Reading a Dotted-Decimal Address

An IP address (Internet Protocol address) is a logical number that identifies a device on a network, much like a street address identifies a house. Every device that sends or receives data needs one so packets can find their way to it.

Version 4 of the protocol, called IPv4, uses a 32-bit address. Those 32 bits give just over 4.2 billion possible addresses, which once seemed endless but eventually ran short as the internet grew.

An IPv4 address is split into four groups of 8 bits each. Each 8-bit group is called an octet. Four octets times 8 bits equals the full 32 bits.

Because 8 bits can represent values from 0 to 255, each octet is a number in that range. The familiar form 192.168.1.10 is simply those four octets written as decimal numbers, separated by dots.

Computers store an address as a long string of binary digits, but humans struggle to read 32 ones and zeros. Dotted-decimal notation makes the address readable by converting each octet to a decimal number and joining them with dots.

So the binary value 11000000.10101000.00000001.00001010 becomes 192.168.1.10. The dots are only a visual aid — the device works entirely in binary.

Each bit in an octet has a place value: 128, 64, 32, 16, 8, 4, 2, and 1, from left to right. Add up the place values where a bit is 1 to get the decimal octet.

• 10000000 = 128
• 11000000 = 128 + 64 = 192
• 11111111 = all bits on = 255

Knowing this lets you move between binary and decimal, a core skill for the Network+ exam.

Because the smallest 8-bit value is 00000000 (0) and the largest is 11111111 (255), every octet falls between 0 and 255. That gives 256 possible values per octet.

A number like 192.168.1.300 is invalid because 300 exceeds 255. Spotting out-of-range octets is an easy way to flag a mistyped address during troubleshooting.

Read an IPv4 address from left to right as four separate numbers. In 10.0.5.42, the octets are 10, 0, 5, and 42.

The leftmost octets generally describe the larger network, while the rightmost octets identify a specific host within it. You will see exactly how that split works in the next lesson on network and host portions.

With 32 bits, the total number of unique IPv4 addresses is 2 to the 32nd power, which is 4,294,967,296 — about 4.3 billion.

That sounds huge, but with billions of phones, servers, and smart devices online, the supply was exhausted. This shortage is the main reason IPv6 was created, a topic you will explore in a later course.

Do not confuse an IP address with a MAC address (Media Access Control address). A MAC address is a 48-bit hardware identifier burned into a network card and used for local delivery on a single link.

An IP address is logical and can change as a device moves between networks. IP works at Layer 3 (Network) while MAC works at Layer 2 (Data Link) of the OSI model.

An address can be assigned in two ways. A static address is set manually and stays fixed, which suits servers and printers that must always be reachable.

A dynamic address is handed out automatically by a DHCP server (Dynamic Host Configuration Protocol) and may change over time. Most everyday client devices use dynamic addressing for convenience.

You meet IPv4 addresses everywhere: a home router often uses 192.168.1.1, public web servers have internet-routable addresses, and your own laptop shows its address in network settings.

Being able to read and sanity-check these numbers is the foundation for subnetting, routing, and troubleshooting — all of which build directly on the dotted-decimal format.

Try reading these aloud as four numbers: 172.16.254.1 is 172, 16, 254, 1, all within range and valid. 8.8.8.8 is a famous public DNS server address.

Confirm each octet is between 0 and 255 and that there are exactly four octets separated by three dots. If any of those checks fail, the address is malformed.

Test your grasp of the dotted-decimal format.

You learned how to read an IPv4 address.

• IPv4 is a 32-bit logical address shown as four octets.
• Each octet is 8 bits, valued 0 to 255, written in dotted-decimal form.
• Place values (128 to 1) convert binary octets to decimal.
• IP is logical (Layer 3); MAC is a fixed hardware address (Layer 2).
• There are about 4.3 billion IPv4 addresses, which drove the move to IPv6.