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What is a CNAME record?

Last updated .

A CNAME (canonical name) record says that a name is an alias for another name. A resolver that asks for the aliased name is told to look up the target instead. Hosted platforms often ask you to point www at a name they provide, so the platform can change the addresses behind it.

Definition
CNAME
A DNS record that makes one name an alias of another name, so lookups follow it to the target; it cannot coexist with other records on the same name.

The apex limit

RFC 2181 states that a name that has a CNAME may hold no other data, apart from DNSSEC records. The root of a domain (example.com) always has other records, such as SOA and NS, and usually MX, so a plain CNAME there is not valid. DNS providers offer alias, flattened or ANAME records as a workaround; they are provider features, not standard records, so check how yours behaves.

Common mistakes

Adding a CNAME where an A record already exists, creating a CNAME chain several steps long, or pointing a CNAME at a name that no longer exists, so the site stops resolving.

An example

www.example.com. 3600 IN CNAME shops.platform.example. says that www is an alias of shops.platform.example. When the platform moves its servers it changes its own records and the client’s site follows without any DNS edit. Run dig www.example.com CNAME +short to print the target. The same name cannot also hold an MX or TXT record in standard DNS, which is why a domain’s mail records stay on the bare domain while only www is an alias.

What to check

Which names are aliases, where they point, and whether the target still belongs to the platform you expect.

Sources

Read on . Standards and vendor pages change; confirm the current text before you rely on it.

Guides that use this term

  • DNS recordA DNS record is one entry in a domain’s zone that maps a name to data such as an address, a mail server or a text value. The common types and what breaks when one changes.
  • TTLTTL is the number of seconds a DNS answer may be cached. How it makes DNS changes spread slowly, how to lower it before a change and why it is a maximum, not a promise.
  • NameserverA nameserver is the server that holds a domain’s DNS records and answers queries for them. Why moving nameservers moves the whole zone and what to copy first.

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