Class A subnetting Help

[macdiesel]

I feel I can pretty much subnet a Class B or Class C network address with no problems. When it comes to class A I get stumbled because the numbers get very large and I can't do the math quickly in my head.

How would you solve the following problem using the binary method and no shortcuts. I would really appreciate it. I can get the subnet mask no problem. How do i determine what the 303rd subnet would be easily??

Network: 14.0.0.0

Need 500 Subnetworks with as many hosts per subnet as possible
--------------------------------------------------------------------------------
Solve for -

Subnet Mask: ____________________________________

For the 303rd usable subnetwork, give the IP address for:

Wire (network) #:________________________

1st Usable:___________________________

Last Usable:_________________________

Broadcast:______________________________

How many usable subnets are possible? _______________
How many usable hosts/subnet are possible? ________________

[27]

Why the insistence on binary and no shortcuts?

[macdiesel]

Because I want to know why it works the way it does, but if you know shortcuts that will work too. So I can at least know how to jump to say the 303rd subnet quickly. Thanks

[27]

Right.
I need you to write on a sheet of paper.

You need to make three columns.

1. Number of subnets
2. Worth
3. Subnet Mask

Let me know when you've made these three headings.

[macdiesel]

Got it.

[27]

Next, you'll need to make a table with those headings.

Column 1 (Number of subnets).
Start with the number 2 and double it until yo reach 256.
2, 4, 8, 16, 32, 64, 128, 256.

Column 2 (Worth).
Start with 128 and divide by 2 it until you reach 1.
128, 64, 32, 16, 8, 4, 2, 1.

Column 3 (Subnet mask).
The cumulative sum of the previous column.
128, 192, 224, 240, 248, 252, 254, 255.

Let me know when that is written.

[macdiesel]

Ok I have done that.

[27]

You implied that you know what class an address belongs to but I'll cover this as well.

A: 1.0.0.0 to 126.0.0.0
B: 128.0.0.0 to 191.255.0.0
C: 192.0.0.0 to 223.255.255.0

[macdiesel]

Yes so the default subnet mask for 14.0.0.0 is 255.0.0.0. Since I need 500 subnetworks we need to borrow 9 bits (creates 512 usable subnetworks), which makes the new mask 255.255.128.0.

[27]

Ah, but you already have 8 bits.
So you only need to "borrow" one bit to get 9.

Therefore, your new subnet mask should be 255.128.0.0. Do you understand?