DNS Interview Questions

Checkout Vskills Interview questions with answers in DNS to prepare for your next job role. The questions are submitted by professionals to help you to prepare for the Interview.

Q.1 What is DNS and why is it important?

DNS translates human-readable domain names (like example.com) into IP addresses that computers use to identify each other on the network. It is crucial for locating resources on the internet.

Report This Question

Q.2 What are the main components of DNS?

The main components are DNS records (such as A, AAAA, CNAME, MX), DNS servers (such as DNS resolvers, authoritative DNS servers), and DNS zones.

Report This Question

Q.3 What is an A record in DNS?

An A (Address) record maps a domain name to an IPv4 address, allowing users to access websites via domain names rather than IP addresses.

Report This Question

Q.4 What is a CNAME record?

A CNAME (Canonical Name) record maps an alias domain name to the canonical (true) domain name. It allows multiple domain names to point to the same IP address.

Report This Question

Q.5 What does TTL stand for and what is its significance?

TTL (Time To Live) specifies how long a DNS record is cached by DNS resolvers before being refreshed. It helps control the duration of DNS record caching.

Report This Question

Q.6 What is DNS caching and how does it work?

DNS caching stores DNS query results locally to reduce the time required for subsequent lookups. It can be implemented in DNS resolvers and web browsers.

Report This Question

Q.7 What are the differences between authoritative and non-authoritative DNS servers?

Authoritative DNS servers hold the original DNS records for a domain and provide definitive answers. Non-authoritative servers cache results from authoritative servers and provide responses based on cached data.

Report This Question

Q.8 What is a MX record and how is it used?

An MX (Mail Exchange) record specifies the mail server responsible for receiving emails for a domain. It helps route emails to the correct mail server.

Report This Question

Q.9 Explain the purpose of reverse DNS lookups.

Reverse DNS lookups map IP addresses back to domain names. They are used for verifying the domain associated with an IP address, often for security and troubleshooting purposes.

Report This Question

Q.10 What is a zone file in DNS?

A zone file is a text file that contains DNS records for a domain. It defines the mapping between domain names and IP addresses, among other DNS settings.

Report This Question

Q.11 What is DNS forwarding?

DNS forwarding refers to the process of configuring a DNS server to forward queries it cannot resolve to another DNS server for resolution.

Report This Question

Q.12 What are DNS zones and how are they used?

DNS zones are segments of the DNS namespace that are managed as a single unit. Each zone contains DNS records for a specific domain or subdomain and is managed by a single DNS server or a set of servers.

Report This Question

Q.13 How does DNS load balancing work?

DNS load balancing distributes incoming network traffic across multiple servers using DNS records. It helps ensure high availability and reliability of services by balancing the load.

Report This Question

Q.14 What is DNS amplification attack?

A DNS amplification attack is a type of Distributed Denial of Service (DDoS) attack that exploits open DNS resolvers to flood a target with large volumes of DNS response traffic.

Report This Question

Q.15 How can DNS security be improved?

DNS security can be improved through measures such as DNSSEC (DNS Security Extensions), using secure DNS resolvers, implementing rate limiting, and configuring proper access controls.

Report This Question

Q.16 What is DNSSEC and how does it enhance DNS security?

DNSSEC (Domain Name System Security Extensions) adds digital signatures to DNS records to ensure their authenticity and integrity, protecting against certain types of attacks like cache poisoning.

Report This Question

Q.17 What is a SOA record?

A SOA (Start of Authority) record provides information about the DNS zone's authority, including the primary DNS server, the email of the zone admin, and timing parameters for zone updates.

Report This Question

Q.18 What is the root DNS server and its role?

Root DNS servers are the highest level of DNS servers in the hierarchy. They respond to queries for the top-level domains and direct requests to appropriate authoritative servers.

Report This Question

Q.19 How do DNS queries and responses work?

A DNS query is a request sent by a client to a DNS server to resolve a domain name. The server responds with the corresponding IP address or an error message if the name cannot be resolved.

Report This Question

Q.20 What is DNS poisoning and how can it be mitigated?

DNS poisoning (or cache poisoning) involves inserting incorrect DNS records into a cache to redirect traffic. It can be mitigated by using DNSSEC, validating DNS responses, and keeping software up to date.

Report This Question

Q.21 What is the difference between recursive and iterative DNS queries?

