Features
of IPv6
The IPv6 header has a new header format that
is designed to minimize header overhead. This
optimization is achieved by moving both
non-essential fields and optional fields to
extension headers that appear after the IPv6
header. Intermediate routes can process the
streamlined IPv6 header more efficiently. IPv4
headers and IPv6 headers do not interoperate.
IPv6 is not a superset of functionality, that
is backward compatible with IPv4 is not
possible. 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.
IPv6 features a
larger address space than
that of IPv4. IPv6 has 128-bit (16 byte)
source and destination IP addresses. Although
128 bits can express over 3.4×1038 possible
combination's, 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.
Multicast, the ability to send a single packet
to multiple destinations, is part of the base
specification in IPv6. This is unlike IPv4,
where it is optional (but usually
implemented). Multicasting is delivering a
data stream to multiple destinations at the
same time, with no duplication unless called
for. Those functionalities are not supported
by IPv4. The other two types of addressing
that are standard practice for IPv6 are
unicast and anycast. The former is a
transmission from just one host to just one
other host; the latter is from one host to the
nearest of many hosts.
The Time-to-Live field of IPv4 has been
replaced by a Hop-Limit field.
IPv6 offers a higher level of built-in
security, and it has been specifically
designed with mobile devices in mind. The
mobility comes in the form of Mobile IP, which
allows roaming between different networks
without losing an established IP address.
Unlike mobile IPv4, Mobile IPv6 (MIPv6) avoids
triangular routing and is therefore as
efficient as normal IPv6.
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.
Jumbograms: IPv4 limits packets to 64 KB of
payload. IPv6 has optional support for packets
over this limit, referred to as jumbograms,
which can be as large as 4 GB. The use of
jumbograms may improve performance over
high-MTU networks. The presence of jumbograms
is indicated by the Jumbo Payload Option
header.
IPv6 also includes standardized support for
QoS. The QoS implementation is set up so that
routers can identify packets belonging to an
individual QoS flow. Furthermore, QoS
instructions are included in the IPv6 packet
header. This means that the packet body can be
encrypted, but QoS will still function because
the header portion containing the QoS
instructions is not encrypted. This will make
it possible to send streaming audio and video
over the Internet with IPSec encryption, but
in a manner that guarantees adequate bandwidth
for real-time playback.
