1.How can you modify your operating system congurations so that when a DNS query

Question

1.How can you modify your operating system congurations so that when a DNS query is made, that is sent to a specic DNS sever (e.g., Google’s)?

2.Suppose within your Web browser you click on a link to obtain a Web page. The IP address for the associated URL is not cached in your local host, so a DNS lookup is necessary to obtain the IP address. Suppose that n DNS servers are visited before your host receives the IP address from DNS; the successive visits incur an RTT of RTT1 + RTT2 + ... + RTTn. Further suppose that the Web page associated with the link contains exactly one object, consisting of a small amount of HTML text. Let RTT0 denote the RTT between the local host and the server containing the object. Assuming zero transmission time of the object, how much time el apses from when the client clicks on the link until the client receives the object?

Explanation / Answer

Answers:

(1). This option is as per the operating system. You need to open the network manager or network settings or similar kind of words in which you can change your network settings. This can't be answered as an exact word because it is different for different os like Windows, Linux etc.

Now, open a network connection in which you want to change the DNS server.

Now, in that network, you will get 2 options: IPv4 settings and IPv6 settings.

In general, now a days, IPv4 is used at most of the places but the trend will be of IPv6 after some time. So, it is advised to change both IP address DNS servers.

Open IPv4 settings, there is an option saying 'Additional DNS Servers' or 'Default DNS Server' and by default one IP address is written in it. You change that address by typing your desired DNS Server IP address. As it is mentioned in the question, Google DNS Server IP address is 8.8.8.8

So, once you type that address in that field and save the configuration settings, every time when you request a DNS query, it is redirected towards Google DNS Server.

Change the same settings in the IPv6 tab also.

(2). Here, the DNS lookup is necessary and from your computer, it goes to many DNS servers and if we start from our computer, the time taken is RTT1 + RTT2 + RTTn. Here, RTT means Round Trip Time. For example, RTT1 means from your computer to first DNS server and then back to your computer.

So, total of RTT1 + RTT2 + ... + RTTn time is required when your computer is finally getting the required server address. Now, you have that address so you are querying that server directly and getting the result in RTT0 time.

As the transmission cost is neglected in the total scenario, the only time you need to consider is the round trip time.

So, for the given scenario, RTT1 + RTT2 + ... + RTTn time is used first and at last RTT0 time is used. So, the total of RTT0 + RTT1 + RTT2 + ... + RTTn time is elapsed.

Please comment for any query. Thank you. :)

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