DNS INTERVIEW QUESTATION

Ø What is DNS?

Domain Naming System. To resolve Host name to IP Address

Ø What’s the difference between forward lookup and reverse lookup in DNS?

Forward lookup is name-to-address, the reverse lookup is address-to-name.

Ø Types of Zones

Primary, Secondary and STUB Zone

Ø What is Primary Zone?

Primary zones, which store their zone information in a writable text file on the name server.

Ø What is Secondary Zone?

Secondary zones, which store their zone information in a read-only text file on the name server.

Ø What is Stub Zone?

Stub zone is a new feature in windows 2003. It is like a secondary zone. But there are certain differences. The differences are while secondary zones contain copies of all the resource records in the corresponding zone on the master name server, stub zones contain only three kinds of resource records:

·      Copy of the SOA record for the zone.

·      Copies of NS records for all name servers authoritative for the zone.

·      Copies of A records for all name servers authoritative for the zone.

Ø What are the common Resource Records

 NS, SOA, MX, SRV, Cname, PTR

Ø What is Conditional Forwarding

Conditional forwarding is a new feature of DNS in Windows Server 2003. Conditional forwarding can be used to speed up the DNS name resolution process by directing queries for specific domains to specific name servers.

Ø What is LMHOSTS file?

It’s a file stored on a host machine that is used to resolve NetBIOS to specific IP addresses.

Ø      What is HOSTS file?

It’s a file stored on a host machine that is used to resolve Host name to specific IP addresses.

Ø What is DNS ?

 It is used to resovle FQDN to IP address.

Ø Types of Zone in DNS ?

 Forward Lookup - it is used to resolve FQDN to IP

Reverse lookup - it is used to resovle IP to FQDN

Ø Types of DNS Zone ?

·      Primary Zone :

·      Secondary Zone :

·      AD integrated Zone :

·      Stub Zone

Ø what is NSlookup ?

Answer : it is a tool used troubleshoot DNS related issues.

·      DNS stands for Domain name systems. The primary and the basic function of DNS is to provide

·      name resolution service. DNS resolves Fully Qualified Name Domain (FQDN) to IP Address

·      .i.e www.visioninfosystems.org to 203.145.10.52. DNS is heart of WWW service. DNS is

·      widely used in Internet to resolve website names to IP address. In Windows 2000/2003 ADS

·      based network DNS plays an important Role.

·      DNS is used to resolve names of host in a ADS based domain.

·      DNS contains and SRV record to all find resources like DC, Global Catalog,

Ø DNS Zones

Before creating entry for domains in DNS server we must first understand what is Zone. A zone

is a storage unit for a domain. The zone can be stored in a zone file or in Active directory. For

every sub-domain we required a zone in DNS. A zone contains information called as Resource

Record (RR) for a specific domain. e.g. for visioninfosystems.org domain we are require to

create a zone called as visioninfosystems.org. Remember that the zone name and domain name

should be same. All domain information is that stored in zone i.e. host(A) record, MX record,

SRV record, PTR record, etc. If a DNS server which is hosting zone for visioninfosystems.org is

down the we cannot resolve names. So it is recommended to place this information on multiple

servers for redundancy and also load balancing. So that if one DNS server is down, the other

DNS server is provide redundancy for the first DNS server. Microsoft has divided DNS zone into

3 categories for provide redundancy and load balancing. They are :

Standard Primary Zone : A standard primary zone stored IP to FQDN mapping in a zone file.

This zone file is a normal TEXT/ASCII file located in default location i.e.

c:\windows\system32\dns\<domain.com.dns> file. Any changes made to the standard primary

zone is replicated to all secondary zone. There can be only one primary zone for a domain.

Primary zone is less secure because anyone can tamper the zone file. Replication between

primary and secondary is full replication.

Standard Secondary Zone : A standard secondary zone contains a copy of primary zone file. A

standard secondary zone is a replica of an existing zone. Secondary zones are read-only and are

stored in standard text files Any changes made to primary are replicated to secondary. Primarysecondary

zone works in master-slave relationship.

Active Directory Integrated Zone : This type of Zone is first introduced in Windows 2000.

