About dns lookup
DNS translates domain names into the addresses computers use. A lookup shows the records that a domain publishes.
Common record types
- A and AAAA: the IPv4 and IPv6 addresses of the site.
- CNAME: an alias pointing to another name.
- MX: where email is delivered.
- TXT: free text used for SPF, DKIM and verification.
- NS: the name servers that answer for the domain.
Caching
Records are cached for a time set by their TTL, so changes may take a while to be seen everywhere.
A worked example
Looking up example.com might show A records for the web server, MX records for the mail provider and a TXT record containing an SPF policy such as v=spf1 include:_spf.google.com ~all. Comparing these with your provider's instructions quickly shows what is wrong when a site or email is not working.
Common problems
- A missing www record, so only one form of the address works.
- An old A record that still points to a previous host.
- Conflicting CNAME and other records on the same name.
