DNS propagation is the process by which a record change spreads across resolvers worldwide. Normally, it follows TTL: after cache expiration, resolvers fetch the new value. But sometimes propagation seems blocked: some regions or ISPs still show the old IP days after the change. Causes vary: residual TTL, aggressive ISP cache, NS not updated, or zone problem.
Symptoms of Blocked Propagation
- Some users access new site, others the old one
- Tests from different regions show different IPs
- Change was made longer ago than the TTL
- A specific ISP or country remains stuck on old value
Causes of Blocking
- Underestimated TTL: TTL was longer than expected, or intermediate caches add their own retention.
- NS not updated: You changed the record at the wrong provider, or NS point to an unupdated zone.
- Aggressive ISP cache: Some ISPs implement minimum TTL or cache beyond authorized TTL.
Propagation Diagnosis
- Test from multiple locations: use dnschecker.org or whatsmydns.net
- Query your NS directly: dig @ns1.yourdns.com example.com to confirm source.
- Verify ALL your NS return the same value (synchronized secondaries).
- For a specific ISP, ask a user from that ISP to flush their local cache.
Propagation Tracking with MoniTao
MoniTao monitors propagation worldwide:
- Verification from multiple geographic points of presence
- Detection of inconsistencies between regions
- Alert if propagation takes longer than expected
Ensuring Good Propagation
- Reduce TTL BEFORE the change, not during
- Verify all NS are synchronized before declaring migration complete
- Keep old server active for 48h after the change
- Communicate a 24-48h timeframe even if TTL is shorter
FAQ - Blocked Propagation
How long does normal propagation take?
Depends on TTL. With 3600s (1h) TTL, 95% of users see change in 1-2h. 100% can take 24-48h.
Why is a specific country blocked?
Local ISPs may have different cache policies. Some countries also have centralized resolvers.
Can I speed up propagation?
Not directly. You can contact a specific ISP to flush their cache, but they rarely accept.
Can propagation fail permanently?
No, all caches eventually expire. If it persists for days, verify NS are correct at registrar level.
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