DNS NOTIFY
DNS NOTIFY, defined in RFC 1996, lets a zone's primary nameserver proactively tell its secondary nameservers that the zone has changed, instead of every secondary waiting out the SOA record's refresh interval before checking again. Without NOTIFY, a secondary only polls the primary's SOA serial number on a fixed timer -- often tens of minutes to hours -- so a zone change doesn't reach secondaries until the next scheduled poll, even if the primary updated moments after the last one. With NOTIFY, the primary sends a small message to each configured secondary immediately after a change, prompting it to check the SOA serial right away rather than waiting; the secondary still compares serial numbers itself before pulling a zone transfer, so a NOTIFY message is only a wake-up signal and isn't trusted blindly to mean new data is actually available. This shortens real-world propagation time for a zone update from however long the refresh interval happens to be down to roughly the time it takes to send one message and complete the resulting transfer, which is why most authoritative DNS server software sends NOTIFY by default whenever a zone's serial number increases.
By AdminKit team, Netbase JSC · Updated