Cisco Cisco IOS Software Release 12.2(14)S

IP QoS can be deployed by defining classes or categories of applications. These classes are defined by 
using various classification techniques available in Cisco IOS software. After these classes are defined 
and attached to an interface, the desired QoS features, such as Marking, Congestion Management, 
Congestion Avoidance, Link Efficiency mechanisms, or Policing and Shaping can then be applied to the 
classified traffic to provide the appropriate network resources amongst the defined classes. 

Classification, therefore, is an important first-step in configuring QoS in a network infrastructure.

NBAR is a classification engine that recognizes a wide variety of applications, including web-based and 
other difficult-to-classify protocols that utilize dynamic TCP/UDP port assignments. When an 
application is recognized and classified by NBAR, a network can invoke services for that specific 
application. NBAR ensures that network bandwidth is used efficiently by classifying packets and then 
applying Quality of Service (QoS) to the classified traffic. Some examples of class-based QoS features 
that can be used on traffic after the traffic is classified by NBAR include:

Class-Based Marking (the set command)

Class-Based Weighted Fair Queueing (the bandwidth and queue-limit commands)

Low Latency Queueing (the priority command)

Traffic Policing (the police command)

Traffic Shaping (the shape command)

For an animated example of NBAR being used with other QoS features to solve a network 
problem, click here.

The NBAR feature is used for classifying traffic by protocol. The other class-based QoS 
features determine how the classified traffic is forwarded and are documented separately 
from NBAR. Furthermore, NBAR is not the only method of classifying network traffic so 
that QoS features can be applied to classified traffic.
For information on the class-based features that can be used to forward NBAR-classified 
traffic, see the individual feature modules for the particular class-based feature as well as 
the Cisco IOS Quality of Service Solutions Guide.
Many of the non-NBAR classification options for QoS are documented in the “Modular 
Quality of Service Command-Line Interface” section of the Cisco IOS Quality of Service 
Solutions Guide. These commands are configured using the match command in class map 
configuration mode.

NBAR introduces several new classification features that identify applications and protocols from 
Layer 4 through Layer 7:

Statically assigned TCP and UDP port numbers

Non-UDP and non-TCP IP protocols

Dynamically assigned TCP and UCP port numbers. Classification of such applications requires 
stateful inspection; that is, the ability to discover the data connections to be classified by parsing 
the connections where the port assignments are made. 

Sub-port classification or classification based on deep packet inspection; that is. classification by 
looking deeper into the packet.

NBAR can classify static port protocols. Although access control lists (ACLs) can also be used for this 
purpose, NBAR is easier to configure and can provide classification statistics that are not available 
when using ACLs.