#19 Jun 2025 Q4(e)(ii) 4 marks 1.3.2 IPv4 valid/invalid tick-table Inferred

Question

Lead-in: A youth centre is creating a network with 20 computers in a LAN. Users will have access to the internet.

(e)(ii) The computers will be allocated an IPv4 address. Tick (✓) one box on each row to identify if the IPv4 address is valid or invalid.

IPv4 addressValid (✓)Invalid (✓)
192.154.21.2☐☐
258.0.0.3☐☐
56.1.2.66.1☐☐
251.58.3.7☐☐

[4]

Why this question is tricky

INFERRED — no Jun 2025 examiner report yet. Distractors map directly to the misconceptions ER documented in Jun22 Q3(b) (lines 209-212) and Jun24 Q2(a)(i) (lines 146-150) — the "0–255 rule" and the "four-octet rule".
MS complexity 4/10: "Do not award rows with 2 ticks" — only one tick per row, no hedging.

Full-marks model answer

IPv4 addressValid (✓)Invalid (✓)
192.154.21.2✓
258.0.0.3✓
56.1.2.66.1✓
251.58.3.7✓
Mark allocation (4 marks — 1 per row)
  • 192.154.21.2 — valid: 4 octets, each between 0 and 255.
  • 258.0.0.3 — invalid: first octet is 258, which exceeds the maximum of 255.
  • 56.1.2.66.1 — invalid: 5 octets, but an IPv4 address must have exactly 4.
  • 251.58.3.7 — valid: 4 octets, each between 0 and 255.

Watch out for...

MS-derived only — no examiner-report guidance yet. Don't hedge by ticking both boxes on a row — the MS will award 0 for any row with two ticks. Remember the two IPv4 rules: exactly four octets AND each octet is 0–255 inclusive.