Guide
Following CNAME aliases to the real address
A CNAME record says “this name is another name for that one”. It is the tool that lets www.example.com follow a hosting provider’s address without copying it, and that lets a provider move servers without telling its customers. It also has strict rules that cause some of the most common DNS mistakes. The page shows the chain from the name you enter to the final address.
How aliases are resolved
When a resolver finds a CNAME in the answer for a name, it starts again at the target. If the target has another CNAME, it follows that, and so on until it reaches a name with the record type that was asked for, usually an A or AAAA record. The page does the same, but shows each hop separately with its TTL, so you can see which name introduced which alias and how long each part will be cached. Resolvers cut off long chains to avoid loops; the page stops after ten hops and says so.
The rules that matter
RFC 1034 and RFC 2181 say that a name with a CNAME cannot have any other record type. That is why you cannot put a CNAME where the zone’s SOA and NS records already sit, which is the apex or “naked” domain, and why adding a CNAME to a name that already has an MX or TXT record breaks them. MX and NS records must point to names that have address records, never to aliases. Following these rules avoids the quiet failures where one resolver tolerates a violation and another does not.
Reading the output
Under the heading “Alias chain for …” the page prints each step: the name, “is an alias of” and the target with its TTL. The last step is the “Final name” with the address it resolves to and its TTL. If the name is not an alias at all, the page says that it has no CNAME and shows its addresses directly. A chain that ends without an address, for instance because the target was deleted, reveals a dangling alias, a classic security issue called subdomain takeover when the target service can be claimed by someone else.
A worked example
Press Sample to look up www.github.com. The page reports that www.github.com is an alias of github.com with a TTL of 3600 seconds, then shows the final name github.com with its IPv4 address and a short TTL. Two details are worth noticing. The alias TTL is long because the alias rarely changes, and the address TTL is short because the provider may redirect traffic at any time. The addresses in the result vary; the shape of the chain is what you are meant to read.
Limits
Resolvers return a flattened answer, so the hops shown are produced by querying each name separately and may differ slightly from what a single client sees if the DNS is geographically aware. The page does not know about server-side alias features that return plain addresses at the apex. Test each name you care about, including those used for email, which should not be aliases. For all record types at once use the DNS Lookup.
Related tools
- A Record Lookup shows the addresses at the end of the chain.
- DNS Lookup lists every record type for a name.
- NS Lookup checks that name server targets are real hosts.
- BIND Zone File Generator warns when a CNAME shares a name with other records.
Checked against the current version of the CNAME Lookup on .