DNS 传播检查
我们向多个公共递归解析器提出同一个问题并比较它们的应答。
覆盖范围：6 个公共解析器，从我们的服务器发起查询。这不是全球测量：anycast 解析器由离我们服务器最近的节点应答，因此显示的是该节点当前缓存的内容。
此内容尚无中文（中国）版本。在发布译文之前以英语显示。
“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.
常见问题
How long does a DNS change take?
At most the old record's TTL, counted from when each resolver last fetched it. Lowering the TTL a day before a planned change shortens the window.
Can I clear a public resolver's cache?
Some operators offer a purge page (Cloudflare and Google do). Otherwise you have to wait for the TTL to expire.