Computer Networks · M2 · read

IPv4 header-length example 2

IP packet details · supporting practice

Unit 4 support · header comparison; fragmentation is additional practice

Optional worked extension. This calculation format was not found in the supplied December 2025 final or February 2026 re-exam. The numbers and practice marks are authored. Study the core concept and actual-paper questions first; this is extra explanation, not a TEE prediction.

Practice question. An IPv4 packet has IHL=6 and Total Length=1200 bytes. Find header and payload sizes. [3 practice marks]

Answer

Given

IHL=6; Total Length=1200 bytes.

To find

Header bytes and payload bytes.

Formula and why

H=4\,\mathrm{IHL},\qquad P=T-HLaTeX: H=4\,\mathrm{IHL},\qquad P=T-H

IHL counts 32-bit words; each word is 4 bytes.

Step-by-step solution

Step 1. Convert IHL to bytes

H=4×6=24 bytes.

Step 2. Subtract the header

P=1200−24=1176 bytes.

Step 3. Add back the parts

24+1176=1200 bytes.

Final answer: Header=24 bytes; payload=1176 bytes.