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Ben Ball
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Ben Ball on
January 18, 2023

Not every DNS traffic spike is a DDoS attack

Distributed Denial of Service (DDoS) attacks are a big challenge, but they aren’t always the root cause of network performance issues. DNS data is the key to distinguishing actual DDoS attack activity from mere misconfigurations.

You’re a network administrator going about your normal business when all hell breaks loose. Suddenly you’re seeing a huge spike in inbound traffic to your website, your application, or your web service. You immediately shift resources around to cope with the changing pattern, using automated traffic steering to shed load away from overburdened servers. Once the immediate danger has passed, your boss asks: what just happened?

Is it really a DDoS attack?

It’s tempting to cry wolf in these situations. Distributed denial of service (DDoS) attacks are an increasingly common issue, with both the number and scale of attacks rising significantly every year. Plenty of network administrators will say “must have been a DDoS attack of some kind” when there’s a notable increase in traffic, even if they don’t have any direct evidence to support the claim.

Proving or disproving that a DDoS attack actually happened can be a thorny issue for network administrators and even security teams.

If you’re using a basic out-of-the-box registrar DNS offering, you probably don’t have access to DNS traffic data at all. If you’re using a premium DNS solution, the data might be there - most authoritative DNS providers have some kind of observability option. At the same time, getting it in the right format (raw logs, SIEM integration, pre-built analysis) and the right level of granularity may be an issue.

What’s actually causing DNS traffic spikes

Here at NS1 we’ve been analyzing a lot of customer data recently as we roll out DNS Insights, a new feature of our flagship Managed DNS product. DNS Insights captures a wide range of data points directly from NS1’s global infrastructure, which we then make available to NS1 customers through pre-built dashboards and targeted data feeds.

As we review these datasets with customers, we’ve found that relatively few of the spikes in overall traffic or error-related responses like NXDOMAIN, SERVFAIL, or REFUSED are actually related to DDoS attack activity. Instead, we’ve found that misconfigurations are often the root cause of rising DNS traffic. Normally you’ll see error codes resulting from around 2-5% of total DNS queries. Yet in some extreme cases, we’ve seen instances where over 60% of a company’s traffic volume results in an NXDOMAIN response!

Here are a few examples of what we’ve seen and heard from DNS Insights users:

“We’re being DDoS-ed by our own equipment”

A company with over 90,000 remote workers was experiencing an extraordinarily high percentage of NXDOMAIN responses. This was a long-standing pattern, but one shrouded in mystery as the network team never had enough data to figure out the root cause.

Once they delved into the data collected by DNS Insights, it became clear that the NXDOMAIN responses were coming from the company’s own Active Directory zones. The geographic pattern of DNS queries provided further proof that the company’s “follow the sun” operating model was replicated in the pattern of NXDOMAIN responses.

At a basic level, these misconfigurations were impacting network performance and capacity. Digging further into the data, they found a more serious security issue as well: Active Directory records were being exposed to the internet through attempted Dynamic DNS updates. DNS Insights provided the missing link the network team needed to correct these entries and plug a serious hole in their network defenses.

“I've been wanting to look into these theories for years”

A company which had acquired multiple domains and web properties over the years through M&A activity routinely saw notable increases in NXDOMAIN traffic. They assumed that these were dictionary attacks against moribund domains, but the limited data they had access to could neither confirm nor deny that this was the case.

With DNS Insights, the company finally pulled back the curtain on the DNS traffic patterns that produced such anomalous results. They discovered that some of the redirects they had put in place for purchased web properties weren’t configured correctly, resulting in misdirected traffic and even the exposure of some internal zone information.

By looking at the source of NXDOMAIN traffic in DNS Insights, the company was also able to identify a Columbia University computer science course as the source of elevated traffic to some legacy domains. What may have appeared to be a DDoS attack was actually a group of students and professors probing a domain as part of a standard exercise.

“Which IP has been causing those high QPS records?”

A company experienced periodic spikes in query traffic, but couldn’t identify the root cause. They assumed it was a DDoS attack of some kind, but had no data to support their theory.

Looking at the data in DNS Insights, it turned out that internal domains - not external actors - were behind these bursts of increased query volume. A misconfiguration was routing internal users to domains intended for external customers.

Using the data captured by DNS Insights, the team was able to rule out DDoS attacks as the cause and address the actual problem by correcting the internal routing issue.

DNS data identifies root causes

In all these cases, the heightened query traffic that network teams initially attributed to a DDoS attack turned out to be a misconfiguration or internal routing error. Only after looking deeper into DNS data were the network teams able to pinpoint the root cause of perplexing traffic patterns and anomalous activity.

At NS1, we’ve always known that DNS is a critical lever that helps network teams improve performance, add resilience, and lower operating costs. The granular, detailed data that comes from DNS Insights is a valuable guide that connects the dots between traffic patterns and root causes. Plenty of companies provide raw DNS logs, but NS1 is taking it a step further. DNS Insights processes and analyzes data for you, lowering the effort and time needed to troubleshoot your network.

Learn more about the valuable information contained in DNS Insights.