The Intricacies of Junos' Traffic Policers

Junos OS, the operating system that powers Juniper Networks' wide range of networking devices, offers a robust and flexible framework for managing network traffic. One of the key components of this framework is the Traffic Policer. In this blog post, we will delve into the intricacies of Junos' Traffic Policers, a topic that is crucial for students studying for the JNCIS-ENT certification.

What is a Traffic Policer?

In Junos, a Traffic Policer is a mechanism that controls the rate of traffic flow in a network. It does this by setting a limit on the amount of traffic that can pass through a specific interface or subinterface. Traffic that exceeds the set limit can either be discarded or re-marked to a lower priority, ensuring that the network is not overwhelmed by excessive traffic.

Configuring a Traffic Policer

To configure a Traffic Policer in Junos, you need to use the policer command in the [edit firewall] hierarchy. Here is an example of how to configure a Traffic Policer:

[edit firewall]
set policer POLICER-1 if-exceeding bandwidth-limit 1m
set policer POLICER-1 if-exceeding burst-size-limit 15k
set policer POLICER-1 then discard

In this example, the Traffic Policer (named POLICER-1) is set to limit the bandwidth to 1 Mbps and the burst size to 15 KB. Any traffic that exceeds these limits will be discarded.

Applying a Traffic Policer

Once you have configured a Traffic Policer, you can apply it to an interface or subinterface using the policer option in the [edit interfaces] hierarchy. Here is an example of how to apply a Traffic Policer:

[edit interfaces]
set ge-0/0/0 unit 0 family inet policer input POLICER-1

In this example, the Traffic Policer POLICER-1 is applied to the input traffic of the ge-0/0/0 interface.

Monitoring a Traffic Policer

You can monitor the operation of a Traffic Policer using the show firewall command. This command displays the current status of all configured Traffic Policers, including the amount of traffic that has been processed and the amount of traffic that has been discarded or re-marked.

show firewall


Understanding the intricacies of Junos' Traffic Policers is essential for managing network traffic effectively. By configuring and applying Traffic Policers, you can control the rate of traffic flow in your network and prevent it from being overwhelmed by excessive traffic. This knowledge is not only useful in real-world networking scenarios, but also crucial for passing the JNCIS-ENT certification exam. So, keep practicing and exploring the various features and capabilities of Junos' Traffic Policers.

© Ben Jacobson.RSS