Class Formet Default Subnet Mask
A network.host.host.host 255.0.0.0
B network.network.host.host 255.255.0.0
C network.network.network.host 255.255.255.0
Valid Subnet- 256-subnet mask=block size or increment number. An example would be256-192=64 . The block size of a 192 mask is always 64. start counting at '0' in block of 64 until you reach the subnet mask value and these are you subnets. 0,64,128,192.
Broadcast Address- Now here the realy easy part since we counted our subnets it the last section as 0,64,128,and 192. The broadcast address is always the number before need the subnets for example of '63' because the next subnet is 128 and so on and remember the broadcast address the last subnet is always 255.
Valid Host- Valid host are numbers between the subnets omitting the all '0' ans '1s'. For example: If 84 is the subnet number and 127 is the broadcast address. Then 65-126 is the valid host range. It is always the number between the subnet address and the bradcast address.
Class C:
Example: 255.255.255.128 (/25)
IIIIIIII:IIIIIIII:IIIIIIII:I0000000
Since 128 is 10000000 in binary, there is only 1 bit for subneting and 7bits for hosts. We are going to subnet the class C network address.
192.168.10.0 = network Address
255.255.255.128=Subnet Mask
How many Subnet
Since 128 is 1bit on (10000000) the answer would be 2x1=126hosts.
How many host per subnets?
256-126=128, Remember willbe start at '0' and count in our block size. So our subnets are 0,128.
What is the broadcast address for each subnet?
"The number right before the valuea of the next subnet is all host bits turned on and equal the broadcast address. This way the valid hosts are obvious. The following Table shows the '0' and 128 subnets. The valid host ranges of each and the broadcast address of both subnets.
Subnets 0 128
First host 1 129
Last host 126 254
Broadcast host 127 255