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In my PC i am using google public DNS as DNS server.In Internet protocol(TCP/IP) properties i have set Preferred DNS server as 8 8 4 4 and Alternate DNS server as 8 8 8 8.

According to me this DNS server should be used to resolve any request to website to its IP by using this DNS servers.(see google DNS and How Domain Name Servers Work).

But when i checked trace route to a website in my PC i got following

 Tracing route to www.google.com [74.125.236.80] over a maximum of 30 hops:   
 1    <1 ms    <1 ms    <1 ms  192.168.1.201  
 2   360 ms   349 ms   292 ms  122.178.216.1    
 3   145 ms   107 ms   148 ms  122.166.32.121    
 4    32 ms    53 ms   120 ms  122.166.32.9   
 5    45 ms    42 ms   121 ms  122.175.255.29  
 6    63 ms    76 ms    51 ms  182.79.255.45    
 7    52 ms   134 ms    61 ms  72.14.194.22    
 8    86 ms    59 ms    72 ms  72.14.232.202    
 9   106 ms   107 ms    60 ms  66.249.94.39   
10   101 ms   103 ms   117 ms  209.85.249.235   
11   148 ms   224 ms   276 ms  74.125.236.80   Trace complete. 

When i checked all these IP in who.is i found that it is of my ISP. So my question is where does Google public DNS is used? Also how come my ISP's nameserver is used even if i set google public dns as my dns server in my PC?(OR does my any settings are wrong)

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How did you check which DNS is used? Where from do you know that your ISP's name servers are used and not Google's? –  Werner Henze Jun 27 '13 at 9:59
    
In who.is i searched for ip address which are present in trace route.So i found that it was registered to ISP which i use. –  IT researcher Jun 27 '13 at 10:05

2 Answers 2

You don't see the DNS request in traceroute. To see which DNS server is used, try nslookup:

# nslookup www.google.com
Server:         10.0.0.100
Address:        10.0.0.100#53

Non-authoritative answer:
Name:   www.google.com
Address: 173.194.75.106
Name:   www.google.com
Address: 173.194.75.147
Name:   www.google.com
Address: 173.194.75.99
Name:   www.google.com
Address: 173.194.75.103
Name:   www.google.com
Address: 173.194.75.104
Name:   www.google.com
Address: 173.194.75.105

Or:

# dig www.google.com |grep SERVER
;; SERVER: 10.0.0.100#53(10.0.0.100)

The Name and Address (or SERVER) part is your DNS server. Traceroute gives you the route from your IP to google, which of course will go through your ISP.

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You are mixing two different things.

One thing is the DNS. The DNS is like a telephone book for server names and IP addresses. The DNS server tells you the IP address for a server name, for example DNS tells you that www.superuser.com is 198.252.206.16. DNS can also reverse lookup the name for a given IP address.

There are lots of DNS servers out there in the internet, and if they allow it, you can use any of them. If configured correctly, they should all give you the same results.

You can check which DNS server you are using for example when starting a nslookup like this (see the first two lines output with Server and Address):

>nslookup www.superuser.com
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non authoritative answer:
Name:    superuser.com
Address:  198.252.206.16
Aliases:  www.superuser.com

When you are looking at traceroute you are looking at the actual way a packet is taking from your computer to the destination computer (web server). This is not related to DNS in any way. First your computer is looking up the IP address for the destination computer, then it checks if the IP is in your local network. If the IP is not in your local network, then he sends the packet to your router. Your router is doing the same thing. For every packet he receives he is looking up in a big routing table to which network interface he must forward the IP packet. All these routers are either at your location (like your 192.168.1.201), at the destination computer owner's location or they belong to an ISP on the way. Which routers are used is determined by the network topology and the involved ISPs. You cannot influence the way a packet takes, you can only influence the destination point.

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