When names do not resolve.
WHAT THE SYMPTOM IS
Addresses work; names do not.
Or one name fails while others work.
WHAT TO CHECK
What the name actually resolves to Whether a different resolver gives a different answer Where the nameservers point Whether the record exists at the authoritative servers
THE DIFFERENT RESOLVER TEST
Query a public resolver directly.
If it answers correctly and yours does not, the problem is caching or your resolver.
WHAT CACHING CAUSES
A change made and not visible.
Wait for the TTL, or test against a resolver that has not cached it.
WHAT TO CHECK ON YOUR DEVICE
Which resolvers it is using Its own cache, which can be cleared
WHAT TO CHECK FOR A DOMAIN
Whether it has expired Whether nameservers are set Whether records exist where the nameservers point
THE MOST COMMON CAUSE
Records added in the wrong place, because DNS is managed elsewhere.
WHAT TO VERIFY AFTER ANY FIX
From more than one resolver.
