Top 30 DNS Interview Questions and Answers

Domain Name System(DNS) is one of the most crucial parts of any network, and it’s been around for a long time. In this article, we’ll explore some DNS interview questions to see if you have what it takes to be an expert on DNS.

1. What is DNS?

Domain Name Service (DNS) is a system that connects domain names to IP addresses. DNS helps everyone browse the internet more easily by translating web addresses written in our alphabet into numeric IPs for computers. Without DNS, you would need to remember complicated strings of numbers like instead of typing and getting the results you want.

2. What is a DNS zone?

Ans. A domain name system (DNS) Zone file contains records for all hosts in your domain and tells servers how to find them.

3. What is an IP address?

Ans. Every device connected to the internet has one or more identifying numbers called its Internet Protocol (IP) address.

4. What is IPv?

Ans. Every device connected to the internet has one or more identifying numbers called its Internet Protocol (IP) address. An IP address can be written in a variety of formats, such as, 2001:db80::a414:cafe:ba00:fefe%144, or 2001:db80::a414:cafe:ba00%144.

5. What is a Domain?

Ans. The domain name is the last element of a URL, for example, or

6. What do you mean by nameserver?

Ans. A nameserver is a computer that looks up domain name-to-IP address translations for the network on which it resides.

7. What are records?

Ans. Records in DNS give you information to connect your web browser with remote machines, like maps and directions to restaurants, or pages from your online shopping cart. Records tell servers how to find the host that is associated with the domain name.

8. Differentiate between primary and secondary name servers.

Ans. Primary name servers are the first in line to answer requests for domain names and IP addresses. Secondary name servers, on the other hand, only respond if they don’t know an answer or can’t get it from a primary server.

9. What is authority?

Ans. Authority refers to the ability of a DNS zone file (the list of where all the domain names and IP addresses reside) to control information for a particular zone. The person or organization that manages one of these files is in charge of setting up records, delegating authority, assigning ownership rights, etc.

10. What are some uses for DNS?

Ans. DNS can be used by other critical internet services like mail servers (to know how to deliver email) and web servers (to know which websites you’re trying to access). It’s also used by security systems like firewalls that use it as a filter for internet traffic.

11. What are some common problems experienced with DNS?

Ans. Some of the most common issues people have with their nameservers include latency, zone transfer, dynamic updates, and recursion.

12. Explain PTR in DNS.

Ans. PTR stands for a pointer, which is the reverse of an IP address. PTRs are used in networks that run on IPv-based protocol. They point to a device’s name server and can also be used as aliases if needed.

13. Explain CNAME records in DNS zones?

Ans. CNAME records are mainly used to create hostnames even when they map back to other hosts within your domain or external sites you own like email providers or social media accounts, making it easier for visitors looking for your site by typing only one name instead of having to remember an entire URL containing many different links. A record with two nameservers called ns01 and ns02 could have a CNAME record pointing from “cnn” at 192.

14. Explain Round Robin DNS.

Ans. Round robin DNS assigns IP addresses to each website based on a rotation. It’s typically used by organizations with many domains or subdomains that need more than one name server to make sure they stay available in case of hardware failure.

15. Explain the term “zone transfer”.

Ans. Zone transfers are updates where all domain names and their associated IP address records are copied from one nameserver to another, often because there is an outage for some reason. Zone transfers can be either automatic (immediate) or manual (requiring human intervention).

16. What is recursion?

Ans. DNS servers typically cache information about what data it has already looked up so it doesn’t have to do as much work going back-and-forth between two nameservers. Recursion is when a DNS server goes to another nameserver for information and then passes that on as the answer back to the original requester, usually with an indication it has done this like a “recursive” query.

17. What are some common problems experienced with recursion?

Ans. Some of the most common issues people have with their recursive responses include latency or timeouts due to too many queries happening concurrently.

18. Explain cache poisoning in DNS.

Ans. Cache poisoning happens when someone gains access to a device’s memory space (for example, if you allow them temporary administrative rights) where they can alter data inside caches before passing it onto other devices which will read that data into their own caches without knowing any better. This allows hackers to change the information in a DNS cache, which can cause all kinds of problems.

