*Determining the Number of IP Subnets
and Hosts*

Created by a valid mask. No CIDR or VLSM.

** **

**Step One**

** **

Use the first octet
of the IP address to determine the class of address (A, B, or C).

**169.199.109.137
= CLASS B**

**255.255.255.192**

**Step Two**

Use the class of
the address to determine which octets are available for hosts.

**CLASS B = Network.
Network. Host. Host**

**
169.199.109.137**

**
255.255.255.192**

**Step Three**

Look at the host
octet(s) in the subnet mask. Use the "Possible
Masks" chart to determine which bits are set to one. If
no bits are set to one, there are no subnets. If any bits are set
to one, proceed to step four.

**169.199.109.137**

**255.255.255.192
= 11111111 11000000 (host octets only)**

**Step Four**

Count the total number of ones in the host octet(s) of the subnet mask. Call this number X. Raise 2 to the power of X. Use the "Powers of 2" chart if necessary. This is the number of potential subnets created by the mask. Two of these potential subnets are normally not usable.

**11111111
11000000 = 10 ones. 2**^{10}** = 1,024 -
2 = 1,022 usable subnets created.**

**Step Five**

Count the total
number of zeros in the host octet(s) of the subnet mask. Call
this number Y. Raise 2 to the power of Y. Use the "Powers of
2" chart if necessary. This is the number of potential
subnets created by the mask. Two of these numbers are never used
to address hosts.

**11111111
11000000 = 6 zeros. 2**^{6}** = 64 - 2 =
62 usable host addresses created.**