Packet Format; Ipv6 Header - D-Link DGS-3600 Series User Manual

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xStack DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch
Expanding the Capabilites for IP Addressing – IPv6 has increased the size of the IP address from 32 bits to 128 bits. As a result,
the addressing hierarchy has been greatly expanded, more nodes now have the capability of having a unique IP address and the
method of assigning an IP address to an interface has become cleaner and quicker. Unicast and multicast addresses still exist but
in a purer form and multicast addresses now have a scope field that increases the scalability of multicast routing. Also, an anycast
address has been added, which will send packets to the closest node that is a part of a group of nodes, thereby eliminating a
specified device for a particular group.
Simplifying the Packet Header – The IPv6 packet header has been simplified from IPv4 as some headers have been modified or
dropped altogether, which improves processing speed and cost. The IPv6 header now has a fixed length of 40 bytes consisting of
an 8-byte header and two 16-byte IP addresses (source and destination).
Extensions and Options Enhancement – Packet header option fields encoding has been enhanced to allow for proficient
forwarding of packets due to lesser restrictions on packet option length and encoding method. This enhancement will also allow
new option fields to be integrated into the IPv6 system without hassles and limitations. These optional headers are placed between
the header and the payload of a packet, if they are necessary at all.
Authentication and Privacy Extension Support – New authentication capabilities use extensions for data integrity and data
confidentiality for IPv6.
Flow Labeling – This new capability allows packets to be streamlined into certain traffic "flows" if labeled by the sender. In this
way, services such as "real time services or non-default quality of service can receive special attention for improved flow quality.

Packet Format

As in IPv4, the IPv6 packet consists of the packet header and the payload, but the difference occurs in the packet header that has
been amended and improved for better packet flow and processing. The following will outline and detail the IPv6 enhancements
and parts of the IPv6 packet, with special attention to the packet header.

IPv6 Header

The IPv6 packet header has been modified and simplified from IPv4. The header length, identification, flags, fragment offset and
header checksum have all been removed in the IPv6 header due to lack of necessity or improvement to a better function of the
header. The minimum header length is now 20 bytes but may be increased to as much as 60 bytes, using 4-byte increment
extensions. The following picture is an example of an IPv6 packet header.
Eight fields make up the basic IPv6 packet header:
Version – This 4-bit field defines the packet version, which is IPv6 and is defined as the number 6.
Traffic Class – This 1-byte field replaces the Type of Service field used in IPv4 and is used to process real-time data and other
data requiring special packet management. This field defines the Class of Service priority of an IPv6 packet.
Flow Label – This 20-bit field is used to facilitate the handling of real-time traffic. Hosts sending data can place a flow label into
this field to identify a sequence of packets that have an identical set of options. In this way, router can process these packets more
efficiently once the flow class has been identified and the rest of the packet header no longer needs to be fully processed, just the
flow label and the source address. All flow label packets must have identical source and destination addresses.
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