IPv6 Header Fixed Length Explained | Generated by AI
Question: What is the length of the basic header of an IPv6 datagram?
Answer:
The correct answer is C. 40B.
Explanation:
In IPv6, the header structure was significantly redesigned compared to IPv4 to improve efficiency, simplify processing, and support much larger addressing.
The IPv6 base header (also called the fixed header or basic header) has a fixed length of 40 bytes (320 bits). This length is constant and does not vary.
Key points about the IPv6 base header:
- Always exactly 40 bytes long
- Contains only the fields that are needed in every packet
- Does not include options in the main header (unlike IPv4)
- Any additional information is placed in extension headers that follow the base header (these are optional and variable in length)
Structure of the IPv6 base header (40 bytes total):
- Version (4 bits)
- Traffic Class (8 bits)
- Flow Label (20 bits)
- Payload Length (16 bits)
- Next Header (8 bits)
- Hop Limit (8 bits)
- Source Address (128 bits = 16 bytes)
- Destination Address (128 bits = 16 bytes)
Total: 4 + 8 + 20 + 16 + 8 + 8 + 128 + 128 = 320 bits = 40 bytes
Comparison with IPv4:
- IPv4 header is typically 20 bytes (without options), but can be longer if options are present.
- IPv6 uses a fixed 40-byte base header — longer than basic IPv4, but simpler and faster to process because the length never changes.
Therefore, the length of the IPv6 basic header is 40 bytes.
Correct choice: C
References:
- None (standard networking knowledge / RFC 8200 - Internet Protocol, Version 6 (IPv6) Specification)