逆順 DNS lookup
Reverse DNS lookup: enter an IP address〜find its hostnameとsee whether forwardとreverse DNS match.
Queries go〜Cloudflare’s public DNS over HTTPS service when you press the button.
逆順 DNS lookupについて
Reverse DNS lookup: enter an IP address〜find its hostnameとsee whether forwardとreverse DNS match.
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逆順 DNS lookupの使い方
何を計算するか、いつ使うか
Finds the hostname that belongs〜an IP address using its reverse DNS (PTR) record,とchecks that the hostname resolves back〜the same address, whichはcalled forward-confirmed reverse DNS. Mail servers use this check〜decide whether〜trust a sender.です
使い方の手順
- Enter an IP address,またはleave the box empty〜use your own.
- Press “求めるもの hostname”.
- Read the hostname 適用 the top.
- Check “Forward-confirmed”〜see whether the name resolves back〜the address.
各入力項目の意味
- IP address – An IPv4またはIPv6 address. Leave it empty〜use your own public address.
結果の読み方
- Hostname – the address’s PTR record.のThe 名前 set
- 逆順 名前 – The special 名前 queried, such as 8.8.8.8.in-addr.arpa.
- Forward-confirmed – はい when the hostname’s AまたはAAAA record points back〜the same address.
計算式
The addressはreversedですとqueried under in-addr.arpa個でIPv4,またはip6.arpa with each hex digit reversed個でIPv6. 8.8.4.4 becomes 4.4.8.8.in-addr.arpa. The returned nameはthen looked up forward to confirm it.です
計算例
8.8.8.8 has the PTR record dns.google,とdns.google resolves back〜8.8.8.8, so the pairはforward-confirmed.です
前提と限界
- Many addresses, especially ホーム connections, have いいえ PTR recordまたはa generic one.
- The lookupはmade through Cloudflare’s DNS over HTTPS service when you press the button.です
よくある間違い
- Expecting every address〜have a hostname.
- the address sets it, so only forward-confirmed names add trust. identity. The owner Treating the hostname as proof
- Setting a PTR record 適用 your domain registrar. Itはset by whoever holds the IP address block, usually your hostingまたはinternet provider.です
よくある質問
Whatはa PTR record?です
A DNS record that maps an IP address back〜a hostname. Itはan A record. the reverseです
Why does my mail server need 逆順 DNS?
Many receiving mail systems rejectまたはflag mail from addresses with no reverse DNSまたはone that does not match.
参加者 缶 変動 a PTR record?
The organisation that controls the IP address block, normally your hosting providerまたはISP.
Is this the same as a hostname lookup?
an IP address Yes. Finding the hostnameは完了 with 逆順 DNS.です