dig：用於測試dns系統(不會查詢hosts文件中的解析)
host：以更簡潔的方式顯示查詢結果
nslookup：以交互式的方式獲取查詢結果
安裝命令：yum install bind-utils -y (上面3個命令都會安裝)
dig命令語法：dig [-t TYPE] name [@SERVER] [+trace]
[-t TYPE]：表示解析類型
A：查詢A記錄
NS：查詢ns
axfs：查詢全量傳送，即查詢所有的資源記錄（生產環境必須關閉）
-x：查詢反向解析記錄
[@SERVER]：表示以指定的DNS服務器進行解析，如果不寫，則以本機上配置DNS進行解析
[+trace]：表示跟蹤解析過程，可不寫
host命令語法：host [-t type] name [SERVER]
[-t TYPE]：表示解析類型
SERVER：表示使用指定的DNS服務器
nslookup命令語法：nslookup [-option] [name | -] [server]
交互式模式：
server IP：表示使用指定的DNS
set q=RR_TYPE：表示使用查詢資源類型
NAME：要查詢的域名
示例：dig -t A www.baidu.com
返回結果解釋：
[root@dns-master named]# dig -t A www.baidu.com ; <<>> DiG 9.9.4-RedHat-9.9.4-73.el7_6 <<>> -t A www.baidu.com ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15788 ;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;www.baidu.com. IN A ;; ANSWER SECTION: www.baidu.com. 380 IN CNAME www.a.shifen.com. www.a.shifen.com. 300 IN A 115.239.210.27 www.a.shifen.com. 300 IN A 115.239.211.112 ;; Query time: 18 msec ;; SERVER: 114.114.114.114#53(114.114.114.114) ;; WHEN: Sat Jun 01 15:23:47 CST 2019 ;; MSG SIZE rcvd: 90
flags：如果有aa，表示權威回答；如果沒有aa表示非權威回答；上例中即非權威回答；可能使用了dns緩存;
QUESTION SECTION：表示問題部分，即你諮詢的內容
ANSWER SECTION：表示針對你的問題，返回的解析結果；
AUTHORITY SECTION：表示權威回答，由哪些DNS服務器進行響應；
ADDITIONAL SECTION：表示如果是權威回答，額外返回更多的解析信息，返回響應的DNS服務器的解析A記錄；
增加@SERVER結果演示：
[root@dns-master named]# dig -t A www.51yunv.com @192.168.1.115 ; <<>> DiG 9.9.4-RedHat-9.9.4-73.el7_6 <<>> -t A www.51yunv.com @192.168.1.115 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17389 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 3 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;www.51yunv.com. IN A ;; ANSWER SECTION: www.51yunv.com. 86400 IN A 192.168.1.116 ;; AUTHORITY SECTION: 51yunv.com. 86400 IN NS ns1.51yunv.com. 51yunv.com. 86400 IN NS ns2.51yunv.com. ;; ADDITIONAL SECTION: ns1.51yunv.com. 86400 IN A 192.168.1.114 ns2.51yunv.com. 86400 IN A 192.168.1.115 ;; Query time: 0 msec ;; SERVER: 192.168.1.115#53(192.168.1.115) ;; WHEN: Sat Jun 01 15:21:39 CST 2019 ;; MSG SIZE rcvd: 127
此例中flags中有aa,表示爲權威回答；
增加+trace解析結果：
[root@shvpuppet01 ~]# dig -t A www.baidu.com +trace ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> -t A www.baidu.com +trace ;; global options: +cmd . 3600 IN NS b.root-servers.net. . 3600 IN NS c.root-servers.net. . 3600 IN NS d.root-servers.net. . 3600 IN NS e.root-servers.net. . 3600 IN NS f.root-servers.net. . 3600 IN NS g.root-servers.net. . 3600 IN NS h.root-servers.net. . 3600 IN NS i.root-servers.net. . 3600 IN NS j.root-servers.net. . 3600 IN NS k.root-servers.net. . 3600 IN NS l.root-servers.net. . 3600 IN NS m.root-servers.net. . 