What Is the Maximum Number of IP Addresses That Are Needed for a Single Subnet?
A subnet is a portion of a computer network that, although physically separated from other portions of the network, shares a network address with those other portions and is distinguished by a subnet number. Creating subnets, otherwise known as subnetting, is essentially a way of splitting a network into smaller, more manageable pieces; to effectively subnet you need to know the maximum number of computers that you can have on a single subnet.
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IP Address
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Each computer on a network is identified by a unique, numeric code known as an Internet Protocol address. The Internet Protocol is the formal set of rules, or protocol, that defines how data is sent from one computer to another. An IP address consists of series of 32 binary digits, or “bits,” which are divided into four groups of eight bits called octets. Each octet represents a decimal number between 0 and 255, so IP addresses are often written as four decimal numbers separated by periods in the form 192.168.1.0, otherwise known as “dotted-decimal notation.”
Network and Host Number
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Each IP address consists of a network portion, which identifies the network, and a host portion, which identifies individual computers, or hosts, on the network. All hosts on a given network share the same network number, but each host must have a unique host number so that it can be identified unambiguously.
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Network Class
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To support networks of different sizes, IP addresses come in three classes: Class A, Class B and Class C. The class of an IP address determines how many octets are used for the network number and how many bits are used for the host number; this, in turn, determines the maximum number of IP addresses that you can have on a single subnet. To calculate the maximum number of IP addresses, you need to look at the different classes of IP address in binary, or base two, form.
Maximum Number of IP Addresses
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In a Class C IP address, only the last octet, or eight bits, is used for the host number, so the maximum number of IP addresses on a single subnet is theoretically 2^8, or 256. In practice, two host addresses must be reserved, so the actual number of IP addresses allowed is 254. In a Class B IP address, the last two octets are used for the host number, so the maximum number of IP addresses on a single subnet is (2^16 - 2), or 16,384. In a Class A IP address, the last three octets are used, giving a figure of (2^24 - 2) or 16,777,214.
Subnet Mask
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Class A, B and C networks have different default address or subnet masks that indicate which part of an IP is a network number and which part is a host number. In dotted decimal notation, a Class A network has a default mask of 255.0.0.0, a Class B network has a default mask of 255.255.0.0 and a Class C network has a default mask of 255.255.255.0.
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References
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