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Networking Fundamentals · Foundational

Binary-to-Decimal Conversion

Translating between base-2 and base-10 values, an essential skill for IP subnetting.

Definition

Each bit in an octet has a positional value of 128, 64, 32, 16, 8, 4, 2 and 1 from left to right. Adding the values of the 1 bits gives the decimal number. Contiguous mask bits produce the only valid mask octet values: 0, 128, 192, 224, 240, 248, 252, 254 and 255.

Example

11100000 equals 128 + 64 + 32 = 224.

Exam tip

Memorize the valid mask octets; a mask with 255.255.253.0 is invalid because its bits are not contiguous.

Related terms