Subnetting
163
Let's take a look at a situation where a subnet bit is turned on in the third
octet. The following table shows the full range of subnets available in the
fourth octet:
This next table shows the last seven subnets.
Subnetting in Your Head: Class B Addresses
Are you nuts? Subnet Class B addresses in our heads? If you think easier
equals crazy, then, yes, I'm a few sails short, but it's actually easier than writ-
ing it out--I'm not kidding! Let me show you how:
Question: What subnet and broadcast address is the IP address
172.16.10.33 255.255.255.224 a member of?
Answer: 256
- 224 = 32. 32 + 32 = 64. Bingo: 33 is between 32 and
64. However, remember that the third octet is considered part of the
subnet, so the answer would be the 10.32 subnet. The broadcast is
10.63, since 10.64 is the next subnet.
Question: What subnet and broadcast address is the IP address
172.16.90.66 255.255.255.192 a member of?
Answer: 256
- 192 = 64. 64 + 64 = 128. The subnet is 172.16.90.64.
The broadcast must be 172.16.90.127, since 90.128 is the next subnet.
Question: What subnet and broadcast address is the IP address
172.16.50.97 255.255.255.224 a member of?
Answer: 256
- 224 = 32, 64, 96, 128. The subnet is 172.16.50.96, and
the broadcast must be 172.16.50.127 since 50.128 is the next subnet.
Subnet
1.0
1.32
1.64
1.96
1.128
1.160
1.192
1.224
First host
1.1
1.33
1.65
1.97
1.129
1.161
1.193
1.225
Last host
1.30
1.62
1.94
1.126
1.158
1.190
1.222
1.254
Broadcast
1.31
1.63
1.95
1.127
1.159
1.191
1.223
1.255
Subnet
255.0
255.32
255.64
255.96
255.128
255.160
255.192
First host
255.1
255.33
255.65
255.97
255.129
255.161
255.193
Last host
255.62
255.62
255.94
255.126
255.158
255.190
255.222
Broadcast
255.63
255.63
255.95
255.127
255.159
255.191
255.223
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