Dot-decimal notation

Dot-decimal notation is a presentation format for numerical data. It consists of a string of decimal numbers, each pair separated by a full stop (dot).

A common use of dot-decimal notation is in information technology where it is a method of writing numbers in octet-grouped base-10 (decimal) numbers separated by dots (full stops). In computer networking, Internet Protocol Version 4 addresses are commonly written using the quad-dotted notation of four decimal integers, ranging from 0 to 255 each.

Definition and use

Dot-decimal notation is a presentation format for numerical data expressed as a string of decimal numbers each separated by a full stop.

For example, the hexadecimal number 0xFF0000 is expressed in dot-decimal notation as 255.0.0.

In computer networking, the term is often used as a synonym of dotted quad notation,^[1] or quad-dotted notation, a specific use to represent Internet Protocol Version 4 addresses. ^[2]

Object identifiers use a style of dot-decimal notation to represent an arbitrarily deep hierarchy of objects identified by arbitrary decimal numbers.^{[citation needed]}

Common decimal fractions are sometimes said to be written in dotted decimal notation.^[3] For example the fraction 1/8 is represented as 0.125.

IPv4 address

An IP address (version 4) in both dot-decimal notation and binary code

An Internet Protocol Version 4 (IPv4) address consists of 32 bits, which may be divided into four octets. These four octets are written in decimal numbers, ranging from 0 to 255, and are concatenated as a character string with full stop delimiters between each number.

For example, the address of the loopback interface, usually assigned the host name localhost, is 127.0.0.1. It consists of the four binary octets 01111111, 00000000, 00000000, and 00000001, forming the full 32-bit address.

Caveat

In information technology, an integer number that starts with the digit 0 is often interpreted as a number in octal representation. Therefore, if an IP address component is written with a leading 0 digit, it may be interpreted incorrectly by some utility programs.^[4] For example, the representation 022.101.031.153, when parsed as octal, would be equivalent to the decimal notation 18.101.25.153.^{[note 1]}

See also

• CIDR notation
• ISO 2145
• IPv6 address notation

Notes

References