DNS Interview Qeustions - BIND

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


What is Root name server?

Root name server is an authoritative name server for the root domain (for the dot). Each root name server is a primary server, which differentiates it from other name servers. 

What is Stealth name server?

Stealth name server is a secret server. This type of name server is not published anywhere. It is only known to the servers that have its IP address statically listed in their configuration. It is an authoritative server. It acquires the data for the zone with the help of a zone transfer. It can be the main server for the zone. Stealth servers can be used as a local backup if the local servers are unavailable. 

What do you mean by "Resource Records"?

Information on domain names and their IP addresses, as well as all the other information distributed via DNS is stored in the memory of name servers as Resource Records(RR).

Explain "TTL"?

Time to live. A 32-bit number indicating the time the particular RR can be kept valid in a server cache. When this time expires, the record has to be considered invalid. The value 0 keeps nonauthoritative servers from saving the RR to their cache memory.

Tell me 5 Types of DNS records?

A, NS, CNAME, SOA, PTR, MX.

Explain "SOA Record"?

The Start of Authority(SOA) record determines the name server that is an authoritative source of information for the particular domain. There is always only one SOA record in the file, and it is placed at the beginning of the file of authoritative resource records. 

What is "A Record"

A (Address) records assign IP addresses to domain names of computers. The IP address cannot have a dot at the end. 

Explain "CNAME Record"?

Synonyms to domain names can be created using CNAME records. This is often referred to as 'creating aliases for computer names'. 

What are "HINFO and TXT Records"?

HINFO and TXT records are for information only. An HINFO record has two items in its data part. The first item is information about hardware, and the second one is information about software. A TXT record contains a general data string in its data part.
Example :
test.com IN SOA …
…
mail IN A 192.1.1.2
IN HINFO My_Server UNIX
IN TXT my server 

What are "MX Records"?

MX records specify the mailing server of the domain. An MX record shows to which computer a mail of a particular domain should be sent. The MX record also includes a priority number, which can be used to determine several computers where the mail for the domain can be sent. The first attempt is to deliver the mail to the computer with the highest priority (lowest value). If this attempt fails, the mail goes to the next computer (with a higher priority value), and so on.

test.com IN SOA …
…
mail                IN        A         192.1.1.2
IN       HINFO    AlphaServer UNIX
IN       TXT       my  server
IN       MX   30    mail2.nextstep4it.com
IN        MX   20    mail3.nextstep4it.com
IN        MX   10    mail2.nextstep4it.com

Explain "PTR Records"?

A Pointer Record(PTR) is used to translate an IP address into a domain name.

What is Dynamic DNS?

Dynamic DNS a method of keeping a domain name linked to a changing IP address as not all computers use static IP addresses. Typically, when a user connects to the Internet, the user's ISP assigns an unused IP address from a pool of IP addresses, and this address is used only for the duration of that specific connection. This method of dynamically assigning addresses extends the usable pool of available IP addresses. A dynamic DNS service provider uses a special program that runs on the user's computer, contacting the DNS service each time the IP address provided by the ISP changes and subsequently updating the DNS database to reflect the change in IP address.

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.

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.

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

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

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.

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

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

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.

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