What Is an Octet?
an Octet — a group of 8 bits — one of the four numbers (0-255) separated by dots in an IPv4 address, like the "192" in 192.168.1.1.
How it works
An IPv4 address is 32 bits, split into four 8-bit octets written in decimal (0-255) and separated by dots. Each octet represents 8 binary digits — 11000000 in binary equals 192 in decimal. Subnet masks work the same way, which is why subnetting involves reasoning about which octet the network boundary falls in.
Why it matters
Understanding octets is the entry point to subnetting — the "interesting octet" (where the subnet boundary sits) is central to the block-size method. Comfort converting octets between decimal and binary makes subnetting far faster. Practise with the binary converter.
Frequently asked questions
What is an octet in an IP address?
One of the four decimal numbers (0-255) in an IPv4 address, each representing 8 bits — so 192.168.1.1 has four octets.
Why is it called an octet?
Because it contains 8 bits (oct = eight) — the term avoids ambiguity since 'byte' historically varied in size.
What is the maximum value of an octet?
255 — the largest value 8 bits can represent (11111111 in binary).
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