4.7.1 IPv6 Packet Format
The format of the IPv6 packet is shown in Figure 4.7-1. The most important changes introduced in IPv6
are evident in the packet format:
● Expanded addressing capabilities. IPv6 increases the size of the IP address from 32 to 128 bits.
This insures that the world won't run out of IP addresses. Now, every grain of sand on the planet
can be IP-addressable. In addition, the address space contains new hierarchical structure,
allocating portions of the enlarged address space to geographical regions [RFC 1884]. In
addition to unicast and multicast addresses, a new type of address, called an anycast address, has
also been introduced, which allows a packet addressed to an anycase address to be delivered to
any one of a group of hosts. This feature could be used, for example, to send an HTTP GET to
the nearest of a number of mirror sites that contain a given document).
● A streamlined 40 byte header. As discussed below, a number of IPv4 fields have ben dropped or
made optional. The resulting 40-byte fixed-length header allows for faster processing of the IP
packet. A new encoding of options allows for more flexible options processing.
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