The CNAME record is one of the first things you will encounter as you begin to learn more about DNS. Whether you are a novice just delving into the intricacies of DNS or a seasoned professional looking to better understand a specific type of DNS record, this article will bring you up to speed on what a CNAME record is, why it matters, and how to create one for your domain name.

Key Takeaways

A CNAME record maps one hostname to another, allowing multiple hosts to share the same IP address.
Misconfigured CNAME records can lead to security vulnerabilities such as subdomain takeover.
The DNS handling process for CNAME records involves additional lookups to resolve to the canonical name’s IP address.
CNAME records are useful for mapping various services and subdomains back to a main domain.
Understanding the differences between CNAME, A records, and Alias records is essential for effective DNS management.

What is a CNAME Record?

A DNS CNAME record is a record type available in the DNS zone that specifies the canonical name for a domain, which can either be an alias for another domain or a subdomain of the main domain.

It maps one hostname to another. This means that you can have multiple hosts with the same IP address, but each with a different name.

A CNAME record example would be, www.mydomain.com being mapped to www1.mydomain.com and www2.mydomain.com so that they all resolve to the same IP address.

Subdomains such as mail and www may have their own DNS records, called CNAMEs, which link them to the content-hosting parent domains. However, if a CNAME record is left misconfigured or abandoned, it can result in a dangling DNS record, potentially exposing the subdomain to security risks like subdomain takeover.

Another CNAME record example shows how the record can map the alias address www.mydomain.com to the canonical address mydomain.com — where nothing has changed about where visitors go: they are still directed towards whatever destination is specified by the actual A records for mydomain.com (which must be kept up-to-date).

The canonical name (CNAME) records are also referred to as “true names” or “canonical names.” It’s because a CNAME record maps an alias name to its true, canonical counterpart.

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How to Create a CNAME Record in Your DNS Step-by-Step

To create a CNAME record for your domain, follow these steps:

Go to the DNS management console.
Click “A Record,” then select “CNAME” from the list of records that appears.
Enter the domain name for which you want to create a CNAME record.
Enter the hostname that will be treated as a subdomain.
Enter TTL (Time to Live) which is the amount of time your record will stay in the cache on systems requesting it.
For systems with a static IP address, the recommended TTL is 1800 or higher. For dynamic IP addresses, use a TTL of 1800 or less.
Select “Create” from the bottom right corner of your screen after filling out all fields to save changes and create your new record.

If you already have a CNAME record published on your DNS, you can perform a CNAME record check using our free CNAME checker tool.

How do DNS CNAME Records work?

A CNAME record points to its canonical name (the true name of the domain). So when you set a CNAME record for your blog, it will return the IP address for your blog (mydomain.com) via its A record.

When you create a subdomain like www.blog.mydomain.com and set it as an alias to the root domain name, then a subdomain like www.blog.mydomain.com will have a CNAME record that points to the root domain mydomain.com

When a DNS server looks up for www.blog.mydomain.com using its A record, it will trigger another lookup using CNAME since this is a subdomain of mydomain.com. This will restart the query using the canonical name and return the IP address for mydomain.com via its A record.

*Note: If a host’s IP address changes, it is only necessary to update the DNS A record for the root domain. All CNAME records, including those of the alias or subdomains, will automatically change when changes are made to the root. Refer to the table below for a better understanding:

(sub)Domain / Hostname	Record Type	Target / Destination
mydomain.com	A	333.444.555.111
www.blog.mydomain.com	CNAME	mydomain.com
ftp.mydomain.com	CNAME	mydomain.com
mail.mydomain.com	CNAME	mydomain.com

Main Uses of DNS CNAME Records

A CNAME record is a type of DNS record that has two fields, the canonical name, and the aliases. It is used to:

direct a group of websites that are owned by the same entity or organization to the entity’s main site
map multiple hostnames for different network services like email or (FTP), each pointing back to the parent domain
create a subdomain for each customer on the provider’s domain (self-service), and use CNAME records to point those subdomains back to the customers’ root domains
point each country’s version of your site to the main domain
set up Content Delivery Network (CDN) by adding the address of CDN as a CNAME record for your website’s origin server–thus ensuring a user trying to access resources on the server is redirected to the CDN, which in turn loads resources from your CDN.

DNS Handling Process of CNAME Records

Consider the example domain PowerDMARC.com: if that is our root, www.powerdmarc.com would map to a CNAME record called “PowerDMARC.com. Here’s how the DNS handling process will work:

Name	Type	Value
www.powerdmarc.com	CNAME	powerdmarc.com
powerdmarc.com	A	172.66.43.156

A DNS client requests www.powerdmarc.com, creating a DNS request in the process
When this request is made, the DNS resolver looks up which Authoritative Name Server holds the zone file for powerdmarc.com and retrieves any matching records from that file.
The DNS client is returned with a CNAME record.
The DNS client realizes that www.powerdmarc.com is an alias, and it issues a new DNS query for the root domain powerdmarc.com
The DNS resolver returns the A record for powerdmarc.com, which contains its IP address.
The DNS client successfully connects to powerdmarc.com via its IP address.

CNAME Record vs A Record vs Alias Record

A record, CNAME record, and Alias record are three DNS records that are used in a DNS infrastructure. Each of these records has its function and purpose. It is important to understand the differences between these three records so you can use them effectively. Let’s look at how each one works.

➜ CNAME Record maps a hostname to another hostname but does not allow other DNS records on the same hostname (such as MX Records).

➜ Alias Record is similar to a CNAME record in that it maps one hostname name to another hostname—but it does allow other DNS records on the same hostname. Because of this addition, it is not possible to apply ALIASES at the apex DNS zone level.

➜ A Record is a single-label mapping between a hostname and one or more IP addresses. The A record maps a single hostname (the label) to one or more IP addresses (the values).

DKIM CNAME Records

Some email vendors may require you to publish a DKIM CNAME record on your DNS for source alignment purposes.

An example of this is when you want to enable office 365 DKIM record.

CNAME Record and 301/302 Redirects: Are They The Same?

Both CNAME records and 301 redirects are used by web browsers to direct users from one domain to another via an intermediary domain. However, there’s a big difference between the two:

A CNAME record maps an existing hostname to another hostname within the same FQDN, while a 301 redirect sends the request to the server that hosts your website.

In other words, the CNAME record points the domain name or subdomain of your site to the IP address of the destination hostname, which means it’s not redirecting; it’s just pointing.

About
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Ahona Rudra

Domain & Email Security Expert at PowerDMARC

Ahona is the Marketing Manager at PowerDMARC, with 5+ years of experience in writing about cybersecurity topics, specializing in domain and email security. Ahona holds a post-graduation degree in Journalism and Communications, solidifying her career in the security sector since 2019.

What is a DNS CNAME Record?