Chapter 1: Review of packet-switching and circuit-switching networks

Consider the network below, where a client is using his laptop to access the intranet web site. There are two main end-to-end communications involved:

1. a) when requesting the IP address of the web server from the DNS server;
2. b) when accessing the web site.

• The standard server port numbers for DNS and HTTP are 53 and 80, respectively. The clients use random port numbers, which we consider in this case are 1220 for DNS and 1530 for HTTP.

• Lets start with the first communication, i.e. getting IP address from the DNS server. Answer the following questions based on the figure. Q1. Switching Table Fill S1 switch table (columns 2 and 3 of the table below) after each of the steps below. If the table will not change (i.e. no entry will be added to the table):
  1. write down NO CHANGE in the related row (in column 2).
  2. Write down NONE in the last column (in column 3).
• Assume:
  1. At the beginning, all the switching tables are empty
  2. At each step, consider that the previous steps have already been processed (i.e. have already occurred).
• Q2. Switch functionality Following the steps in Q1 (i.e. the previous question),
  1. (1) where will the switch S1 send the frame in each step? --> Column 3 of the table
  2. (2) which devices will receive the message? --> Column 4 of the table
• NOTE: if a cell is left empty, you will get zero for that cell (i.e. because I dont know if it is empty because nothing is added or because you dont know the answer).

Step	MAC address (a wrongly written MAC address is a wrong answerr)	Output interface		Frame sent via interface (list the interfaces via which the frame will be sent, separated by a comma.)	List of devices receiving/hearing the message (List all the devices in the figure that will receive/hear the message, except S1 and the message source, separated by a comma.)
1- The laptop sends an ARP request to get the MAC address of the default gateway.	Blank 1	Blank 2		Blank 3	Blank 4
2- The gateway sends the reply to the request in step 1	Blank 5	Blank 6		Blank 7	Blank 8
3- The laptop sends a DNS request to get the IP address of the web server.	Blank 9	Blank 10		Blank 11	Blank 12
4- The DNS server replies to the request in step 3	Blank 13	Blank 14		Blank 15	Blank 16
5- The laptop sends a message to the desktop.	Blank 17	Blank 18		Blank 19	Blank 20