3600 IN NS a.root-servers.net. ;; Received 257 bytes from 10.10.2.98#53(10.10.2.98) in 3954 ms com. 172800 IN NS a.gtld-servers.net. com. 172800 IN NS b.gtld-servers.net. com. 172800 IN NS c.gtld-servers.net. com. 172800 IN NS d.gtld-servers.net. com. 172800 IN NS e.gtld-servers.net. com. 172800 IN NS f.gtld-servers.net. com. 172800 IN NS g.gtld-servers.net. com. 172800 IN NS h.gtld-servers.net. com. 172800 IN NS i.gtld-servers.net. com. 172800 IN NS j.gtld-servers.net. com. 172800 IN NS k.gtld-servers.net. com. 172800 IN NS l.gtld-servers.net. com. 172800 IN NS m.gtld-servers.net. ;; Received 491 bytes from 199.7.91.13#53(199.7.91.13) in 260 ms baidu.com. 172800 IN NS ns2.baidu.com. baidu.com. 172800 IN NS ns3.baidu.com. baidu.com. 172800 IN NS ns4.baidu.com. baidu.com. 172800 IN NS ns1.baidu.com. baidu.com. 172800 IN NS ns7.baidu.com. ;; Received 201 bytes from 192.41.162.30#53(192.41.162.30) in 341 ms www.baidu.com. 1200 IN CNAME www.a.shifen.com. a.shifen.com. 1200 IN NS ns5.a.shifen.com. a.shifen.com. 1200 IN NS ns2.a.shifen.com. a.shifen.com. 1200 IN NS ns3.a.shifen.com. a.shifen.com. 1200 IN NS ns4.a.shifen.com. a.shifen.com. 1200 IN NS ns1.a.shifen.com. ;; Received 228 bytes from 202.108.22.220#53(202.108.22.220) in 25 ms
可以看到解析過程爲：從根DNS服務器中找com.，從com.的DNS服務器中找baidu.com.，從baidu.com.的DNS服務器中找www.baidu.com.
查詢反向解析記錄：
[root@dns-master named]# dig -x 192.168.1.116 @192.168.1.115 ; <<>> DiG 9.9.4-RedHat-9.9.4-73.el7_6 <<>> -x 192.168.1.116 @192.168.1.115 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47182 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 3 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;116.1.168.192.in-addr.arpa. IN PTR ;; ANSWER SECTION: 116.1.168.192.in-addr.arpa. 86400 IN PTR www.51yunv.com. 116.1.168.192.in-addr.arpa. 86400 IN PTR mx1.51yunv.com. ;; AUTHORITY SECTION: 1.168.192.in-addr.arpa. 86400 IN NS ns2.51yunv.com. 1.168.192.in-addr.arpa. 86400 IN NS ns1.51yunv.com. ;; ADDITIONAL SECTION: ns1.51yunv.com. 86400 IN A 192.168.1.114 ns2.51yunv.com. 86400 IN A 192.168.1.115 ;; Query time: 0 msec ;; SERVER: 192.168.1.115#53(192.168.1.115) ;; WHEN: Sat Jun 01 16:51:19 CST 2019 ;; MSG SIZE rcvd: 169
查詢全量區域傳送：
[root@dns-master named]# dig -t axfr 51yunv.com @192.168.1.115 ; <<>> DiG 9.9.4-RedHat-9.9.4-73.el7_6 <<>> -t axfr 51yunv.com @192.168.1.115 ;; global options: +cmd 51yunv.com. 86400 IN SOA ns1.magedu.com. admin.51yunv.com. 2015042201 3600 300 604800 86400 51yunv.com. 86400 IN NS ns1.51yunv.com. 51yunv.com. 86400 IN NS ns2.51yunv.com. 51yunv.com. 86400 IN MX 10 mx1.51yunv.com. 51yunv.com. 86400 IN MX 20 mx2.51yunv.com. mx1.51yunv.com. 86400 IN A 192.168.1.116 mx2.51yunv.com. 86400 IN A 192.168.1.117 ns1.51yunv.com. 86400 IN A 192.168.1.114 ns2.51yunv.com. 86400 IN A 192.168.1.115 www.51yunv.com. 86400 IN A 192.168.1.116 51yunv.com. 86400 IN SOA ns1.magedu.com. admin.51yunv.com. 2015042201 3600 300 604800 86400 ;; Query time: 0 msec ;; SERVER: 192.168.1.115#53(192.168.1.115) ;; WHEN: Sat Jun 01 16:45:17 CST 2019 ;; XFR size: 11 records (messages 1, bytes 288)
hosts命令用法示例：
[root@shvpuppet01 ~]# host -t A www.baidu.com www.baidu.com is an alias for www.a.shifen.com. www.a.shifen.com has address 61.135.169.121 www.a.shifen.com has address 61.135.169.125