A CNAME record makes its owner an alias of another domain name. It changes
DNS name resolution; it is not an HTTP redirect and does not alter the URL in a
browser.
Purpose and type code
IANA registers CNAME as type code 5
[1]. RFC 1035
defines its RDATA as one canonical domain name
[3]. When a resolver
encounters the alias while answering another type, it follows the target name
and continues resolution
[2].
Presentation format
www.example.com. 300 IN CNAME app.example.net.Both names are absolute because they end in dots. The owner is the alias;
app.example.net. is the target. The target may be outside the owner’s zone.
Owner-name and coexistence rules
A CNAME owner may not have other ordinary data. RFC 2181 describes the owner as having one CNAME or having one or more non-CNAME records, but not both [4]. Do not add A, AAAA, MX, TXT, or NS data at the same alias owner.
A zone apex already needs SOA and NS records, so a standard CNAME cannot be placed there. Some DNS providers offer flattening or proprietary alias records at an apex. Those features synthesize or resolve answers using provider behavior; they are not standard CNAME records.
Avoid chains and loops. A target should resolve to useful terminal data, not point back to the alias.
Caching and changes
The CNAME RRset and the target’s terminal RRsets have their own TTLs. A resolver can cache both layers. Changing the target therefore does not guarantee that every cached address changes at the same moment.
Security and operational limits
A CNAME delegates resolution of the alias to another name’s data. It does not transfer domain ownership, issue a certificate, configure an HTTP host, or prove the target service accepts the alias. Removing a vendor dependency before removing the alias can also create a dangling reference.
Verify
Query the alias for CNAME, then follow the target to its terminal A, AAAA, or other requested data. Capture every owner, target, TTL, and authoritative boundary. Test TLS and the application using the original alias hostname.
Next step
Read the NS record reference to distinguish an alias from delegation and zone-authority data.