Private address classes
| class |
from |
to |
CIDR notation |
subnet mask |
| A |
10.0.0.0 |
10.255.255.255 |
/8 |
255.0.0.0 |
| B |
172.16.0.0 |
172.31.255.255 |
/12 |
255.240.0.0 |
| C |
192.168.0.0 |
192.168.255.255 |
/16 |
255.250.0.0 |
| APIPA |
169.254.0.0 |
169.254.255.255 |
/16 |
255.250.0.0 |
CIDR notation rules
- identifies the subnet mask by the number of leading 1s in the subnet mask
- subnet mask tells what portion of the address is
- network part (255)
- host part (0)
2^0 = 1
2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 16
2^5 = 32
2^6 = 64
2^7 = 128
/25 = 8+8+8+1
255 255 255 128
11111111 11111111 11111111 10000000
N = first value after last 255 e.g. 128
network increment: 256 - N = 256 - 128 = 128
number of subnets: 256 / 128 = 2
first valid address: network id + 1
last valid address: next network id - 2
| network id |
first valid address |
last valid address |
broadcast address |
| x.x.x.0 |
x.x.x.1 |
x.x.x.126 |
x.x.x.127 |
| x.x.x.128 |
x.x.x.129 |
x.x.x.254 |
x.x.x.255 |
/26 = 8+8+8+2
255 255 255 192 = (128+64)
11111111 11111111 11111111 11000000
N = first value after last 255 e.g. 192
network increment: 256 - N = 256 - 192 = 64
number of subnets: 256 / 64 = 4
first valid address: network id + 1
last valid address: next network id - 2
| network id |
first valid address |
last valid address |
broadcast address |
| x.x.x.0 |
x.x.x.1 |
x.x.x.62 |
x.x.x.63 |
| x.x.x.64 |
x.x.x.65 |
x.x.x.126 |
x.x.x.127 |
| x.x.x.128 |
x.x.x.129 |
x.x.x.190 |
x.x.x.191 |
| x.x.x.192 |
x.x.x.193 |
x.x.x.254 |
x.x.x.255 |
/27 = 8+8+8+3
255 255 255 224 = (128+64+32)
11111111 11111111 11111111 11100000
N = first value after last 255 e.g. 224
network increment: 256 - N = 256 - 224 = 32
number of subnets: 256 / 32 = 8
first valid address: network id + 1
last valid address: next network id - 2
| network id |
first valid address |
last valid address |
broadcast address |
| x.x.x.0 |
x.x.x.1 |
x.x.x.30 |
x.x.x.31 |
| x.x.x.32 |
x.x.x.33 |
x.x.x.62 |
x.x.x.63 |
| x.x.x.64 |
x.x.x.65 |
x.x.x.94 |
x.x.x.95 |
| x.x.x.96 |
x.x.x.97 |
x.x.x.126 |
x.x.x.127 |
| x.x.x.128 |
x.x.x.129 |
x.x.x.158 |
x.x.x.159 |
| x.x.x.160 |
x.x.x.161 |
x.x.x.190 |
x.x.x.191 |
| x.x.x.192 |
x.x.x.193 |
x.x.x.222 |
x.x.x.223 |
| x.x.x.224 |
x.x.x.225 |
x.x.x.254 |
x.x.x.255 |
