D-Link DGS-3612G Product Manual - Page 184

xStack® DGS-3600 Series Layer 3 Managed Gigabit Ethernet Switch larger pool of IP addresses was required. IPv6 has addressed that issue, along with other issues that enhance routing over the network, provide better security and improve Quality of Service for Internet users. Some of the improvements made were: 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 168