DNS Resource Records

Each zonefile contains resource records:

Record Type	Description
A	IPv4 Address record
AAAA	IPv6 Address record
CNAME	Canonical Name: a name (an alias) which redirects to another a host.
MX	Mail eXchange record: includes a preference value for the mail server.
NS	Name Server
PTR	PoinTeR record: used to reverse map IP addresses to hostnames.
SOA	Start of Authority: provides the name of the zone, email address, and other data.
SRV	SeRVices record: lists the services available such as SIP, XMPP, LDAP, HTTP. This helps for discovering services.
TXT	TeXT record: any text can be provided with a name, such as an SPF record or a DKIM record

Creating DNS records

Each record in the zone file is written in this format:

Name TTL Class Type Data

; zone file for example.com
$TTL 2d    ; 172800 secs default TTL for zone
$ORIGIN example.com.
@             IN      SOA   ns1.example.com. hostmaster.example.com. (
                        2003080800 ; se = serial number
                        12h        ; ref = refresh
                        15m        ; ret = update retry
                        3w         ; ex = expiry
                        3h         ; min = minimum
                        )
              IN      NS      ns1.example.com.
              IN      MX  10  mail.example.net.
joe           IN      A       192.168.254.3
www           IN      CNAME   joe