19. Explain how NS records work in DNS?

Ans. NS or name servers are some of the most critical components of any domain on either IPv-based networks (IPv) or IPX/SPX-based networks (Novell Netware). They contain the lists and pointers to where people can find domains and their associated data; for example, an NS record for “” might list two nameservers called and that control access to specific files with domain information stored inside them so they can be accessed by other devices like web browsers looking for content from this website when typed in their browser’s URL bar.

20. Explain how to trace a DNS lookup from start to finish.

Ans. A device on the internet sends out an initial request for “” and it starts its journey at one of the thirteen root servers, which are assigned domains (in this case .com), each with multiple nameservers that point back into other pools of data storage where they can find information about in question as well as any associated subdomains like or These records contain pointers to specific name server IP addresses that control access to file locations containing domain-related content so someone looking up either example’s web address would be given a list of nameservers that might lead them to the right location for’s content, which is often cached locally so they don’t have to go back out onto the internet and do another query every time someone requests webpages from this site or subdomain(s) associated with it.

21. Explain a scenario where you would need NS records in DNS?

Ans. If multiple servers are providing data for one domain but they’re not all being used at once (for instance, if there were three different software-based hosting locations), then each server can be assigned an NS record pointing people looking up either “example” or “blog.example” towards whichever one is currently working best without any downtime experienced by users who are trying to get access to their website.

22. Explain TTL.

Ans. TTL stands for “Time To Live” and it’s a designated amount of time (in seconds) that the information inside DNS caches is considered valid before being expired. If TTL was greater than zero, then people would have to wait until the timer ran out or repeat their query if they wanted fresh results; otherwise, when TTL is set to zero, it means the information is considered invalid and has been removed from the cache completely.

23. What is a resource record?

Ans. Resources are anything that a DNS server might need to know about, like the IP address of where is hosted or what its MX record (mail exchanger) points towards for email-based transactions on this domain so it can send and receive messages in an efficient manner without any interruptions.

24. What does reverse failover mean?

Ans. Reverse failover is a DNS failover configuration in which two servers are configured to take over the other’s tasks should it become unavailable, so if became inaccessible for some reason (like someone hacked into its router and redirected all traffic elsewhere), then would automatically start serving up data instead.

25. What does it mean when a web browser says “no connection”?

Ans. When someone is browsing the internet and their browser reports that they have no connection, this could be due to several different reasons: the ISP might be having an outage or there could even be something wrong with your modem if you’re using shared internet (since other people are connecting and disconnecting on the same hardware).

26. what is nslookup?

Ans. nslookup is an antiquated command used to query DNS servers and get information about domain names, like what their SOA record (start of authority), NS records, A records for IP address mapping purposes, etc might look like – it’s been replaced by the “dig” command.

27. what is A record?

Ans. An A Record in DNS terms stands for the address that instructs people where a particular domain can be found on the internet – so if someone wanted to find and they knew its IP address was, then they could just type that in the browser bar and it would take them to where this site is located.

28. What is Real-Time Traffic Management?

Ans. Real-time traffic management(RTTM) refers to the dynamic rerouting of network traffic in real-time according to changing conditions. Data packets are routed based on the information available about the network traffic loads and speeds at various links. Thus, routers may be made to monitor channels; determine whether there is congestion, and then initiate reroute transactions for handling that congestion.

29. What is SOA Record?

Ans. A SOA record or Start Of Authority is a DNS record that provides the ‘correct’ name and mail server for an internet domain. There are several types of records: SOA, NS, MX, and CNAME.

30. What is a TLD?

Ans. The TLD (Top-level domain) is the bit that comes after the last dot in a web address. Or put another way, it’s like the street name or town name in a postal address – for example: In the web address, → The TLD for this site is .com.

31. What is a Fully Qualified Domain Name?

Ans. A fully qualified domain name is a complete web address including the protocol, that is http:// or https://, and the hostname. For example, if you want to open, this means that the hostname is ‘google’ and the protocol used for accessing it over the network is ‘http://’.

32. What is TSIG?

Ans. TSIG (Transaction SIGnature) is a technology used mostly in DNS, which provides security for transactions between an authoritative nameserver and its secondary server(s). It works by calculating a TSIG digital signature based on the key name, secret key, and transaction ID. The primary server stores this information in its local database so that it can later verify transactions.

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