Thread: Class A subnetting Help
-
January 22nd, 2009, 12:08 PM #1Junior Member
- Join Date
- Jan 2009
- Posts
- 16
Class A subnetting Help
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? ________________
-
January 22nd, 2009, 03:48 PM #2
Why the insistence on binary and no shortcuts?
-
January 22nd, 2009, 03:54 PM #3Junior Member
- Join Date
- Jan 2009
- Posts
- 16
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
-
January 22nd, 2009, 04:01 PM #4
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.
-
January 22nd, 2009, 04:06 PM #5Junior Member
- Join Date
- Jan 2009
- Posts
- 16
Got it.
-
January 22nd, 2009, 04:13 PM #6
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.
-
January 22nd, 2009, 04:15 PM #7Junior Member
- Join Date
- Jan 2009
- Posts
- 16
Ok I have done that.
-
January 22nd, 2009, 04:23 PM #8
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
-
January 22nd, 2009, 04:26 PM #9Junior Member
- Join Date
- Jan 2009
- Posts
- 16
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.
-
January 22nd, 2009, 04:29 PM #10
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?
-
January 22nd, 2009, 04:35 PM #11Junior Member
- Join Date
- Jan 2009
- Posts
- 16
I thought you didn't count the first octet because it is the default mask. You can only have 1 network with the default mask correct? If you only borrow 1 bit you can't subnet I thought because of the 0 subnet.
-
January 22nd, 2009, 04:37 PM #12Junior Member
- Join Date
- Jan 2009
- Posts
- 16
The website I got the problem from even shows the subnet mask of 255.255.128.0
-
January 22nd, 2009, 04:39 PM #13
I believe you do count the first octet.
If you don't and go for 255.255.128.0, you'll end up with 17 network bits and 15 host bits.
That'll give you far more than 500 subnets.
Online IP Subnet Calculator
-
January 22nd, 2009, 04:39 PM #14
-
January 22nd, 2009, 04:43 PM #15Junior Member
- Join Date
- Jan 2009
- Posts
- 16
If I use the calculator you provided and punch in 14.0.0.0 and then 17 mask bits it shows 512 subnets like I stated.
POD #301 Problem 301
-
January 22nd, 2009, 04:48 PM #16
-
January 22nd, 2009, 04:50 PM #17Junior Member
- Join Date
- Jan 2009
- Posts
- 16
So what is the easiest way to get to the 303rd subnet knowing 14.0.0.0/17
-
January 22nd, 2009, 05:02 PM #18
Right.
So we know that:
subnet 0 is 14.0.0.0
subnet 1 is 14.0.128.0
For each next subnet, you add 128 to the 3rd octet.
The 303rd usable subnet would be subnet 304 (due to subnet 0).
You need a quicker way than writing each one down, I presume?
-
January 22nd, 2009, 05:06 PM #19Junior Member
- Join Date
- Jan 2009
- Posts
- 16
That is correct. That would take for ever to write each subnetwork down.
-
January 22nd, 2009, 05:12 PM #20
Are you doing this to prepare for an exam?
Thread Information
Users Browsing this Thread
There are currently 1 users browsing this thread. (0 members and 1 guests)
Similar Threads
-
subnetting?
By moekad in forum Certification and EducationReplies: 7Last Post: January 22nd, 2009, 08:26 PM -
Class B Subnetting help...
By Larfin_Man in forum Networking and InternetReplies: 2Last Post: November 14th, 2008, 09:18 AM -
Networks IP/Subnetting
By asciigrief in forum Networking and InternetReplies: 0Last Post: September 26th, 2008, 12:38 AM -
Subnetting question
By skybolt_1 in forum Networking and InternetReplies: 4Last Post: March 12th, 2004, 12:14 AM -
Subnetting Question
By mAdMaLuDaWg in forum Networking and InternetReplies: 5Last Post: July 11th, 2003, 05:49 PM



LinkBack URL
About LinkBacks



Reply With Quote

I prefer not to be stopped in the street just because someone decided my clothes were "wrong" or my hair was "too long". I do understand and partly agree with your point, but this was too much, IMO.
Do you think this was a legitimate...