DNS lookup
Look up the DNS records of a domain as a public resolver sees them: addresses, aliases, mail servers, name servers and text records, with their TTLs.
DNS 查询
以公共解析器的视角查询一个域名的 DNS 记录：地址、别名、邮件服务器、域名服务器和文本记录，以及它们的 TTL。
Record types
- A / AAAA: The IPv4 and IPv6 addresses the name points to.
- CNAME: An alias: the name is answered by another name, which is then looked up in turn.
- MX: The mail servers for the domain, with a priority; the lowest number is tried first.
- NS: The authoritative name servers, usually those of your DNS host or registrar.
- TXT: Free text, used for SPF, DMARC, DKIM and domain verification.
- CAA: The certificate authorities allowed to issue certificates for the domain.
- SOA: The zone's primary server, contact, serial number and cache timers.
When a domain stops resolving
No records at all (NXDOMAIN) usually means the domain expired, the name servers were changed, or the record was deleted. Look up NS first: if it does not return your DNS host, the registrar no longer points the domain there.
Records that point to an old address are common after a migration. Lower the TTL a day before you move, then raise it again once the new address is in place.
Catch DNS problems as they happen
A broken record takes a site offline as reliably as a crashed server, and it is easy to miss because everything still works for anyone with a cached answer. An OpenUptime DNS monitor checks the record on a schedule and alerts you when it disappears or changes.
Questions
Which resolver does this lookup use?
Cloudflare's public resolver (1.1.1.1), over DNS-over-HTTPS. It answers like any public resolver your visitors might use, cached records included, so a change may show here before or after it shows elsewhere.
Why don't I see my new DNS record yet?
Resolvers keep an answer for as long as its TTL says. If the old record had a TTL of 3600, some resolvers can serve it for up to an hour after you change it. A name that did not exist can also be cached as missing for the zone's negative TTL, set in its SOA record.
What do the record types mean?
A and AAAA give the IPv4 and IPv6 addresses of a name. CNAME makes a name an alias of another. MX names the mail servers for a domain, NS its authoritative name servers, TXT holds text such as SPF, DKIM and verification tokens, CAA lists the certificate authorities allowed to issue for it, and SOA holds the zone's serial and timers.
How do I check SPF, DKIM or DMARC?
They are TXT records. SPF sits on the domain itself (look up TXT for example.com), DMARC on _dmarc.example.com and DKIM on <selector>._domainkey.example.com, where the selector comes from your mail provider.
Can I be alerted when a DNS record changes?
Yes. A DNS monitor in OpenUptime looks up an A, AAAA, CNAME, MX, TXT or NS record on a schedule and fails when the name stops resolving, or when the answer no longer matches or contains the value you expect.
记录类型
- A / AAAA: 名称指向的 IPv4 和 IPv6 地址。
- CNAME: 别名：这个名称由另一个名称来回答，然后再继续解析那个名称。
- MX: 域名的邮件服务器及优先级，数字最小的优先使用。
- NS: 权威域名服务器，通常是你的 DNS 托管商或注册商的服务器。
- TXT: 自由文本，用于 SPF、DMARC、DKIM 和域名验证。
- CAA: 允许为这个域名签发证书的证书颁发机构。
- SOA: 区域的主服务器、联系人、序列号和缓存计时参数。
域名无法解析时
完全没有记录（NXDOMAIN）通常意味着域名过期、域名服务器被更换，或记录被删除。先查询 NS：如果返回的不是你的 DNS 托管商，说明注册商已经不再把域名指向那里。
迁移之后，记录仍指向旧地址的情况很常见。迁移前一天先调低 TTL，新地址生效后再调高。
第一时间发现 DNS 问题
一条错误的记录和服务器崩溃一样会让网站下线，而且很容易被忽略，因为有缓存的人仍然一切正常。OpenUptime 的 DNS 监控会按计划检查记录，在记录消失或变化时提醒你。
常见问题
这个查询使用哪个解析器？
Cloudflare 的公共解析器（1.1.1.1），通过 DNS-over-HTTPS 查询。它的回答和访问者可能用到的任何公共解析器一样，包含缓存，所以一次变更在这里出现的时间可能比别处早，也可能晚。
为什么我还看不到新加的 DNS 记录？
解析器会按照 TTL 缓存答案。如果旧记录的 TTL 是 3600，修改后某些解析器最多还会返回它一小时。一个之前不存在的名称，也可能按区域 SOA 记录中的否定缓存 TTL 被缓存为“不存在”。
各种记录类型是什么意思？
A 和 AAAA 给出名称的 IPv4 和 IPv6 地址；CNAME 把一个名称设为另一个名称的别名；MX 指定域名的邮件服务器；NS 指定权威域名服务器；TXT 存放文本，例如 SPF、DKIM 和验证令牌；CAA 列出允许为它签发证书的证书颁发机构；SOA 记录区域的序列号和各项计时参数。
怎么检查 SPF、DKIM 或 DMARC？
它们都是 TXT 记录。SPF 在域名本身上（查询 example.com 的 TXT），DMARC 在 _dmarc.example.com 上，DKIM 在 <selector>._domainkey.example.com 上，selector 由你的邮件服务商提供。
DNS 记录变化时能收到提醒吗？
可以。OpenUptime 的 DNS 监控会按计划查询 A、AAAA、CNAME、MX、TXT 或 NS 记录，当名称无法解析，或答案不再等于或包含你预期的值时，检查就会失败并提醒你。