Why DNS Changes Take Time to Propagate

Problem

You changed a DNS record, but the old value is still returned in lookups.

Top 3 Causes

1. TTL cache — Resolvers cache records for the TTL duration. A high TTL (e.g., 86400s = 24h) means up to a full day before the new value is seen everywhere.
2. Recursive resolver caching — ISP resolvers or corporate DNS may cache aggressively beyond TTL.
3. Negative caching — If a record didn’t exist before, NXDOMAIN might be cached (RFC 2308).

Diagnosis with DechoNet

• DNS Lookup — query the domain, check the A/AAAA TTL in the Records tab.
• If TTL is still high, the old value will persist until expiry.

Resolution Checklist

• Lower the TTL to 300s (5 min) before making DNS changes.
• After changing, verify with dig @8.8.8.8 example.com A from multiple resolvers.
• Wait at least one full previous-TTL cycle before assuming propagation is complete.
• After confirming propagation, restore TTL to a normal value (3600–86400s).