DNS伝播チェック
複数の公開再帰リゾルバーに同じ質問をして回答を比較します。
対象：欧州にある自社サーバーから問い合わせた6台の公開リゾルバー。世界規模の測定ではなく、これらのリゾルバーが現在キャッシュしている内容を示します。
このテキストはまだ日本語で提供されていません。翻訳が公開されるまで英語で表示しています。
“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.
よくある質問
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.