DNS (Domain Naming System or Distributed Naming System) Related Interview Question & Answer.


The Domain Name System (DNS) is a hierarchical distributed naming system for computers. The Domain Name System distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating authoritative name servers for each domain. Authoritative name servers are assigned to be responsible for their particular domains, and in turn can assign other authoritative name servers for their sub-domains.

2) What is the main purpose of a DNS server?

DNS servers are used to resolve FQDN hostnames into IP addresses and vice versa.

3) How does a computer know to which DNS server it has to sent the request

The DNS server IP address is configured on the TCP/IP adapter setting of the computer. With this information, the computer knows the DNS server to which the request has to be sent.

4) What is the port no of DNS?

UDP port number - 53

5) How many root DNS servers are available in the world?

6) What is a Forward Lookup?

Resolving Host Names to IP Addresses, Address mapping (A) records maps a host name to an IP address

7) What is a Forward Lookup?

Reverse-lookup pointer (PTR) records map an IP address to a host name.

8) What is a Resource Record?

It is a record provides the information about the resources available in the N/W infrastructure.

9) What is the different DNS Roles?

Standard Primary, Standard Secondary, & AD Integrated.

10) What is a Zone?

Zone is a sub tree of DNS database.

11) Why we create PTR Records

Secure services in your network require reverse name resolution to make it more difficult to launch successful attacks against the services. To set this up, you configure a reverse lookup zone and proceed to add records.

12) SOA records must be included in every zone. What are they used for?

SOA records contain a TTL value, used by default in all resource records in the zone. SOA records contain the e-mail address of the person who nis responsible for maintaining the zone. SOA records contain the current serial number of the zone, which is used in zone transfers.

13) What is primary, Secondary, stub & AD Integrated Zone?


Primary Zone: - zone which is saved as normal text file with filename (.dns) in DBS folder. Holds the master copy of a zone and can replicate it to secondary zones. All changes to a zone are made on the standard primary.

Secondary Zone: - maintains a read only copy of zone database on another DNS server. Provides fault tolerance and load balancing by acting as backup server to primary server.Information in a primary zone is replicated to the secondary by use of the zone transfer mechanism.

Stub zone: - contains a copy of name server and SOA records used for reducing the DNS search orders. Provides fault tolerance and load balancing.

Active Directory-integrated: -A Microsoft proprietary zone type, where the zone information is held in the Windows 2000 Active Directory (AD) and replicated using AD replication. 
DNS record types 

14) What is the main purpose of SRV (Service)records?

SRV records are used in locating hosts that provide certain network services.

15) Which of the following conditions must be satisfied to configure dynamic DNS updates for legacy clients?

The zone to be used for dynamic updates must be configured to allow dynamic updates. The DHCP server must support, and be configured to allow, dynamic updates for legacy clients.

16) Benefits of using AD-integrated zones.

a) Active Directory integrated DNS enables Active Directory storage and replication of DNS zone databases. Windows 2000 DNS server, the DNS server that is included with Windows 2000 Server, accommodates storing zone data in Active Directory.

b) When you configure a computer as a DNS server, zones are usually stored as text files on name servers that is, all of the zones required by DNS are stored in a text file on the server computer.

c) These text files must be synchronized among DNS name servers by using a system that requires a separate replication topology and schedule called a zone transfer However, if you use Active Directory integrated DNS when you configure a domain controller as a DNS name server, zone data is stored as an Active Directory object and is replicated as part of domain replication.


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