Guide
Has my DNS change spread? Comparing two big resolvers
Nothing in DNS changes everywhere at once. When you edit a record, the authoritative servers know immediately, but thousands of resolvers around the world may still hold the old answer in their caches. “Propagation” is the name for those caches expiring one by one. The page helps you see where two of the biggest resolvers stand.
Why there is no single moment
Each cached answer carries a time to live (TTL) set by the zone when the resolver fetched it. A resolver that looked the record up one second before your change keeps the old data for the full TTL, while one that looked it up an hour earlier will refresh sooner. Operating systems, browsers and home routers add their own caches. The result is a patchwork: during the window, some visitors see the new site and some the old, and the same visitor may even flip between them as different resolvers answer. The worst case is the TTL that was in place before the change, not the one you set afterwards.
What the page does
Enter a domain, choose a record type (A, AAAA, CNAME, MX, NS, TXT, SOA or CAA) and press Compare resolvers. The page asks Cloudflare (1.1.1.1) and Google Public DNS (8.8.8.8) over HTTPS and shows each answer side by side: status, response time, whether DNSSEC validated, and the records with their TTLs. A banner above the two panels says whether they agree and the time of the check, for example “Both resolvers return the same A records for example.com. The records you see are consistent”. Records that differ are called out.
What agreement means
If both resolvers show the new record, the biggest share of users will see it, since a large part of the world uses one of these two or a resolver that forwards to them. It is a good sign, not proof: other providers’ resolvers, your visitors’ routers and devices may hold the old data. The reverse is more informative. If one resolver still shows the old record, you can read its remaining TTL and know the longest it can take. A TTL counting down from a few hundred seconds means a few minutes; one from 86,400 means up to a day.
A change routine that avoids surprises
- A day or more ahead, lower the TTL to 300 seconds, and wait for the old TTL to pass (the DNS TTL Calculator works out the times).
- Make the change and run this comparison until both resolvers agree.
- Test the site from a couple of networks, including mobile data.
- Raise the TTL again once you are sure.
A worked example
Press Sample to compare the A records of example.com. The page reports that both resolvers return the same records and that the result is consistent. Each panel shows two addresses with a TTL, and the two panels list them in different order with different TTLs, for example 264 and 300 seconds, because each resolver cached them at a different moment. The response times differ too, which has nothing to do with the data.
Limits
Only two resolvers can be compared. Results from a different place or network can differ, and an authoritative server that returns different answers to different clients (geo-DNS) will make the two resolvers disagree even without a stale cache. For a direct view of what one resolver returns use the DNS Lookup.
Related tools
- DNS TTL Calculator plans when to lower and raise TTLs.
- DNS Lookup shows all record types from one resolver.
- DNS Compare compares two different domains instead of two resolvers.
- NS Lookup shows which servers hold the authoritative data.
Checked against the current version of the DNS Propagation Checker on .