Dig understands DNS resolution process

Article Title: dig understands the DNS resolution process. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

[Root @ localhost ~] # Dig www.a.com

; <> DiG 9.2.4 <> www.a.com

; Global options: printcmd

; Got answer:

;-> HEADER <-opcode: QUERY, status: NOERROR, id: 25746

; Flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 6, ADDITIONAL: 6

; Question section:

; Www.aslibra.com. IN

; Answer section:

Www.aslibra.com. 900 in a 222.76.215.25

; Authority section:

Aslibra.com. 33024 in ns k8.hkidc.com.

Aslibra.com. 33024 in ns B .hkidc.com.

Aslibra.com. 33024 in ns j6.hkidc.com.

Aslibra.com. 33024 in ns ns8.hkidc.com.

Aslibra.com. 33024 in ns ns5.hkidc.com.

Aslibra.com. 33024 in ns a.hkidc.com.

; Additional section:

K8.hkidc.com. 55596 in a 125.65.112.32

B .hkidc.com. 53594 IN A 221.122.64.81

J6.hkidc.com. 54375 in a 222.76.219.74

Ns8.hkidc.com. 53598 in a 221.122.64.81

Ns5.hkidc.com. 55596 in a 222.76.219.81

A.hkidc.com. 53594 in a 125.65.112.32

; Query time: 71 msec

; SERVER: 211.99.25.1 #53 (211.99.25.1)

; WHEN: Mon Jun 1 12:05:17 2009

; Msg size rcvd: 268

How to Understand the above meaning?

Question section: Query content

Answer section: the corresponding content. Generally, at least one A record is obtained. Otherwise, it is not defined.

Authority section: authorization information

Additional section: IP address of each authorized Server

SERVER: The queried dns SERVER may be cached.

The process is generally:

1. query www.a.com from the SERVER. If there is a valid cache, return

2. If not, find the authorization server of a.com. The following is an example.

3. query results from one of them (A record)

Let's take a look at the specific parsing process.

"Dig www.a.com + trace" allows you to view more specific parsing processes.

Let's use a big website, such as www.163.com.

First, let's see what we get without trace:

[Root @ localhost ~] # Dig www.163.com

; <> DiG 9.2.4 <> www.163.com

; Global options: printcmd

; Got answer:

;-> HEADER <-opcode: QUERY, status: NOERROR, id: 46550

; Flags: qr rd ra; QUERY: 1, ANSWER: 11, AUTHORITY: 2, ADDITIONAL: 2

; Question section:

; Www.163.com. IN

; Answer section:

Www.163.com. 51561 in cname www.cache.gslb.netease.com.

Www.cache.gslb.netease.com. 1604 in a 61.135.253.16

Www.cache.gslb.netease.com. 1604 in a 61.135.253.17

Www.cache.gslb.netease.com. 1604 in a 61.135.253.18

Www.cache.gslb.netease.com. 1604 in a 61.135.253.9

Www.cache.gslb.netease.com. 1604 in a 61.135.253.10

Www.cache.gslb.netease.com. 1604 in a 61.135.253.11

Www.cache.gslb.netease.com. 1604 in a 61.135.253.12

Www.cache.gslb.netease.com. 1604 in a 61.135.253.13

Www.cache.gslb.netease.com. 1604 in a 61.135.253.14

Www.cache.gslb.netease.com. 1604 in a 61.135.253.15

; Authority section:

Gslb.netease.com. 1604 in ns gslb1.netease.com.

Gslb.netease.com. 1604 in ns gslb2.netease.com.

; Additional section:

Gslb1.netease.com. 15896 in a 61.135.20.143

Gslb2.netease.com. 15900 in a 220.181.28.168

; Query time: 56 msec

; SERVER: 211.99.25.1 #53 (211.99.25.1)

; WHEN: Mon Jun 1 12:29:51 2009

; Msg size rcvd: 298

The answer section tells you:

Www.163.com alias to www.cache.gslb.netease.com

Www.cache.gslb.netease.com has such A series of machines (A records) that you can choose to access.

Let's see what information is after trace is added:

[Root @ localhost ~] # Dig www.163.com + trace

; <> DiG 9.2.4 <> www.163.com + trace

; Global options: printcmd

. 223628 in ns e.root-servers.net.

. 223628 in ns f.root-servers.net.

. 223628 in ns g.root-servers.net.

. 223628 in ns h.root-servers.net.

. 223628 in ns I .root-servers.net.

. 223628 in ns j.root-servers.net.

. 223628 in ns k.root-servers.net.

. 223628 in ns l.root-servers.net.

. 223628 in ns m.root-servers.net.

. 223628 in ns a.root-servers.net.

. 223628 in ns B .root-servers.net.

. 223628 in ns c.root-servers.net.

. 223628 in ns d.root-servers.net.

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