How to Link Classifiers to Traffic Flows in Junos

After you create a classifier that matches types of traffic based on the Differentiated Services Code Point (DSCP) value, Junos assigns traffic to a forwarding class that corresponds to some queue on the router. Classifiers must be linked to one or more flows of traffic before they’re useful. The traffic itself flows through interfaces. You must link your newly configured classifiers to the interfaces through which the traffic is flowing.

You have a couple of options here. You can apply your classifiers to all, some, or one of the interfaces on your router. Even on the interfaces, you can apply your classifiers to all, some, or one of the logical interfaces (units). To make this process a bit easier, Junos supports wildcards.

In this case, you have only a single classifier, so it’s easy enough to configure it on all interfaces:

[edit class-of-service]
interfaces {
  all {
   unit * {
     classifiers {
      dscp dscp-classifier;
     }
   }
  }
}

In this configuration, you’re applying the dscp-classifier to all interfaces. Notice that you must specify which unit you’re applying it to. In this case, you’re using the wildcard (asterisk) to indicate that it’s to be applied to all units on all interfaces. If you want to apply the dscp-classifier to only unit 0 on all interfaces, you can replace the asterisk with a 0.

If you configure several classifiers and want to apply them on different interfaces, you can use the asterisk wildcard with the interface name. For example, if you know that your video traffic travels only on Gigabit Ethernet interfaces, and you’ve configured a classifier to handle only video, you can have a configuration that resembles this:

[edit class-of-service]
interfaces {
  ge-* {
   unit * {
     classifiers {
      dscp dscp-video-classifier;
     }
   }
  }
}

In this configuration example, the wildcard indicates that all Gigabit Ethernet interfaces should use the specified voice classifier on all units.

Take care when you apply one classifier to many interfaces. In this example, all interfaces share a single classifier, and they’re contending for the same classifier. What you want to do is configure the per-unit-classifiers statement so that each unit has its own classifier treatment.

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