DNS TTL Controls How Long Resolvers Cache Records
When you update a DNS record, the change doesn't propagate instantly — resolvers around the world keep serving the old value until the TTL (Time To Live) expires.
How It Works
Every DNS record has a TTL value in seconds. When a resolver fetches a record,
it caches it for that many seconds before checking again. A TTL of 3600 means
any resolver that looked up your domain in the last hour may still be serving
the old IP — regardless of what you've set at your registrar.
# Check a record's TTL with dig
dig +noall +answer markgravestock.github.io
# Output includes TTL in the second column:
# markgravestock.github.io. 3600 IN A 185.199.108.153
Practical implication: If you're planning a migration, lower the TTL to
something like 300 (5 minutes) at least one TTL period before the change.
That way, after you update the record, propagation is fast.