# IPv4 header-length example 3

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/practice/packet-support/ihl-3

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/practice/packet-support--ihl-3/

Optional extension · no matching calculation in the two supplied papers

**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=8 and Total Length=800 bytes. Find header and payload sizes. [3 practice marks]

#### Answer

## Given

IHL=8; Total Length=800 bytes.

## To find

Header bytes and payload bytes.

## Formula and why



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



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

## Step-by-step solution

#### Step 1. Convert IHL to bytes

H=4×8=32 bytes.

#### Step 2. Subtract the header

P=800−32=768 bytes.

#### Step 3. Add back the parts

32+768=800 bytes.

**Final answer:** Header=32 bytes; payload=768 bytes.

#### What this result means

IPv4 Total Length includes its own header. IPv6 Payload Length uses a different convention.