Subnetting
157
broadcast address is 63. (Remember that the broadcast address of a subnet
is always the number right before the next subnet.) The valid host range is
33
-62. This is too easy! No, it's not?
Okay, then let's try another one. We'll subnet another Class C address:
192.168.10.33
= Node address
255.255.255.240
= Subnet mask
What subnet and broadcast address is the above IP address a member of?
256
- 240 = 16. 16 + 16 = 32. 32 + 16 = 48. And bingo--the host address is
between the 32 and 48 subnets. The subnet is 192.168.10.32, and the broad-
cast address is 47. The valid host range is 33
-46.
Okay, we need to do more, just to make sure you have this down!
You have a node address of 192.168.10.174 with a mask of
255.255.255.240. What is the valid host range?
The mask is 240, so we'd do a 256
- 240 = 16. This our block size. Just
keep adding 16 until we pass the host address of 174: 16, 32, 48, 64, 80, 96,
112, 128, 144, 160, 176. Whew... we made it. The host address of 174 is
between 160 and 176, so the subnet is 160. The broadcast address is 175, so
the valid host range is 161
-174. That was a tough one.
One more--just for fun. This is the easiest one of all Class C subnetting:
192.168.10.17
= Node address
255.255.255.252
= Subnet mask
What subnet and broadcast address is the above IP address a member of?
256
- 252 = 4, 8, 12, 16, 20 . You've got it! The host address is between the
16 and 20 subnets. The subnet is 192.168.10.16, and the broadcast address
is 19. The valid host range is 17
-18.
Now that you're all over Class C subnetting, Let's move on to Class B sub-
netting!
Subnetting Class B Addresses
Before we dive into this, let's look at all the possible Class B subnet masks
first. Notice that we have a lot more possible subnets than we do with a
Class C network address:
255.255.128.0 (/17) 255.255.255.0 (/24)
255.255.192.0 (/18) 255.255.255.128 (/25)
255.255.224.0 (/19) 255.255.255.192 (/26)
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