BIND – DNS Server Interview Questions & Answers

Q:1 What does BIND Stands for ?
Ans:  BIND stands for Berkeley Internet Name Domain.

Q:2  What is DNS Server and its fundamentals ?
Ans: The Domain Name System (DNS) is a hierarchical, distributed database. It stores information for mapping Internet host names to IP addresses and vice versa, mail routing information, and other data used by Internet applications. Clients look up information in the DNS by calling a resolver library, which sends queries to one or more name servers and interprets the responses. The BIND 9 software distribution contains a name server, named, and a resolver library, liblwres.

Q:3  What is the default port of BIND ?
Ans: The BIND server is accessed via the network on port 53. Both TCP and UPD ports are used. Queries are made via UDP & Responses are made via UDP unless the response is too large to fit in a single packet , If the response won’t fit in a single UDP packet, then the response is returned via TCP.

Q:4 How will you define Domain Name ?
Ans: The data stored in the DNS is identified by domain names that are organized as a tree according to organizational or administrative boundaries. Each node of the tree, called a domain, is given a label. The domain name of the node is the concatenation of all the labels on the path from the node to the root node. This is represented in written form as a string of labels listed from right to left and separated by dots. A label need only be unique within its parent domain.
For example, a domain name for a host at the company Linuxtechi, Inc. could be mail.linuxtechi.com, where com is the top level domain to which mail.linuxtechi.com belongs, example is a subdomain of com, and ‘mail’ is the name of the host

Q:5 What are zone files in DNS server ?
Ans: The files which contain the data being served by the DNS system are called “Zone Files” They are made up of a series of “Resource Records”. A Zone File will always contain an SOA record as well as additional records.

Q:6 What are the different types of DNS Server ?
Ans: Primary Master : The authoritative server where the master copy of the zone data is maintained is called the primary master server, or simply the primary. Typically it loads the zone contents from some local file edited by humans or perhaps generated mechanically from some other local file which is edited by humans. This file is called the zone file or master file.
Slave Server :  The other authoritative servers, the slave servers (also known as secondary servers) load the zone contents from another server using a replication process known as a zone transfer. Typically the data are transferred directly from the primary master, but it is also possible to transfer it from another slave. In other words, a slave server may itself act as a master to a subordinate slave server.
Caching Name Server : Caching Name server is not authoritative for any zone, all queries are forwarded to other DNS servers if they are not stored in the DNS-cache zone. Answers for all queries are cached in DNS-cache zone for a time.
Forwarding : In this type of DNS server , all queries are forwarded to a specific list of name servers

Q:7 How the load balancing is achieved using DNS ?
Ans: A primitive form of load balancing can be achieved in the DNS by using multiple records (such as multiple A records) for one name. For example, if you have three WWW servers with network addresses of 10.0.0.1, 10.0.0.2 and 10.0.0.3, a set of records such as the following means that clients will connect to each machine one third of the time

multiple-a-records

When a resolver queries for these records, BIND will rotate them and respond to the query with the records in a different order. In the example above, clients will randomly receive records in the order 1,2, 3; 2, 3, 1; and 3, 1, 2. Most clients will use the first record returned and discard the rest.

Q:8 How to check syntax of named.conf is correct or not ?
Ans: named-checkconf is the command,  which checks the syntax of  named.conf file.

# named-checkconf /etc/named.conf

If bind is running in chroot environment use below command
# named-checkconf -t /var/named/chroot /etc/named.conf

Q:9 What are the different types of Resource Records in bind ?
Ans: Below are the list of resource records in bind :
SOA – start of authority, for a given zone
NS – name server
A – name-to-address mapping
PTR – address-to-name mapping
CNAME – canonical name (for aliases)
MX – mail exchanger (host to receive mail for this name)
TXT – textual info
RP – contact person for this zone
WKS – well known services
HINFO – host information
Comments start with ; continue to end of line

Q:10 Explain Bind chroot environment ?
Ans: Running bind in a chroot environment means named process will be limited to their directory only (/var/named/chroot). This can help improve system security by placing BIND in a ”sandbox”, which will limit the damage done if a server is compromised.

Q:11 What is domain delegation in Bind ?
Ans: Domain delegation means fully delegate the responsibility for a sub-domain to another name server.

Exmaple :

squid.linuxtechi.com      IN NS       ns2.linuxtechi.com
ns2.linuxtechi.com         IN A          192.168.1.51


2 Responses

  1. Praveen Kumar says:

    Everything is explained clear and crisp…..

    Thanks & Regards
    Praveen Kumar

  2. Chiza says:

    thanks. very helpful site

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