DNS Interview Questions and Answers | Domain Name System
This article is about the DNS Interview Questions and Answers for network job interview. Domain Name System (DNS) is very important concept of Networking. Here you will understand the most important DNS Interview Questions and Answers. These (Domain Name System) DNS Interview Questions and Answers will help in preparation of networking job interview. Go through these DNS questions and Answers and share your comments in comments section.
What is DNS Domain Name System?
Domain Name System stands for domain name system. DNS associates domain names with the IP addresses of computers or websites corresponding to these domains. With DNS resolve the IP address into domain name, which makes the entire internet address easy to remember. In any network all communication are made through IP address, it is difficult to remember the IPs of all website. On internet we are accessing all websites though their domain names instead of IPs. For example you can access different websites like “google.com” or youtube.com by their instead instead of IP addresses, on backend DNS make domain name to IP conversion and make it accessible for us.
What are different DNS zones?
Following are 3 types of DNS Zones:
- Primary Zone
- Secondary Zone
- Stub Zone
A primary DNS zone is the zone type where you can edit or update the data. Updates made to the primary DNS zone are made through DNS server that is authoritative for the specific primary zone.
A secondary DNS zone is a read only zone and it is copied from the master-server during zone transfer. You can update secondary zone through zone transfer.
The stub DNS zone is a new feature of Windows Server introduced in 2003. This zones only contain the resource & records necessary to identify the authoritative-DNS-servers for the master zone. You can learn more about DNS zone types from here.
What is DNS Server?
A DNS-server on internet is a computer system which holds the database of public IP addresses & their associated domain-names. DNS server resolves or translates the IP addresses into hostnames as requested. DNS Server mainly designed to find and provide websites to end-users on Internet or a private-network. It is always connected to the Internet or a network. DNS servers run special software & communicate with each other using special-protocols.
What Is Caching-Only Server?
Caching only servers are DNS servers which only handle name resolution requests, cache the answers, & return the results to the user. When the query is saved in cache, next-time the request in resolved locally from cached instead of going to the actual site. Caching only server handle the queries more fast.
What are the main types of DNS servers?
Following are the three main types of DNS servers:
- Authoritative Name Server
- DNS Resolver
- DNS Root Server
What are the various DNS record types?
All necessary connections between the domain name and IP addresses are reflected in a special file located on the DNS server. The contents of this file are called a DNS zone description, or simply a DNS zone.
It may contain records of various types.
|A Record (Address Mapping record)||A record contains the website address of the corresponding domain name.|
|AAAA Record||Contain THE hostname and it’s corresponding IPv6 address.|
|MX Record (Mail exchanger record)||Mail server address in the corresponding domain & used to route outgoing emails to an email-server.|
|CNAME (Canonical Name record)||A synonym for the domain being described. |
For example, here you can indicate that the domain name www.w7cloud.com is a synonym for the w7cloud.com domain name, and requests for this synonym will be redirected to the address of the main domain name
|NS record (Name Server records)||The domain names of the DNS servers serving the described domain are indicated here. |
For example, ns1.w7cloud.com and ns2.w7cloud.com
|Txt Record||Any text note|
|PTR Record (Reverse-lookup Pointer records)||Allows the DNS server to provide IP address and receive a hostname ( reverse DNS-lookup ).|
|CERT Record (Certificate record)||It contains encryption certificates like SPKI, PKIX, PGP etc|
This is not a complete list of possible field types. It has been shortened to simplify the presentation.
What is Recursive DNS RESOLVER?
Recursive DNS RESOLVER is a middle server which provides the IP address of domain from authoritative DNS servers. Any DNS query on internet first goes to Recursive DNS RESOLVER. When a client request for DNS query, the Recursive server takes the time to track down DNS record. After collecting the desire information
What is the Authoritative DNS server?
The authoritative server is a DNS server that originally holds DNS records and resource. This server lies at end of the DNS-lookup chain that will respond with the queried resource record. Authoritative DNS server finally allow the web-browser making the query to reach the IP address required to access a website.
How DNS Lookup Process works, describe some Steps?
If we consider the example of DNS quires for a website, you divide this DNS lookup process into following steps:
- When you type the URL of website for example ‘w7cloud.com’ in a web-browser & then request send to DNS recursive resolver through your ISP.
- This DNS recursive resolver then sends the query to a DNS root nameserver (.).
- The root DNS server then replies to the DNS resolver by IP address of a Top Level Domain (TLD) DNS server, which have the information about the domains.
- The DNS resolver then queries the .com Top Level Domain (TLD.
