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The
Internet Protocol (IP) knows each logical host
interface by a number, the so-called IP address.
On any given network, this number must be unique
among all the host interfaces that communicate
through this network. Users of the
Internet are sometimes given a
host name in addition to their numerical IP
address by their
Internet service provider.
The IP addresses of
users browsing the
world wide web are used to enable communications
with the server of the web site. Also, it is usually
in the header of
email messages one sends. In fact, for all
programs that utilize the
TCP/IP protocol, the sender IP address and
destination IP address are required in order to
establish communications and send data.
Depending on one's
Internet connection the IP address can be the
same every time one connects (called a
static IP address), or different every time one
connects, (called a
dynamic IP address). In order to use a dynamic
IP address, there must exist a server which can
provide the address. IP addresses are usually given
out through a service called DHCP or the
Dynamic Host Configuration Protocol.
Internet addresses
are needed not only for unique enumeration of hosted
interfaces, but also for routing purposes, therefore
a high fraction of them are always unused or
reserved.
The unique nature of
IP addresses makes it possible in many situations to
track which computer - and by extension, which
person - has sent a message or engaged in some other
activity on the internet. This information has been
used by law enforcement authorities to identify
criminal suspects. The dynamically-assigned nature
of many IP addresses can make this more difficult,
however.
IP
version 4
Addressing
In
version 4 of the Internet protocol (IPv4), the
current standard protocol for the Internet, IP
addresses consist of 32
bits, which makes for 4,294,967,296 (over 4
billion) unique host interface addresses in theory.
In practice, because addresses are allocated in
blocks, a large number of unused addresses are
unavailable (much like unused phone numbers in a
sparsely-populated area code), so that there is some
pressure to extend the address range via IP version
6 (see below).
IPv4 addresses are
commonly expressed as a dotted quad, four
octets (8 bits) separated by periods. The host
known as www.wikipedia.org currently has the number
3482223596, written as 207.142.131.236 in
base-256: 3482223596 equals 207×2563
+ 142×2562 + 131×2561 +
236×2560. (Resolving the name "www.wikipedia.org"
to its associated number is handled by
Domain Name System servers.)
IPv4 addresses were
originally divided into
two parts: the network and the host. A later
change increased that to three parts: the network,
the
subnetwork, and the host, in that order.
However, with the advent of
classless inter-domain routing (CIDR), this
distinction is no longer meaningful, and the address
can have an arbitrary number of levels of
hierarchy. (Technically, this was already true
any time after the advent of subnets, since a site
could elect to have more than one level of
subnetting inside a
network number.)
See also:
Classful network
Assignment
The actual assignment
of an address is not arbitrary. An organization,
typically an Internet service provider, requests an
assignment of a netblock from a registry such as the
American Registry for Internet Numbers (ARIN).
The network number comprises a range of addresses
which the organization is free to allocate as they
wish. An organization that has exhausted a
significant part of its allocated address space can
request another netblock.
For example, ARIN has
allocated the addresses 64.78.200.0 through
64.78.207.255 to Verado, Inc. In turn, Verado has
allocated the addresses 64.78.205.0 through
64.78.205.15 to Bomis. Bomis, in turn, has assigned
the specific address 64.78.205.6 to the host
interface that is named www.wikipedia.com.
As of February 2005, some large blocks assigned
include:
Class A Addresses
Exhaustion
Some
private IP address space has been allocated via
RFC 1918. This means the addresses are available
for any use by anyone and therefore the same
RFC 1918 IP addresses can be reused. However
they are not routable on the Internet. They are used
extensively due to the shortage of registerable
addresses.
Network address translation (NAT) is required to
connect those networks to the Internet.
While a number of
measures have been taken to conserve the limited
existing IPv4 address space (such as the use of NAT
and
Private Addressing), the number of 32-bit IP
addresses is not sufficient to accommodate the
long-term growth of the Internet. For this reason,
there is a general consensus that the Internet
128-bit
IPv6 addressing scheme will be adopted over the
next 5 to 15 years.
See also:
IPv4 address exhaustion
IP
version 5
What would be
considered as IPv5 existed only as an
experimental non-IP real time streaming protocol
called ST2 described in
RFC 1819. This protocol was abandoned in favour
of
RSVP.
IP
version 6
In
IPv6, the new (but not yet widely deployed)
standard protocol for the Internet, addresses are
128 bits wide, which, even with generous assignment
of netblocks, should suffice for the foreseeable
future. In theory, there would be exactly 2128,
or about 3.403 × 1038 unique host
interface addresses. If the earth were made entirely
out of 1 cubic millimetre grains of sand, then you
could give a unique address to each grain in 300
million planets the size of the earth. This large
address space will be sparsely populated, which
makes it possible to again encode more routing
information into the addresses themselves.
A version 6 address
is written as eight 4-digit (16-bit)
hexadecimal numbers separated by colons. One
string of zeros per address may be left out, so that
1080::800:0:417A is the same as
1080:0:0:0:0:800:0:417A.
Global
unicast IPv6 addresses are constructed as two
parts: a 64-bit routing part followed by a 64-bit
host identifier.
Netblocks are
specified as in the modern alternative for IPv4:
network number, followed by a slash, and the number
of relevant bits of the network number (in decimal).
Example: 12AB::CD30:0:0:0:0/60 includes all
addresses starting with 12AB00000000CD3.
IPv6 has many
improvements over IPv4 other than just bigger
address space, including
autorenumbering and mandatory use of
IPsec.
Further reading:
Internet RFCs including
RFC 791,
RFC 1519 (IPv4 addresses), and
RFC 2373 (IPv6 addresses).
See
also
External links
Retrieved from "http://en.wikipedia.org/wiki/IP_address"
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