Information Technology Reference
In-Depth Information
The next sections compare IPv4 and IPv6 in each of these categories.
Expanded Addressing Capabilities
In IPv4, addresses are 32 bits long. This creates the potential for approximately 4.2 billion
addresses. However, a combination of factors have resulted in a significant inefficiency
in address utilization:
•
Subnet sizing
•
Current address allocations
•
Classful deployments
•
One-eighth of the address space is reserved (Class E) or designated for multicast
(Class D)
The IETF formed a working group, Address Lifetime Expectation (ALE), to determine the
expected lifetime of the IPv4 address space in the early 1990s. The ALE working group pre-
dicted that the IPv4 address space would be exhausted between 2005 and 2011. The use of
Network Address Translation (NAT) has extended this timeframe. The need for additional
address space is felt most strongly outside the U.S.
IPv6 addresses are 128 bits long. Only one-eighth of the address space is assigned for
unicast addressing. However, even one-eighth of the available address space is still virtually
limitless from the perspective of network-addressable devices.
Autoconfiguration Capabilities
The IPv4 protocol was not designed with inherent address autoconfiguration capabilities.
This prompted the IETF to develop Dynamic Host Configuration Protocol (DHCP) to
decrease the administrative overhead involved in managing a large network. Automatic
Private IP Addressing (APIPA) was added eventually to allow a host to automatically
configure itself with a locally routable address. However, these autoconfigured addresses
cannot be routed over the global Internet.
The IPv6 protocol lets a host automatically configure itself with a globally routable address.
The autoconfiguration capabilities involve the use of Internet Control Message Protocol
version 6 (ICMPv6) to determine the local subnet. The host then automatically configures
a 64-bit portion of the address, called the
interface identifier
, to form a unique address,
which can be globally routed.
Header Simplification
The IPv4 header format allows various options to be included directly in the IPv4 header.
This results in increased processing during the forwarding of IPv4 packets.
