DNS (Domain Naming System)

            Domain Name System is the service which is use to resolve host name to IP and IP to host name. It also provides a hierarchical name space in domain environment. It has many records in a domain . It is most preferred name resolution technology over the TCP/IP network.

DNS Server Types-

1- Primary DNS server-

It is created on a first DNS server in a domain . It may integrated with ADDS or It may be different to ADDS. When we install ADDS and DNS on same server then Active Directory Integrated zone is created.Integrated zone is always made a primary zone.  We don't have to create new zone. It has many records like.

•    Host records  (A, AAAA)- It stores host name and IP address of DNS clients.
•     Pointer records ( PTR )- It stores IP address of hosts.
•     Name Server Records (NS)- It stores server name on which DNS zone is delegated.
•     Mail Exchanger Records (MX)- It stores mail server's record
•     CName record (Alia's) - It stores an alternate name for any host
•    Service Location (SRV) - It stores records about servers which hosts various services       like ftp,http etc.

2- Secondary DNS Server-   

        Ssecondary DNS server is created for load balancing of primary . It stores all DNS records but has read only permissions . We cannot edit or create  any records on Secondary DNS  but it is able to resolve all clients queries. It replicates from primary server and updates all records. 

3- Stub DNS server- 

It is also a type of DNS zone which stores only three DNS records. These records are NS,SOA and Host records. This zone also has read only permission. It updates it's records from primary server. 

4- Cache Only DNS server- 

 It is a type of DNS server which does not have any records but it is able to resolve all clients queries. When it receives any queries it forwards to primary DNS . Primary DNS gives reply to stub. Stub sends result to client and also stores this result in it's cache. If again same query is asked by client the Stub DNS will not forward query to primary .It will resolve from it's cache. There is no security issue in Caching Only DNS server. 

There are two Look up Zones-

1- Forward Look up Zone-   It is responsible for resolving host name to IP address. It contains all DNS records except PTR record.

2-  Reverse Look up Zone- It is responsible for resolving IP address to host name . It stores all records except Host record.