Subnetting question

[mab1376]

My colleague are cramming for our CCNA and for some reason one subnet example is for the network 192.168.10.0 255.255.255.224 and it shows only 6 valid subnets for Class C.

Based on what I know, there should be 8, the book doesn't recognize the subnets 192.168.10.0-192.168.10.31 or the network 192.168.10.224-192.168.10.255

(low numbers being network address and high number being broadcast address.)

Does that seem right?

 

[exodusprime1337]

this may help you subnetting a class c address

 

[exodusprime1337]

bare in mind that each class c subnet has 2 values you cannot use.

 

[mab1376]

Practice Example #2C: 255.255.255.224 (/27)



This time, we’ll subnet the network address 192.168.10.0 and subnet mask 255.255.255.224.

192.168.10.0 = Network address

255.255.255.224 = Subnet mask



1_ How many subnets? 224 is 11100000, so our equation would be 23= 8.



2_ How many hosts? 25 – 2 = 30.



3_ What are the valid subnets? 256 – 224 = 32. We just start at zero and count to the subnet mask value in blocks (increments) of 32: 0, 32, 64, 96, 128, 160, 192, 224.



4_ What’s the broadcast address for each subnet (always the number right before the next subnet)?



5_ What are the valid hosts (the numbers between the subnet number and the broadcast address)?

To answer questions 4 and 5, first just write out the subnets, then write out the broadcast addresses—the number right before the next subnet. Lastly, fill in the host addresses. The following table gives you all the subnets for the 255.255.255.224 Class C subnet mask:



The subnets (do this first) 0 64 128 192

Our first host (perform host addressing last) 1 65 129 193

Our last host 62 126 190 254

The broadcast address (do this second) 63 127 191 255

The subnet address 0 32 64 96 128 160 192 224

The first valid host 1 33 65 97 129 161 193 225

The last valid host 30 62 94 126 158 190 222 254

The broadcast address 31 63 95 127 159 191 223 255

According to the link its the same example but with the other addresses that the book is missing.

i.e. the 0 and 224 network addresses

 

[Hybrid_theory]

The 0 - .31 and 224 - 255 are referring to old technology. Years ago those subnets would not be usable. But that has been fixed in current router technologies and they are now usable

Any other questions, feel free to ask. I've taken 4 CCNA courses.

Also a tip for easy host figuring outness (class C only).

for the mask 255.255.255.224 or /28. In the last subnet you have 11100000

Take the value of the last bit that is on so: 11(1) and whats its value? 32. 32-2 = 30.

 

[mab1376]

The 0 - .31 and 224 - 255 are referring to old technology. Years ago those subnets would not be usable. But that has been fixed in current router technologies and they are now usable

Any other questions, feel free to ask. I've taken 4 CCNA courses.

Also a tip for easy host figuring outness (class C only).

for the mask 255.255.255.224 or /28. In the last subnet you have 11100000

Take the value of the last bit that is on so: 11(1) and whats its value? 32. 32-2 = 30.

Great thanks!

That's exactly the info I was looking for.