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对于不存在的名称，主机返回 0

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对于不存在的名称，主机返回 0

host通常返回0现有主机

$ host www.google.com ; echo $?
www.google.com has address 172.217.16.132
www.google.com has IPv6 address 2a00:1450:400a:805::2004
0

如果1出现错误

$ host does.not.exist ; echo $?
Host does.not.exist not found: 3(NXDOMAIN)
1

我现在有一个不存在的主机，它host返回 0 而没有任何输出

$ host red3.ethz.ch; echo $?
0

nslookup生成错误（如预期）：

$ nslookup red3.ethz.ch
Server:     129.132.98.12
Address:    129.132.98.12#53

Non-authoritative answer:
*** Can't find red3.ethz.ch: No answer

并且我在输出中看不到任何-d部分-vANSWER

$ host -v -d red3.ethz.ch
Trying "red3.ethz.ch"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55752
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;red3.ethz.ch.          IN  A

;; AUTHORITY SECTION:
ethz.ch.        246 IN  SOA dummy-ns.ethz.ch. hostmaster.ethz.ch. 2008016728 10800 3600 1814400 600

Received 86 bytes from 129.132.98.12#53 in 30 ms
Trying "red3.ethz.ch"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31530
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;red3.ethz.ch.          IN  AAAA

;; AUTHORITY SECTION:
ethz.ch.        246 IN  SOA dummy-ns.ethz.ch. hostmaster.ethz.ch. 2008016728 10800 3600 1814400 600

Received 86 bytes from 129.132.98.12#53 in 0 ms
Trying "red3.ethz.ch"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43023
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;red3.ethz.ch.          IN  MX

;; AUTHORITY SECTION:
ethz.ch.        246 IN  SOA dummy-ns.ethz.ch. hostmaster.ethz.ch. 2008016728 10800 3600 1814400 600

Received 86 bytes from 129.132.98.12#53 in 0 ms

为什么host返回0？

编辑

看看评论，我们似乎可以将范围缩小到 DNS 上的不同配置。

在同一域上 ( ethz.ch)

$ host doesnotexist.ethz.ch; echo $?
Host doesnotexist.ethz.ch not found: 3(NXDOMAIN)
1
$ host red3.ethz.ch; echo $?
0
$ host www.ethz.ch; echo $?
www.ethz.ch has address 129.132.19.216
www.ethz.ch has IPv6 address 2001:67c:10ec:4380::216
0

看起来没有 IP 的响应被“hosts”认为是可以的，但被“nslookup”认为不行。

答案1

看，根据tshark，DNS 服务器返回不同的协议消息为您的域名。为does.not.exist您收到DNS 149 Standard query response 0x0d51 No such name。为red3.ethz.ch您收到Standard query response 0xe4db0 个答案。主机返回不同代码的原因是什么。

至于解析 does.not.exist，DNS 服务器响应是：

DNS 149 Standard query response 0x0d51 No such name

至于red3.ethz.ch tshark显示 DNS 服务器在 Answer 部分仅响应 0 条记录：

这是tshark：

DNS 128 Standard query response 0xe4db

这是楼主的回复：

Trying "red3.ethz.ch"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1542
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

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