In a recursive query, the DNS server performs the complete lookup process and returns the result to the client. In an iterative query, the server provides a referral to another DNS server if it cannot resolve the query directly.

Report This Question

Q.22 How does DNS work with IPv6 addresses?

DNS handles IPv6 addresses using AAAA records, which map domain names to IPv6 addresses, similar to A records for IPv4 addresses.

Report This Question

Q.23 What is a NS record?

An NS (Name Server) record specifies the DNS servers authoritative for a domain or subdomain, directing queries to the correct DNS servers.

Report This Question

Q.24 What are SRV records used for in DNS?

SRV (Service) records specify the location of services such as VoIP or LDAP servers within a domain, including port numbers and priority.

Report This Question

Q.25 What is DNS forwarding and how is it configured?

DNS forwarding is the process of directing DNS queries from one server to another for resolution. It is configured by setting up forwarders in the DNS server settings.

Report This Question

Q.26 Explain the concept of split-horizon DNS.

Split-horizon DNS refers to using different DNS records or responses depending on whether the query comes from inside or outside a network, often used for internal and external DNS views.

Report This Question

Q.27 What is the DNS query lifecycle?

The DNS query lifecycle includes the client sending a query, the DNS resolver processing the query, contacting authoritative servers if necessary, and returning the response to the client.

Report This Question

Q.28 How does DNS-based Authentication of Named Entities (DANE) work?

DANE uses DNSSEC to secure the association of domain names with X.509 certificates, adding an extra layer of security for TLS and email protocols.

Report This Question

Q.29 What is DNS load balancing and how can it be implemented?

DNS load balancing distributes incoming traffic across multiple servers by using multiple A or CNAME records with the same domain name. It can be implemented using round-robin DNS or more sophisticated methods.

Report This Question

Q.30 What is DNS zone transfer and when is it used?

DNS zone transfer is the process of copying DNS zone data from a primary DNS server to a secondary DNS server. It ensures consistency between authoritative servers.

Report This Question

Q.31 What are DNS view configurations?

DNS views allow administrators to create different sets of DNS records for different clients or networks, providing different responses based on the source of the DNS query.

Report This Question

Q.32 How do you troubleshoot DNS resolution issues?

Troubleshoot DNS issues by checking DNS server configurations, using tools like dig or nslookup, verifying network connectivity, and ensuring DNS records are correctly configured.

Report This Question

Q.33 What is DNS over HTTPS (DoH)?

DNS over HTTPS (DoH) is a protocol for encrypting DNS queries using HTTPS, enhancing privacy and security by preventing eavesdropping and tampering.

Report This Question

Q.34 What are DNS response codes and what do they indicate?

DNS response codes indicate the result of a DNS query, such as NOERROR for successful responses, NXDOMAIN for non-existent domains, and REFUSED for query refusals.

Report This Question

Q.35 What is DNS cache poisoning and how can it be prevented?

DNS cache poisoning involves corrupting DNS cache entries to redirect traffic. Prevention methods include using DNSSEC, validating responses, and configuring proper cache timeout settings.

Report This Question

Q.36 Explain DNS anycast and its benefits.

DNS anycast involves assigning the same IP address to multiple DNS servers located in different geographical areas. It improves redundancy and reduces latency by directing queries to the nearest server.

Report This Question

Q.37 How does DNSSEC work and what are its main components?

DNSSEC adds cryptographic signatures to DNS records to ensure their authenticity. Main components include DNSKEY (public keys), RRSIG (digital signatures), and DS (delegation signer) records.

Report This Question

Q.38 What is DNS zone delegation?

DNS zone delegation involves assigning authority for a subdomain to a different DNS server. It is done using NS records to point to the name servers responsible for the subdomain.

Report This Question

Q.39 What are wildcard DNS records and when are they used?

Wildcard DNS records use an asterisk (*) to match any subdomain under a specific domain, allowing the same DNS record to apply to multiple subdomains without explicitly listing each one.

Report This Question

Q.40 What is the role of TTL in DNS caching and propagation?

TTL (Time To Live) specifies how long a DNS record should be cached by resolvers and DNS servers. It affects how quickly changes to DNS records propagate across the internet.

Report This Question

Q.41 What is the root hint file in DNS?

