IP Version 6 (IPV6)
IPV4 addressing scheme provides over 4 billion possible addresses. However, due to increase in internet use, there isn’t enough addresses to accommodate all the hosts on the internet.
An IP address is divided into a network and local portion which are managed separately. The address space is divided in classes A, B and C. The IP addressing model requires unique network numbers be assigned to all IP networks.
Other restrictions in IPv4 include:
- IP backbone routers are becoming harder to manage
- Traffic priority is not enforced
IPv6 Overview
Features:
- larger address space
- addressing based on prefixing rather than address classes
- autoconfiguration of network interfaces
- encapsulation support
- ability to distinguish different types of data
- improved multicast routing support
- authentication and encryption (built in)
- methods to migrate to IPv6
- compatible with Ipv4
IPv6 header format
The length of the Ipv6 header is 40 bytes. It contains 2 16-byte addresses. The 2 addresses are source and destination preceded by 8 bytes of control information. Reduction of control information and elimination of options improves processing time per packet in router.
Packet Sizes
Nodes dynamically determine MTU (Maximum Transmission Unit) supported by links along a path. Source nodes will send packets that do not exceed path MTU. IPv6 requires that every link has a minimum 1280 bytes MTU.
Extension Headers
IPv6 packet starts with basic header. In majority of cases basic header is the only thing needed. Sometimes it is necessary however to submit other information with the packet.
Extension packets are placed after the basic header packet and are counted as part of the payload length. The extension header has its own 8-bit next header field byte of the header. This identifies the type of the following header. This allows IPv6 to chain multiple extension headers together. A limited number of extension headers. Each one must have a maximum of one in the IP packet. The nodes have to be in a specific order, although nodes that receive the packets do not verify this. When the Next Header field contains a value other than one for the extension header, this indicates the end of the headers and the start of the higher level protocol.
Encapsulation is done with a next header value of 41. Routers should not add extension headers to a packet because size of packet is calculated by the originating node to match the path MTU.
Hop-By-Hop Header
Contains options that must be examined by every node the packet traverses along with the destination node. It follows the IPv6 header and is identified by a 0 in the Next header field. The format is TLV (Type-Level-Format)
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