Subnetting
153
How many hosts? 2
5
- 2 = 30.
What are the valid subnets? 256
- 224 = 32. 32 + 32 = 64. 64 + 32 =
96. 96
+ 32 = 128. 128 + 32 = 160. 160 + 32 = 192. 192 + 32 = 224,
which is invalid because it is our subnet mask (all subnet bits on). Our
subnets are 32, 64, 96, 128, 160, and 192.
What's the broadcast address for each subnet (always the number
right before the next subnet)?
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.
Practice Example #3C: 255.255.255.240 (/28)
Let's practice on another one:
192.168.10.0
= Network address
255.255.255.240
= Subnet mask
Subnets? 240 is 11110000 in binary. 2
4
- 2 = 14.
Hosts? Four host bits, or 2
4
- 2 = 14.
Valid subnets? 256
- 240 = 16. 16 + 16 = 32. 32 + 16 = 48. 48 + 16
= 64. 64 + 16 = 80. 80 + 16 = 96. 96 + 16 = 112. 112 + 16 = 128. 128
+ 16 = 144. 144 + 16 = 160. 160 + 16 = 176. 176 + 16 = 192. 192 +
16
= 208. 208 + 16 = 224. 224 + 16 = 240, which is our subnet mask
and therefore invalid. So, our valid subnets are 16, 32, 48, 64, 80, 96,
112, 128, 144, 160, 176, 192, 208, and 224.
Broadcast address for each subnet?
Valid hosts?
The subnet address
32
64
96
128
160
192
The first valid host
33
65
97
129
161
193
The last valid host
62
94
126
158
190
222
The broadcast address
63
95
127
159
191
223
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