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Q4A · IPv6 packet format

Re-exam · 4 February 2026

TEE · Actual TEE paper · all questions · current syllabus 702AI0C023

Actual PYQ · Q4A. Construct the IPv6 packet format and explain the purpose of each field. [10 marks]

Answer

Swipe across the diagram to read its labels ↔
IPv6 base header · each horizontal row is 32 bits wide
Diagram: IPv6 base header · each horizontal row is 32 bits wide. Labels: IPv6 base header · each horizontal row is 32 bits wide | IPv6 base header · each horizontal row is 32 bits wide | Version | 4 | Traffic Class | 8 | Flow Label · 20 | Payload Length · 16 | Next Header | 8 | Hop Limit | 8 | Source address · 128 bits (four rows) | Destination address · 128 bits (four rows)
Eight base-header fields occupy 320 bits = 40 bytes.
FieldBitsPurpose
Version4Value 6
Traffic Class8Traffic treatment/congestion-related marking
Flow Label20Identifies a flow for appropriate handling
Payload Length16Bytes after the base header; includes extension headers when present
Next Header8Type of the next extension header or upper-layer protocol
Hop Limit8Decremented on forwarding; limits packet lifetime in hops
Source address128Sending interface address
Destination address128Destination address

The first two 32-bit rows contain 64 bits and the two addresses contain 256 bits, giving a 320-bit base header. Payload Length excludes these 40 bytes. Next Header can identify an extension header or upper-layer protocol. IPv6 has no base-header checksum; optional information is carried through extension headers.

Source: Re-exam · 4 February 2026, original question paper page 2. Original marks retained; solution independently authored.