QoS - classification

QoS classification is the mechanism that identifies the type of traffic that passes through a network device. It is the first step in the process of applying QoS.

Before we can configure any QoS methods like queuing, policing or shaping we have to look at the traffic that is running through our device and identify (classify) it so we know to which application it belongs. That’s what classification is about.

Classification uses several methods to classify traffic:

  • It can use the information in the fields of the headers of packets using ACLs to identify source and destination IPv4 or IPv6 addresses and source and destination ports.
  • It can also use payload inspection (using NBAR) to determine what kind of packet (VoIP, video, web, FTP, email, etc…) each one is.

Classification is essentially used to identify the application from which packets are sent. Classification is locally significant and is not communicated to any other network device. Marking is used in order to inform other devices of the potential "special treatment" that these packets may require.

Once classification takes place, traffic can then be marked and eventually acted upon by QoS policies based on those markings.