QoS is the concept of providing different levels of service to selected traffic. With this, information is provided to devices to determine how to handle traffic crossing the devices when it is greater than the resources available. These resources can be bandwidth, access lists, processing, and other resources.

It's important to recognize that, while your traffic may not appear to exceed your link, micro-bursts of traffic can cause hard-to-trace issues. It is always advisable, even with QoS and other traffic management tools, to keep a link below 80 percent utilization.

QoS has two main ways in which it can manage traffic: either prioritizing specific flow(s) or limiting all other flows. On a standard device, QoS allows you to differentiate services based on any matchable packet header information, for example, source or destination address. Some devices that do deep packet inspection can match almost anything in the packet.

When applying QoS to a link, there are multiple ways to handle...