Let's look at what the other part of the question was. Therefore, the subnet mask /26 in dotted decimal notation is 255.255.255.192. The second and third octets are also all '1's adding up to 255:įor the fourth octet, the '1's are under 128 and 64: Then we can just add up the '1's to find the subnet mask in dotted decimal notation. Then, you can fill in the remainder with '0's for the host portion of the address:ĭraw a line in after the 26 '1's to indicate the demarcation point between the network and host portions of the address (the network portion is to the left of the line, the host portion is to the right of it): Under your bit pattern at the top of the paper, write out 26 '1's underneath starting from the left side. The subnet mask in our example question is /26. Proceed to the next octet, until you've written down the bit pattern for the four octets in a subnet mask. So, take a piece of paper, start at the top, and from right to left write out '1, 2, 4, 8, 16, 32, 64, 128' and put a dot in between each number. Later on, you'll be able to do this in your head, but when you're first learning, it's way easier to write it all out.

The second part of the question was, what is the subnet mask, /26, in dotted decimal? The way to do this when you're first learning subnetting is to write out the bit pattern at the top of a piece of paper. We're going to do the second part first because it's easier and more logical to answer the question that way.

Let's look at how we're going to figure out the answer to the question.

What are the network address, broadcast address, and valid host addresses for the IP subnet of which the host is a member of?Īnd the second part of the question - what is the subnet mask in dotted-decimal notation?

Subnetting chart during exam