Domains and DNS

What is a CNAME record, and how is it different from an A record?

CNAME and A records look interchangeable until the day you try to put a CNAME on your root domain, and your provider refuses, and nobody can tell you why.

A CNAME (Canonical Name) record points one host name at another host name; an A record points a host name at an IPv4 address. The rule that matters in practice is that a name with a CNAME cannot have any other record of any type — so you cannot put a CNAME on the apex of your domain, because the apex must already carry NS and SOA records. That is why www.example.com can be a CNAME and example.com cannot, and why providers offer ALIAS, ANAME or “CNAME flattening” to fake the effect at the apex.

Worked out 2026-09-11 (IST) · standard DNS behaviour as specified in RFC 1034 and RFC 2181

The record types you will actually meet

What each record answers
Record	Question it answers	Value it holds
A	What IPv4 address serves this name?	93.184.216.34
AAAA	What IPv6 address serves this name?	2606:2800:220:1:248:1893:25c8:1946
CNAME	What other name should I look up instead?	target.example.net.
MX	Which server takes email for this domain?	10 mail.example.com.
NS	Which name servers are authoritative here?	ns1.example.com.
TXT	What arbitrary text is published here?	v=spf1 include:_spf.google.com ~all
SOA	Who owns this zone and how should it be cached?	Serial, refresh, retry, expire, minimum
SRV	Which host and port run this service?	_sip._tcp 10 60 5060 sip.example.com.
CAA	Which certificate authorities may issue for this name?	0 issue "letsencrypt.org"

The coexistence rule, stated exactly

What may sit alongside what
At one name	Allowed?	Why
A + AAAA	Yes	Different address families for the same host
A + TXT	Yes	TXT carries verification strings, not addressing
A + MX	Yes	A web server and a mail route can share a name
CNAME + anything else	No	RFC 1034: a CNAME replaces the name entirely
CNAME at the zone apex	No	The apex must carry NS and SOA
CNAME at a subdomain	Yes	Nothing else is required to exist there
CNAME pointing at a CNAME	Legal but discouraged	Each hop costs a lookup; resolvers cap the chain

What to use, when

Decision table
You want to	Use
Point www at a hosting platform that gives you a host name	CNAME on www
Point your root domain at a platform that gives you a host name	ALIAS/ANAME, or the platform's A records
Point a name at a fixed server you control	A record (plus AAAA if you have IPv6)
Verify ownership with Google, Microsoft or a SaaS tool	TXT record, occasionally a CNAME they specify
Send visitors from an old domain to a new one	HTTP 301 redirect, not DNS
Restrict which CA may issue certificates for you	CAA record

Whatever you change, the wait afterwards is set by the TTL on the record you replaced, not by how fast your provider applies the edit.

Sources: IETF RFC 1034 and RFC 1035 (domain names), RFC 2181 (clarifications to the DNS specification), RFC 5321 (SMTP) and RFC 7505 (null MX).

Check your own numbers

See which of a domain's names are aliases and which resolve directly.

DNS LookupA, AAAA, MX, NS, TXT, CNAME and SOA records, live from the resolver.

Frequently asked

Why does my DNS provider refuse a CNAME on the root domain?

Because the root of your zone already has NS and SOA records, and RFC 1034 forbids a CNAME from coexisting with any other record at the same name. It is not a limitation of your provider - a zone that broke that rule would be rejected or would resolve inconsistently. Providers that appear to allow it are running ALIAS or CNAME flattening, which resolves the target on their side and publishes a normal A record.

Is a CNAME slower than an A record?

Marginally, and almost never enough to notice. A CNAME costs the resolver one extra step because it must look up the target after following the alias, though most authoritative servers return both in a single response. Chained CNAMEs - an alias pointing at another alias - are the version worth avoiding; each hop is another round trip and resolvers cap how many they will follow.

Can an MX or NS record point at a CNAME?

No. RFC 2181 is explicit that MX and NS targets must be real host names with address records, not aliases. Doing it anyway produces intermittent failures: some senders and resolvers follow the alias, others treat the record as broken, and you end up debugging a fault that only affects some of your correspondents.

What is the difference between CNAME and a redirect?

A CNAME operates in DNS and is invisible to the browser - the address bar keeps showing the name you typed, and the target server must be configured to answer for it. A redirect operates in HTTP, returns a 301 or 302, and changes the address bar. If you want visitors to end up on a different URL, you want a redirect; if you want a different server to answer for the same URL, you want a CNAME.

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