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IPv4 Address Validity: Selecting the Correct Dotted-Decimal Notation

IPv4 Address Validity: Selecting the Correct Dotted-Decimal Notation

Verified Sources
Nov 4, 2026

An IPv4 address in dotted-decimal form must consist of exactly four decimal octets separated by dots, where each octet is a number in the range 00 to 255255 (because each octet represents 8 bits).

A common additional constraint in typical dotted-decimal parsing is that an octet must not contain an invalid “extra” dot count (i.e., it must be four octets total), and each octet must be within the decimal range.

Footnotes

  1. IPv4 address - Wikipedia - Describes dotted-decimal notation and that an IPv4 address is 32-bit represented as four 8-bit octets (0–255). ↩ ↩2

IPv4 Addressing Basics (dotted-decimal and octets)

Let’s evaluate each option against the rules “four octets” and “each octet is 00–255255”.

Key checks you should apply

  • Octet: each part between dots
  • Dotted-decimal: exactly four numbers
  • Range constraint: no octet beyond 255

Validate each proposed IPv4 address

  1. 1
    Step 1

    An IPv4 dotted-decimal address must have three dots, yielding exactly four octets.

  2. 2
    Step 2

    Each octet must be a valid decimal number (no missing/extra separators).

  3. 3
    Step 3

    If any octet is less than 00 or greater than 255255, the address is invalid.

  4. 4
    Step 4

    "Some parsers treat leading zeros specially, but in many educational contexts the key issue is: the octet must still represent a value within 00–255255 and follow the dotted-decimal structure."

    Footnotes

    1. Dotted-decimal notation - Wikipedia - Discusses representations of IP addresses in dotted-decimal and parsing considerations such as leading zeros. ↩

Evaluate the given options

  1. (i) 124.201.3.1.52
  • Problem: It has 5 octets (there are 4 dots), but IPv4 dotted-decimal must have 4 octets total.
    ✅ Conclusion: Invalid.
  1. (ii) 300.142.210.64
  • Problem: First octet is 300, which is greater than 255.
    ✅ Conclusion: Invalid.
  1. (iii) 01.200.128.123
  • Structure: Four octets is correct.
  • Range: 01 represents the value 1, which is within 00–255255.
    ✅ Conclusion: Typically considered valid in dotted-decimal notation used in coursework/standard decimal interpretation. Leading zeros may vary by strict parser rules, but range + four-octet format are satisfied. 2
  1. (iv) 128.64.0.0
  • Structure: Four octets correct.
  • Range: 128, 64, 0, 0 all within 00–255255.
    ✅ Conclusion: Valid.

Footnotes

  1. IPv4 address - Wikipedia - Describes dotted-decimal notation and that an IPv4 address is 32-bit represented as four 8-bit octets (0–255). ↩ ↩2 ↩3 ↩4

  2. Dotted-decimal notation - Wikipedia - Discusses representations of IP addresses in dotted-decimal and parsing considerations such as leading zeros. ↩

Validity of Each Option (Based on IPv4 Format Rules)

Check counts: four-octet structure and octet range (0–255).

Common mistake: counting octets

IPv4 dotted-decimal always has exactly 4 octets. If you see 5 segments like 124.201.3.1.52, it’s automatically invalid regardless of values.

Common mistake: octet range

Even if there are exactly four parts, any octet above 255 (e.g., 300) makes the entire IPv4 address invalid.

Edge cases & strictness

IPv4 Validity Quick Checks

1 / 5
Question · Term

How many octets does an IPv4 dotted-decimal address have?

Click to reveal
Answer · Definition

Exactly 4 octets (four decimal numbers separated by 3 dots).

Knowledge Check

Question 1 of 4
Q1Single choice

Which of the following is a syntactically valid IPv4 dotted-decimal address?

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