DNS - CNAME (Canonical Name) record (Alias)

1 - About

A CNAME (Canonical Name) is a type of DNS record that maps one domain name to another name.

It brings a Domain Name Alias functionality (synonym).

With a CNAME, no other record type can be set with the same name.

It means that you shouldn't create a CNAME for your apex domain because the apex domain is generally also set:

  • in the MX record in order to receive email
  • or other validation TXT records (SPF, …)

When a DNS resolver encounters a CNAME record:

  • it will query the server again using the result of the CNAME as input
  • until it found an IP.
You can achieve the same alias functionality with the alias record but faster because there is only one query needed.

3 - Example

On the below domain data, we see:

NAME                    TYPE   VALUE
bar.example.com.        CNAME  foo.example.com.
foo.example.com.        A

When a DNS query is performed against bar.example.com, the resolver:

  • will get a CNAME record with the value foo.example.com
  • will query the domain table again with the value foo.example.com and get an A record
  • and will return the IP

4 - Usage

5 - Documentation / Reference

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