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4.1.6 System IPv6
IPv6 (Internet Protocol version 6), also called IPng (IP next generation), was developed by the
IETF (Internet Engineering Task Force) as the successor to IPv4 (Internet Protocol version 4).
Compared with IPv4, IPv6 increases the IP address size from 32 bits to 128 bits; this solves the
IPv4 address exhaustion problem.
IPv6 features
IPv6 has the following features:
1. Adequate address space: The source and destination IPv6 addresses are both 128 bits (16
bytes) long. IPv6 can provide 3.4 x 10
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addresses to completely meet the requirements of
hierarchical address division as well as allocation of public and private addresses .
2. Header format simplification: IPv6 cuts down some IPv4 header fields or move them to IPv6
extension headers to reduce the load of basic IPv6 headers, thus making IPv6 packet handling
simple and improving the forwarding efficiency. Although the IPv6 address size is four times
that of IPv4 addresses, the size of basic IPv6 headers is 40 bytes and is only twice that of IPv4
headers (excluding the Options field).
3. Flexible extension headers: IPv6 cancels the Options field in IPv4 packets but introduces
multiple extension headers. In this way, IPv6 enhances the flexibility greatly to provide
scalability for IP while improving the handling efficiency. The Options field in IPv4 packets
contains 40 bytes at most, while the size of IPv6 extension headers is restricted by that of IPv6
packets.
4. Built-in security: IPv6 uses IPSec as its standard extension header to provide end-to-end
security. This feature provides a standard for network security solutions and improves the
interoperability between different IPv6 applications.
5. Automatic address configuration: To simplify the 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, DHCP server).
Stateless address configuration means that a host automatically configures an IPv6
address and related information on 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 basis of its own link-layer address and
the default prefix (FE80::/64) to communicate with other hosts on the link.
6. Enhanced neighbor discovery mechanism: The IPv6 neighbor discovery protocol is a
group of Internet control message protocol version 6 (ICMPv6) messages that manages the
information exchange between neighbor nodes on the same link. The group of ICMPv6
messages takes the place of Address Resolution Protocol (ARP) message, Internet Control
Message Protocol version 4 (ICMPv4) router discovery message, and ICMPv4 redirection
message to provide a series of other functions.
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