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Dotted decimal notation writes an IPv4 address as four decimal numbers separated by periods. Each number represents one 8-bit octet and ranges from 0 to 255—for example, 10.1.0.52.
How dotted decimal notation represents an IPv4 address
An IPv4 address is 32 bits long. Dotted decimal notation displays those bits as four 8-bit fields, commonly called octets. Each field is written as a decimal number, with a period between adjacent fields.
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RFC 1062 describes the format as dividing a 32-bit address into four 8-bit fields and writing each field as a decimal number separated by periods. Its example is 10.1.0.52. Read RFC 1062.
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- Four numbers: They correspond to the four 8-bit portions of the IPv4 address.
- Decimal values: Each octet is written as a base-10 number from 0 through 255, inclusive.
- Three periods: The dots separate the four written octets; they are not extra address values.
RFC 3986 defines an IPv4 literal in URI syntax as four decimal numbers in the range 0 to 255 separated by periods. Read RFC 3986.
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How to recognize the standard IPv4 form
A standard dotted-decimal IPv4 literal has four components and three periods. For instance, 10.1.0.52 has four components—10, 1, 0, and 52—and each is within the permitted range. A string with a component below 0 or above 255 does not fit this four-octet form.
Why some software may accept other dotted strings
Some platform-dependent routines accept legacy dotted forms with fewer than four numbers. That permissive behavior does not change the standard four-octet IPv4 literal syntax defined for URIs by RFC 3986. When interpreting or validating an IPv4 address, distinguish what a particular parser happens to accept from the standard dotted-decimal form.
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