Junos® OS For Dummies®, 2nd Edition

Chapter 15

Enabling Class of Service

In This Chapter

• Understanding the components of a CoS configuration
• Finding out how to classify traffic
• Using multifield classifiers

In a basic IP network, all traffic is treated the exact same way. Packets and frames come into your routers and switches, and packets and frames go out of your routers and switches. It really doesn't matter what kind of packets or frames they are or what their transport requirements are.

As you see in this chapter, you can use class of service to group similar types of traffic into classes and treat each class of traffic in a specific way, granting preference to traffic that is less tolerant to jitter, delay, and packet loss. Essentially, class of service lets you determine which traffic in your network is a first class passenger and which traffic has to ride economy.

It was once common in networking to call the provision of service levels on a network Quality of Service (QOS or QoS). This implied that applications could tell the network almost any value they needed: a delay of 25 milliseconds or 26 milliseconds. To keep things simpler, service providers established fixed services classes such as “best effort,” “voice,”or “gold,” and called this practice COS or CoS. However, now with mobility, in spite of the popularity of classes, the term QoS seems to be making a comeback.

Because service classification is more commonly understood and performed at the packet level, this chapter considers how routers use class ...