dig：用于测试dns系统(不会查询hosts文件中的解析)
host：以更简洁的方式显示查询结果
nslookup：以交互式的方式获取查询结果
安装命令：yum install bind-utils -y (上面3个命令都会安装)
dig命令语法：dig [-t TYPE] name [@SERVER] [+trace]
-t TYPE：表示解析类型
A：查询A记录
NS：查询ns
axfs：查询全量传送，即查询所有的资源记录（生产环境必须关闭）
-x：查询反向解析记录
@SERVER：表示以指定的DNS服务器进行解析，如果不写，则以本机上配置DNS进行解析
+trace：表示跟踪解析过程，可不写
+short：表示以短格式显示解析的内容，即只显示域名解析后的IP
host命令语法：host [-t type] name [SERVER]
[-t TYPE]：表示解析类型
SERVER：表示使用指定的DNS服务器
nslookup命令语法：nslookup [-option] [name | -] [server]
交互式模式：
server IP：表示使用指定的DNS
set q=RR_TYPE：表示使用查询资源类型
NAME：要查询的域名
options参数：
-debug：以调试模式运行
示例：dig -t A www.baidu.com
返回结果解释：
[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.. www.. 300 IN A 115.239.210.27 www.. 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，表示权威回答；如果没有aa表示非权威回答；上例中即非权威回答；可能使用了dns缓存;
QUESTION SECTION：表示问题部分，即你咨询的内容
ANSWER SECTION：表示针对你的问题，返回的解析结果；
AUTHORITY SECTION：表示权威回答，由哪些DNS服务器进行响应；
ADDITIONAL SECTION：表示如果是权威回答，额外返回更多的解析信息，返回响应的DNS服务器的解析A记录；
增加@SERVER结果演示：
[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 . 51yunv.com. 86400 IN NS . ;; ADDITIONAL SECTION: . 86400 IN A 192.168.1.114 . 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,表示为权威回答；
增加+trace解析结果：
[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 . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . . 3600 IN NS . ;; Received 257 bytes from 10.10.2.98#53(10.10.2.98) in 3954 ms com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . com. 172800 IN NS . ;; Received 491 bytes from 199.7.91.13#53(199.7.91.13) in 260 ms baidu.com. 172800 IN NS . baidu.com. 172800 IN NS . baidu.com. 172800 IN NS . baidu.com. 172800 IN NS . baidu.com. 172800 IN NS . ;; Received 201 bytes from 192.41.162.30#53(192.41.162.30) in 341 ms www.baidu.com. 1200 IN CNAME www.. . 1200 IN NS ns5.. . 1200 IN NS ns2.. . 1200 IN NS ns3.. . 1200 IN NS ns4.. . 1200 IN NS ns1.. ;; Received 228 bytes from 202.108.22.220#53(202.108.22.220) in 25 ms
可以看到解析过程为：从根DNS服务器中找com.，从com.的DNS服务器中找baidu.com.，从baidu.com.的DNS服务器中找www.baidu.com.
查询反向解析记录：
[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 . ;; AUTHORITY SECTION: 1.168.192.in-addr.arpa. 86400 IN NS . 1.168.192.in-addr.arpa. 86400 IN NS . ;; ADDITIONAL SECTION: . 86400 IN A 192.168.1.114 . 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
查询全量区域传送：
[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 . . 2015042201 3600 300 604800 86400 51yunv.com. 86400 IN NS . 51yunv.com. 86400 IN NS . 51yunv.com. 86400 IN MX 10 . 51yunv.com. 86400 IN MX 20 . . 86400 IN A 192.168.1.116 . 86400 IN A 192.168.1.117 . 86400 IN A 192.168.1.114 . 86400 IN A 192.168.1.115 www.51yunv.com. 86400 IN A 192.168.1.116 51yunv.com. 86400 IN SOA . . 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.. www. has address 61.135.169.121 www. has address 61.135.169.125
