Question : How to compute subnets

I need to learn subnetting. What are the steps to figure out the 3  network addresses below
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1.I have a network address of 202.20.2.0 I want to create 8 subnets. I want to maximize the number of hosts per subnet. What would the subnet mask be for this network?

2.I also have a network address of 150.56.0.0 and need to create 1000 subnets. I want to maximize thenumber of hosts per subnet. What will the subnet mask be for the network?

3.I have a netowrk address of 200.43.29.0  I want to create as many subnets as possible that can have 30 hosts. What will the subnet mask be for the network?

Also,Is there any software out there that will give me the answers to this,so farwhat I have tried downloading gave me an incorrect answers.

Can someone explain it in simple terms so that I can understand how to do this.

Thanks!

Answer : How to compute subnets

First learn the powers of 2

1    2
2    4
3    8
4    16
5    32
6    64
7    128
8    256

You can keep going up, but you at least need to learn the first 8.

Then, learn counting in binary, backwards from 10000000

8 10000000 128
7 11000000 192
6 11100000 224
5 11110000 240
4 11111000 248
3 11111100 252
2 11111110 254
1 11111111 255

Now, onto your problems

1. 202.20.2.0 I want to create 8 subnets.  First know that 202 is a class C address and it's classful network mask is 255.255.255.0.  So, you need 8 subnets - looking at my first chart, counting down to get at least 8 numbers you see 8 right?  But lets say you're doing it the old fashioned way and don't have subnet zero available so you have to go to 16 and subtract 2 (1 for the subnetwork ID, and 1 for the broadcast ID) so this gives you 16-2 or 14 addresses if you borrow 4 bits.  Now the normal mask is 255.0 right?  Think of that 0 as 00000000 and you have to take four of them - which makes it 11110000.  Looking at my second chart, you can see that that in decimal is 240.  So, the mask is now 255.255.255.240 giving you 14 subnetworks and 14 hosts per subnetwork.

2. 150.56.0.0 and need to create 1000 subnets.  Ok, so keep going on my first chart - 512 for 9 bits, 1024 for 10 bits.  Take 2 from 1024 and you have 1022 networks.  So, you need 10 bits for 1000 subnets.  Your mask is 255.255.0.0 with a class B so you need to take the entire 3rd octet of 8 bits to get another .255 and you need 2 more bits from the 4th octet.  So, second chart tells you that two bits is .192.  So, your mask is now 255.255.255.192.  This leaves you 6 bits for hosts.

3. 200.43.29.0  I want to create as many subnets as possible that can have 30 hosts.  So, instead of counting up the chart for networks, count up for hosts.  5 bits will give you 30 hosts (32-2).  So, you need five bits in the host portion leaving 3 for the subnetwork.  2nd chart says 3 down is 224.  So, the mask on what was your class C is now 255.255.255.224.

One of the best calculators is Solar Winds subnet calculator - google it.  However, until you learn subnetting I wouldn't recommend it - you need to be able to do it without a calculator, off the top of your head, if you're getting into networking.

HTH