GATE CSE 2016 Set 2 | Question: 25

Question

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.

Comments

similar question.

https://gateoverflow.in/1792/gate2014-1-25

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This line "assuming that the host has just been restarted".

Simply weed out options (a) and (d) and from option (b) and (c)

-------> option B) w/o making TCP connection establishment with server doing HTTP GET request.

 

 

Answer 1

Here,

C) Seems correct answer.

Say you type www.google.com

FIrst you send DNS request to get IP address. Then you establish connection with IP of google using TCP. Finally you start talking in HTTP !

Comments

@Akash & @Sachin Thanks nice explanation.

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@Akash Kanase can you please tell that do we here need a udp connection before dns query?

because DNS uses udp at transport layer.

 

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UDP do't required any connection establishment like TCP. but yes we use UDP in DNS.

Answer 2

DNS --> Domain name converted to IP  address for that we need DNS

TCP --> Connection established using TCP

FTP --> web pages which is prepared in ur local host  move to a server for that we need FTP

HTTP -->  using HTTP we get web pages

Answer 3

The question is asking for the correct sequence of events when a browser requests a webpage from a remote server, given that the host has just been restarted.

The correct sequence is:

1. DNS query: The client needs to resolve the server's domain name into an IP address to know where to send the request. This is accomplished using the Domain Name System (DNS).
2. TCP SYN: Once the client has the server's IP address, it initiates a TCP connection with the server. This is done using a SYN (synchronize) packet, which is part of the TCP three-way handshake (SYN, SYN-ACK, ACK).
3. HTTP GET request: Once the TCP connection is established, the client can send an HTTP GET request to the server to ask for the webpage.

So, option 3 (DNS query, TCP SYN, HTTP GET request) is the correct answer.