Determine the Number of IP Subnets and Hosts

Before calculating the total number of host and subnets of a certain IP address you have to have a clear idea about the IP classes. By looking at the first four bits of IP address you can determine the class of address.

• Class A- It begins with 0xxx, or 1 to 126 decimal. 
• Class B- It begins with 10xx, or 128 to 191 decimal.
• Class C- It begins with 110x, or 192 to 223 decimal.
• Class D- It begins with 1110, or 224 to 239 decimal.
• Class E- It begins with 1111, or 240 to 254 decimal.

Every IP address has two parts- Network and Host. For different classes the network and host parts-

• Class A- Network.Host.Host.Host
• Class B- Network.Network.Host.Host
• Class C- Network.Network.Network.Host
• Class D- Network.Network.Network.Network

For this tutorial we will use the following IP address:

162.190.107.127

255.255.255.224

Step 01: 

Determine the class of address using the first octet of the IP address.

162.190.107.127 = Class B

255.255.255.224

Step 02:

Now, determine the host and network octets.

Network.Network.Host.Host = Class B

162.190.107.127

255.255.255.224

Step 03:

Find out which bits are set to one in the host octets. Notice, if no bits are set to one then there is no subset.

162.190.107.127

255.255.255.224 = xxxxxxxx.xxxxxxxx.11111111.11100000 

Step 04:

Assume 'X' denotes the total number of ones. Then we will use this formula '(2^X)-2' to find out number of usable subnets. Example-

11111111.11100000 = 11 ones.

(2^11)-2= 2048-2= 2046 subnets in total for use.

Step 05:

Assume 'Y' denotes the total number of zeros. Then we will use this formula '(2^Y)-2' to find out number of usable hosts. Example-

11111111.11100000 = 5 zeros.

(2^5)-2= 32-2= 30 host address for use.