- Subnet Mask is short for "Subnetwork Mask".
- Subnet is a logical sub division of an IP network.The process of dividing the network into two or more networks is called "subnetting".
- A Subnet Mask is a 32-bit number used to differentiate the network component of an IP address by dividing the IP address into Network address and Host address.
- Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s.
- Subnet Mask is a binary number format but it also communicated with decimal format.
The IP is divide into five classes and each class has it's default subnet mask as shown below:
| Class | Address range | Subnet Mask (decimal) | Subnet Mask (binary) | Format | Number of Networks (2^N) | Number of Hosts (2^H -2) |
|---|---|---|---|---|---|---|
| A |
1-127
|
255.0.0
|
11111111 00000000 00000000 00000000
| N.H.H.H |
2^8 = 256
|
2^24 -2 = 16,777,214
|
| B |
128-191
|
255.255.0.0
|
11111111 11111111 00000000 00000000
|
N.N.H.H
|
2^16 = 65,536
|
2^16 -2 = 65,534
|
| C |
192-223
|
255.255.255.0
|
11111111 11111111 11111111 00000000
| N.N.N.H |
2^24 = 16,777,216
|
2^8 -2 = 254
|
| D |
224-239
| Multicast | Multicast | N/A | N/A | N/A |
E
|
240-255
| Experimental | Experimental | N/A | N/A | N/A |
Examples of Subnet Masking:
