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+2 votes
Consider that $15$ machines need to be connected in a LAN using $8$-port Ethernet switches. Assume that these switches do not have any separate uplink ports. The minimum number of switches needed is ______
asked in Computer Networks by Veteran (413k points)
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6 Answers

+5 votes
Best answer

.................. . 

Ans = 3

answered by Loyal (9.1k points)
selected by

@Tuhin Dutta

Plz tell me

what this line means

switches do not have any separate uplink ports

why 1 port interconnected? 

It means the links are duplex.
If ports are not interconnected how can all machines be connected?
Each and every node is connected to a machine and one single node is for connection to neighbor switch so that all machines are connected.
but in our home no switch is interconnected


Ethernet itself can give connection to the machine

isnot it?

Yes but here there are 15 machines. Let's give you an example - We have 3 labs Network lab, OS lab, and Programming lab. Each having 5 machines. Now we have to interconnect all of them. here comes the need for a switch. 

FYR please refer below

book Forouzan,  chp Introduction, sub-topic Network Types.

yes, I opened forouzan, but didnot find the line

"that switch need to be interconnected itself."


Can u plz mention the line of that book, where u find one extra switch need to interconnect other switches?

There's no such line but for interconnection, we need to connect the switches either by a router or directly using one of their port. Refer below images which are taken from Forouzan,5th edition.


The above two images hopefully will clear your doubt.

connection with circuit switching

Yes correct!
+4 votes

So, Answer is $3$
answered by Junior (501 points)
edited by
is this question for 1 mark or 2 marks?
+3 votes
3 is the answer i think
answered by Active (1.1k points)
Yeah, I also wrote 3 :0
how much marks for this question?
Can you explain how?
+2 votes
Out of 8 ports 1 port dedicated to the switch itself .hence 7 available ports for the clients.there are 15 clients s no of switches =3
answered by Junior (745 points)
+2 votes
There are 15 devices. And there are 8 ports in 1 Ethernet switch. So it's obvious that one switch is not sufficient. So one more switch is required. So in 1st switch only 7 ports are connected to 7 devices and 8th one is used for connecting to another switch. Now come to second switch. Only 7 ports are left as 1st port is used for connecting to 1st switch. Those 7 ports can be connected to 7 devices. But there are total 15 devices and so 1 would be left. So we need another switch. So now, in second switch we connect 6 devices to 6 ports and last port to third switch. And in the last switch 1st port is connected to 2nd switch and two ports to two left devices.So we require 3 switches in total.
answered by (303 points)
0 votes
3 are required
answered by (11 points)

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