What is DNS Propagation?
A complete beginner's guide to understanding DNS propagation - why DNS changes don't happen instantly and what's actually going on behind the scenes.
In this article
DNS Propagation Defined
DNS propagation is the time it takes for changes to DNS records to update across all DNS servers on the internet. When you modify your domain's DNS settings (like changing your website's IP address or switching hosting providers), that update needs to spread from your DNS provider to thousands of DNS servers worldwide.
Quick Definition
DNS propagation = the time between making a DNS change and that change being visible everywhere on the internet. Typically 24-48 hours, sometimes faster, occasionally up to 72 hours.
The term "propagation" suggests that DNS changes spread outward like ripples in water. In reality, it's more about cached records expiring and being refreshed - but the effect is the same: gradual, worldwide updating of DNS information.
Simple Analogy: The Phone Book
Think of DNS like a global phone book for the internet. Every domain name (like example.com) has an "address" (IP address) listed in this phone book.
The Phone Book Analogy
You change your phone number
You update your listing in the official directory (your DNS provider).
Phone books need reprinting
Thousands of local directories around the world need to update their copies.
Some people have old copies
During this time, some people call your old number, others reach the new one.
Eventually everyone gets the update
Once all directories refresh, everyone has your new number.
This is exactly what happens with DNS. Your DNS change is made, but thousands of servers worldwide have cached (saved) your old information. Until their cache expires and they fetch the new data, some users see old information while others see new.
How DNS Propagation Works
Here's the step-by-step process of what happens when you make a DNS change:
You make a DNS change
You update a record in your DNS provider's control panel (e.g., changing an A record to point to a new IP address).
Authoritative server updates
Your DNS provider's authoritative nameserver (the "source of truth" for your domain) stores the new record. This happens almost instantly.
Caches hold old data
DNS servers worldwide (ISPs, Google DNS, Cloudflare, etc.) still have your old record cached. They won't check for updates until their cache expires.
TTL expires, servers refresh
When a server's cache expires (based on TTL - Time to Live), it queries the authoritative server and gets the new record.
Propagation complete
Once all major DNS servers have refreshed, propagation is complete. Users worldwide now see your new DNS record.
DNS Servers Involved
Understanding the different DNS servers helps explain why propagation takes time. Four types of servers work together:
Recursive Resolver
The first server your computer contacts, usually run by your ISP. It does the work of finding your domain's IP address by querying other servers. This server caches results to speed up future requests.
Root Nameserver
The top of the DNS hierarchy. It doesn't know your domain's IP, but it knows which TLD server (.com, .net, etc.) to ask next.
TLD Nameserver
Manages all domains with a specific extension (.com, .org, .net). It points to the authoritative nameserver for your specific domain.
Authoritative Nameserver
The final source of truth for your domain. This is where your DNS records actually live. When you make DNS changes, they're made here first.
Each of these servers can cache information. When you make a DNS change, it starts at the authoritative server, but all the caching servers need time to expire their old data and fetch the new records.
Why It Takes 24-48 Hours
Several factors combine to make DNS propagation take time:
TTL (Time to Live)
Every DNS record has a TTL value (in seconds) that tells servers how long to cache it. A TTL of 3600 means servers keep the cached record for 1 hour. Common TTLs range from 300 seconds (5 minutes) to 86400 seconds (24 hours). Until TTL expires, servers won't check for updates.
ISP Caching Behavior
Internet Service Providers cache DNS to reduce load and speed up browsing. Some ISPs ignore TTL values and keep records cached longer than specified. This is one of the main reasons propagation can exceed expected times.
Multiple Cache Layers
Your computer, router, ISP, and public DNS servers all maintain separate caches. Each layer needs to expire independently. Even if Google DNS updates quickly, your ISP might still have old data.
Global Distribution
There's no central "update all" button. Thousands of DNS servers worldwide operate independently. They refresh at different times based on their own schedules and cache expiry.
From my experience in web hosting support, most DNS changes propagate to major regions within 2-6 hours. The "48 hour" guideline accounts for edge cases like stubborn ISP caches or high TTL values.
Real-World Example
Let's walk through a real scenario to see DNS propagation in action:
Scenario: Moving to a New Web Host
You update your A record to point to your new host's IP address (e.g., 192.168.1.1 → 203.0.113.50)
Your authoritative nameserver has the new record. Changes here are instant.
Users on Google DNS (8.8.8.8) start seeing the new site - Google refreshes frequently.
Most users in your region see the new site. Some ISPs still serve old data.
Major global regions have updated. A few remote ISPs still lag behind.
Propagation essentially complete. 99%+ of users see the new site.
Check Your DNS Propagation Status
Use DNSFly to see how your DNS changes are propagating across 20+ global locations. Track which regions have updated and which are still caching old data.
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