Headers

IPv6 introduces a number of changes to the format of headers contained in a standard IPv4 packet. The following fields are common to IPv4 and IPv6:

Version
Length
Service Type
Packet Length
Identification
Fragment Offset
TTL
Transport
Header Checksum
Source Address
Destination Address
Options
Padding

However, there are several brand new headers that contain important information in standard format:

Version Number A “6” identifies IPv6.
Priority Sets a priority value, depending on whether a packet is noncongestion (priority) or congestion-controlled.
Flow Label Sets a QualityOfService parameter for the packet.
Payload Length Size of the packet’s data.
Next Header Determines whether an extension header follows.
Hop Limit Sets a limit on the number of nodes that can handle the packet (graceful degradation).

Several extensions to the standard headers are available in the extended header if flagged in the Next Header field of the standard header. The following extensions are currently being developed: