Internet Protocol Version 6

IPv6

IPv6, like the more commonly used IPv4 (as of 2013), is an Internet Layer protocol for packet-switched internetworking and provides end-to-end datagram transmission across multiple IP networks.  IPv6 also implements features not present in IPv4. It simplifies aspects of address assignment (stateless address autoconfiguration), network renumbering and router announcements when changing network connectivity providers. It simplifies processing of packets by routers by placing the need for packet fragmentation into the end points. The IPv6 subnet size has been standardized by fixing the size of the host identifier portion of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from link-layer media addressing information (MAC address). Network security is also integrated into the design of the IPv6 architecture, including the option of IPsec.

IPv6 does not implement interoperability features with IPv4, but essentially creates a parallel, independent network. Exchanging traffic between the two networks requires special translator gateways or other transition technologies, such as tunneling protocol like 6to4, 6in4, or Teredo.

Comparison To IPv4

Network-layer security

Internet Protocol Security (IPsec) was originally developed for IPv6.  IPsec was a mandatory specification of the base IPv6 protocol suite but has since been made optional.

Simplified processing by routers

In IPv6, the packet header and the process of packet forwarding have been simplified. Although IPv6 packet headers are at least twice the size of IPv4 packet headers, packet processing by routers is generally more efficient thereby extending the end-to-end principle of Internet design. Specifically:

• The packet header in IPv6 is simpler than that used in IPv4, with many rarely used fields moved to separate optional header extensions.
• IPv6 routers do not perform fragmentation. IPv6 hosts are required to either perform path MTU discovery, perform end-to-end fragmentation, or to send packets no larger than the IPv6 default minimum MTU size of 1280 octets.
• The IPv6 header is not protected by a checksum; integrity protection is assumed to be assured by both link-layer and higher-layer (TCP, UDP, etc.) error detection. UDP/IPv4 may actually have a checksum of 0, indicating no checksum; IPv6 requires UDP to have its own checksum. Therefore, IPv6 routers do not need to recompute a checksum when header fields (such as the time to live (TTL) or hop count) change. This improvement may have been made less necessary by the development of routers that perform checksum computation at link speed using dedicated hardware, but it is still relevant for software-based routers.
• The TTL field of IPv4 has been renamed to Hop Limit, reflecting the fact that routers are no longer expected to compute the time a packet has spent in a queue.

Mobility

Unlike mobile IPv4, mobile IPv6 avoids triangular routing and is therefore as efficient as native IPv6. IPv6 routers may also allow entire subnets to move to a new router connection point without renumbering.

Options extensibility

The IPv6 packet header has a fixed size (40 octets). Options are implemented as additional extension headers after the IPv6 header, which limits their size only by the size of an entire packet. The extension header mechanism makes the protocol extensible in that it allows future services for quality of service, security, mobility, and others to be added without redesign of the basic protocol.

Jumbograms

IPv4 limits packets to 65535 (216-1) octets of payload. An IPv6 node can optionally handle packets over this limit, referred to as jumbograms, which can be as large as 4294967295 (232-1) octets. The use of jumbograms may improve performance over high-MTU links. The use of jumbograms is indicated by the Jumbo Payload Option header.