A Junos OS classifier identifies and separatestraffic flows and provides the means to prioritize traffic later inthe class-of-service (CoS) process.A behavior aggregate (BA) classifier performs this functionby associating well-known CoS values with forwarding classes and losspriorities. To enable a default classifier, you simply apply it toyour device interfaces. If a default classifier is not applied toan interface, it does not take effect.Junos OS provides multiple default BA classifier types, whichyou can combine and supplement with custom BA classifiers as neededto achieve your overall traffic classification goals. This exampleshows how to apply the default (BA) DiffServ code point (DSCP) classifierand verify its functionality.

1. Juniper Qos Configuration

RequirementsTo verify this procedure, this example usesa traffic generator. The traffic generator can be hardware-based orit can be software running on a server or host machine. If you donot have access to a traffic generator, you can use extended pingfor verification. This approach is shown as well.The functionality in this procedure is widely supported on devicesthat run Junos OS. The example shown here was tested and verifiedon MX Series routers running Junos OS Release 10.4. OverviewThe basis of Junos OS CoS is traffic differentiation.

1. Not all Juniper devices or line cards in those devices have the same ASICs. Therefore, not all QoS functionality will be identical. This is exactly what you find with other vendors. Similar to Cisco hierarchical QoS, it’s possible to build complex Junos QoS policies using the “class-of-service” command hierarchy.
2. The original configuration and thought process behind the QoS profile is listed below. The upload speed is limited by a shaper (egress on an interface), and the download speed is limited via a policer (ingress on an interface). Ingress Shaper. Unlike Cisco, Juniper does not support a shape command that queues the traffic by default.

Juniper Qos Configuration

Assigningtraffic to different classes of service provides the necessary differentiation.From the point of view of a router, the class of service assignedto a packet defines how the router behaves toward the packet. Theconcept of traffic differentiation is present in every CoS tool, andas a result, classes of service are present across the entire CoSdesign. A classifier has one input, the incoming packet, and it has N possible outputs, where N is thenumber of possible classes of service into which the packet can beclassified.BA classification is used when the traffic coming into yourdevice already has trusted CoS values in the packet header. For example,the default DSCP BA classifier specifies that packets coming in withcode points 000000 are assigned to the best-effort forwarding classand given a loss priority of low.A forwarding class and loss priority are assigned by defaultto each well-known DSCP. To view this, run the command.

Classification of Packets and Queue Selection. On Juniper devices, traffic is classified and enqueued on input to the device. For IP traffic, Juniper devices map incoming traffic to output transmission queues according to the value of the packet header's IP precedence bits or DiffServ codepoint setting.

Forwarding class ID Queuebest-effort 0 0expedited-forwarding 1 1assured-forwarding 2 2network-control 3 3The loss priority is used by schedulers in conjunction withthe random early detection (RED) algorithm to control packet discardduring periods of congestion. When you are thinking about loss priorities,keep in mind that unless you configure them, they have no meaning.The default drop behavior is to wait until the queue is 100 percentfull and then begin dropping packets indiscriminately.

When the queuedips below 100 percent full, packets stop dropping.The default drop behavior is shown in the show class-of-servicedrop-profile command. Drop profile:, Type: discrete, Index: 1Fill level Drop probability100 100To create meanings for the various loss priorities, you mustconfigure custom drop profiles. For example, you might define thelow loss priority to mean a 10 percent drop probability when the queueis 75 percent full and a 40 percent drop probability when the queuefill level is 95 percent.

You might define the high loss priorityto mean a 50 percent drop probability when the fill level is 25 percentand a 90 percent drop probability when the fill level is 50 percent.Custom drop profiles are not included in this example, but are mentionedhere for clarity because classifiers assign loss priorities. It isimportant to understand that these assignments are meaningless untilyou create drop profiles.The default classifier operation is shown in. The figure shows two IPv4packets entering an interface and being classified according to theDSCP code points in the packet headers. Figure 1: Behavior AggregateClassifier with Two Queues. It is important to apply your class-of-service configurationacross the topology, instead of applying it to a single device. Furthermore,even though classification takes effect on incoming interfaces, youshould apply BA classifiers to all core and core-facing interfaces.This is because a single interface can be either incoming or outgoing,depending on the direction of the traffic.

For example, as trafficflows from Host 1 to Host 2, the incoming interfaces are ge-1/0/7on Device R2 and ge-2/0/6 on Device R3. As traffic flows in the otherdirection, from Host 2 to Host R1, the incoming interfaces are ge-1/0/3on Device R2 and ge-1/0/7 on Device R1.The BA classifier is not applied to ge-1/0/1 on Device R1 orge-2/0/5 on Device R3, because these interfaces are not core facing.Generally, at the edge-facing interfaces, you would use a multifieldclassifier, not a BA classifier.shows theconfiguration for all of the Juniper Networks devices in. The section describes the stepson Device R2. User@R2 clear interface statistics ge-1/0/3.Using extended ping from Device R1 or a packet generatorrunning on a host or server, send packets with the code point setto 001010.Both methods are shown here. The packet generator used is hping.When you are using extended ping to set the DSCP codepoints in the IPv4 packet header, the type-of-service (ToS) decimalvalue (in this case, 40) is required in the tos optionof the ping command.When you are using hping to set the DSCP code points inthe IPv4 packet header, the ToS hex value (in this case, 28) is requiredin the -tos option of the hping command.If your binary-to-hex or binary-to-decimal conversion skillsare rusty, you can use an online calculator, such as. NoteWhen you convert a binary DSCP code point value, be sureto add two extra zeros at the end.

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So instead of 001010, use 00101000.These 0 values (the 7th and 8th bits) are reserved and ignored, butif you do not include them in the conversion, your hex and decimalvalues will be incorrect.

Classifying and Marking MPLS EXPThe QoS EXP Matching feature allows you to classify and mark network traffic by modifying the Multiprotocol Label Switching(MPLS) experimental bits (EXP) field in IP packets. This module contains conceptual information and the configuration tasksfor classifying and marking network traffic using the MPLS EXP field.Finding Feature InformationYour software release may not support all the features documented in this module. For the latest caveats and feature information,seeand the release notes for your platform and software release.

To find information about the features documented in this module,and to see a list of the releases in which each feature is supported, see the feature information table at the end of thismodule.Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco FeatureNavigator, go to.