A CNAME record is a DNS record that aliases one domain name to another. For example, the track.dnscheck.co CNAME record maps to mandrillapp.com.
CNAME records are also called "aliases" and "canonical name records".
A CNAME record's FQDN (fully qualified domain name) cannot be the same as any other DNS record's FQDN. For example, creating an MX record for track.dnscheck.co is invalid since a CNAME record by that name already exists. This restriction exists both to prevent contradictory information from being present in DNS, and to allow the use of cached CNAME records without performing additional queries. Similarly, you cannot have more than one CNAME record for any FQDN.
RFC 1034 and RFC 2181 define CNAME records.
DNS Check can monitor your CNAME records, and notify you if they become unresolvable, or start aliasing to the wrong domain name.
Fields
Here are the fields that make up a CNAME record:
| Field | Description | Example |
|---|---|---|
| Name | A fully qualified domain name (FQDN). | track.dnscheck.co. |
| Type | The DNS record type. Always set to "CNAME". | CNAME |
| Value | The fully qualified domain name that the Name aliases. | mandrillapp.com. |
DNS Zone File Examples
Here's an example of how a CNAME record which uses the example values from this page's "Fields" section looks in a DNS zone file:
; Name Type VALUE
track.dnscheck.co. CNAME mandrillapp.com.
The name ends in a period in the above example, so it's a fully qualified domain name.
Alternatively, you can create a CNAME record that's relative to the zone file's $ORIGIN. Here's an example of how to do this using the example values from this page's "Fields" section:
$ORIGIN dnscheck.co.
; Name Type VALUE
track CNAME mandrillapp.com.
Additional Resources
- RFC 1034 - section 3.62 (Aliases and canonical names) provides the initial definition for CNAME records.
- RFC 2181 - this RFC clarifies CNAME records. Section 10.1 (CNAME resource records), in particular, clarifies CNAME resource record terminology.