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Transcript for this video

In this scenario we will learn how sensitive or dependent our application is on delays in the Domain Name Service, or DNS.

Many applications, such as web browsing, are very dependent on fast DNS resolution.

A fast application can appear slow if DNS is slow.

In this example, we want to explore how an application response time degrades when DNS is slow.

Our overall strategy will be to take the incoming traffic, classify it into a DNS flow, and then apply a delay or drop to the DNS flow.

Now let’s begin. Go to the “Filter Map” screen.

We select the two filters called “UDP DNS Destination Port” and “UDP DNS Source Port.”

We will select these filters for band 3 in both directions.

We will then click on the submit button.

Next we will go to the bands and impairments.

Select the “Band 3” tab.

The first impairment is the delay and jitter impairment. We will add 100ms of fixed delay in both directions.

All the non-DNS traffic goes to band number 5 and will not be effected.

DNS is a query and response, too, so by adding 100ms to both sides, we effectively added 200ms of delay to each DNS cycle.

This is a common occurrence on networks.

Click on the submit button.

Most systems cache DNS data.

This test is more revealing when you’re running your application after a reboot.

Reboot your application and now observe your application’s performance with DNS delays.


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