DNS工具

（1）host 命令

host命令可以看作dig命令的简化版本，返回当前请求域名的各种记录。

$ host github.com

github.com has address 192.30.252.121
github.com mail is handled by 5 ALT2.ASPMX.L.GOOGLE.COM.
github.com mail is handled by 10 ALT4.ASPMX.L.GOOGLE.COM.
github.com mail is handled by 10 ALT3.ASPMX.L.GOOGLE.COM.
github.com mail is handled by 5 ALT1.ASPMX.L.GOOGLE.COM.
github.com mail is handled by 1 ASPMX.L.GOOGLE.COM.

$ host facebook.github.com

facebook.github.com is an alias for github.map.fastly.net.
github.map.fastly.net has address 103.245.222.133

host命令也可以用于逆向查询，即从IP地址查询域名，等同于dig -x 。

$ host 192.30.252.153

153.252.30.192.in-addr.arpa domain name pointer pages.github.com.

（2）nslookup 命令

nslookup命令用于互动式地查询域名记录。

➜  dist git:(dev) ✗ nslookup www.baidu.com
Server:     10.39.1.10
Address:    10.39.1.10#53

Non-authoritative answer:
www.baidu.com   canonical name = www.a.shifen.com.
Name:   www.a.shifen.com
Address: 220.181.112.244
Name:   www.a.shifen.com
Address: 220.181.111.188

（3）whois 命令

whois命令用来查看域名的注册情况。

➜  dist git:(dev) ✗ whois github.com
   Domain Name: GITHUB.COM
   Registry Domain ID: 1264983250_DOMAIN_COM-VRSN
   Registrar WHOIS Server: whois.markmonitor.com
   Registrar URL: http://www.markmonitor.com
   Updated Date: 2017-06-26T16:02:39Z
   Creation Date: 2007-10-09T18:20:50Z
   Registry Expiry Date: 2020-10-09T18:20:50Z
   Registrar: MarkMonitor Inc.
   Registrar IANA ID: 292
   Registrar Abuse Contact Email: abusecomplaints@markmonitor.com
   Registrar Abuse Contact Phone: +1.2083895740
   Domain Status: clientDeleteProhibited https://icann.org/epp#clientDeleteProhibited
   Domain Status: clientTransferProhibited https://icann.org/epp#clientTransferProhibited
   Domain Status: clientUpdateProhibited https://icann.org/epp#clientUpdateProhibited
   Name Server: NS-1283.AWSDNS-32.ORG
   Name Server: NS-1707.AWSDNS-21.CO.UK
   Name Server: NS-421.AWSDNS-52.COM
   Name Server: NS-520.AWSDNS-01.NET
   Name Server: NS1.P16.DYNECT.NET
   Name Server: NS2.P16.DYNECT.NET
   Name Server: NS3.P16.DYNECT.NET
   Name Server: NS4.P16.DYNECT.NET
   DNSSEC: unsigned
   URL of the ICANN Whois Inaccuracy Complaint Form: https://www.icann.org/wicf/
>>> Last update of whois database: 2017-10-16T01:40:30Z <<<

For more information on Whois status codes, please visit https://icann.org/epp

NOTICE: The expiration date displayed in this record is the date the
registrar's sponsorship of the domain name registration in the registry is
currently set to expire. This date does not necessarily reflect the expiration
date of the domain name registrant's agreement with the sponsoring
registrar.  Users may consult the sponsoring registrar's Whois database to
view the registrar's reported date of expiration for this registration.

TERMS OF USE: You are not authorized to access or query our Whois
database through the use of electronic processes that are high-volume and
automated except as reasonably necessary to register domain names or
modify existing registrations; the Data in VeriSign Global Registry
Services' ("VeriSign") Whois database is provided by VeriSign for
information purposes only, and to assist persons in obtaining information
about or related to a domain name registration record. VeriSign does not
guarantee its accuracy. By submitting a Whois query, you agree to abide
by the following terms of use: You agree that you may use this Data only
for lawful purposes and that under no circumstances will you use this Data
to: (1) allow, enable, or otherwise support the transmission of mass
unsolicited, commercial advertising or solicitations via e-mail, telephone,
or facsimile; or (2) enable high volume, automated, electronic processes
that apply to VeriSign (or its computer systems). The compilation,
repackaging, dissemination or other use of this Data is expressly
prohibited without the prior written consent of VeriSign. You agree not to
use electronic processes that are automated and high-volume to access or
query the Whois database except as reasonably necessary to register
domain names or modify existing registrations. VeriSign reserves the right
to restrict your access to the Whois database in its sole discretion to ensure
operational stability.  VeriSign may restrict or terminate your access to the
Whois database for failure to abide by these terms of use. VeriSign
reserves the right to modify these terms at any time.

The Registry database contains ONLY .COM, .NET, .EDU domains and
Registrars.

（4）dig 命令

➜  dist git:(dev) ✗ dig www.baidu.com 

; <<>> DiG 9.8.3-P1 <<>> www.baidu.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39734
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.baidu.com.         IN  A

;; ANSWER SECTION:
www.baidu.com.      528 IN  CNAME   www.a.shifen.com.
www.a.shifen.com.   528 IN  A   220.181.111.188
www.a.shifen.com.   528 IN  A   220.181.112.244

;; Query time: 22 msec
;; SERVER: 10.39.1.10#53(10.39.1.10)
;; WHEN: Mon Oct 16 09:41:54 2017
;; MSG SIZE  rcvd: 90

参考文章
http://www.ruanyifeng.com/blog/2016/06/dns.html