IP Subnetting Notes

WAN Link Example

For a WAN link you would use a subnet mask of 255.255.255.252, which gives you the following allocation:

Subnet address:    203.8.7.248
Host address 1:    203.8.7.249  (one end of link)
Host address 2:    203.8.7.250  (other end of link)
Broadcast address: 203.8.7.251
Next subnet:       203.8.7.252

Calculating Addresses per Subnet

To calculate the number of addresses in a subnet mask, subtract the final byte from 255 and add 1:

255 - 252 + 1 = 4 addresses per subnet

The reason for adding one is because the numbering range is 0 to 255, which actually gives 256 values, hence the add 1. This method works for all subnet masks.