بررسی انتشار DNS

“DNS propagation” isn’t really propagation: when you change a record, the authoritative name server has the new value at once, but every recursive resolver keeps its cached copy until that copy’s TTL runs out. Different resolvers cached the record at different moments, so for a while some return the old value and some the new one.

This tool asks the same question to several large public resolvers at the same moment and lists their answers side by side, with the remaining TTL each one reports. When they all agree, the change is visible to most of the internet. Some names deliberately return different answers depending on where the question comes from (CDNs, geo-DNS), so disagreement isn’t always a stale cache.