Class A subnetting Help  | | |
January 22nd, 2009, 12:08 PM
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#1 (permalink)
| | Junior Member
Join Date: Jan 2009
Posts: 16
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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? ________________ |
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January 22nd, 2009, 03:48 PM
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#2 (permalink)
| | Ultimate Member
Join Date: Jun 2004 Location: England
Posts: 1,407
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Why the insistence on binary and no shortcuts? |
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January 22nd, 2009, 03:54 PM
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#3 (permalink)
| | Junior Member
Join Date: Jan 2009
Posts: 16
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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 |
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January 22nd, 2009, 04:01 PM
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#4 (permalink)
| | Ultimate Member
Join Date: Jun 2004 Location: England
Posts: 1,407
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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. |
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January 22nd, 2009, 04:06 PM
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#5 (permalink)
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January 22nd, 2009, 04:13 PM
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#6 (permalink)
| | Ultimate Member
Join Date: Jun 2004 Location: England
Posts: 1,407
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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. |
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January 22nd, 2009, 04:15 PM
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#7 (permalink)
| | Junior Member
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January 22nd, 2009, 04:23 PM
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#8 (permalink)
| | Ultimate Member
Join Date: Jun 2004 Location: England
Posts: 1,407
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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 |
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January 22nd, 2009, 04:26 PM
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#9 (permalink)
| | Junior Member
Join Date: Jan 2009
Posts: 16
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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. |
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January 22nd, 2009, 04:29 PM
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#10 (permalink)
| | Ultimate Member
Join Date: Jun 2004 Location: England
Posts: 1,407
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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? |
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