One format, dotted-decimal notation (DDN), converts each set of 8 bits into the decimal equivalent. Two alternative subnet mask formats exist so that we humans do not have to work with 32-bit binary numbers. The following two binary values meet the requirements, in that they have all 1s on the left, followed by all 0s, with no interleaving of 1s and 0s: The first is illegal because the value interleaves 0s and 1s, and the second is illegal because it lists 0s on the left and 1s on the right: The value must not interleave 1s and 0s.įor example, the following values would be illegal.In particular, the binary subnet mask must follow these rules: Subnet masks can be written as 32-bit binary numbers, but not just any binary number.
#Subnetting chart during exam how to#
In particular, it shows how to determine the three-part format of the IPv4 address and describes the facts about the subnetting design that are implied by the mask. The second section explains how to take an IP address and its subnet mask and analyze those values. The first focuses totally on the mask formats and the math used to convert between the three formats. Prefix (also called classless interdomain routing ).The math converts masks between the three different formats used to represent a mask: However, to analyze a subnet mask, you first need some basic math skills with masks. The subnet mask holds the key to understanding several important subnetting design points. The subnet part defines the number of subnets that could exist inside one classful IP network, assuming that one mask is used throughout the classful network.
Then, the class (A, B, or C) further divides the structure of addresses in a subnet, breaking the prefix part into the network and subnet parts. First, the mask divides addresses into two parts: prefix and host, with the host part defining the size of the subnet. The subnet mask used in one or many subnets in an IP internetwork says a lot about the intent of the subnet design.
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