7 DNS Interview Questions (With Explanations And Answers)

Updated 30 September 2022

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If you are applying for jobs related to networking, you may receive questions about DNS. This can allow interviewers to understand your knowledge and competence for possible future work. If you are going to have an interview for a networking or similar job, preparing for some common interview questions and practising how to answer them can improve your chances of getting the job. In this article, we share seven common DNS interview questions, explain why employers often ask these questions, and offer sample answers to guide you in preparing your own.

7 DNS interview questions

Here are seven DNS interview questions to consider, along with an explanation and sample answer for each:

1. Could you tell me what DNS is and its zones?

An interviewer might start by asking this question to assess your general knowledge. Try to be accurate yet concise in your response. Explaining what the system is in simple terms can help demonstrate your foundational understanding, which you can elaborate on throughout the rest of the interview.

Sample answer: 'DNS stands for domain name system. This allows us to attach names to IP addresses for identification. There are three zones, namely the primary, secondary and stub. The primary zone is where you can edit data or update it. The second zone is read-only, being a copy from the master server during zone transfer. This is the only way to update the secondary zone. Lastly, the stub zone just contains the records and resources for identifying names, allowing for resolution of names between domains.'

2. Can you tell me about spoofing and how you can address it?

Interviewers like to ask practical questions to see if you have working knowledge or relevant experience. If you hear a question like this, you can cite an example where you dealt with spoofing in the past. If you haven't yet encountered spoofing, you can simply state what you might do to either combat or prevent it.

Sample answer: 'Spoofing happens when a security threat introduces corrupted DNS data into the DNS resolver cache. Another name for this is cache poisoning. This is a cyber security risk because it can redirect traffic to unsafe websites, which can then acquire customer data. I encountered this at my last job, so we implemented measures to prevent it from happening again.

The first measure was to circulate a warning to all of our customers and show them how to verify a website. The other measure was to filter our DNS servers, as we were not running an actual DNS name server. This was possible by disallowing DNS requests on port 53. We also used DNSSEC to help determine the authenticity of the DNS records.'

3. What is the difference between a domain name and URL?

This is an example of a general question to determine your understanding of the basics. You are more likely to hear this question at the beginning of the interview. It is important to be concise with your response. You can answer this by giving a brief definition of each and how they differ.

Sample answer: 'A domain name is a user-friendly type of IP address. It contains the name of a website and the top-level domain, like .com or .net. URL stands for uniform resource locator and contains this information, along with other elements. These are the protocol, the subdomain, the path plus internal page and GET parameters. This means that the domain is part of the URL. A typical internet user is usually going to search for a site using its domain, not the full URL.'

4. Please describe the DNS lookup process

This is a rather simple question with a somewhat complex answer. For questions like these, it is useful to find a way of memorising the steps to ensure that you include every key point. Remember that the number of steps can vary depending on how you define and separate them.

Sample answer: 'There are many steps in this process. The first is when you actually type a domain name into the browser, which the DNS recursive resolver then receives. Next, the resolver is going to query a DNS root name server. The root server can then respond with a TLD DNS server, from which it can make a request. This TLD server then provides the IP address of the domain's name server. The recursive resolver can then send a query to the domain's name server, and the IP address returns to the resolver.

The DNS resolver can then respond to the web browser's initial query with an IP address. The browser can then make an HTTP request to the IP address. Finally, the server can render the appropriate webpage in the browser for the user to see.'

5. Can you tell me what DDNS is?

Interviewers may often ask simple definition questions to see whether you know what is relevant and what is not. In this case, they are typically looking for more than the explanation of the acronym. You can focus on giving additional information that is relevant, rather than getting into too much detail. To answer this, explain the acronym, summarise how DDNS works and discuss what its benefits are.

Sample answer: 'DDNS stands for dynamic DNS, or dynamic domain name system. This is a system that allows us to overcome the issue of limited IP address availability. It does this by giving dynamic IP addresses, which means that they change frequently. The DDNS software can then automatically log these changes to ensure that new IP addresses relate to the appropriate domain name. This also means that we do not require constant manual configuration of DNS records.'

6. What is the difference between an authoritative and recursive DNS server?

Answering a question like this can demonstrate more in-depth knowledge of DNS. Focus on keeping the definitions concise to maintain clarity, as this can also help you present your response with confidence. This can leave you with an opportunity to demonstrate further knowledge by mentioning the advantages of these differences.

Sample answer: 'An authoritative DNS server contains DNS record information, such as a domain registrar. These are the repositories of domain names and IP addresses which can match the two. A recursive DNS server is able to search an authoritative one to find matching domains and IP addresses. Anyone, anywhere in the world can reach an authoritative DNS server, whereas only local users can reach a recursive one. These exist because there are advantages to separating these functions. For instance, this can aid server security, reduce privacy attacks and boost performance.'

6. Could you explain what scavenging and ageing are?

These are two support mechanisms for maintaining DNS databases. Since these are important functions, the interviewer wants to know if you understand them. It is also a good idea to go into a little more detail than a simple definition to demonstrate your knowledge. To answer this question, define each function, briefly explain what this means and then mention why this is useful.

Sample answer: 'These are two complementary processes for maintaining good DNS records. Ageing is the identification of stale DNS records, using a non-refresh and refresh interval which involves the use of a resource record time stamp, which indicates if the record is stale.

The next stage is scavenging, which is the removal of these stale DNS records. You can set scavenging in three different places, namely the server, zone and individual record. It is important to note that the ageing and scavenging features are disabled by default, so you would want to enable them for the zone and on the DNS server.'

Frequently asked questions about DNS

Below are some answers to frequently asked questions about DNS interview questions and related careers:

Who works with DNS?

People who work with DNS are usually involved in networks, cloud computing and similar. This means that they could be an infrastructure engineer, cloud support engineer, active directory engineer, IT infrastructure analyst, network engineer, systems administrator, network manager or systems engineer. There are also roles like security consultant, penetration tester and OSS engineer.

How much do DNS-related roles pay?

This depends on the role itself, experience and the employer. For instance, the national average salary for a network engineer is ₹17,686 per month. For a senior network engineer, the national average salary can increase to ₹41,260 per month. Alternatively, there is the role of systems administrator. The national average salary for a systems administrator is ₹20,156 per month. A senior systems administrator's national average salary is ₹40,637 per month. The national average salary for a penetration tester is ₹52,917 per month.

Salary figures reflect data listed on Indeed Salaries at time of writing. Salaries may vary depending on the hiring organisation and a candidate's experience, academic background and location.