How CNAME works
If blog.example.com has a CNAME record pointing to example.com, the resolver that receives it continues the lookup for example.com — finds its A record (or AAAA) and returns the final address. This lets one canonical domain serve many aliases, and changing the IP address means editing a single place.
Rules of use
CNAME has some important limitations:
- Alias only — a CNAME cannot be set for the root domain (example.com), usually only for subdomains.
- Not combinable — a name cannot have a CNAME together with other records (such as MX or TXT).
- Chains — a CNAME can point to another CNAME, but long chains increase the time to resolve.
CNAME is handy for pointing subdomains at external services and a CDN without tracking their IP addresses by hand.
