CNAME flattening is a provider feature that makes a root domain (such as example.com) behave like an alias. The authoritative server resolves the target hostname itself and returns the resulting A and AAAA records to the client, instead of a CNAME record.
Why it matters
DNS rules say a name with a CNAME cannot hold other records, and the zone apex must carry SOA, NS and often MX records, so a true CNAME there would break the zone. Yet hosting and CDN services give you a hostname, not an IP. Flattening, sold under names like ALIAS or ANAME, solves this. The trade-off is that the answer is only as fresh as the provider's resolution, and geographic steering by the target may not follow the client.
Example
A zone file entry in a provider that supports it:
example.com. 300 ALIAS mysite.cdn-provider.example.A client running dig example.com A sees ordinary A records. The record type name and behavior are provider-specific, not standard DNS, so check your provider's docs and verify the apex answers correctly.
Common mistakes
- Creating a real CNAME at the apex, which can break email and other records.
- Moving DNS providers and losing the ALIAS record, because it is not portable.
- Assuming flattened answers always match the target's regional routing.
Related
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