- Definition
- Classless Inter-Domain Routing
Classles IP Addressing
Example: Let’s suppose we need only 30 IP address
IP range = 150.101.45.0/27
How do we get?:
- Network address
- Valid IP range
- Broadcast address
Network address
The network address is simply 150.101.45.0
Network mask
First 3 octets are set –> Netmask = 255.255.255.*224*
because 3 bits set correspond to:
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
and if we had those values we get 224.
Block size
The last value of the Bit turned out gives the the Block Size. In our case:
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
Valid IP range
The first valid IP address is 150.101.45.1. The last possible IP address is 150.101.45.30 (Block Size - 2).
Broadcast adress
The broadcast address is 150.101.45.31 (Block Size - 1)
-
Use the formula
We have 5 host bits since:
128 64 32 16 8 4 2 1 1 1 1 0 0 0 0 0 Network Host 2^5 - 2 = 30 Possible IP addresses
Supposing we have 150.101.45.0/30
This way you’ll get only 2 valid IP addresses. This CIDR is used in point-to-point connection (e.g. between routers).
What is the valid host range for 150.101.64.0/19
Network mask is. 255.255.224.0
The block size is: 32
We have following networks/subnets (each time we had the block size):
| # Network | Beginning |
|---|---|
| 1 | 150.101.0.0/19 |
| 2 | 150.101.32.0/19 |
| 3 | 150.101.64.0/19 |
| 4 | 150.101.96.0/19 |
So the first valid IP address for 150.101.64.0/19 starts at 150.101.64.0/19 and ends at 150.101.95.255 (150.101.96.0/19 is the next network).
But since the last IP address is the broadcast address we have these valid IP range: 150.101.64.1 - 150.101.95.224