DNS Propagation & TTL (Beginner)

> “DNS propagation” is mostly caching. Different networks may see different answers until caches expire.

1) Why DNS changes take time

DNS answers get cached by:

• ISP resolvers
• corporate networks
• routers
• and sometimes browsers/apps

2) What TTL means

**TTL (Time To Live)** tells caches how long they may keep an answer before asking again.

3) Typical propagation times

• With a low TTL (300–900s), changes often appear in minutes.
• With a high TTL (3600–86400s), some users may see old values for hours.

4) The “works for me but not others” explanation

Your network may have refreshed DNS, while someone else is still using a cached answer.

5) Safe migration playbook (beginner-friendly)

1. **Lower TTL** 24–48 hours before a move (e.g., 300–900 seconds).

2. Update records (A/CNAME/MX) to the new target.

3. Verify from multiple networks/devices.

4. After stable, **raise TTL** again (e.g., 3600–86400 seconds).

6) Common mistakes

• Changing records at the wrong DNS host (nameservers point elsewhere).
• Switching nameservers without copying old records.
• Assuming “instant” updates while TTL is still high.

What to learn next

• Nameservers vs DNS Records
• Domains & DNS Basics
• DNS Records Explained