How the comparison works
Type a domain or hostname and run the check. We find the authoritative zone it belongs to, look up every nameserver's address, and ask each address directly for its SOA record. When a server answers the same way over IPv4 and IPv6, we keep those together in one row. When a server hands back a different serial or a different timing value, it gets its own row so the odd one out stands out.
Your zonens1ns2Compare SOAWhat the serial tells you
Think of the serial as a version number for your zone. Every time you change your DNS, it should go up. When two nameservers show the same serial, they are almost certainly holding the same copy of your records. When the numbers differ, one server is behind, and the higher serial is the one a healthy secondary should catch up to.
One catch: a smaller number is not always the older one. Serials are counters that roll back to zero after they reach 4,294,967,295, so a server that just wrapped can show a low number while actually being newest. To handle that, this page compares serials with DNS serial arithmetic rather than treating them as plain numbers.
What each SOA value means
| Primary | The nameserver listed as the original source of the zone, the one every other server copies from. |
|---|---|
| Mailbox | The contact for the zone, written as a DNS name. Read the first dot as the @ in an email address, so admin.example.com means admin@example.com. |
| Refresh | How often a secondary checks with the primary to see if anything changed. |
| Retry | How long a secondary waits before trying again after a failed check. |
| Expire | How long a secondary keeps serving its copy while it cannot reach the primary at all, before it gives up. |
| Negative cache | How long a resolver is allowed to remember that a name does not exist. It is the lower of the SOA TTL and the MINIMUM value. |
When a mismatch is worth worrying about
A brief difference is normal. It usually just means a change is still spreading from the primary to the secondaries and has not landed everywhere yet. What deserves a closer look is a mismatch that outlasts the refresh and retry schedule, since by then every server should have caught up. If one is stuck, check whether it can reach the primary, whether zone transfers are allowed to it, and whether it is still meant to serve the zone at all. There is no single correct timing value, so this tool just shows you what differs instead of handing out a made-up grade.