The document discusses IPv6 headers and extension headers. It clarifies that extension headers are separate from the IPv6 header, and are not included in the IPv6 header length. The payload length of an IPv6 packet does include the length of any extension headers. For example, a packet may have an 8 byte Hop-by-Hop option header, so the ICMPv6 payload would be 36 bytes minus the 8 bytes for the extension header. Extension header lengths must always be considered separately from the IPv6 header length.

1. IPv6 headers, Neighbor
solicitation, and Router Advt
(Part 1)
By: Indraneel Pole

2. IPv6 headers
• This week I was solving some questions regarding IPv6 headers, when
I came across some wireshark frames which were confusing in many
ways.
• So here is the explanation that I found out in the process.
• The explanation is quite scattered and not aligned to some specific
streamline, but you might find something useful if you are planning to
look into any of the aforementioned headings.

3. IPv6 Header and confusion regarding
extension headers
• The main confusion can be regarding the way IPv6 header is designed
with extension headers keeping in mind.
• Many of the people I interacted with seem to thought that extension
header length is usually calculated in the IPv6 header length and is
not included in the payload length of IPv6 packet. I used to think this
for a long time as well.
• However when I looked into RFC, the picture was more or less clear.

4. • As you can see in this snippet, the extension header is considered as a
separate header, and not inside the IPv6 header itself.
• This also means, the header length should be calculated separately.

5. So if you see in following Wireshark snippet, the payload length of IPv6 includes
8 byte of Hop-by-hop option header, and IMCPv6 has 36 – 8 = 28 Byte

6. End of Part 1
• And this is true for all other option headers.
• You always need to consider header length of option
header seperately than IPv6 header length.