dig 命令
2013-11-28 by dongnan
举个栗子
查看 mx 记录：
dig mx 163.com
; <<>> DiG 9.8.1-P1 <<>> mx 163.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27783
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 6, ADDITIONAL: 9
;; QUESTION SECTION:
;163.com. IN MX
;; ANSWER SECTION:
163.com. 17427 IN MX 10 163mx02.mxmail.netease.com.
163.com. 17427 IN MX 10 163mx03.mxmail.netease.com.
163.com. 17427 IN MX 50 163mx00.mxmail.netease.com.
163.com. 17427 IN MX 10 163mx01.mxmail.netease.com.
设置超时参数
由于超时时间设置为1秒，所以没有得到结果：
dig @172.27.233.1 zongming.net +time=1
; <<>> DiG 9.8.1-P1 <<>> @172.27.233.1 zongming.net +time=1
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be reached
简化输出信息
默认输出
dig ywwd.net
; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.37.rc1.el6_7.2 <<>> ywwd.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56013
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;ywwd.net. IN A
;; ANSWER SECTION:
ywwd.net. 3597 IN A Server_IP
;; Query time: 1 msec
;; SERVER: 202.106.0.20#53(202.106.0.20)
;; WHEN: Tue Dec 29 16:23:30 2015
;; MSG SIZE rcvd: 42
简化信息 +nocmd +nocomment
dig +nocmd +nocomment ywwd.net
;ywwd.net. IN A
ywwd.net. 590 IN A Server_IP
;; Query time: 0 msec
;; SERVER: 127.0.1.1#53(127.0.1.1)
;; WHEN: Wed Oct 21 11:24:50 CST 2015
;; MSG SIZE rcvd: 48
迭代解析
使用 +trace 参数开始迭代解析：
dig +trace ywwd.net
; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.37.rc1.el6_7.2 <<>> +trace ywwd.net
;; global options: +cmd #13个根域名服务器地址
. 154709 IN NS e.root-servers.net.
. 154709 IN NS m.root-servers.net.
. 154709 IN NS f.root-servers.net.
. 154709 IN NS l.root-servers.net.
. 154709 IN NS h.root-servers.net.
. 154709 IN NS d.root-servers.net.
. 154709 IN NS a.root-servers.net.
. 154709 IN NS j.root-servers.net.
. 154709 IN NS b.root-servers.net.
. 154709 IN NS g.root-servers.net.
. 154709 IN NS k.root-servers.net.
. 154709 IN NS c.root-servers.net.
. 154709 IN NS i.root-servers.net.
;; Received 228 bytes from 202.106.0.20#53(202.106.0.20) in 94 ms
# 13个.net 域名服务器地址
net. 172800 IN NS b.gtld-servers.net.
net. 172800 IN NS f.gtld-servers.net.
net. 172800 IN NS e.gtld-servers.net.
net. 172800 IN NS k.gtld-servers.net.
net. 172800 IN NS j.gtld-servers.net.
net. 172800 IN NS l.gtld-servers.net.
net. 172800 IN NS a.gtld-servers.net.
net. 172800 IN NS d.gtld-servers.net.
net. 172800 IN NS g.gtld-servers.net.
net. 172800 IN NS m.gtld-servers.net.
net. 172800 IN NS c.gtld-servers.net.
net. 172800 IN NS i.gtld-servers.net.
net. 172800 IN NS h.gtld-servers.net.
;; Received 511 bytes from 192.36.148.17#53(192.36.148.17) in 112 ms
# ywwd.net 域名管理服务器地址
ywwd.net. 172800 IN NS f1g1ns1.dnspod.net.
ywwd.net. 172800 IN NS f1g1ns2.dnspod.net.
;; Received 237 bytes from 192.31.80.30#53(192.31.80.30) in 279 ms
ywwd.net. 3600 IN A 103.56.115.37 #ywwd.net A记录
ywwd.net. 86400 IN NS f1g1ns1.dnspod.net.
ywwd.net. 86400 IN NS f1g1ns2.dnspod.net.
;; Received 106 bytes from 182.140.167.188#53(182.140.167.188) in 32 ms
请求流程：
- dig 请求ISP
DNS：202.106.0.20并不知道ywwd.net的 A记录是什么。 - 通知
dig去问根（root）域名服务器。 - 根域名服务器仍然没有此记录，通知
dig去问.net的域名服务器。 .net域名服务器仍然没有此记录，通知dig去问f1g1ns1.dnspod.net(ywwd.net域名管理服务器)。- 最后在
f1g1ns1.dnspod.net域名服务器，找到了ywwd.net的A记录。
这种一问一答的解析方式，叫做迭代解析（Iterative resolution）。这种方式下，每个域名服务器只是给出它所知道的最佳答案。
递归解析
默认为递归解析
dig ywwd.net
; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.37.rc1.el6_7.5 <<>> ywwd.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 588
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;ywwd.net. IN A
;; ANSWER SECTION:
ywwd.net. 3598 IN A 103.56.xx.37
;; Query time: 2 msec
;; SERVER: 202.106.0.20#53(202.106.0.20)
;; WHEN: Wed Jan 6 11:06:26 2016
;; MSG SIZE rcvd: 42
请求流程:
- 上面示例的解析方式是递归解析（
recursive resolution）。 - 也是
dig默认的请求方式，对ISPDNS：202.106.0.20请求一个递归解析。 - 由
ISP DNS负责去解析到最终答案，最后直接返回给dig。
通常情况下客户端（dig）对域名服务器发起的递归解析请求，而域名服务器对其他域名服务器的请求（如根域名服务器）是迭代解析请求。
命令帮助
NAME
dig - DNS lookup utility
SYNOPSIS
dig [@server] [-b address] [-c class] [-f filename] [-k filename]
[-m] [-p port#] [-q name] [-t type] [-v] [-x addr] [-y [hmac:]name:key]
[[-4] | [-6]] [name] [type] [class] [queryopt...]
DESCRIPTION
dig is a flexible tool for interrogating DNS name servers.
It performs DNS lookups and displays the answers that are returned from the name server(s) that were queried.
QUERY OPTIONS
+timeout=T
Sets the timeout for a query to T seconds. The default timeout is 5 seconds.
An attempt to set T to less than 1 will result in a query timeout of 1 second being applied.
+[no]cmd
Toggles the printing of the initial comment in the output identifying
the version of dig and the query options that have been applied. This comment is printed by default.
+[no]comments
Toggle the display of comment lines in the output. The default is to print comments.
+[no]trace
Toggle tracing of the delegation path from the root name servers for the name being looked up.
Tracing is disabled by default. When tracing is enabled, dig makes iterative queries to resolve the
name being looked up. It will follow referrals from the root servers,
showing the answer from each server that was used to resolve the lookup.
If @server is also specified, it affects only the initial query for the root zone name servers.
+dnssec is also set when +trace is set to better emulate the default queries from a nameserver.