The domain name system, or DNS, is a global system responsible for mapping human-readable hostnames to their corresponding Internet Protocol (IP) addresses. For example, if you want to access a website using a domain name like example.com, that domain name must point to a valid IP address.
The human-readable hostname is a string of words that are easy to remember. IP addresses (IPV4), on the other hand, contain numbers separated by dots and are harder to remember. In our example above, example.com is the human-readable hostname or domain name, while 18.104.22.168 is the current IP address for example.com. Also, note that the IP address associated with a domain name may change depending on the server hosting the website.
Multiple components make up the domain name system, and DNS record types are an important part of the system. A DNS resolver does the actual work of finding the correct IP address for a hostname.
In this post, you'll learn about various DNS record types and see examples of how each record type works.
We'll start by defining what DNS record types are.
DNS record types are records that provide important information about a hostname or domain. These records include the current IP address for a domain.
Also, DNS records are stored in text files (zone files) on the authoritative DNS server. The content of a DNS record file is a string with special commands that the DNS server understands.
The following are the five major DNS record types:
The use for each of the above types varies. So let's look at more details about each DNS record type.
The A record is the most important DNS record type. The "A" in A record stands for "address." An A record shows the IP address for a specific hostname or domain. For example, a DNS record lookup for the domain example.com returns the following result:Fig. 1: DNS record lookup result.
From figure 1 above, we can see that the current IP address is 22.214.171.124. The A record only supports IPV4 addresses. Later in this post, we'll see how to point a domain to an IPV6 address using another DNS record type.
The main use of A record is for IP address lookup. Using an A record, a web browser is able to load a website using the domain name. As a result, we can access websites on the internet without knowing their IP addresses.
Another use of A record is in the domain name system-based blackhole list (DNSBL). Here, the A record is used to block mail from known spam sources.
AAAA record, just like A record, point to the IP address for a domain. However, this DNS record type is different in the sense that it points to IPV6 addresses.
IPV6 is an upgrade over IPV4 as it offers more IP addresses. As a result, IPV6 solves the issue of running out of unique IP addresses. An IPV6 address looks something like the following:
A colon separates each field in an IPV6 address.
Usage of the AAAA record for DNS resolution has great potential because it uses IPV6, which is an improvement over IPV4. Also, as the internet keeps growing and we're running out of IPV4 addresses, the potential for AAAA records is high.
AAAA records are used to resolve a domain name to the newer IPV6 protocol address.
CNAME—or, in full, "canonical name"—is a DNS record that points a domain name (an alias) to another domain. In a CNAME record, the alias doesn't point to an IP address. And the domain name that the alias points to is the canonical name. For example, the subdomain ng.example.com can point to example.com using CNAME. Here example.com points to the actual IP address using an A record.
A practical example for the use of CNAME records is running multiple subdomains for different purposes on the same server. For example, we can use ftp.example.com for file transfer protocol (FTP) and serve webpages via www.example.com. We can then use a CNAME record to point both subdomains to example.com. The main domain example.com then points to the server's IP address using an A record.
It's also possible to point a CNAME to another CNAME. However, doing so is inefficient and can lead to slow load speed and poor user experience.
A nameserver (NS) record specifies the authoritative DNS server for a domain. In other words, the NS record helps point to where internet applications like a web browser can find the IP address for a domain name. Usually, multiple nameservers are specified for a domain. For example, these could look like ns1.examplehostingprovider.com and ns2.examplehostingprovider.com.
If you've purchased a web hosting service or set up a simple website, you probably received an email with nameserver details. Those nameservers, in simple terms, connect your domain name to the actual server your site is hosted on. The nameserver contains other DNS records for the domain like an A record and MX record.
A mail exchange (MX) record, is a DNS record type that shows where emails for a domain should be routed to. In other words, an MX record makes it possible to direct emails to a mail server.
You can have multiple MX records for a single domain name. And what this means is that you can have backup email servers. The following shows an example of a domain with multiple MX records:
From the above table, the MX record with priority 10 will be the primary mail server, while the secondary server will only be used when the primary server is unavailable (or fails to send emails). The lower the priority value, the higher the actual priority.
With an MX record, it's possible to hand off emails to a dedicated email server. For example, you can decide to leave all the trouble of setting up webmail on a server you own to a specialized email provider. This comes with many benefits, including custom email clients for reading and sending emails, and improved security and spam filters. Also, you can use a service like Site24x7 to monitor and verify issues with the mail server your MX records point to.
In addition to the five DNS record types covered so far, here are some other record types:
In this post, we learned what DNS record types are. We also defined several DNS record types and saw examples of what each type is used for.
DNS makes it possible for us to use human-readable domain names to access resources on the internet. DNS records and the various record types are an important part of the domain name system.
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