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IPv6 includes the following features that fix most of the limitations of IPv4:
1. New Header Format
The IPv6 header has a new format designed to minimize header overhead and this optimization is achieved by moving both non-essential fields and optional fields to extension headers that appear after the IPv6 header.
IPv4 headers and IPv6 headers do not interoperate. IPv6 is not a superset of functionality that is backward compatible with IPv4. A host or router must use an implementation of both IPv4 and IPv6 to recognize and process both header formats. The IPv6 header is only twice as large as the IPv4 header, even though IPv6 addresses are four times as large as IPv4 addresses.
2. Larger Address Space
IPv6 has 128-bit (16-byte) source and destination IP addresses. Although 128 bits can express over 3.4×1038 possible combinations, the large address space of IPv6 has been designed for multiple levels of subnetting and address allocation from the Internet backbone to the individual subnets within an organization.
With a much larger number of available addresses, address-conservation techniques, such as the deployment of NATs, are no longer necessary.
3. Efficient and Hierarchical Addressing and Routing Infrastructure
IPv6 global addresses that are used on the IPv6 portion of the Internet are designed to create an efficient, hierarchical, and summarizable routing infrastructure that is based on the common occurrence of multiple levels of Internet service providers.
4. Stateless and Stateful Address Configuration
To simplify host configuration, IPv6 supports both stateful address configuration (as in the presence of a DHCP server) and stateless address configuration (as in the absence of a DHCP server).
With stateless address configuration, hosts on a link automatically configure themselves with IPv6 addresses for the link (called link-local addresses) and with addresses that they derive from prefixes that local routers advertise. Even in the absence of a router, hosts on the same link can configure themselves with link-local addresses and communicate without manual configuration.
5. Built-in Security
The IPv6 protocol suite requires support for IPSec. This requirement provides a standards-based solution for network security needs and promotes interoperability between different IPv6 implementations.
6. Better Support for QoS
New fields in the IPv6 header define how traffic is handled and identified. Traffic identification (using a Flow Label field in the IPv6 header) allows routers to identify and provide special handling for packets belonging to a flow, which is a series of packets between a source and a destination. Because the IPv6 header identifies the traffic, QoS can be supported even when the packet payload is encrypted through IPSec.
7. New Protocol for Neighboring Node Interaction
The Neighbor Discovery protocol for IPv6 is a series of Internet Control Message Protocol for IPv6 (ICMPv6) messages that manage the interaction of nodes on the same link (known as neighboring nodes). Neighbor Discovery replaces the broadcast-based Address Resolution Protocol (ARP), ICMPv4 Router Discovery, and ICMPv4 Redirect messages with efficient multicast and unicast Neighbor Discovery messages.
IPv6 can easily be extended by adding extension headers after the IPv6 header. Unlike options in the IPv4 header, which can support only 40 bytes of options, the size of IPv6 extension headers is constrained only by the size of the IPv6 packet.
There are three types of communication for IPv6
1. Unicast : used for one-to-one communication. A unicast address identifies a single network interface. The protocol delivers packets sent to a unicast address to that specific interface.
There are 3 types of unicast addresses namely global, unique-local and link-local
2. Multicast : used for one-to-many communication. Multicast address is also assigned to a set of interfaces that typically belong to different nodes. A packet that is sent to a multicast address is delivered to all interfaces identified by that address. Multicast addresses are easily identifiable because the value of a IPv6 multicast address begins with "FF"
3. Anycast : used for one-to-one-of-many communication An anycast address is assigned to a group of interfaces, usually belonging to different nodes. A packet sent to an anycast address is delivered to just one of the member interfaces, typically the “nearest” according to the routing protocol’s choice of distance.
An important point to note here is that broadcast communication type is eliminated from IPv6 which was there in IPv4.
Broadcasts can be thought of as a special case of multicasting, where every device is the intended recipient. In IPv4, sending a broadcast causes all devices to process the packet, even those that are not concerned with the contents. Using multicasts is much more efficient because the packets can be targeted to a subset of devices, such as routers running Open Shortest Path First (OSPF).
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