GATE | GATE-CS-2016 (Set 2) | Question 35

Identify the correct sequence in which the following packets are transmitted on the network by a host when a browser requests a webpage from a remote server, assuming that the host has just been restarted.

(A) HTTP GET request, DNS query, TCP SYN
(B) DNS query, HTTP GET request, TCP SYN
(C) DNS query, TCP SYN, HTTP GET request
(D) TCP SYN, DNS query, HTTP GET request


Answer: (C)

Explanation: Step 1 : Whenever the client request for a webpage, the query is made in the form say www.geeksforgeeks.org.
As soon as the query is made the server makes the DNS query to identify the Domain Name Space. DNS query is the process to identify the IP address of the DNS such as www.org. The client’s computer will make a DNS query to one of its internet service provider’s DNS server.

Step 2 : As soon as DNS server is located a TCP connection is to be established for the further communication. The TCP protocol requests the server to establishing a connection by sending a TCP SYN message. Which is further responded by the server using SYN_ ACK from server to client and then ACK back to server from client (3- way hand shaking protocol).

Step 3 : Once the connection has been established the HTTP protocol comes into picture. It requests for the webpage using its GET method and thus, sending an HTTP GET request.

Hence, the correct sequence for the transmission of packets is
DNS query, TCP SYN, HTTP GET request.

This explanation has been contributed by Namita Singh.

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