Network Administration: NS and A Records

Each DNS database zone file consists of one or more resource records, including the Name Server (NS) and Address (A) records. Creating and updating the resource records that comprise the DNS zone files is one of the primary tasks of a DNS administrator.

NS records

Name Server (NS) records identify the name servers that are authoritative for the zone. Every zone must have at least one NS record. Using two or more NS records is better so that if the first name server is unavailable, the zone will still be accessible.

The owner field should either be the fully qualified domain name for the zone, with a trailing dot, or an @ symbol. The RDATA consists of just one field: the fully qualified domain name of the name server.

The following examples show two NS records that would serve the lowewriter.com domain:

lowewriter.com.  IN  NS  ns1.lowewriter.com.
lowewriter.com.  IN  NS  ns2.lowewriter.com.

A records

Address (A) records are the meat of the zone file: They provide the IP addresses for each of the hosts that you want to make accessible via DNS. In an A record, you usually list just the host name in the owner field, thus allowing DNS to add the domain name to derive the fully qualified domain name for the host. The RDATA field for the A record is the IP address of the host.

The following lines define various hosts for the LoweWriter.com domain:

doug        IN  A  192.168.168.200
server1     IN  A  192.168.168.201
debbie      IN  A  192.168.168.202
printer1    IN  A  192.168.168.203
router1     IN  A  207.126.127.129
www         IN  A  64.71.129.102

Notice that for these lines, the fully qualified domain names are not specified for each host. Instead, I just provide the host name. DNS will add the name of the zone’s domain to these host names in order to create the fully qualified domain names.

A more explicit example could list these A records like this:

doug.lowewriter.com.     IN  A  192.168.168.200
server1.lowewriter.com.  IN  A  192.168.168.201
debbie.lowewriter.com.   IN  A  192.168.168.202
printer1.lowewriter.com. IN  A  192.168.168.203
router1.lowewriter.com   IN  A  207.126.127.129
www.lowewriter.com.      IN  A  64.71.129.102

However, all this does is increase the chance for error. Plus, it creates more work for yourself later if you decide to change your network’s domain.

dummies

Source:http://www.dummies.com/how-to/content/network-administration-ns-and-a-records.html