DNS Propagation
DNS propagation is the time it takes for updates to DNS records to take full effect across all DNS servers on the internet. When you make changes to your domain's DNS records, those changes don't happen instantaneously everywhere. Instead, the updates gradually spread (propagate) throughout the global DNS infrastructure as cached records expire and are refreshed based on their TTL (Time to Live) values.
How it works
DNS propagation is essentially the time it takes for ISPs and DNS resolvers worldwide to update their caches with your new DNS changes. The process is governed by TTL (Time to Live) values set on DNS records, which tell DNS servers how long to cache the information before requesting fresh data from authoritative name servers.
When you visit a website, your device and various DNS servers along the way cache the DNS information to speed up future requests. Here's how propagation works:
**The Propagation Process:**
1. **Change Made**: You update a DNS record (e.g., changing your A record to point to a new server)
2. **Authoritative Update**: The change is immediately reflected on your authoritative name servers
3. **Cached Records Persist**: DNS resolvers and servers worldwide that previously cached your old record continue serving the old information until their cached copy expires
4. **TTL Expiration**: Each cached record has a TTL value (e.g., 3600 seconds = 1 hour). When the TTL expires, the cache is considered stale
5. **Cache Refresh**: The next time a DNS query is made after TTL expiration, the resolver fetches the new record from your authoritative server
6. **Gradual Propagation**: Different servers have cached your record at different times, so they'll refresh at different times, causing propagation to be gradual rather than instant
**Why It Takes Time:**
The variation in propagation time occurs because different DNS resolvers cache records at different moments, have different TTL respect policies (some ISPs ignore TTL), and serve users in different geographic regions. This means some users see the new records immediately while others may see old cached data for hours.
Key Points
- Propagation typically takes a few minutes to 48 hours, though 72 hours is possible in rare cases
- TTL (Time to Live) values determine how long DNS records are cached before being refreshed
- Changes are instant on authoritative servers but gradual across the global DNS infrastructure
- Some ISPs ignore TTL values and cache records longer than specified, extending propagation time
- Lowering TTL before making changes can speed up propagation
Common Use Cases
- Server Migration: When moving your website to a new server with a different IP address, DNS propagation determines how long before all users are directed to the new server
- DNS Provider Changes: Switching DNS providers requires updating NS records, which can take 24-48 hours to fully propagate as caches expire
- Email Server Updates: Changes to MX records when migrating email providers need to propagate before all senders route email to the new servers
- Emergency Updates: When rapid DNS changes are needed (e.g., DDoS mitigation), propagation delay means some users continue accessing old records
code Example Propagation Timeline
| Type | Host / Name | Value / Points to | TTL |
|---|---|---|---|
| Time | 00:00 - Change Made | 192.0.2.1 → 192.0.2.100 | 3600 |
| Time | 00:15 - 15 Minutes | Mixed results | — |
| Time | 01:00 - 1 Hour | Mostly propagated | — |
| Time | 24:00 - 24 Hours | Fully propagated | — |
* This example shows how a DNS change with a 1-hour TTL propagates over time across different DNS resolvers.
Frequently Asked Questions
Why does DNS propagation take so long?expand_more
DNS propagation isn't actually about the changes 'traveling' across the internet - it's about waiting for cached records to expire. Different DNS servers cached your old record at different times, and each cache has a TTL (Time to Live) that must expire before the server requests fresh data. Additionally, some ISPs ignore recommended TTL values and cache records longer, extending the apparent propagation time. The global, distributed nature of DNS means there's no single switch to flip for instant updates.
How can I speed up DNS propagation?expand_more
Lower your DNS record's TTL value 24-48 hours before making changes. For example, if your TTL is 86400 seconds (24 hours), lower it to 300 seconds (5 minutes). Wait for the old TTL to expire, then make your DNS changes. With the lower TTL, caches will refresh every 5 minutes instead of every 24 hours, dramatically speeding up propagation. After propagation is complete, you can raise the TTL back to a higher value for better performance.
Is there a way to check DNS propagation status?expand_more
Yes, several online tools let you check DNS propagation from multiple locations worldwide. Tools like whatsmydns.net, dnschecker.org, and Google's DNS checker query DNS servers in different countries and show whether they're returning your old or new records. You can also use command-line tools like
dig or nslookup to query specific DNS servers directly.Does DNS propagation affect website downtime?expand_more
Properly managed DNS changes shouldn't cause downtime. During propagation, some users access the old server while others access the new one - both should serve the website. The best practice is to keep your old server running with the same content until propagation completes. For critical changes, use techniques like lowering TTL in advance, maintaining parallel infrastructure, or using a DNS provider with instant updates to minimize any potential disruption.
Why do some people see my changes immediately while others don't?expand_more
Different users query different DNS resolvers (based on their ISP or DNS provider), and these resolvers cached your old DNS record at different times. Someone whose resolver cached your record 23 hours ago will get the new record soon, while someone whose resolver just cached it 5 minutes ago won't see the change until their cache expires. Additionally, if someone has previously visited your site, their browser or OS may have locally cached the DNS result separately, showing them old data even after global propagation.