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Traffic for a network application includes DNS query/response traffic and the actual application flow. Using the DNS Protocol
Classification Change feature, NBAR2 can be configured to classify and handle DNS traffic in the same way as its associated
application traffic.
This module describes DNS Protocol Classification Change and the how to enable it.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information,
see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module,
and to see a list of the releases in which each feature is supported, see the feature information table.
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Prerequisites for DNS Protocol Class Change
None.
Information About DNS Protocol Classification Change
DNS Protocol Classification Change
Traffic for a network application includes DNS query/response traffic and the actual application flow. When classifying traffic,
most attention is given to the application flow, both for reporting (application visibility) and control (QoS policy).
The DNS Protocol Classification Change feature enables an NBAR client, such as a router, to classify and handle DNS traffic
in the same way as its associated application traffic. This is accomplished using the domain name that appears in the DNS
flow.
Use of DNS Protocol Classification Change
DNS Protocol Classification Change can be especially useful in networks employing Cisco Intelligent WAN (IWAN), for optimizing
the performance of network applications.
For example, in an IWAN spanning a wide geography, it might happen that a specific type of application traffic (example: Microsoft
Office 365) may be routed first to a geographically distant node in the IWAN, and then to the relevant server. This route
may diminish performance of the application. Using DNS protocol classification change, it is possible to redirect the DNS
query/response to a local DNS server, and route the application traffic directly to the relevant cloud-based application server,
improving application performance.
Figure 1. DNS Protocol Classification Change Improving Application Performance in an IWAN Environment
Usage Notes
DNS Protocol Classification Change classifies the DNS flow in the same way as the application, based on built-in protocols
or custom signatures.
The DNS flow classification inherits the attributes of the application – category, business-relevance, traffic-class, encryption,
and so on. For example, for a DNS flow classified as “Google-accounts” the encryption attribute is TRUE.
DNS flows are not cached using the socket cache mechanism.
To catch all DNS traffic for QoS, use the following “transport hierarchy” CLI:
match protocol dns in-app-hierarchy
Default: enabled.
How to Enable DNS Protocol Classification Change
Enabling DNS Protocol Classification Change
Enabling the DNS Protocol Classification Change feature enables an NBAR client, such as a router, to classify and handle
DNS traffic in the same way as its associated application traffic.
The no form of the command disables the feature.
[no ] ip nbar classification dns classify-by-domain
SUMMARY STEPS
enable
configure terminal
ip nbar classification dns classify-by-domain
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Device> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Device# configure terminal
Enters global configuration mode.
Step 3
ip nbar classification dns classify-by-domain
Example:
Device(config)# ip nbar classification dns classify-by-domain
Enables the DNS Protocol Classification Change feature.
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