BIND -DNS

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Q. What is BIND? What are the key  Components of DNS ?



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

a) Domain Name space  :-Provides structure of DNS distributed space.Domain name space  has hierarchical structure.The root domain is at the TOP.Below the root domain the TOP or First level domain.
e.g...com,edu,biz.. 
  
Second Level Domains are registered to individual domains,such hp.com,Google.com. Second level domain have many sub domains and any domain can have host.A host is a specific computer with in a domain Such webserver1.it.hp.com ,computer.it.hp.com  .etc
FQDN parts for webserver1.it.hp.com  is as described below. 
webserver1 -->  host    
it. --> sub domain
hp. --> 2nd level domain              
com  --> TLD    
"."  --> root

b). Zones :-
For administrative purpose domain can be organized into zones.Zone is discrete and contiguous area of Domain name space.One reason for to divide name space to zone is to delegate different authorities for diff portions.One large domain is difficult  to administer.

 c.)Name Servers:-
The named IP address data for the computer is located   in zone is stored in  zone database file in a DNS server.
One name server Store Primary Zone file data file for a zone.that name server have a authority to make changes on file.Copy of zone file will be stored other name server to share load.Its is referred as secondary zone database file.Secondary zone database file will regularly updated from primary zone file by a process called zone transfer. 
Q.How DNS works ?
Lets see how DNS query works when user try to  resolve webserver1.it.hp.com (Diagram:1.0)
The local Name server Sends numerous queries to resolve a FQDN to an IP address.
When User types webserver1.it.hp.com ,client pc queries its local name server(NS1) for the IP address of that particular FQDN.
Name Server(NS1)checks its local zone database file to see it has an Authority for that hp.com.If it doesn't have authority but the NS1 does contain the information that points to the root name servers .NS!1 will now begin the search for the name server which holds the authority for webserver1.it.hp.com starting with root name servers.

So NS1 Send A query to root Name server.The root name server(NS7) contains the IP address of the names ever for  Top level domain ".com".
The root name server(NS7) send back the IP address to the Local NS1  ,which then queries .com NS4. .com Name server(NS4) receives the query and responds with Hp.com Name severs(NS6)
The local Name server(NS1) then send the request to hp.com name server (NS4).Hp.com Servers has its own database file that connection  name to IP mapping information for the webserver1.it.hp.com.
The hp.com name sever(NS4) passes the requested IP address to the local name server (NS1) .Local Name server(NS1) passes the IP address info to the client.Then the client establishes TCP/IP connection with webserver1.it.hp.com and data can be transferred.

Diagram 1.1.Working of DNS




Q. which are the important configuration files for DNS server?



Ans: 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.On which versions of bind u have worked?



Ans : BIND 9



Q.What is the role of DNS?


Ans: 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?



Ans: 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 ndc on the name server, connections on this TCP port from local host 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?



Ans: 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?



Ans: 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 Secondary name server/slave name server?



Ans: 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 Stealth name server?



Ans: 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"?



Ans: 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"?



Ans: 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?



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



Q. Explain "SOA Record"?



Ans : 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"



Ans: 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"?



 Ans: 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"?



Ans: 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"?



Ans: 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"?



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



Q.What is Dynamic DNS?



Ans: 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"?


Ans: 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"?

           

Ans: The named-checkzone utility checks the syntax and consistency of the zone file.

           

Syntax:     named-checkzone [-dgv]   [-c class] zone   [filename]







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