Today we’ll show you how to configure QoS. What this component is, we will also describe in detail below. We will start with the definition, and then we will touch on the intricacies of settings and various approaches to the application of rules for processing traffic.
Definition
Quality of Service (QoS) is a technology for providing certain classes of traffic with specified service priorities. This approach only makes sense when a queue occurs. The latter is formed in particularly “narrow” places. And they often call it the "bottleneck." A typical example of a queue can be considered the Internet in the office, where computers are connected to the network at a speed of about 100 Mbit / s. Moreover, 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 the data packets are placed.
Parameters
Next, QoS configuration will be discussed in detail. Making changes to the queue is to adjust the classes. Next, they should determine the parameters for
the bandwidth. Now you should apply the created design to the interface. A further QoS setup is to sort the packages into classes. You can use various attributes for this. For example, based on the DSCP field, highlighting the corresponding specific protocol or specifying as an ACL template. Let's see how the entire lane is known to the router. The data comes from the bandwidth attribute in the interface. Even when it is not explicitly configured, some value of it arises necessarily. It can be seen with the sh int command.
Principle of operation
When setting up QoS, it is important to consider that by default, we do not have the entire band, but only 75%. Packages that are not included in other classes arrive in class-default. Routers make sure that the administrator does not give out more bandwidth than he has at his disposal. Similar attempts are thwarted. It seems that politics intends to give classes no more than a given indicator. However, a similar situation is created only if all the queues are full. In case of emptying, any band intended for it is proportionately divided by filled “neighbors”. If data comes from a class that has priority status, the router focuses on the transmission of such packets. Moreover, there are several priority queues. In this case, the band between them is divided in proportion to the specified percent. When priority packets end, it is the turn for CBWFQ.
For each time count, a fraction of the data is scooped out of all the queues. It must be specified in the configuration of the corresponding class. If part of the queues is empty for certain reasons, their band is proportionally divided. Now we will analyze what to do when it is necessary to strictly chop data from a class that goes beyond the specified speed. It is important to remember that specifying bandwidth only distributes the band when the queues are fully loaded. You can specify the required average speed and maximum “surge”. The higher the last figure, the faster the transmission can deviate to the side. We briefly described on what principles QoS tuning is based.