the IPv4 address size, the basic IPv6 header size is 40 bytes and is only twice the IPv4 header size
(excluding the Options field).
Figure 1-1 Comparison between IPv4 packet header format and basic IPv6 packet header format
Adequate address space
The source and destination IPv6 addresses are both 128 bits (16 bytes) long. IPv6 can provide 3.4 x
addresses to fully meet the requirements of hierarchical address division as well as allocation of
public and private addresses.
Hierarchical address structure
IPv6 adopts the hierarchical address structure to quicken route search and reduce the system sources
occupied by the IPv6 routing table by route aggregation.
Automatic address configuration
To simplify host configuration, IPv6 supports stateful and stateless address configuration.
Stateful address configuration means that a host acquires an IPv6 address and related information
from a server (for example, a DHCP server).
Stateless address configuration means that a host automatically generates an IPv6 address and
related information on the basis of its own link-layer address and the prefix information advertised
by a router.
In addition, a host can generate a link-local address on the basis of its own link-layer address and the
default prefix (FE80::/10) to communicate with other hosts on the same link.
IPv6 uses IPSec as its standard extension header to provide end-to-end security. This feature provides
a standard for network security solutions and enhances the interoperability between different IPv6
The Flow Label field in the IPv6 header allows the device to label packets of a flow and provide special
handling for these packets.