Domain Name System

DNS ( Domain Name System)

It is a service that translates hostnames to ip address.In very simple terms, it can compare it to a phone book. DNS was invented in 1983, shortly after TCP/IP was developed. It uses TCP/IP port 53.

DNS Zones

1. Forward Lookup Zone : It searches for an IP address based on a provided host name. For example, when you browse to http://shaikhmajeed.blogspot.com your operating system's DNS resolver queries DNS for a www host record in the http://shaikhmajeed.blogspot.com domain.

2. Reverse Lookup Zone : It performs the opposite. It queries DNS for a host name based on an IP address.

DNS Sub Zones

1.Primary Zone : It holds read and write copies of all resource records like A,NS and SRV.

2.Secondary Zone : It stores read only copies of records, gets updates from the primary server by zone transfer.

3.Stub Zone : A tiny zone with just pointers to another domain. For example A,NS ans SRV record of the main server in that Stub domain. Think of Stub Domains like secondary zones, but with only 3 records.

DNS Resource Records

1. A (Host) - It maps hostnames to ip address.
2. PTR (Pointer) - It maps ip address to hostnames.
3. CName - Canonical name, in plain English an alias.
4.NS - Identifies DNS name servers. Important for forwarders.
5.MX - Mail servers, particularly for other domains. MX records required to deliver internet email.
6. _SRV and _MSDCS - Required for Active Directory. Whole family of underscore service records, for example, gc = global catalog. dc = domain controller.
7.SOA - Make a point of finding the Start of Authority (SOA) tab at the DNS Server.

See this : http://www.youtube.com/watch?v=Rw96pH_Kdxo