DNS Records DNS Records

What are DNS records?


The Domain Name System (DNS) is the phone book of the Internet. People access information online through easy-to-remember domain names. Computers communicate through Internet Protocol (IP) addresses. DNS translates domain names to IP addresses so browsers can load Internet resources.

DNS records are instructions that are created in authoritative DNS servers or name servers and provide information about a domain such as what IP address it is mapping to and where the emails for the domain name should go. All the DNS records constitute the domain's DNS zone which is stored in a text file called a zone file on the authoritative DNS servers. A typical zone file in BIND format with some of the common DNS records looks like the below:

$TTL	1800 ; $TTL used for all DNS records without explicit TTL value
$ORIGIN example.com.   ; designates the start of this zone file in the namespace 
@ 86400 IN SOA ns1.dynu.com. administrator.dynu.com. (
         25101 ; serial
         1800 ; refresh
          300 ; retry
         86400 ; expire
         300 ; nxdomain TTL
        )
@ 86400 IN NS ns1.dynu.com.  ; Name Server Record for example.com 
@ 86400 IN NS ns2.dynu.com.  ; Name Server Record for example.com 
*  3600 IN  A      192.168.0.10  ; A Record for *.example.com 
bill  3600 IN  A      192.168.0.3  ; A Record for bill.example.com 
@ 3600 IN AAAA ::1  ; AAAA Record for example.com 
@ 10800 IN CAA 0 issue "comodoca.com"  ; CAA Record for example.com 
portal 3600  IN  A  example.com.  ; CNAME Record for portal.example.com 
testhinfo 90 IN HINFO "INTEL-386" "Windows"  ; HINFO Record for testhinfo.example.com
@ 3600 IN  LOC 31.000 N 106 28 29.000 W 10.00m 1m 10000m 10m ; LOC Record for example.com
@ 3600 IN MX 10 mx1.dynu.com. ; MX Record for example.com 
rp 1800 IN RP admin.example.com. other.example.com.  ; RP Record for rp.example.com 
_sip._udp 3600 IN SRV 10 5 5060 siphost.com.  ; SRV Record for for example.com 
@ 90 IN TXT "v=spf1 a mx a:mx1.resolute.com ~all"  ; TXT Record for example.com 
_ftp._tcp 3600 IN URI 10 1 "ftp://ftp.example.com/public"  ; URI Record for example.com 

Types of DNS records


A Record
An A record maps hostnames to an IPv4 address. For example, the A record for google.com points the IP address 172.217.3.174. Learn more about A Record.

AAAA Record
An A record maps hostnames to an IPv6 address. For example, the AAAA record for google.com points the IPv6 address 2607:f8b0:400a:800::200e. Learn more about AAAA Record.

CAA Record
A CAA record lets you specify which certificate authorities (CAs) are allowed to issue certificates for a domain or subdomain. Creating a CAA record helps to prevent the wrong CAs from issuing certificates for your domains. Learn more about CAA Record.

CNAME Record
A Canonical Name record (CNAME record) maps an alias name to a true or canonical domain name. CNAME is often used to associate new subdomains with an existing domain's DNS records. Learn more about CNAME Record.

HINFO Record
A HINFO record defines the hardware type and Operating System (OS) in use at a host. This record can be used by applications such as FTP, because FTP uses special procedures when communicating with computers of a known CPU and Operating System (OS). Learn more about HINFO Record.

LOC Record
A LOC record contains geographic location information such as Latitude, Longitude, Altitude, host/subnet physical size and location accuracy for a domain name. It contains WGS84 Latitude, Longitude and Altitude (ellipsoidal height). Learn more about LOC Record.

MX Record
A Mail Exchange (MX) entry directs mail to an email server. Essentially, it specifies how email should be routed when sent to an address at your domain. Learn more about MX Record.

PTR Record
PTR records (Pointer Records) are used for reverse DNS lookups. It is a mapping of an IP address to a hostname. Learn more about PTR Record.

RP Record
RP record stands for Responsible Person. RP records include information about the mailbox name for the responsible person(s) for the domain. This mailbox name is then mapped to a TXT record within the same zone subsequently queried to retrieve additional information if available. Learn more about RP Record.

SPF Record
An SPF record is a type of TXT record that specifies a list of authorized hostnames/IP addresses that mail can originate from for a given domain name and it prevents spammers from using your domain to send unauthorized emails. Learn more about SPF Record.

SRV Record
An SRV record establishes connections between a service and a hostname. and it contains specific information that can be used to locate a specific resource at an address. When an application needs to find the location of a specific service, it will search for a related SRV record. Learn more about SRV Record.

TXT Record
A TXT record holds free-form text of any type. A fully qualified domain name may have many TXT records. Some of the common TXT records are Sender Policy Framework (SPF), DomainKeys Identified E-mail (DKIM). Learn more about TXT Record.

URI Record
A URI record is used to publish mappings from hostnames to URIs. Learn more about URI Record. Learn more about URI Record.

DNS record glossary


Zone File
A zone file is a text file on an authoritative name server that describes a DNS zone which contains mappings between domain names and IP addresses and other resources, organized in the form of text representations of resource records (RR).

BIND
Berkeley Internet Name Daemon - is the most commonly used DNS software on the Internet and Dynu observes BIND format.

DNS
The Domain Name System (DNS) is the phone book of the Internet. People access information online through easy-to-remember domain names. Computers communicate through Internet Protocol (IP) addresses. DNS translates domain names to IP addresses so browsers can load Internet resources.

DNS Caching
DNS caching is the amount of a time that a DNS server will retain existing DNS records before checking with the authoritative name servers for updates. The amount of time that records are cached is usually determined by the TTL set by the authoritative nameserver, but some ISPs may cache the records longer.

Master/Primary Zone
Both master and slave servers are authoritative for the zones they handle. The master does not have any more power over the zones than the slave when it comes to answering DNS queries. The only difference between a master and a slave server is where they read their zone files from. A master server reads its zone files from files on the system's disk. These are usually where the zone administrator creates, edits, or transfers the original zone files.

Slave/Secondary Zone
The slave server receives the zones that it is authoritative for through a zone transfer from one of the master servers for the zone.

Authoritative Name Server
An authoritative Name Server is a nameserver (DNS Server) that holds the actual DNS records (A, AAAA, TXT, etc) for a particular domain/ address. Authoritative Name Servers need to be set up at the domain registrar and they only respond to DNS queries for the domain names that they host.

DNS Recursive Resolver
A DNS server that queries an authoritative nameserver to resolve a domain/ address.

Dynamic DNS
A method of mapping a static hostname to a dynamic IP address automatically. A computer software or router built-in software is needed to achieve this.