Today we will explain how to configure QoS.What is this component, we will also describe in detail below. We will begin with a definition, and then we will touch on the intricacies of settings and various approaches to the application of rules for handling traffic.
Definition
Quality of Service (QoS) is a technology.providing certain traffic classes with specified priorities for servicing. This approach makes sense only when a queue occurs. The latter is formed in a particularly "narrow" places. And they often call it the "bottleneck." A typical example of a queue is the Internet in an office where computers are connected to the network at a speed of about 100 Mbit / s. In this case, they all use a single channel. However, QoS technology cannot be considered a panacea. If the “neck” is too narrow, the interface buffer is often full. It is in it that data packets are placed.
Options
Next will be discussed in detail the configuration of QoS.Making changes to the queue is to adjust the classes. Further, they should determine the parameters for the bandwidth. Now you should apply the created structure to the interface. Further QoS setup is to sort the packages into classes. For this you can use various attributes. For example, based on the DSCP field, highlighting the corresponding specific protocol or pointing out as an ACL pattern. Let's figure out where the entire band is known to the router. The data comes from the bandwidth attribute in the interface. Even when it is not explicitly configured, its value necessarily arises. You can see it with the sh command.
Principle of operation
When setting up QoS, it is important to considerthat by default we do not have the entire band, but only 75%. Packages that are not included in the other classes come in class-default. Routers ensure that the administrator does not issue more bandwidth than he has available. Such attempts are stopped. It seems that the policy intends to issue classes no more than a given indicator. However, a similar situation is created only if all the queues are full. In the case of a desertion, a strip intended for it is proportionally divided by the filled “neighbors”. If the data comes from a class that has the priority status, the router focuses on the transmission of such packets. And there are several priority queues. In this case, the band between them is divided in proportion to the specified percentage. When priority packets end, it is the turn for CBWFQ.
For each time count of all the queues"Scooped" the proportion of data. It must be specified in the setting of the corresponding class. If part of the queues for some reason is empty, their band is proportionally divided. Now we will analyze what to do when it is necessary to strictly cut the data from the class, which are beyond the specified speed. It is important to remember that the indication bandwidth only distributes the band when the queues are fully loaded. You can specify the desired average speed and maximum "outlier". The more the last figure, the faster the transfer can deviate to the side. We briefly described on what principles the QoS setting is based.
