Example: Classifying All Traffic from a Remote Device by Configuring Fixed Interface-Based Classification

To verify this procedure, this example uses a traffic generator. The traffic generator can be hardware-based or it can be software running on a server or host machine.

The functionality in this procedure is widely supported on devices that run Junos OS. The example shown here was tested and verified on SRX Series Firewalls running Junos OS Release 12.1. The SRX Series Firewalls are configured to run as routers.

A fixed interface classifier is the simplest way to classify all packets from a specific interface to a forwarding class. You typically use this approach on edge routers to classify all traffic from a remote router or server to a certain forwarding class and queue. A fixed interface classifier simply looks at the ingress interface on which the packet arrives and assigns all traffic received on that interface to a certain class of service.

The fixed interface classifier cannot set the locally-meaningful packet-loss-priority, which is used by rewrite rules and drop profiles. The implicit packet-loss-priority is low for all fixed interface classifiers.

A fixed interface classifier is inadequate for scenarios in which interfaces receive traffic that belongs to multiple classes of service. However, interface-based classification can be useful when it is combined with other classification processes. Filtering based on the inbound interface can improve the granularity of classification, for example, when combined with filtering based on code point markings. Combining the processes for interface and code point marking classification allows a single code point marking to have different meanings, depending on the interface on which the packet is received. If you want to combine a fixed interface classifier with a code point classifier, this is in effect a multifield classifier.

More Granular Alternative to Fixed Interface Classifier

In Junos OS, you can combine interface-based classification and code-point classification by using a multifield classifier, as follows:

The following Juniper Networks Learning Byte video describes classifiers in more detail.

Topology

Figure 1 shows the sample network.

Figure 1: Fixed-Interface Classifier Scenario

To simulate voice traffic, this example shows TCP packets sent from the host to a downstream device. On Device R2, a fixed interface classifier routes the packets into the queue defined for voice traffic.

The classifier is assigned to interface ge-0/0/0 on Device R2. As always, verification of queue assignment is done on the egress interface, which is ge-0/0/1 on Device R2.

CLI Quick Configuration shows the configuration for all of the Juniper Networks devices in Figure 1. The section Step-by-Step Procedure describes the steps on Device R2.

Confirm that the configuration is working properly.