CNAME check: test a CNAME chain and its target
Follow the CNAME of a domain or subdomain step by step to its IP address and spot dangling records that would let others take over your subdomain.
Check CNAME
Enter the name you want to check, usually a subdomain such as www.your-domain.co.uk or shop.your-domain.co.uk.
Lookups run through the Quad9 DNS resolver (Switzerland). We keep the checked domain and an anonymised IP address for no longer than 30 days.
How CNAME records work
What is a CNAME?
A CNAME (canonical name) makes one name an alias of another. If shop.your-domain.co.uk points via CNAME to yourshop.platform.com, DNS returns that target's IP address. When the provider changes its servers, you do not need to change anything. That is the big advantage over a fixed A record.
Chains and where they end
A CNAME can point to another CNAME. The chain must always end at a name with an A or AAAA record. Every step costs an extra lookup, so chains should stay short. If two names point at each other in a circle, the name cannot be reached at all.
Dangling CNAMEs and subdomain takeover
When you cancel a service, the CNAME often stays and points to a name that no longer exists. Whoever registers that name on the platform suddenly controls your subdomain and can, for example, show phishing pages under your domain. Our check spots such dangling CNAMEs.
Common CNAME mistakes
CNAME on the main domain
A CNAME is not allowed on your-domain.co.uk itself, because SOA and NS records must sit there. Use an A record or, if your DNS provider supports it, ALIAS or ANAME.
Dangling CNAME after cancelling
Delete CNAMEs straight away when you cancel a service such as a shop, a help desk or a landing page platform.
CNAME next to other records
A name with a CNAME must not have any other records, such as MX or TXT. Many DNS interfaces prevent this, some do not.
Frequently asked questions
Enter the name above, for example www.your-domain.co.uk. The CNAME check shows the complete chain to the IP address and warns about loops, chains that are too long and dangling targets.
Use an A record when you know the IP address and it rarely changes. Use a CNAME when a service provider gives you a hostname, for example for a shop, CDN or newsletter tracking.
A CNAME rules out every other record for the same name. But the main domain must have SOA and NS, and usually MX too. Some DNS providers offer ALIAS or ANAME records for this, which work like a CNAME but are served as an A record.
If your CNAME points to a name on a platform that no longer exists, someone else can register it there. From then on, your subdomain serves their content. So delete dangling CNAMEs straight away.
There is no fixed limit, but many resolvers give up after about eight steps. Every step takes time. More than two or three hops are rarely needed.
Because CNAMEs usually sit on subdomains, such as www. Check exactly the name that is set up as an alias.
