DNS Records: A Comprehensive Guide For Beginners

A DNS record, also known as a resource record (RR), maps a domain to an IP address. DNS records contain important information about the domain’s IP address and request handling, thus serving as DNS servers’ instructions.

The resource records are physical text files written in DNS syntax and stored inside zone files. A zone file is a primary location where all the DNS records are stored for the domain. Whenever someone performs a DNS query, the servers pull information from zone files to answer it. 

Every record has an expiration date (time to live) which indicates when a DNS server will refresh that record. RRs also have a type (name and number), class and type-specific data. 

In this article, we are discussing the most common types of DNS records and their purposes. 

What is DNS?

Getting familiar with common DNS record types can help you understand your network better. However, it’s impossible to comprehend resource records unless you know what DNS is. 

The Domain Name System (DNS) is a global system that translates domain names to IP addresses.

The purpose of DNS is to make websites easily accessible to humans. Computer scientist Paul Mockapetris invented DNS in 1983 after recognizing that users would benefit from using names instead of long and complex IP addresses. 

What is an IP address? As you may already know, the web is compiled of a large network of computers, all connected to the internet. Since machines communicate using numbers, every one of those devices, including web servers, is assigned a numerical code ​​– IP address. 

The most common type of IP address, IPv4, is a string of numbers separated by dots. For example, here’s one of Google’s IPs: 172.253.123.100.

What is DNS lookup?

As you can see, IPs are not user-friendly. That’s why today we use domain names when accessing websites. The process which connects domains with machine-readable IP addresses is called DNS lookup. Here’s how it works:

1. Once you enter a website’s name, let’s say ipxo.com, into the browser’s web address bar, the lookup immediately tries to find if you have visited the website before. Your computer stores all previously visited DNS records in the DNS cache. If the lookup process finds the record data, it takes you directly to the website. 
2. The lookup sends a query to your local DNS server if this is your first time visiting the website. This server is known as a resolving name server (recursive resolver).
3. If the request can’t find DNS records on the resolving name servers, it travels to a root name server and then through a TLD server lookup. Once the lookup process obtains DNS data, your computer caches it.
4. The lookup ends by loading the website after locating the DNS record and connecting with a server storing the website. 

What is DNS propagation?

DNS propagation is the duration of time it takes for DNS records’ updates to be in full effect. If you decide to change the IP address of a specific host name, it can take up to 72h to propagate it. 

The Domain Name System is a large and complex structure. While it can access most websites within milliseconds, it is not well adapted to change. When you make any modifications on the DNS, such as editing a DNS record, you don’t know exactly when users will see the change. 

Every smallest alteration can take either several hours or even days to be propagated across the web. Why does DNS propagation take so long? Several factors come into play.

Time to Live (TTL) settings

The DNS resolvers periodically purge their DNS information and gather new data from DNS servers. The duration of time between each refresh is called time to live. The length of DNS propagation depends on the length of TTL settings. 

For instance, setting TTL for 30 minutes results in every server in the world relying on old data for half an hour until the local system refreshes DNS information again.

Internet Service Provider (ISP)

To make sure that users can access websites quickly, ISPs cache DNS records. Some ISPs retain DNS records even after the TTL period expires, causing propagation time to take longer. 

Domain name registry

A root server that extracts the Top Level Domain (TLD) from the user’s query might have a TTL of 48 hours or more to prevent overuse. That’s why if you change the authoritative name server for your website, you need to reflect the change in the root server, which might take the change longer to propagate.

If you’ve recently made changes to your DNS record, you can check DNS propagation using third-party tools, such as DNSchecker. 

List of DNS records

There are over 90 DNS record types, but you don’t have to know all of them. After all, many of the resource records aren’t even used anymore. We compiled a list of several most common DNS records you’re bound to encounter. 

NS record

Name server (NS) records are the top-most records that store a website’s domain information. When you’re querying a domain, the NS record is responsible for providing you with a list of authoritative DNS servers. Essentially, name server records allow you to find where other records are stored. 

NS records are essential for efficient DNS management because they show where the DNS zone is managed. Name servers point to a single location, and an NS record can only be changed via your hosting provider. Therefore, if you change service providers and point the domain elsewhere, DNS management moves to the new provider too. 

A record

An Address record (A Record), also known as a DNS host record, maps a domain to the physical IPv4 address of the computer hosting that domain’s services. 

Example of A record

AAAA record

AAAA records map a domain to the IPv6 address. 

Example of AAAA record

MX record

A Mail Exchanger Entry, or MX entry, is a DNS zone file record that directs emails to mail servers.

Example of MX record

CNAME record

A CNAME, or Canonical Name Record, points one domain to another domain name but never points to an IP address. 

Example of CNAME record

TXT record

DNS TXT records allow entering human-readable text into DNS. While the TXT record is intended to be read by humans, you can also put machine-readable data into it. 

Example of TXT record

Other DNS records

While much less commonly used, these DNS record types are worth noting, too. 

SRV record

A Service (SRV) record directs specific services such as instant messaging or VoIP to a separate host and port location.

Example of SRV record

PTR record

A pointer (PTR) record maps a domain name associated with an IP address for rDNS lookups. 

TLSA record

The TLSA record is used to associate a TLS (Transport Layer Security) server certificate or public key with the domain name where the record is found. 

Example of TLSA record

SPF record

A Sender Policy Framework (SPF) record helps mail servers identify whether an incoming message is trustworthy and prevent spam or email spoofing.

Example of SPF record

CERT record

The CERT records are used to provide a space in the DNS for certificates and related certificate revocation lists (CRLs). 

Example of CERT record

SOA record

A Start of Authority (SOA) record contains information about domains, such as a domain serial number, and directs how a DNS zone propagates to secondary name servers.

Example of SOA record

Conclusion

DNS records, or resource records, are a crucial part of the internet. They serve as instructions for the DNS servers, guiding them through the DNS lookup process. In short, resource records provide a user-friendly way for mapping domain names to machine-readable IP addresses. 

There are many types of DNS records, but the most common are A, AAAA, MX, CNAME and TXT records. Getting familiar with the purposes of these records will provide you with knowledge of how your network works and help manage it more efficiently. 

Knowing how every common resource record is used can also help you protect your mail server, troubleshoot errors and ensure that your website visitors see the most up-to-date version of it.