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Sunday, May 8, 2011

DNS Server Interview Questions And Answers for linux admin

DNS Server Interview Questions And Answers for linux admin


Q: - which are the important configuration files for DNS server ?
BIND uses /etc/named.conf as its main configuration file, the /etc/rndc.conf file as the
configuration file for name server control utility rndc, and the /var/named/ directory for zone files and the like.

Q: - What is BIND ?

BIND stands for Berkeley Internet Name Domain which is the most commonly used Domain Name System (DNS) server on the Internet.

Q: - On which version of bind u have worked ?

BIND 9

Q: - What is the role of DNS ?

A DNS server, or name server, is used to resolve an IP address to a hostname or vice versa.

Q: - On which port DNS server works ?

DNS servers use port 53 by default. Incoming and outgoing packets should be allowed on
port 53. Also allow connections on port 921 if you configure a lightweight resolver server.
The DNS control utility, rndc, connects to the DNS server with TCP port 953 by default. If
you are running rndc on the name server, connections on this TCP port from localhost
should be allowed. If you are running rndc on additional systems, allow connections to
port 953 (or whatever port you have chosen to configure) from these additional systems.
Q: - What is round robin DNS?

Round robin DNS is usually used for balancing the load of geographically distributed Web servers. For example, a company has one domain name and three identical home pages residing on three servers with three different IP addresses. When one user accesses the home page it will be sent to the first IP address. The second user who accesses the home page will be sent to the next IP address, and the third user will be sent to the third IP address. In each case, once the IP address is given out, it goes to the end of the list. The fourth user, therefore, will be sent to the first IP address, and so forth. 
Q: - What is Name Server?

A name server keeps information for the translation of domain names to IP addresses   and IP addresses to domain names. The name server is a program that performs the translation at the request of a resolver or another name server.
Q: - What is Primary name server or primary master server?

Primary name server/primary master is the main data source for the zone. It is the authoritative server for the zone. This server acquires data about its zone from databases saved on a local disk. The primary server must be published as an authoritative name server for the domain in the SOA resource record, while the primary master server does not need to be published.
Q: - What is Secondary name server/slave name server?

Secondary name server/slave name server acquires data about the zone by copying the data from the primary name server (respectively from the master server) at regular time intervals. It makes no sense to edit these databases on the secondary name servers, although they are saved on the local server disk because they will be rewritten during further copying.
Q: - 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.
Q: - 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.

Q: - 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). 

Q: - 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.
Q: - Tell me 5 Types of DNS records?

A, NS, CNAME, SOA, PTR, MX.
Q:- 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. 
Q: - 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.
Q: - Explain "CNAME Record"?

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

Q: - Explain "PTR Records"?

A Pointer Record (PTR) is used to translate an IP address into a domain name.
Q: - 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.
Q: - What is the role of "named-checkconf Utility"?

The named-checkconf utility checks the syntax of the named.conf configuration file.
Syntax: named-checkconf    [-t directory] [filename] 

Q: - what is the role of "named-checkzone Utility"?

The named-checkzone utility checks the syntax and consistency of the zone file.
Syntax:     named-checkzone [-dgv]   [-c class] zone   [filename]