CNAME Record

A CNAME (Canonical Name) record maps an alias domain name to a different, canonical domain name. The DNS resolver follows the CNAME target and returns whatever records exist at the canonical name.

How CNAME Records Work

When a resolver queries a name that has a CNAME record, it does not get an IP address directly. Instead, it gets the canonical name and must perform a second lookup to resolve that name to an address. This creates a lookup chain.

blog.example.com.   CNAME   example.github.io.
example.github.io.  A       185.199.108.153

In this example, a query for blog.example.com returns the CNAME pointing to example.github.io. The resolver then queries for the A record of example.github.io and returns that IP to the client.

When to Use a CNAME

• Subdomains pointing to hosting providers such as GitHub Pages, Netlify, or Vercel. The provider controls the IP, and a CNAME lets them change it without requiring updates on your side.
• CDN configuration where your subdomain needs to resolve to a CDN-provided hostname like d1234.cloudfront.net.
• SaaS custom domains where the vendor asks you to CNAME a subdomain to their platform for verification and routing.

Restrictions

• Cannot exist at the zone apex. RFC 1034 prohibits a CNAME at the root of a zone (e.g., example.com) because a CNAME cannot coexist with SOA and NS records, which must exist at the apex. Some providers offer proprietary workarounds like ALIAS or ANAME records.
• Cannot coexist with other record types. If a name has a CNAME, it must not have any other records (A, MX, TXT, etc.) at the same name. This is the most commonly violated rule.
• Adds lookup latency. Each CNAME introduces an extra DNS resolution step. In practice, most resolvers handle this quickly, but chaining multiple CNAMEs compounds the delay.

Common Mistakes

• CNAME at the apex. Setting example.com CNAME provider.com breaks DNS for the entire zone because it conflicts with SOA and NS records. Use an A record or your provider's ALIAS/ANAME feature instead.
• CNAME chains. Pointing a CNAME to another CNAME that points to yet another CNAME creates fragile, slow resolution paths. Keep chains to a single hop.
• MX alongside CNAME. Adding an MX record at a name that already has a CNAME is invalid. Mail delivery will fail unpredictably because resolvers may return either the CNAME or the MX depending on implementation.

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