The root hint file contains a list of IP addresses for the root DNS servers. It helps DNS resolvers find the root servers when they need to start a DNS query.

Report This Question

Q.42 What is a DNS resolver and what is its function?

A DNS resolver is a server or software that queries DNS records on behalf of clients. It translates domain names into IP addresses and handles the process of DNS lookups.

Report This Question

Q.43 What is DNS failover and how does it work?

DNS failover is a technique used to ensure high availability by automatically redirecting traffic to a backup server if the primary server becomes unavailable. It can be configured using health checks and DNS records.

Report This Question

Q.44 How do DNS stub resolvers work?

A DNS stub resolver is a client-side DNS resolver that forwards DNS queries to a DNS server for resolution. It typically relies on a full resolver to handle the query process.

Report This Question

Q.45 What is the difference between forwarding and recursive DNS servers?

Forwarding servers pass queries to another DNS server for resolution, while recursive servers perform the full resolution process by querying multiple DNS servers until the answer is found.

Report This Question

Q.46 What is a zone delegation in DNS?

Zone delegation involves specifying which DNS servers are authoritative for a subdomain. It is done by creating NS records in the parent zone pointing to the name servers of the subdomain.

Report This Question

Q.47 What is DNS tunneling and why is it a concern?

DNS tunneling is a technique that encodes data within DNS queries and responses to bypass network security measures. It is a concern because it can be used for data exfiltration and unauthorized communication.

Report This Question

Q.48 How does DNS resolution work for a domain with multiple A records?

When a domain has multiple A records, DNS resolvers typically use round-robin load balancing to distribute requests among the available IP addresses listed in the A records.

Report This Question

Q.49 What is a DNS glue record?

A DNS glue record is a type of A record that provides the IP address of a name server that is authoritative for a domain. It is used to resolve the name servers' addresses to avoid circular dependencies.

Report This Question

Q.50 How do DNS lookups impact performance and latency?

DNS lookups can impact performance and latency based on factors like the number of DNS queries, DNS server response times, and caching. Reducing the number of lookups and using efficient DNS servers can improve performance.

Report This Question

Q.51 What is a DNS query and what types exist?

A DNS query is a request sent to a DNS server to resolve a domain name. Types include A queries (for IPv4 addresses), AAAA queries (for IPv6 addresses), and MX queries (for mail servers).

Report This Question

Q.52 What is the role of DNS TTL in cache invalidation?

DNS TTL determines how long a DNS record is cached by resolvers. When TTL expires, the cached record is invalidated, and a new query is sent to retrieve the updated information.

Report This Question

Q.53 How can DNS records be used for load balancing?

DNS records can be used for load balancing by providing multiple IP addresses for a single domain (using A or AAAA records) and distributing traffic among those addresses.

Report This Question

Q.54 What is the purpose of DNS nameserver records (NS records)?

NS records specify the DNS servers that are authoritative for a domain or subdomain. They direct queries to the correct DNS servers responsible for the domain's DNS records.

Report This Question

Q.55 How does DNSSEC prevent DNS spoofing attacks?

DNSSEC prevents DNS spoofing by using cryptographic signatures to ensure the authenticity and integrity of DNS records, preventing attackers from injecting false information into DNS responses.

Report This Question

Q.56 What is DNS resolution caching and where is it typically performed?

DNS resolution caching stores previously resolved DNS queries to improve performance. It is typically performed by DNS resolvers, web browsers, and operating systems.

Report This Question

Q.57 What are dynamic DNS updates and how are they used?

Dynamic DNS updates allow clients to automatically update their DNS records with changes in their IP addresses. This is useful for devices with frequently changing IP addresses, like home routers.

Report This Question

Q.58 What is the DNS query EDNS and its purpose?

EDNS (Extension mechanisms for DNS) is an extension to the DNS protocol that allows for larger DNS messages and additional features, such as support for newer DNS record types and better performance.

Report This Question

Q.59 How do DNS query EDNS options improve DNS functionality?

EDNS options extend DNS functionality by providing additional information in DNS queries and responses, such as client-subnet information, which helps improve DNS performance and accuracy.

Report This Question

Q.60 What is DNS anycast and how does it improve DNS reliability?

DNS anycast assigns the same IP address to multiple DNS servers located in different geographical areas. It improves reliability and performance by routing queries to the nearest or most responsive server.

Report This Question