# IP Ranges for 291 exam

Member Posts: 12 ■□□□□□□□□□
Hi

I am a little confused for the assigment of IP ranges for subnets. I am OK with working out how many subnets and or hosts to allocate etc. but when it comes to the actual IP ranges for these subnets i get confused.... >

On the exam do Microsoft use allocate all subnets or total - 2 i.e. s/mask of 240gives 2^4 = 16 -2 = 14 subnets. OR do they use the RFC 1812(??!) solution and allocate all possible subnets??? i.e. 240 = 2^4 = 16 subnets?

It is the IP ranges that i really am getting probs with, and which host number to begin with etc...

Also how deep do they go on the exam on subnetting/addressing problems? Are there many qustions or sims on it???

I have not been reading this module long, and can see a mountain of material to read!
I thought i could see a light at the end of the tunnel but alas it was just some b_*&^\$£ with a torch bringing me more work!

Any advise would be greatly appreciated.

/Life is just a moment

• Member Posts: 1,192
16 - 2 or 2^N - 2

Net ID = 0
1st Host = 1
Last Host = 14

I suggest understanding Network ID & Broadcast because - 2 address is assigned to this.

So if you got 16 IP address you will take out 2 IP address because Network ID and Broadcast will use them.
• Member Posts: 1,192
You will need to convert Z (WXYZ) 240 to octet binary, then segregate the 1 bits to 0 bits then the 1st bit you see starting from your right you will find out the decimal value of that 1st bit to your right, you should call that decimal number "Magic Number" depending on the value of that number you will keep on adding same value to it. I tried putting my formula but tab sucked.

So let's say:

255.255.255.240
1111 | 0000

The 1st 1 bit to your right is "16"

You will then start with 0 - 15 = 16 - 2

Therefore

IP Address Range = xxx.xxx.xxx.1 - xxx.xxx.xxx.14

Net ID = 0
1st Host = 1
Last Host = 14