NETWORK NOTES

DNS and cached answers

The Domain Name System maps names to records. An A record contains an IPv4 address; an AAAA record contains an IPv6 address. A CNAME points to another name rather than directly to an address.

Why an update is not immediate

Resolvers cache answers for their time to live, or TTL. A resolver can also cache a negative answer when a name did not exist. Different devices may therefore see a change at different times.

Read the answer

nslookup example.com
dig example.com A
dig example.com AAAA

Compare the answer with the authoritative records. A successful DNS lookup does not prove that the destination is reachable.

IPv4 and IPv6

Check both address families. A working IPv4 service with a stale AAAA record can fail on networks that prefer IPv6.