This DNS zone stores zone information in Active Directory. We can place multiple AD

integrated zone for a domain. Any changes made to a zone is replicated to all zones. AD

integrated zone support multi-master replication i.e. it support two way replication which is not

possible in primary-secondary zones. AD integrated zones also supported incremental

replication.

Ø Stub Zone : A stub zone is like a secondary zone and also read-only like a secondary

·      zone. But the differences end here, as stub zones are quite different from secondary

·      zones in a couple of significant ways. First, while secondary zones contain copies of all

·      the resource records in the corresponding zone on the master name server, stub zones

·      contain only three kinds of resource records:

§  A copy of the SOA record for the zone.

•      Copies of NS records for all name servers authoritative for the zone.

·      Copies of A records for all name servers authoritative for the zone.

·      There is CNAME records, MX records, SRV records, or A records for other hosts in the zone. So

·      while a secondary zone can be quite large for a big company's network, a stub zone is always

·      very small, just a few records.

Ø DNS Zone Types

o  There are two zone lookup types: forward lookup zones and reverse lookup zones.

o  Forward Lookup Zones

o  A forward lookup zone enables forward lookup queries. On name servers, you must configure at

o  least one forward lookup zone for the DNS service to work A forward look zone resolves Host

o  name to IP address

o  Reverse Lookup Zones

o  A reverse lookup zone enables reverse lookup queries. Reverse lookup zones are not required. It

o  resolve IP address to host name. However, a reverse lookup zone is required to run

o  troubleshooting tools, such as NSLOOKUP, and to record a name instead of an IP address in

§  Internet Information Services (IIS) log files.

Ø DNS Query type

·      Recursive Queries : In a recursive query, the DNS name server is requested to respond with the

·      requested data from client, or with an error stating that data does not exist or that the domain

·      name specified does not exist. The DNS name server cannot refer or query the request to a

·      different name server.

·      Iterative Queries : In an iterative query, the DNS name server gives the best answer it currently

·      has back to the requester client. This answer may be the resolved name or a referral to another

o  name server that may be able to answer the client's original request.

Resource Records

·       

·      Resource records are entries in the zone database file that associate DNS domain names to

·      related data for a given network resource, such as an IP address. There are many different types

·      of resource records. When a zone is created, DNS automatically adds two resource records: the

·      Start of Authority (SOA) and the Name Server (NS) records

·      Resource Record

·      Host (A) : Lists the host name-to-IP-address mappings for a forward

·      lookup zone.

·      Alias (CNAME) : Creates an alias, or alternate name, for the specified host

·      name. You can use a Canonical Name (CNAME) record to

·      use more than one name to point to a single IP address. For

·      example, you can host a File Transfer Protocol (FTP)

·      server, such as ftp.visioninfosystems.org, and a Web server,

·      such as www.visioninfosystemst.org, on the same computer.

·      Host Information (HINFO) : Identifies the CPU and operating system used by the host.

·      Use this record as a low-cost resource-tracking tool. Mail

·      Exchanger (MX) Identifies which mail exchanger to

·      contact for a specified domain and in what order to use

·      each mail host.

·      Name Server (NS) : Lists the name servers that are assigned to a particular

·      domain.

·      Pointer (PTR) : Points to another part of the domain namespace. For

·      example, in a reverse lookup zone, it lists the IP-address-toname

o  mapping.

    What’s the difference between forward lookup and reverse lookup in DNS?

Forward lookup is name-to-address, the reverse lookup is address-to-name.

              Types of Zones

Primary, Secondary and STUB Zone

              What is Primary Zone?

Primary zones, which store their zone information in a writable text file on the name server.

          What is Secondary Zone?

Secondary zones, which store their zone information in a read-only text file on the name server.

          What is Stub Zone?

Stub zone is a new feature in windows 2003. It is like a secondary zone. But there are certain differences. The differences are while secondary zones contain copies of all the resource records in the corresponding zone on the master name server, stub zones contain only three kinds of resource records:

Copy of the SOA record for the zone.

Copies of NS records for all name servers authoritative for the zone.

§  Copies of A records for all name servers authoritative for the zone.

What is Conditional Forwarding

§  Conditional forwarding is a new feature of DNS in Windows Server 2003. Conditional forwarding can be used to speed up the DNS name resolution process