IPv6 Packet Format:

For Internet Protocol version 6 (IPv6), the specification began with making modifications and deletions to the existing IPv4 header. The diagram below indicates which IPv4 fields were modified or deleted.

The resulting IPv6 PDU looks as follows:

IPv6 Packet Field Descriptions

Version (4 bits)---Indicates the version of IP currently used (IPv4 → 0100 / IPv6 → 0110).
Traffic Class (8 bits)---Establishes the class or priority of IPv6 packet (was TOS in IPv4).
Flow Label (20 bits)---
Payload Length (16 bits)---Specifies the length, in octets, of the data only. Note this includes extension headers.
Next Header (8 bits)---identifies the type of header immediately following the IPv6 header (was protocol in IPv4). Uses the same values as IPv4.
Hop Limit (8 bits)---Field decremented by 1 at each arriving node, when it becomes zero, the packet is dropped (was TTL in IPv4).
Source Address (128 bits)---Specifies the IP address of the sending node.
Destination Address (128 bits)---Specifies the IP address of the receiving node.
Data---Contains upper-layer information.

IPv4 PDU