A wildcard DNS record is a record whose leftmost label is *. It matches queries for names under the zone that do not already exist, so *.example.com can answer for anything.example.com.
Why it matters
Wildcards support multi-tenant apps that create a subdomain per customer, catch-all setups and development environments. They also have side effects. A wildcard hides typos, because misspelled subdomains resolve instead of returning NXDOMAIN, and it can make subdomain enumeration and monitoring misleading. Explicit records always take precedence, and a wildcard does not match the apex name itself. It also does not apply to a name that has any record of another type, which surprises many people.
Example
*.example.com. 300 IN A 203.0.113.10
www.example.com. 300 IN A 203.0.113.20shop.example.com returns 203.0.113.10, while www.example.com returns its own explicit record. example.com is not covered.
Common mistakes
- Expecting
*.example.comto cover the bare domain. - Pairing a wildcard record with a wildcard certificate and forgetting the apex needs its own coverage.
- Pointing a wildcard at a service you later cancel, creating takeover risk.
Related
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