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Chapter 3
Internet Protocols
Broadcast address for each subnet?
Valid hosts?
The following table shows the first four subnets, valid hosts, and broad-
cast addresses in a Class B 255.255.254.0 mask.
Practice Example #4B: 255.255.255.0 (/24)
Contrary to popular belief, 255.255.255.0 used with a Class B network
address is not called "a Class B network with a Class C subnet mask." It's
amazing how many people see this mask used in a Class B network and think
it's a Class C subnet mask. This is a "Class B subnet mask with 8 bits of
subnetting"--it's considerably different from a Class C mask. Subnetting
this address is fairly simple:
Subnets? 2
8
- 2 = 254.
Hosts? 2
8
- 2 = 254.
Valid subnets? 256
- 255 = 1, 2, 3, etc. all the way to 254.
Broadcast address for each subnet?
Valid hosts?
The next table shows the first three subnets and the last one, valid hosts,
and broadcast addresses in a Class B 255.255.255.0 mask:
Practice Example #5B: 255.255.255.128 (/25)
Oh no! This one's got to be illegal, right? What type of mask is it? (Don't you
wish it were illegal?) Well, it's a drag, but it's not. It is one of the hardest
Subnet
2.0
4.0
6.0
8.0
...
First host
2.1
4.1
6.1
8.1
...
Last host
3.254
5.254
7.254
9.254
...
Broadcast
3.255
5.255
7.255
9.255
...
Subnet
1.0
2.0
3.0
...
254.0
First host
1.1
2.1
3.1
...
254.1
Last host
1.254
2.254
3.254
...
254.254
Broadcast
1.255
2.255
3.255
...
254.255
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