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Chapter 3
Internet Protocols
255.255.240.0 (/20) 255.255.255.224 (/27)
255.255.248.0 (/21) 255.255.255.240 (/28)
255.255.252.0 (/22) 255.255.255.248 (/29)
255.255.254.0 (/23) 255.255.255.252 (/30)
We know the Class B network address has 16 bits available for host
addressing. This means we can use up to 14 bits for subnetting because we
have to leave at least two bits for host addressing.
By the way, do you notice anything interesting about that list of subnet
values--a pattern maybe? Ah ha! That's exactly why I had you memorize the
binary-to-decimal numbers at the beginning of this section. Since subnet
mask bits start on the left, move to the right, and can't skip bits, the numbers
are always the same. Memorize this pattern.
The process of subnetting a Class B network is pretty much the same as it
is for a Class C, except that you just have more host bits. Use the same subnet
numbers you used with Class C, but add a zero to the network portion and
a 255 to the broadcast section in the fourth octet. The following table shows
you a host range of two subnets used in a Class B subnet:
Just add the valid hosts between the numbers, and you're set!
Subnetting Practice Examples: Class B Addresses
This section will give you an opportunity to practice subnetting Class B
addresses.
Practice Example #1B: 255.255.192.0 (/18)
172.16.0.0
= Network address
255.255.192.0
= Subnet mask
Subnets? 2
2
- 2 = 2.
Hosts? 2
14
- 2 = 16,382. (6 bits in the third octet, and 8 in the fourth.)
Valid subnets? 256
- 192 = 64. 64 + 64 = 128.
Broadcast address for each subnet?
Valid hosts?
16.0
32.0
16.255
32.255
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