What is a CNAME Record?

This article explains what a CNAME record is, as well as some common limitations of this record type from a DNS perspective.

Eric Johnson avatar
Written by Eric Johnson
Updated over a week ago

What is a CNAME Record?

A CNAME record is a type of DNS (Domain Name System) record that is used to associate a domain name with another domain name.

When a CNAME record is created for a domain name, it essentially maps the domain name to another domain name (called the canonical name), which serves as its alias. This means that any requests for the original domain name will be automatically redirected to the canonical name.

For example, suppose you have a website called "www.example.com" and you want to create a subdomain called "blog.example.com" that points to a different server. Instead of creating a new A record for "blog.example.com", you could create a CNAME record that points "blog.example.com" to the canonical name "www.example.com". This would mean that any requests for "blog.example.com" would be automatically redirected to "www.example.com".

Common Limitations of CNAME Records

While CNAME records are useful for aliasing one domain name to another, there are some common limitations to consider:

  1. CNAME records can only point to other domain names and not to IP addresses. Also, using a CNAME record can affect website performance because it requires an additional DNS lookup, which can cause a slight delay in loading the website.

  2. Cannot be used for the root domain: CNAME records cannot be used for the root domain (i.e., the domain name without any subdomains). This means that if you want to alias the root domain to another domain, you will need to use another type of record, such as an A or ALIAS record.

  3. Can negatively impact performance: When a client requests a CNAME record, the DNS server must perform an additional lookup to resolve the canonical name. This can add latency and potentially negatively impact performance, especially if multiple CNAME records are chained together.

  4. Can create issues with SSL certificates: When using a CNAME record to alias one domain to another, any SSL certificates associated with the original domain may not be valid for the new domain. This can create issues with SSL certificate validation, resulting in security warnings for users.

  5. Not supported by some DNS providers: While CNAME records are a standard DNS record type, some DNS providers may not support them or may impose additional limitations on their use.

  6. Can cause issues with email delivery: Using a CNAME record for a domain that is used for email can create issues with email delivery, as some mail servers may not properly handle CNAME records in DNS lookups. In this case, it may be necessary to use other record types, such as MX or A records, to ensure proper email delivery.

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