dns zone file NS PTR SOA A CNAME records

A Domain Name System (DNS) zone file is a text file that describes a DNS zone. A DNS zone is a subset, often a single domain, of the hierarchical domain name structure of the DNS. The zone file contains mappings between domain names and IP addresses and other resources

Example A Dyn Zone File

This an example of a zone file downloaded from Dyn’s DNS system.

$ORIGIN example.com.
@                      3600 SOA   ns1.p30.dynect.net. (
                              zone-admin.dyndns.com.     ; address of responsible party
                              2016072701                 ; serial number
                              3600                       ; refresh period
                              600                        ; retry period
                              604800                     ; expire time
                              1800                     ) ; minimum ttl
                      86400 NS    ns1.p30.dynect.net.
                      86400 NS    ns2.p30.dynect.net.
                      86400 NS    ns3.p30.dynect.net.
                      86400 NS    ns4.p30.dynect.net.
                       3600 MX    10 mail.example.com.
                       3600 MX    20 vpn.example.com.
                       3600 MX    30 mail.example.com.
                         60 A     204.13.248.106

In the following example, an A record binds a hostname to an IP address, while a CNAME record points the commonly used www hostname to it.

server1 IN A 10.0.1.5 
www IN CNAME server1

 IN     MX     10     mail.example.com.       
 IN     MX     20     mail2.example.com.

In this example, the first mail.example.com email server is preferred to the mail2.example.com email server when receiving email destined for the example.com domain.

This refers to the NameServer record, which announces the authoritative nameservers for a particular zone.

The following illustrates the layout of an NS record:

      IN     NS     <nameserver-name>

Here, <nameserver-name> should be an FQDN.
Next, two nameservers are listed as authoritative for the domain. It is not important whether these nameservers are slaves or if one is a master; they are both still considered authoritative.

 IN     NS     dns1.example.com.
 IN     NS     dns2.example.com.

PTR

This refers to the PoinTeR record, which is designed to point to another part of the namespace.

PTR records are primarily used for reverse name resolution, as they point IP addresses back to a particular name. Refer to Section 16.3.4, “Reverse Name Resolution Zone Files” for more examples ofPTR records in use.

SOA

This refers to the Start Of Authority resource record, which proclaims important authoritative information about a namespace to the nameserver.

Located after the directives, an SOA resource record is the first resource record in a zone file.
The following shows the basic structure of an SOA resource record:

@     IN     SOA    <primary-name-server> <hostmaster-email> (
 <serial-number>
 <time-to-refresh>
 <time-to-retry>
 <time-to-expire>
 <minimum-TTL> )