# subnet design

#### chronic9

##### Supreme [H]ardness
A company was assigned their primary IP address 210.110.16.1. The general manager decided to have 3 major subnets under the top network. Design those 3 subnets IP addresses. Under each subnet you designed, tell the maximum how many host computers you can add in?

i understand a lil' bit about subnets and the professor posted that simply as extra credit....

cany anyone help me?

Here's to hoping I'm first and somebody else didn't cheap out and use and online tool while I was doing the math because it's good to stay in practice.
You can't actually do three subnets from a Class C network. Math doesn't work out like that. So you would actually be creating 4 networks from that Class C IP range.

So you would have 210.110.16./26
/26 means 2 Network bits used and 6 Network bits NOT used

n
2 = N Where n is the number of Network bits used.

n
2 - 2 = H Where n is the number of Network bits NOT used. The bits not used are Host bits.

2
2 = 4N for 4 different Networks .0/.64/.128/.192

6
2 - 2 = 62H for 62 possible Hosts .0-.63/.64-.127/.128-.191/.192-.255 (as always first and last cannot be used)

So you would have these 4 networks available if my math is correct.

210.110.16.1 - 210.110.16.62
210.110.16.65 - 210.110.16.126
210.110.16.129 - 210.110.16.190
210.110.16.193 - 210.110.16.254

EDIT: Those should be 2 to the power of the letter/number above it...it's formatted correctly in the box but posts differently.

Corrected thanks to tar's catch.

Shouldn't all the subnet masks be 255.255.255.192?

Here's a simple chart we learned in class that is quite useful for doing subnetting questions by hand. The first column are your powers of 2. The second is their value which mean either number of subnets or total number of IPs (including network and broadcast) and the third column is the subnet mask.

Code:
``````2^0	1	0
2^1	2	128
2^2	4	192
2^3	8	224
2^4	16	240
2^5	32	248
2^6	64	252
2^7	128	254
2^8	256	255``````

Shouldn't all the subnet masks be 255.255.255.192?

Here's a simple chart we learned in class that is quite useful for doing subnetting questions by hand. The first column are your powers of 2. The second is their value which mean either number of subnets or total number of IPs (including network and broadcast) and the third column is the subnet mask.

Code:
``````2^0	1	0
2^1	2	128
2^2	4	192
2^3	8	224
2^4	16	240
2^5	32	248
2^6	64	252
2^7	128	254
2^8	256	255``````

You are correct sir. I was thinking something else since it's been awhile since I had to do that. I corrected it above. At least my math was right!

You can't actually do three subnets from a Class C network. Math doesn't work out like that. So you would actually be creating 4 networks from that Class C IP range.

not true. you could do a /25 and 2x /26 networks.

not true. you could do a /25 and 2x /26 networks.

So you're talking subnet part of the subnet. Can you show the math for that? I'm not a Cisco guy so I am interested in seeing the math since my subnet knowledge isn't at that level. I'm an MS guy: MCSE/MCSA, Exchange 03/07, MCTS, soon MCITP.

So you're talking subnet part of the subnet. Can you show the math for that? I'm not a Cisco guy so I am interested in seeing the math since my subnet knowledge isn't at that level. I'm an MS guy: MCSE/MCSA, Exchange 03/07, MCTS, soon MCITP.

Yeah its Classless subnetting, the problem you showed was Classful subnetting.

I wrote this in another topic...

I'm not going to do your homework/extra credit for you because you aren't going to learn that way... so read through this:
Subnetting the easy way!

CIDR:
When you've chosen a possible subnet mask for your network and need to determine the number of subnets, valid hosts, and broadcast addresses of a subnet that the mask provides, all you need to do is answer five simple questions:

How many subnets does the chosen subnet mask produce?
How many valid hosts per subnet are available?
What are the valid subnets?
What are the valid hosts in each subnet?

At this point, it's important that you both understand and have memorized your powers of 2.

How many subnets? 2x = number of subnets. x is the number of masked bits, or the 1s. For example, in 11000000, the number of 1s gives us 22. In this example, there are 4 subnets

How many hosts per subnet? 2y- 2 = number of hosts per subnet. y is the number of unmakes bits, or the 0s. For example, in 1100000, the number of 0s gives us 26- 2 hosts. In this example, there are 62 hosts per subnet. you need to subtract 2 fro the subnet address and the broadcast address, which are not valid hosts.

What are the valid subnets? 256 - subnet mask = block size, or increment number. An example would be 256 - 192 = 64. The block size of a 192 mask is always 64. Start counting at zero in blocks of 64 until you reached the subnet mask value and these are your subnets. 0, 64, 128, 192. easy huh?

What's the broadcast address for each subnet? Now here's the really easy part. Since we counted our subnets in the last section as 0, 62, 128, and 192, the broadcast address is always the number right before the next subnet. For example, the 0 subnet has a broadcast address of 63 because the next subnet is 64. The 64 subnet has a broadcast address of 127 because the next subnet is 128. And so on. And remember, the broadcast address of the last subnet is always 255.

What are the valid hosts? Valid hosts are the numbers between the subnets, omitting the all 0s and all 1s. For example, if 64 is the subnet number and 127 is the broadcast address, then 65-126 is the valid host range-it's always the numbers between the subnet address and the broadcast address.

Practice Example for a Class B /23:
255.255.255.254.0 or /23 = Subnet

Subnets? 2^7 = 128
Hosts? 2^9 - 2 = 510
Valid Subnets? 256-254-0,2,4,6,8, etc up to 254
Valid hosts?

Subnet 0.0 2.0 4.0 6.0 8.0
First Host 0.1 2.1 4.1 6.1 8.1
Last Host 1.254 3.254 5.254 7.254 9.254
Broadcast 1.255 3.255 5.255 7.255 9.255

So you're talking subnet part of the subnet. Can you show the math for that? I'm not a Cisco guy so I am interested in seeing the math since my subnet knowledge isn't at that level. I'm an MS guy: MCSE/MCSA, Exchange 03/07, MCTS, soon MCITP.

Subnet is: 210.110.16.0/24 I am assuming

210.110.16.0/25 for first subnet

210.110.16.128/26 for the second subnet
210.110.16.129 - .190 would be the usable IP addresses

210.110.16.192/26 for the third subnet
210.110.16.193 - .254 would be the usable IP addresses

I'm not going to do all the math but that was the gist of it. Provided you are allowed to use subnet zero that will work. Most devices can do that these days.

Subnet is: 210.110.16.0/24 I am assuming

210.110.16.0/25 for first subnet