DNS - Domain Name System. Basics, DNS Record Types

DNS record types

DNS resource records (RRs) describe the characteristics of a zone (or domain) and have a binary or wire-format, which is used in queries and responses, and a text format used in zone files and which is described in this chapter.

We will describe only few RR types, full list of DNS RRs can be obtained from IANA DNS Parameters.

 A record

A records (also known as host records) are the central records of DNS. These records link a domain, or subdomain, to an IP address.

A records and IP addresses do not necessarily match on a one-to-one basis. Many A records correspond to a single IP address, where one machine can serve many web sites. Alternatively, a single A record may correspond to many IP addresses. This can facilitate fault tolerance and load distribution, and allows a site to move its physical location.

NS record

Name server records determine which servers will communicate DNS information for a domain. Two NS records must be defined for each domain. Generally, you will have a primary and a secondary name server record - NS records are updated with your domain registrar and will take 24-72 hours to take effect.

If your domain registrar is separate from your domain host, your host will provide two name servers that you can use to update your NS records with your registrar.

MX record

A mail exchanger record (MX record) is a type of resource record in the Domain Name System that specifies a mail server responsible for accepting email messages on behalf of a recipient's domain, and a preference value used to prioritize mail delivery if multiple mail servers are available. The set of MX records of a domain name specifies how email should be routed with the Simple Mail Transfer Protocol.

CNAME record

A CNAME record or Canonical Name record is a type of resource record in the Domain Name System (DNS) that specifies that the domain name is an alias of another, canonical domain name. This helps when running multiple services (like an FTP server and a webserver; each running on different ports) from a single IP address.

Each service can then have its own entry in DNS (like ftp.example.com. and www.example.com.). Network administrators also use CNAMEs when running multiple HTTP servers on the same port, with different names, on the same physical host.

AAAA record

A AAAA record (quad-A record) maps hostname to 128-bit IPv6 address. This type of record becomes more important as IPv6 comes into play. We have, also, A6 records which are experimental at this moment, but it is high probability that they will replace current quad-A records.

As we mentioned before, this are most common RRs used. List of all RRs can be found on IANA site.

In next part of tutorial we will explain what are zone files and how to write a zone file.

See U! :)