CNAME Record Lookup Tool
CNAME Lookup is a free tool used to find the canonical name (the true domain) that an alias domain or subdomain points to. It is essential for verifying CDN and cloud service configurations.
Find out where a subdomain is pointing. Verify aliases for services like Heroku, AWS CloudFront, or Shopify.
Type a domain to check DNS records.
Understanding CNAME (Canonical Name) Records
In the Domain Name System (DNS), a CNAME (Canonical Name) record is a type of resource record used to map one domain name (an alias) to another (the canonical name). Unlike an A record, which maps a hostname directly to an IP address, a CNAME record creates a pointer that directs resolvers to look up the target domain instead.
This aliasing mechanism is incredibly powerful for web administrators. It allows multiple services—like your website, your blog, and your customer support portal—to all point to a single central hub. If the IP address of that hub changes, you only need to update one A record, and all your CNAME aliases will automatically follow.
The Alias Chain
Think of a CNAME as a forwarding address. When a user requests blog.example.com, the DNS server replies: "I don't have an IP for that, but you can find it at ghs.googlehosted.com." The user's computer then performs a second lookup for the Google host to get the final IP.
Real-World Applications
Cloud Services & CDNs
When using Shopify, Heroku, or AWS CloudFront, they provide you with a long system-generated domain. You use a CNAME to map your pretty domain (www.yoursite.com) to their infrastructure.
SSL/TLS Validation
Certificate Authorities (like Let's Encrypt or DigiCert) often ask you to add a specific CNAME record to your DNS. Use our SSL Checker to verify your final certificate status.
Simplified Migration
Moving hosting? If you use CNAMEs for subdomains, you only need to change the A record of the target host. Monitor the switch with our DNS Propagation tool.
External Mail Filters
Some security services require a CNAME for mail.yourdomain.com. Ensure your email routing is correct by checking your MX records as well.
The RFC 1912 Restriction: No CNAME at the Apex
One of the most frequent mistakes in DNS configuration is attempting to set a CNAME for the root domain (e.g., trying to point example.com directly to a store address).
Why is this forbidden?
According to RFC 1912, if a CNAME record is present at a node, no other data should be present. However, the root of a domain (the apex) must have other records to function, such as SOA (Start of Authority) and NS (Name Server) records. If you place a CNAME at the apex, it makes the rest of the records invisible, effectively breaking your domain.
CNAME Record FAQ
Can a CNAME point to an IP address?
No. This is a common point of confusion. A CNAME must always point to another hostname. If you want to point a subdomain directly to an IP address, you must use an A record (for IPv4) or an AAAA record (for IPv6).
Does a CNAME slow down my website?
Technically, yes, but usually by an imperceptible amount. Each CNAME in a chain requires an additional DNS lookup. This is why it is best to avoid "CNAME Chaining" (where Alias A points to Alias B, which points to Alias C). Keep your chains short for optimal performance.
What is CNAME Flattening?
CNAME Flattening is a feature offered by some managed DNS providers. At the edge, the provider follows the CNAME chain to its final IP address and serves that IP directly to the user as if it were an A record. This allows CNAME-like behavior at the domain root while remaining RFC compliant.
Can I use CNAME for MX records?
No. RFC 2181 explicitly states that the target of an MX record cannot be a CNAME. Mail servers are required to ignore CNAME aliases when routing email, which can lead to rejected messages or delivery failures.
Pro Tip: When setting up a new service via CNAME, set the TTL (Time to Live) to a low value (like 5 minutes) during the initial testing phase. This allows you to revert any mistakes quickly. Once everything is working, increase it to 1 hour (3600s) to reduce DNS overhead.