quetion about subnetmask on techexams.net

patelhari

hi i have found this question here on techExams.net and i dont understand how they have counted.

44. You are designing an IP addressing scheme for a company using CIDR compliant routing protcol and routers configured with the ip subet-zero command. You have been assigned a class B network address 172.16.4.0 and you have to divide it into 15 subnets with at minimum of 3000 hosts each. What subnet should you use?

a. 255.255.0.0
b. 255.255.192.0
c. 255.255.255.240
d. 255.255.224.0
e. 255.255.240.0
f. 255.255.248.0

and they said the anwser is e. how come according to my knowledge if u have 16 subnets then u can use only 16-2=14 and it doesnt match the criteria. If i m doing any mistake plz help me here.

EdTheLad

You should read the questions carefully,its stated in the question ip subnet-zero is enabled therefore you can use the first and the last subnet.
i.e you dont have 16-2 subnets you have 16!!

patelhari

thank you for your help. i didnt realised and i didnt knew about that. i will take care of that subnet zero.

milliamp

Also, there has been some discussion of subnet-zero in the past here.

I took the exam 3 days ago, and the CCNA seems to have caught up with real life, in that most questions will now allow it.

There were a few related questions on the exam, but each of them stated to use ip subet-zero as your example question did above.

patelhari

i m going to take exam in the next month and this will help me definately. by the way what was the result for your exam.

mog27

Do you mean ip subnet-zero or ip subet-zero?

patelhari

hey i have copied that from this site only so i think may be he did mistake in typing. but i m not sure.