Old Quizzes - Questions

Old Quizzes - Questions

by Devrim Celik -
Number of replies: 2

Hello, I just trained with the old quizzes and have some questions



1) You type a URL in your web client (for the first time). How many HTTP requests does the web client generate?

A: 1 or more

Question: 1 is for the base file and possibly more for referenced files on the base file?



2) You type a URL in your web client. What is the minimum number of DNS requests that your computer may generate?

A: 0

Question: I though it is 1, since the client DNS request the data from a local DNS that may have it cached? What am I missing? That my browser itself may cache it?



3)  A massive denial-of-service (DoS) attack starts against the epfl.ch authoritative DNS servers. As a result:

A: After some time, non-EPFL Internet end-systems cannot reach any EPFL destination

Question: After some time refers to the expiration date of cached data of it?



4)  You access a web page that consists of 1 HTML file and 3 pictures, all stored on the same server. Suppose your browser uses a single non-persistent connection, and that DNS resolution has already been completed. What is the minimum number of round-trip-times needed to display the web page?

A: 8 RTTs

Question: My initial thought was 5 (1 RTT for TCP connection and then 4 for the HTTP requests). Is it 8, because TCP needs to establish contact before every new request?


Thank you in advance!

In reply to Devrim Celik

Re: Old Quizzes - Questions

by Katerina Argyraki -

Hi Devrim,

Answers point by point:

1) Yes, exactly.

2) Almost. It's not the web browser that may have cached the mapping. It's the DNS client that may have cached it. It's not only DNS servers that cache, it's. also the DNS clients.

3). Yes, exactly.

4) Yes, because the TCP connections are non-persistent.  (This year we did not really discuss non-persistent connections, so I won't focus on them. In previous years we did.)