Which statement is true about IPv6 compared to IPv4 regarding header size and fragmentation behavior?

• A. IPv6 header is 60 bytes and includes a header checksum
• B. IPv6 header is 20 bytes and has a header checksum
• C. IPv6 fragmentation is performed by routers along the path
• D. IPv6 header is 40 bytes with extension headers, and IPv6 has no IP header checksum

Answer: (D)

IPv6 changes how headers and fragmentation are handled compared to IPv4. The fixed IPv6 header is 40 bytes, and any additional options are carried in extension headers that follow the main header. There is no IP header checksum in IPv6, so routers don’t recompute or verify a header checksum at each hop; integrity is handled at higher layers or by end-to-end checksums.

Frag­mentation in IPv6 is not done by routers along the path. The sender is responsible for fragmentation when the packet size may exceed the path MTU, and it uses the Fragment extension header if needed. If a packet still doesn’t fit, an intermediary router will drop it and send back an ICMPv6 “Packet Too Big” message, prompting the sender to retransmit a smaller packet.

So the statement that the IPv6 header is 40 bytes with extension headers, and that IPv6 has no IP header checksum, aligns with how IPv6 is designed to operate.