- The Top Level Domain server then replies with the IP address of the domain’s name-server, w7cloud.com.
- In last, the DNS resolver sends a request to the website’s name-server.
- The IP address for w7cloud.com is then returned to the resolver from the name-server.
- Then DNS recursive resolver responds to the web-browser with the IP address of the domain requested initially.
Why we Use DNS?
- DNS is used to access the location of websites on the internet.
- DNS provides a unique IP address and it uniquely identify a web page.
- Domain Name systems makes it easy for the user to remember the name instead of IP address and access the website with the name.
How many look-up zones are in DNS?
There are two lookup-zones in DNS:
- Forward lookup zone: helps to resolve domain name to IP address. A-record creates in forward-lookup zone.
- Reverse lookup zone: helps to resolve IP Address (10.251.87.121) to domain name (w7cloud.com). PTR-record creates in Reverse Lookup Zone.
Which TCP/IP port is used by DNS server?
DNS server uses the Port 53 for zone transfers and for keeping coherence between DN- database & DNS server.
What is Static and Dynamic DNS Record?
Manually created DNS entry is called static DNS record & A Static IP address points your domain name s on the Internet. Whereas the Dynamic DNS allows users to set up automatic updates to their DNS records.
What is Round Robin DNS?
Round Robin DNS is a method used for load distribution of DNS request against a domain name.
Suppose we have a domain w7cloud.com and it is configured Round Robin DNS which has two IP mapping to the same domain w7cloud.com as follow:
- w7cloud.com 184.108.40.206
- w7cloud.com 220.127.116.11
The DNS request will go to 18.104.22.168 and second goes to 22.214.171.124.
How you will check the status of DNS online?
You can use different tools like NSLOOKUP, DNSCMD, DNS Console, IPCONFIG, DNS Logs. And these DNS tools are available online on different websites.
What Is Authoritative Name-Server?
Authoritative name-server provides responses to queries and it is configured by an original-source. An authoritative name server only gives answers to queries about domain names that have been specifically configured by the administrator. The authoritative name server is final-holder of the IP of the domain you are looking for.
What Is the Difference between Authoritative and Recursive DNS?
Answer in comment.
What Is Forwarder (DNS Server)?
Forwarder DNS server handles the DNS quires if the main DNS server cannot receive the query. In this case queries are forwarded to another DNS configured as forwarder DNS server.
What Is Secondary DNS Server?
Secondary DNS server is a backup server for handling DNS quires. Secondary DNS server has a read only copy of DNS.
What is the importance of DNS to Active Directory?
DNS plays the central role in Internet name resolution. You can configure the DNS in active directory environment very easily and can configure the name resolution for your clients. AD can enlarge upon the standard feature set of DNS & provide new capabilities like AD-Integrated DNS. Active Directory can easily adapt to exist in a foreign DNS environment, such as Unix BIND.
What are the different types of DNS Queries?
A DNS query is a request made by the DNS-client to get the name-server information. Following are the different types of DNS queries:
- Recursion Query
- Iteration Query
- Non-recursive query
How you can clear the DNS cache from the DNS server?
On your DNS server you can use the command “ipconfig /flushdns” in command prompt.
Do I need to configure forwarders in DNS?
No, but DNS server configured with forwarder behaves differently than a normal DNS-server in following ways”
- If a query cannot be resolved from local database, then DNS-server will forward the request to the forwarder DNS server.
- When the DNS-server receives a request, it tries to resolve this request by using the zones that it hosts & by using its cache.
- If forwarders DNS servers are unavailable, the DNS server attempts to use its root hints to resolve the query.
A forwarder DNS is a DNS server on a ISP or on network that forwards DNS requests for external DNS names to DNS servers outside that network. You can configure forwarder DNS to forward queries according to specific domain-names using conditional forwarders.
What is DNS Spoofing?
DNS spoofing is an attack in which attacker change the DNS records and redirect online traffic to a fake website that resembles its intended destination. Once user is there, it may ask to login into their account (look like their website), giving the hacker the chance to steal their login credentials & other types of sensitive info. These malicious website is often used to spread viruses on a user’s PC and giving the hacker long term access to their PC.
What is TTL and what is suitable TTL for your DNS?
TTL stands for “Time to Live”. DNS TTL is a time that how long a resolver is supposed to cache the DNS-query for each DNS-record that specifies before the query expires and a new one needs to be done. Generally a recommend TTL of 24 hours is suitable if you don’t need to make the DNS changes. However, if you are planning to change DNS record, you can set a lower TTL value around 1 to 5 minutes at least 24 hours in advance of making the changes.