has a greater priority than all other queues and as such is serviced before all other queues. Only packets with a DSCP value of 46 (EF - Expedited Forwarding, Voice) are placed into this queue. This feature is available and enabled on all MX14+ networks.

## Examples

Here are some examples on a 7 Mbps Uplink:

*Case 1:*

With 2 high priority rules each get 2Mbps for a total of 4Mbps

With 2 normal priority rules each get 1Mbps for a total of 2Mbps

With 2 low priority rules each get .5Mbps for a total of 1 Mbps

*Case 2:*

With 2 high priority rules each get 2Mbps for a total of 4Mbps

With 1 normal priority rule it gets 2Mbps for a total of 2Mbps

With 10 low priority rules each get .1Mbps for a total of 1 Mbps

*Case 3:*

With 2 high priority rules each get 3Mbps for a total of 6Mbps

With no normal priority rules there is a total of 0Mbps

With 5 low priority rules each get .2Mbps for a total of 1 Mbps

*Case 4:*

With 5 high priority rules each get 1Mbps for a total of 5Mbps

With 4 normal priority rules each get .5Mbps for a total of 2Mbps

With no low priority rules there is a total of 0Mbps

*Case 5:*

With no high priority rules there is a total of 0Mbps

With 3 normal priority rules each get 2Mbps for a total of 6Mbps

With 2 low priority rules each get .5Mbps for a total of 1Mbps