I have add a line in my /etc/hosts file on the local pc.

220.181.57.217 baidu.com


Now reboot my pc,and input dig command in the console.

dig +trace baidu.com

; <<>> DiG 9.9.5-9+deb8u3-Debian <<>> +trace baidu.com
;; global options: +cmd
. 479168 IN NS c.root-servers.net.
. 479168 IN NS d.root-servers.net.
. 479168 IN NS f.root-servers.net.
. 479168 IN NS a.root-servers.net.
. 479168 IN NS l.root-servers.net.
. 479168 IN NS j.root-servers.net.
. 479168 IN NS e.root-servers.net.
. 479168 IN NS b.root-servers.net.
. 479168 IN NS g.root-servers.net.
. 479168 IN NS m.root-servers.net.
. 479168 IN NS h.root-servers.net.
. 479168 IN NS i.root-servers.net.
. 479168 IN NS k.root-servers.net.
. 479168 IN RRSIG NS 8 0 518400 20151229170000 20151219160000 62530 . oOJd1U9xP2VwRw/QaOyTRrRS0fqNBNvJcH4NMpEx5xodWsKUX3G1Azf6 DBZoEMdqlu8LQn/BgIUD54hzh/Z58+hus1CHmbN+ic6Ys6Fz1PRXtbts lfX9PjQ/snk2KfkWc/+U5Zouild611+ynR612cNm21Va9wigdywDlTuu Sws=
;; Received 397 bytes from 192.168.1.1#53(192.168.1.1) in 5502 ms

com. 172800 IN NS m.gtld-servers.net.
com. 172800 IN NS l.gtld-servers.net.
com. 172800 IN NS k.gtld-servers.net.
com. 172800 IN NS j.gtld-servers.net.
com. 172800 IN NS i.gtld-servers.net.
com. 172800 IN NS h.gtld-servers.net.
com. 172800 IN NS g.gtld-servers.net.
com. 172800 IN NS f.gtld-servers.net.
com. 172800 IN NS e.gtld-servers.net.
com. 172800 IN NS d.gtld-servers.net.
com. 172800 IN NS c.gtld-servers.net.
com. 172800 IN NS b.gtld-servers.net.
com. 172800 IN NS a.gtld-servers.net.
com. 86400 IN DS 30909 8 2 E2D3C916F6DEEAC73294E8268FB5885044A833FC5459588F4A9184CF C41A5766
com. 86400 IN RRSIG DS 8 1 86400 20151230050000 20151220040000 62530 . mW3cdOQcjyRga66RZ81q0CWdSYD8nOxNCDoCCTeQlJMEq0Fi9l4gwUuX IAEB/JO+KWYA9xX8VF1oTuqfrVQyDId7vRqI6DO008T1LGyi/nM+RXMc 5lTXPtROTNwxwz+fbhARdysttbtLG9ZWOoI3m4nh4Q2ufVtuELEwVXAH VT8=
;; Received 733 bytes from 192.58.128.30#53(j.root-servers.net) in 5290 ms

baidu.com. 172800 IN NS dns.baidu.com.
baidu.com. 172800 IN NS ns2.baidu.com.
baidu.com. 172800 IN NS ns3.baidu.com.
baidu.com. 172800 IN NS ns4.baidu.com.
baidu.com. 172800 IN NS ns7.baidu.com.
CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN NSEC3 1 1 0 - CK0Q1GIN43N1ARRC9OSM6QPQR81H5M9A NS SOA RRSIG DNSKEY NSEC3PARAM
CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN RRSIG NSEC3 8 2 86400 20151226055326 20151219044326 51797 com. SpiAXslRV5sdT+l4wrsYTn/W3dH1UJcmd2eO0cXluTAkaS9TDp4an0qd jNxu6U51N4K09aaj8tkSqPi4JlGFUV9Yx3c//ytPaqWt7dOmUaEvnihL egFcLcTL6DD7RVvEoLT6aANmg8jDS9pQXjFIR3wDRDqLvfs6L96uqGvc V1w=
HPVV2B5N85O7HJJRB7690IB5UVF9O9UA.com. 86400 IN NSEC3 1 1 0 - HPVV9UNFR23OVV2EH3NNTJ1A7JE3ETFH NS DS RRSIG
HPVV2B5N85O7HJJRB7690IB5UVF9O9UA.com. 86400 IN RRSIG NSEC3 8 2 86400 20151224055400 20151217044400 51797 com. lgVCSGarWuNm8H3sGsL67h0zDnhl8ZaH0U35a5ixBI7vEOSHeFQcbdOY FGDzeCGlJteVGJclePrcQ6hOwI16FJTu4x5UEBpSI1CeibKBqVddUWOC Gr1od28i4UTsifloURwinfm0TdLGdbdK6E4egQ5MdbW1B+Zhfp24IVpy 0zo=
;; Received 693 bytes from 192.31.80.30#53(d.gtld-servers.net) in 3330 ms

baidu.com. 600 IN A 123.125.114.144
baidu.com. 600 IN A 180.149.132.47
baidu.com. 600 IN A 220.181.57.217
baidu.com. 600 IN A 111.13.101.208
baidu.com. 86400 IN NS ns4.baidu.com.
baidu.com. 86400 IN NS dns.baidu.com.
baidu.com. 86400 IN NS ns2.baidu.com.
baidu.com. 86400 IN NS ns3.baidu.com.
baidu.com. 86400 IN NS ns7.baidu.com.
;; Received 272 bytes from 119.75.219.82#53(ns7.baidu.com) in 463 ms

We can get the conclusion that ： to 192.168.1.1（my net gateway on local net）
to j.root-servers.net
to d.gtld-servers.net
to ns7.baidu.com
to 220.181.57.217 (one ip of many baidu.com's)

why the path is not :
to 192.168.1.1（my net gateway on local net）
directly to 220.181.57.217

I have set /etc/hosts `220.181.57.217 baidu.com`.

dig is a dns testing tool, so it uses exclusively nameservers to resolve a domain
Other tools/commands like ping are first using the entries in /etc/hosts and then dns lookups
You can use "127.0.0.1 baidu.com" in /etc/hosts and then ping baidu.com to see what happens

Regards

1 members found this post helpful.

And even if you have a local nameserver/forwarder like dnsmasq which consults /etc/hosts, the "+trace" option to dig tells it to start from the root servers and report each step along the way. That's never going to look at what you've done locally (unless you happen to be the registered nameserver for the domain, of course).

1 members found this post helpful.