- Every IP address is divided into a network portion and a host portion.
- The size of the network/host portions is defined by the subnet mask.
- Subnet Masks can only have a consecutive number of bits that have the values of 1.
11111111.0.0.0 (255.0.0.0) is a valid subnet mask.
11111101.0.0.0 (253.0.0.0) is not a valid subnet mask - CIDR Notation (/x) refers to the number of bits that has a value of one in the subnet mask (Binary Form).
IPv4 Classes
|
Class |
IP Range |
Private IP Range |
Default Subnet Mask |
Notes |
|
A |
1.0.0.0-127.255.255.255 |
10.0.0.0-10.255.255.255 |
255.0.0.0 |
127 is reserved for Loopback addresses |
|
B |
128.0.0.0-191.255.255.255 |
172.16.16.0-172.31.255.255 |
255.255.0.0 |
|
|
C |
192.0.0.0 – 223.255.255.255 |
192.168.0.0-192.168.255.255 |
255.255.255.0 |
|
|
D |
224.0.0.0-239.255.255.255 |
N/A |
N/A |
Used for Multicast |
|
E |
240.0.0.0-255.255.255.255 |
N/A |
N/A |
Experimental use only |
- Private addresses are the addresses that are not routable on the internet, in other words they would be dropped by the ISP.
- With the enablement of VLSM, the default subnet mask can be changed to any preferred value.
- In a real world implementation, there’s no functional difference between Class A, B or C IP addresses other than the size of its private range.
