Wildcard DNS

A DNS configuration that uses an asterisk (*) to point all subdomains to a single IP address with one record, enabling efficient management of large numbers of subdomains.

Dec 4, 2025 · About 1 min read

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Wildcard DNS is a DNS record configuration that uses an asterisk (*) in the hostname field to direct any subdomain to the same IP address or domain with a single record. Setting "*.example.com" routes abc.example.com, xyz.example.com, and anything.example.com to the same server.

The configuration is as simple as "*.example.com A 93.184.216.34." If an explicit record exists for a specific subdomain, it takes precedence; the wildcard acts as a fallback.

In URL shortening services, wildcard DNS enables per-user custom subdomains. Assigning "user1.short.example.com" and "user2.short.example.com" to individual users requires no per-subdomain DNS records when a wildcard is in place. The server inspects the Host header to identify the user.

SaaS platforms such as Shopify and WordPress.com rely on wildcard DNS to provision customer subdomains at scale.

A key caveat is that wildcard DNS accepts requests for any subdomain, including non-existent ones. The server must validate the requested hostname and return an appropriate error page for unknown subdomains. Combining wildcard DNS with a wildcard SSL certificate (*.example.com) enables HTTPS across all subdomains. You can find related books on Amazon.

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Related Terms

DNS Resolution

The process of translating a human-readable domain name into the IP address of the server hosting the website.

A Record

A DNS record that maps a domain name to an IPv4 address. The foundational building block of web hosting.

CNAME Record

A DNS record that maps one domain name to another, commonly used to point custom domains to URL shortening services.

Custom Domain

A privately owned domain name used with a URL shortening service instead of the service's default domain.

Subdomain

A prefix added before the main domain name, used to organize different sections or services of a website.

Subdomain Takeover

An attack where a third party hijacks a subdomain with orphaned CNAME records, exploiting the trust of the legitimate domain.

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FAQ

When is wildcard DNS used?

It is common in SaaS platforms that assign subdomains per customer, multi-tenant applications, and URL shortening services with custom domain features. It eliminates the need to create individual DNS records for each subdomain.

What are the security risks of wildcard DNS?

Because any subdomain resolves to your server, requests for non-existent subdomains also arrive. The server must validate hostnames and return a 404 for unrecognized subdomains.

Do I need a wildcard SSL certificate?

If you use wildcard DNS and want HTTPS on every subdomain, a wildcard SSL certificate (*.example.com) is required. You can obtain one for free from Let's Encrypt.

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