Remotely Manage your DNS

Continued from page: 1

Wednesday, December 01, 2004

DNS primer

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You might already know that computers care less about human words and more about its numeric representation. So, while we would call a computer, 'officepc', the computer would refer to it as '192.168.0.1'. The human name is called its DNS name and the numeric form is its IP address. The system that performs the translation between the two is known as the DNS or Domain Name System.

Domains and domain names are organized into hierarchical entities called 'zones'. Depending on the mindset of your DNS Administrator, your zone can be single-tiered or multi-tiered. That is, if you have a domain name called 'pcquest.com', you can either have 'com' as a zone and 'pcquest' as a subzone under it. Or, can have 'pcquest.com' as a single zone. 

These zones can be Primary, Secondary or Stub. Primary zones are considered the masters (authoritative) and secondaries are 'backups'. Stub zones simply improve lookup speed for commonly searched for zones. Again, zones can be forward or reverse. Forward zones translate names to their corresponding IP addresses and reverse zones translate IP addresses to names. Each zone can contain a number of records of different types, called 'Resource Records' (RRs).

There are many types of RRs and it is not necessary to have all of them in a zone. The commonly used types are – Host (A), Pointer (PTR), Name Server (NS), Mail Exchange (MX), Canonical Name (CNAME) and Start of Authority (SOA). A brief description of these types follows:

Host (A) : Maps a name to an IP address, eg, the domain 'pcquest.com' maps to its IP address '147.208.184.149'

Pointer (PTR) : Map an IP address to a name, ie, reverse of 'A' record

Name Server (NS) : The DNS servers authoritative for a particular zone

Mail Exchange (MX) : Specify the POP/IMAP mail servers that receive mail for a zone

Canonical Name (CNAME) : Alternative name for an 'A' record, eg, 'pcquest.com' could also be 'www.pcquest.com' or 
'pcquest.cybermedia.com'. This is used to simplify access to a host 

Start of Authority (SOA) : Provide various administrative values (such as expiry time, e-mail address of zone-administrator, etc)

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