dig 可以工作，但 ping 无法解析主机

Question

我已经为主机（admin.example-preprod.foobar.it使用 IP 100.100.100.100）配置了 DNS 设置，但它并没有从我尝试的每台服务器上进行解析（对某些服务器来说是这样）。

例如，我的服务器使用以下 3 个 DNS 服务器：

foobar@server:~$ cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 200.200.200.1
nameserver 200.200.200.2
nameserver 200.200.200.3

dig对他们所有人都有效。

第一的：

foobar@server:~$ dig admin.example-preprod.foobar.it @200.200.200.1

; <<>> DiG 9.9.5-3ubuntu0.7-Ubuntu <<>> admin.example-preprod.foobar.it @200.200.200.1
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6540
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 2
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;admin.example-preprod.foobar.it.        IN      A

;; ANSWER SECTION:
admin.example-preprod.foobar.it. 86400 IN A      100.100.100.100

;; AUTHORITY SECTION:
foobar.it.               86400   IN      NS      qwert.foobar.it.
foobar.it.               86400   IN      NS      ns0.xname.org.
foobar.it.               86400   IN      NS      ns1.xname.org.

;; ADDITIONAL SECTION:
qwert.foobar.it.         86400   IN      A       200.200.200.1

;; Query time: 46 msec
;; SERVER: 200.200.200.1#53(200.200.200.1)
;; WHEN: Fri Nov 04 10:35:46 EET 2016
;; MSG SIZE  rcvd: 156

第二：

foobar@server:~$ dig admin.example-preprod.foobar.it @200.200.200.2

; <<>> DiG 9.9.5-3ubuntu0.7-Ubuntu <<>> admin.example-preprod.foobar.it @200.200.200.2
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 40127
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;admin.example-preprod.foobar.it.        IN      A

;; AUTHORITY SECTION:
foobar.it.               85817   IN      SOA     qwert.foobar.it. webmaster.foobar.it. 2016092901 10800 900 1814400 10800

;; Query time: 3 msec
;; SERVER: 200.200.200.2#53(200.200.200.2)
;; WHEN: Fri Nov 04 10:36:05 EET 2016
;; MSG SIZE  rcvd: 111

第三：

foobar@server:~$ dig admin.example-preprod.foobar.it @200.200.200.3

; <<>> DiG 9.9.5-3ubuntu0.7-Ubuntu <<>> admin.example-preprod.foobar.it @200.200.200.3
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2392
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;admin.example-preprod.foobar.it.        IN      A

;; ANSWER SECTION:
admin.example-preprod.foobar.it. 86400 IN A      100.100.100.100

;; AUTHORITY SECTION:
foobar.it.               86400   IN      NS      qwert.foobar.it.
foobar.it.               86400   IN      NS      ns1.xname.org.
foobar.it.               86400   IN      NS      ns0.xname.org.

;; ADDITIONAL SECTION:
qwert.foobar.it.         81845   IN      A       200.200.200.1

;; Query time: 2309 msec
;; SERVER: 200.200.200.3#53(200.200.200.3)
;; WHEN: Fri Nov 04 10:35:56 EET 2016
;; MSG SIZE  rcvd: 156

但是，当我尝试 ping 时，它给了我unknown host：

foobar@server:~$ ping admin.example-preprod.foobar.it
ping: unknown host admin.example-preprod.foobar.it

这怎么可能？我应该从哪里着手解决这个问题？

Answer 1

dig 不适用于所有这些 - 您的第二个名称服务器（200.200.200.2在您的示例中）无法解析记录。

默认情况下，Linux 解析器在 resolv.conf 中的条目之间随机化，我猜您的 ping 已经命中了失败的解析器。