Another simple subnetting Q please - Simple can be harder than complex.

sarahanand

So I can do most of the Q's, but cant figure this one out.

How many subnets and hosts per subnet can you get from the network 172.16.0.0 255.255.255.0?

Answer: 256 subnets and 254 hosts

2^??? = ?

jvrlopez

Your formulas for calculating subnets per network and hosts per subnet are as follows:

Subnets: 2^X where X equals the number of bits "on" in the subnet mask.

Hosts per subent: 2^X -2 where X equals the number of bits "off" in the mask. We subtract 2 during the equation due to hosts being unable to use the network ID and broadcast address in each subnet.

On our mask of 255.255.255.0, we are only concerned about the last two octets since the first two are already part of the overall network and will not be changing (the 172.16 portion).

So in the last two octets, we have 8 bits "on" in the third octet and none on in the last. 2^8 = 256

In the last octet, we have 8 "off" in the last octet. 2^8 - 2 = 254

256 subnets with 254 hosts per subnet.

sarahanand

Thanks, I was confused on the bits "on". Since its Class B, makes sense having the third octet on. I would have totally gotten the answer right if I saw the third bit as 254...but 255, it's like the mind game $9.99 vs $10.