What is DNS ?

What is DNS ?

Domain Name System (DNS) is the default name resolution service used in a Microsoft Windows Server 2003 network. DNS is part of the Windows Server 2003 TCP/IP protocol suite and all TCP/IP network connections are, by default, configured with the IP address of at least one DNS server in order to perform name resolution on the network. Windows Server 2003 components that require name resolution will attempt to use this DNS server before attempting to use the previous default Windows name resolution service, Windows Internet Name Service (WINS).
Typically, Windows Server 2003 DNS is deployed in support of Active Directory directory service. In this environment, DNS namespaces mirror the Active Directory forests and domains used by an organization. Network hosts and services are configured with DNS names so that they can be located in the network, and they are also configured with DNS servers that resolve the names of Active Directory domain controllers.

Types of DNS records

Types of DNS records

A name server can act as a primary for multiple zones and as secondary for others. Some valid record types on a DNS server are stated as follows.

SOA record (Start of Authority), which consist of crucial information like the

SERIAL number, which is monitor by other name servers for change, which indicates to them a change in information for a zone, REFRESH which tell how often a secondary name server should check for a change in the serial number, RETRY is to inform a secondary server how long it should use it current entry if it is unable to perform a refresh and MINIMUM is how long the other name servers should hold these information.

NS record which show the authoritative DNS for the zone

A record which points a hostname to an IP address

CNAME record (canonical naming) which allows a node to be address using more than one hostname

MX record, which is used for message routing where there are multiple mail exchange hosts. A (A) record host address is needed for every MX record set.

PTR records, which are just the reverse of A records, it maps IP address to a hostname. These records can only be meaningful in-addr.arpa zones have been delegated to your control by your service provider of your IP block.

There are also some other lesser used record types like HINFO which indicate CPU and operating system types for mapping to specific hostnames and Text (TXT) record that provides a descriptive text associated with a domain name.

Understanding Zone Types

Understanding Zone Types

The DNS Server service provides for three types of zones:

• Primary zone
  
• Secondary zone
  
• Stub zone
  

Note
If the DNS server is also an Active Directory Domain Services (AD DS) domain controller, primary zones and stub zones can be stored in AD DS. See Understanding Active Directory Domain Services Integration for more information.

The following sections describe each of these zone types.

Primary zone

When a zone that this DNS server hosts is a primary zone, the DNS server is the primary source for information about this zone, and it stores the master copy of zone data in a local file or in AD DS. When the zone is stored in a file, by default the primary zone file is named zone_name.dns and it is located in the %windir%\System32\Dns folder on the server.

Secondary zone

When a zone that this DNS server hosts is a secondary zone, this DNS server is a secondary source for information about this zone. The zone at this server must be obtained from another remote DNS server computer that also hosts the zone. This DNS server must have network access to the remote DNS server that supplies this server with updated information about the zone. Because a secondary zone is merely a copy of a primary zone that is hosted on another server, it cannot be stored in AD DS.

Stub zone

When a zone that this DNS server hosts is a stub zone, this DNS server is a source only for information about the authoritative name servers for this zone. The zone at this server must be obtained from another DNS server that hosts the zone. This DNS server must have network access to the remote DNS server to copy the authoritative name server information about the zone.
You can use stub zones to:

• Keep delegated zone information current. By updating a stub zone for one of its child zones regularly, the DNS server that hosts both the parent zone and the stub zone will maintain a current list of authoritative DNS servers for the child zone.
  
• Improve name resolution. Stub zones enable a DNS server to perform recursion using the stub zone's list of name servers, without having to query the Internet or an internal root server for the DNS namespace.
  
• Simplify DNS administration. By using stub zones throughout your DNS infrastructure, you can distribute a list of the authoritative DNS servers for a zone without using secondary zones. However, stub zones do not serve the same purpose as secondary zones, and they are not an alternative for enhancing redundancy and load sharing.
  

There are two lists of DNS servers involved in the loading and maintenance of a stub zone:

• The list of master servers from which the DNS server loads and updates a stub zone. A master server may be a primary or secondary DNS server for the zone. In both cases, it will have a complete list of the DNS servers for the zone.
  
• The list of the authoritative DNS servers for a zone. This list is contained in the stub zone using name server (NS) resource records.
  

When a DNS server loads a stub zone, such as widgets.tailspintoys.com, it queries the master servers, which can be in different locations, for the necessary resource records of the authoritative servers for the zone widgets.tailspintoys.com. The list of master servers may contain a single server or multiple servers, and it can be changed anytime.

DNS Lookup Types

1. •   DNS lookup queries find different kinds of information.

     William Shakespeare once asked, "What's in a name?" With website domain names, additional information exists beneath the surface, and it's easy to access. The domain name system (DNS) translates user-friendly, easily memorized domain names like "Google.com" to unique numeric Internet Protocol (IP) addresses, such as 74.125.157.104, used by computers to connect to websites. The DNS also stores records containing information such as a website's server names and mail servers.

   Forward DNS Lookup

   • The forward DNS lookup, also known as an A (for address) record lookup, performs a query to a host server using the domain name. The server then responds, providing the associated unique IP address. A simple operation known as a "ping" can also perform a forward DNS lookup. Pinging a website sends a series of tiny packets of data to the domain name server to test its status and response time, and also returns the IP address for the requested domain name. Multiple free resources on the Internet provide tools to perform forward DNS lookups as well as other DNS queries.

   Reverse DNS Lookup

   • The reverse DNS lookup allows users to find the domain name of a numeric IP address through a server query similar to the forward DNS lookup. If the server has the proper record in place, this query will return the domain name for the IP address provided. Often used on mail servers, the reverse lookup authenticates emails and weeds out spammers. The mail server performs a reverse DNS lookup on the IP address located in the email's headers. If a corresponding domain name cannot be found--often the case with spammers using invalid IP addresses--the server then rejects and blocks the email.

   BIND Version Lookup

   • The BIND version lookup yields version information from a Unix/Linux Berkeley Internet Name Domain server. Security concerns may cause the queried server to either ignore or deny the lookup request, however.

   Additional DNS Lookups

   • A domain name server query can return several specific DNS records, including the A, or address, which maps the website's registered domain name to an IP address. This record enables the forward DNS lookup, while a PTR, or pointer, record created on a host server connects the IP address to the domain name, enabling reverse DNS lookups. An MX, or mail exchange, record query returns a list of mail servers associated with the domain name host server.
     The NS, or name server, record identifies the name of a host server that contains information about its associated domain name. The SOA, or start of authority, record identifies the domain name server as the best, most "authoritative" source of information about a given domain name, according to Microsoft's Technet website.