When to compare two names
Moving a site or mail to a new provider means copying every record across. Comparing the old and new setup before switching nameservers shows what was missed. Comparing example.com with www.example.com shows whether both point at the same servers.
- Before a nameserver move: compare a record on the old zone with the same name served by the new provider.
- After setting up a second domain: check it has the same mail and verification records as the first.
- When www works but the bare domain does not, or the other way round.
How values are compared
Both names are looked up on the same validating public resolver. Records are compared as sets, so order does not matter, and names are compared without case or the trailing dot. TXT records are compared after joining their quoted parts.
TTLs are shown but not compared: they count down in the resolver's cache, so two identical records rarely show the same TTL.
Questions
- Why does a CNAME name show A records too?
- A resolver follows the alias and returns the address records of the target, so a name with a CNAME also shows the target's addresses.
- Can I compare the same name on two different DNS providers?
- Look the name up on each provider's nameservers with the propagation checker, which asks the domain's own servers and twelve public resolvers.