[日常] DNS解析概述

dns domainnamesystem域名系统，根据域名查出ip地址
1.dig命令可以显示整个查询的过程

root@vm-38-204-ubuntu:~# dig www.sopans.com
//这一段是查询参数和统计
; <<>> dig 9.10.3-p4-ubuntu <<>> www.sopans.com
;; global options: +cmd
;; got answer:
;; ->>header<<- opcode: query, status: noerror, id: 1899
;; flags: qr rd ra; query: 1, answer: 2, authority: 0, additional: 1

//这一段是查询内容，查询www.sopans.com的a记录，a是address意思
;; opt pseudosection:
; edns: version: 0, flags:; udp: 4096
;; question section:
;www.sopans.com.                        in      a

//dns服务器的答复，两条a记录，575是ttl的值（time to live）缓存时间575秒内不用重新查询
;; answer section:
www.sopans.com.         575     in      a       123.206.7.231
www.sopans.com.         575     in      a       115.159.28.111

//dns服务器的一些传输信息，本机dns服务器是10.236.158.106，端口53，返回了75字节
;; query time: 58 msec
;; server: 10.236.158.106#53(10.236.158.106)
;; when: wed nov 28 21:36:03 cst 2018
;; msg size  rcvd: 75

2.
+short参数只返回两条a记录ip地址
root@vm-38-204-ubuntu:~# dig www.sopans.com +short
123.206.7.231
115.159.28.111

3.
本机dns服务器的ip地址位于/etc/resolv.conf
root@vm-38-204-ubuntu:~# cat /etc/resolv.conf
nameserver 10.236.158.106
nameserver 10.236.158.114
options timeout:1 rotate

4.使用@参数指定dns服务器地址，例如指定dns服务器地址为8.8.8.8
dig www.sopans.com @8.8.8.8

5.域名的层级结构
主机名.次级域名.*域名.根域名 www.sopans.com.root ,root可以省略因此会显示成www.sopans.com.

6.使用+trace参数，查看分级查询的过程，
ns记录是管理该级域名的域名服务器，按每一级逐级查询的过程
root@vm-38-204-ubuntu:~# dig www.sopans.com +trace
.                       294897  in      ns      c.root-servers.net.
.                       294897  in      ns      d.root-servers.net.
.                       294897  in      ns      e.root-servers.net.
.                       294897  in      ns      f.root-servers.net.
.                       294897  in      ns      g.root-servers.net.
.                       294897  in      ns      h.root-servers.net.
.                       294897  in      ns      i.root-servers.net.
.                       294897  in      ns      a.root-servers.net.
.                       294897  in      ns      j.root-servers.net.
.                       294897  in      ns      k.root-servers.net.
.                       294897  in      ns      l.root-servers.net.
.                       294897  in      ns      m.root-servers.net.
.                       294897  in      ns      b.root-servers.net.
;; received 239 bytes from 10.236.158.106#53(10.236.158.106) in 0 ms

com.                    172800  in      ns      e.gtld-servers.net.
com.                    172800  in      ns      b.gtld-servers.net.
com.                    172800  in      ns      j.gtld-servers.net.
com.                    172800  in      ns      m.gtld-servers.net.
com.                    172800  in      ns      i.gtld-servers.net.
com.                    172800  in      ns      f.gtld-servers.net.
com.                    172800  in      ns      a.gtld-servers.net.
com.                    172800  in      ns      g.gtld-servers.net.
com.                    172800  in      ns      h.gtld-servers.net.
com.                    172800  in      ns      l.gtld-servers.net.
com.                    172800  in      ns      k.gtld-servers.net.
com.                    172800  in      ns      c.gtld-servers.net.
com.                    172800  in      ns      d.gtld-servers.net.
com.                    86400   in      ds      30909 8 2 e2d3c916f6deeac73294e8268fb5885044a833fc5459588f4a9184cf c41a5766
com.                    86400   in      rrsig   ds 8 1 86400 20181211050000 20181128040000 2134 . fesgjrqqq/ly82e1pam38eiu07pepp53ziy23ola65vdqa4ynhkwb8ov okiwzhhwb=
;; received 1174 bytes from 198.41.0.4#53(a.root-servers.net) in 224 ms

sopans.com.             172800  in      ns      dns2.hichina.com.
sopans.com.             172800  in      ns      dns1.hichina.com.
ck0pojmg874ljref7efn8430qvit8bsm.com. 86400 in nsec3 1 1 0 - ck0q1gin43n1arrc9osm6qpqr81h5m9a ns soa rrsig dnskey nsec3param
ck0pojmg874ljref7efn8430qvit8bsm.com. 86400 in rrsig nsec3 8 2 86400 20181202054332 20181125043332 37490 com. r+qjjnuxe+1bs7+kvcustafanlugt+wxlpwdpf9mxkccm+re8yjs2r=
o7k3mhposl4gcsk01o8er0lq04klnnut.com. 86400 in nsec3 1 1 0 - o7k5etu7svnp269r4u7kiqre79h62bpm ns ds rrsig
o7k3mhposl4gcsk01o8er0lq04klnnut.com. 86400 in rrsig nsec3 8 2 86400 20181203062329 20181126051329 37490 com. oktu40+7gclv+ywhdxu9geuklwokrjtgevye51v8c7cgimibh0cysy=
;; received 886 bytes from 192.43.172.30#53(i.gtld-servers.net) in 362 ms

www.sopans.com.         600     in      a       115.159.28.111
www.sopans.com.         600     in      a       123.206.7.231
;; received 75 bytes from 140.205.41.23#53(dns1.hichina.com) in 4 ms


7.ns参数和+short参数可以直接查询该级域名的ns记录
root@vm-38-204-ubuntu:~# dig ns +short sopans.com    
dns1.hichina.com.
dns2.hichina.com.

8.
a记录：地址记录，域名指向的ip地址
mx记录：邮件记录，使用邮箱时设置的服务器地址
cname:别名记录，当前查询的域名跳转到另一个域名，
    比如www.baidu.com.          1080    in      cname   www.a.shifen.com.
    这样的好处是，当要变更www.baidu.com指向的ip地址时，只需更改www.a.shifen.com的就可以了，www.baidu.com不需要变动；一旦设置了cname,就不能设置其他记录了
ns记录：管理该级域名的域名服务器
ptr:逆向查询记录，从ip地址查询域名

9.-x参数是查询ptr记录，从ip地址反查域名
dig -x 192.30.252.153