Subnetting Reference
IP Classes
|
Class
|
Range
|
Hosts
|
| Class A | 1-126 | 16,777,216 |
| Loopback | 127 | 0 |
| Class B | 128-191 | 65,534 |
| Class C | 192-223 | 254 |
| Class D | 224-240 | Multicast |
| Class E | 240-255 | Reserved |
Subnet Masking Within a Class C (Modifying the fourth octet only - 255.255.255.xxx)
| Bits in the fourth octet (8) |
1
|
1
|
1
|
1
|
1
|
1
|
1
|
1
|
| Real values in the fourth octet |
128
|
64
|
32
|
16
|
8
|
4
|
2
|
1
|
| Possible subnet masks in the fourth octet |
128
|
192
|
224
|
240
|
248
|
252
|
254
|
255
|
| True hosts available with each subnet mask |
128
|
64
|
32
|
16
|
8
|
4
|
2
|
1
|
| Valid hosts available with each subnet mask |
126
|
62
|
30
|
14
|
6
|
2
|
0
|
0
|
| Networks available with each subnet mask |
2
|
4
|
8
|
16
|
32
|
64
|
128
|
0
|
Subnetting Example
One 24 bit Class C network becomes eight 27 bit networks
|
Decimal
|
Binary
|
|
| Old Address | 192.168.1.1 | 11000000101010000000000100000001 |
| Old Mask | 255.255.255.0 | 11111111111111111111111100000000 |
| New Address | 192.168.1.1 | 11000000101010000000000100000001 |
| New Mask | 255.255.255.224 | 11111111111111111111111111100000 |
The Valid Networks are
|
Address Range
|
Mask
|
| 192.168.1.1-30 | 255.255.255.224 |
| 192.168.1.33-62 | 255.255.255.224 |
| 192.168.1.65-94 | 255.255.255.224 |
| 192.168.1.97-126 | 255.255.255.224 |
| 192.168.1.129-158 | 255.255.255.224 |
| 192.168.1.161-190 | 255.255.255.224 |
| 192.168.1.193-222 | 255.255.255.224 |
| 192.168.1.225-254 | 255.255.255.224 |