DNS propagation
The window of time during which a DNS change has been made at the authoritative server but not yet reached every recursive resolver. Usually minutes to hours.
DNS propagation is the lag between "I updated my DNS record" and "every resolver on the internet returns the new value." It's not a real network event; it's the natural consequence of recursive resolvers caching old answers until their TTL expires.
Why it "takes time"
Every recursive resolver on the internet (your ISP's, Google's 8.8.8.8, Cloudflare's 1.1.1.1, your office network's) caches the answers they get. They cache for the TTL set on each record. If example.com has a TTL of 86400 (24 hours), some resolvers will keep serving the old value for up to 24 hours after you change it.
The change itself happens instantly on the authoritative server. The "propagation" is just the slow drain of stale cache entries.
Practical timing
| TTL on the changed record | Worst-case propagation |
|---|---|
| 60 seconds | 1–2 minutes |
| 300 seconds | 5–10 minutes |
| 3600 seconds | 1–2 hours |
| 86400 seconds | 24–48 hours |
The worst case is roughly "TTL × 2" because some resolvers don't honor TTLs strictly.
How to make DNS changes faster
- Lower the TTL before the change. A day before you plan to change a record, lower its TTL to 60 seconds. After 24 hours, every resolver has refreshed and is now caching with a short TTL. Make the change; resolvers update within minutes. After it's stable, raise the TTL back up.
- Check from multiple regions. Tools like dnschecker.org show what different resolvers see right now. If most are still showing the old value, propagation isn't done.
- Bypass the cache on your test machine.
dig +trace example.comqueries from the root and bypasses your local cache.
What you can tell your customers
When a customer adds a custom domain to your SaaS, the change is on their DNS provider's authoritative server immediately. The wait is for the rest of the internet to refresh. "Usually under 5 minutes, occasionally up to an hour" is a fair generic answer.