Subnet

Class A:

00000000 = 0

011111111 = 127

Class B

10000000 =128

10111111 = 191

Class C

11000000 = 192

11011111 = 223

Class D (224 - 239)

Class E (240 - 255)

Subnet Mask (Default)

Class A 255.0.0.0

Class B 255.255.0.0

Class C 255.255.255.0

Subnetting a Class C Address

1. How many subnets does the chosen subnet mask produce?
2. How many valid hosts per subnet are available?
3. What are the valid sunbets?
4. What 's the broadcast address of each subnet?
5. What are the valid hosts in each subnet?

Practice Example #1: C: 255.255.255.192(/26)

192.168.10.0

255.255.255.192

Practice Example #2: C: 255.255.255.224 (/27)

192.168.10.0

255.255.255.224

Practice Example #3 C: 255.255.255.240 (/28)

192.168.10.0

255.255.255.240

Practice Example #4 C: 255.255.255.248 (/29)

192.168.10.0

255.255.255.248

Practice Example #5 C: 255.255.255.252 (/30)

192.168.10.0

255.255.255.252

Classless Inter-Domain Routing (CIDR)

• 255.0.0.0 /8
• 255.128.0.0 /9
• 255.192.0.0 /10
• 255.224.0.0 /11
• 255.240.0.0 /12
• 255.248.0.0 /13
• 255.252.0.0 /14
• 255.254.0.0 /15
• 255.255.0.0 /16
• 255.255.128.0 /17
• 255.255.192.0 /18
• 255.255.224.0 /19
• 255.255.240.0 /20
• 255.255.248.0 /21
• 255.255.252.0 /22
• 255.255.254.0 /23
• 255.255.255.0 /24
• 255.255.255.128 /25
• 255.255.255.192 /26
• 255.255.255.224 /27
• 255.255.255.240 /28
• 255.255.255.248 /29
• 255.255.255.252 /30

Subnetting a Class B Address

The process of subnetting a Class B network is the same as it is for a Class C, except that yu just have more host bits. Use the same subnet numbers for the third octer with Class B that you used for the fourth octer with Class C, but add a zero to the nework portion and a 255 to the boradcast section in the fourth octer.

Practice #1 B: 255.255.192.0

172.16.0.0

255.255.192.0

subnets = 2

hosts = 16.382

subnet 64.0

first host 64.1

last host 127.254

broadcast 127.255

subnet 128.0

first host 128.1

last host 191.254

broadcast 191.255

Practice #2 B: 255.255.240.0 (/20)

172.16.0.0

255.255.240.0

Practice #3 B: 255.255.254.0 (/23)

172.16.0.0

255.255.254.0

Practice #4 B: 255.255.255.0 (/24)

172.16.0.0

255.255.255.0

Practice #5 B: 255.255.255.128 (/25)

172.16.0.0

255.255.255.128