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Networking Fundamentals · Foundational

Dotted-Decimal Notation

The format for writing IPv4 addresses as four decimal numbers (0-255) separated by periods.

Definition

Each of the four numbers represents one 8-bit octet of the 32-bit address. Subnet masks are also written this way, as in 255.255.255.0. Values above 255 in any octet make an address invalid.

Example

11000000.10101000.00000001.00000001 in binary is 192.168.1.1 in dotted decimal.

Exam tip

Any octet above 255, such as 192.168.1.256, is invalid; look for this in "which is a valid host" questions.

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