解決辦法：

[root@docker-registry ~]# yum install bind-utils // 安裝dig工具

[root@docker-registry ~]# dig @114.114.114.114 registry-1.docker.io

; < <>> DiG 9.9.4-RedHat-9.9.4-61.el7_5.1 < <>> @114.114.114.114 registry-1.docker.io

; (1 server found)

;; global options: +cmd

;; Got answer:

;; ->>HEADER< <- opcode: QUERY, status: NOERROR, id: 51198

;; flags: qr rd ra; QUERY: 1, ANSWER: 8, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:

; EDNS: version: 0, flags:; udp: 4096

;; QUESTION SECTION:

;registry-1.docker.io. IN A

;; ANSWER SECTION:

registry-1.docker.io. 31 IN A 34.206.236.31

registry-1.docker.io. 31 IN A 54.175.43.85

registry-1.docker.io. 31 IN A 34.205.207.96

registry-1.docker.io. 31 IN A 34.233.151.211

registry-1.docker.io. 31 IN A 52.70.175.131

registry-1.docker.io. 31 IN A 34.200.28.105

registry-1.docker.io. 31 IN A 54.165.149.19

registry-1.docker.io. 31 IN A 34.201.236.93

;; Query time: 10 msec

;; SERVER: 114.114.114.114#53(114.114.114.114)

;; WHEN: Wed Oct 31