What does the Next Header field indicate in the IPv6 header?

• A. The type of the next header following IPv6 header, such as TCP, UDP, ICMPv6, or an extension header
• B. The payload length
• C. The time to live
• D. The source address

Answer: (A)

The key idea is that the Next Header field tells you what comes immediately after the IPv6 header. It designates the type of the next header, which can be a higher‑level protocol like TCP, UDP, or ICMPv6, or an IPv6 extension header (such as Hop-by-Hop Options, Routing, Fragment, or Destination Options). If the value points to an extension header, that header itself contains its own Next Header value to indicate what follows, creating a chain until the actual transport header (TCP/UDP/ICMPv6) is reached. This field is an 8‑bit number defined in the IANA registry. It’s independent from the payload length, which is given by a separate field, and from the hop limit (time to live). For example, values like 6, 17, and 58 correspond to TCP, UDP, and ICMPv6, while values like 0, 43, 44, and 60 indicate various IPv6 extension headers.