common carrier communications networks.... use links and
concepts originally designed for another purpose -- voice.... we
might wish to consider an alternative approach -- a standardized
message block... composed
of perhaps 1024 bits. Most of the message block would be
reserved for whatever type data is to be transmitted, while
the remainder would contain housekeeping information such
as error detection and routing data.
Distributed Communications, Volume I, 1964.
What is an IP address? Every computer on the Internet has
a unique numerical address, called an Internet Protocol (IP) address,
to route packets to it across the Internet.
Just as your postal address enables the postal system to send
mail to your house from anywhere around the world, your computer's
IP address gives the Internet routing protocols
the unique information they need to route packets of
information to your desktop from anywhere across the Internet.
If a machine needs to contact another by a domain
name, it first looks
up the corresponding IP address with the domain
name service. The IP address is the geographical descriptor
of the virtual world, and the addresses of both source and destination
systems are stored in the header of every packet that flows across
You can find your IP address on a Windows computer by opening
an MSDOS or Command window and typing one of "winipcfg" or "ipconfig".
You can find your IP address on a Mac computer by checking
your Network control panel.
No matter what electronic device you are using and where you are,
if you are connected to the web you can visit the following sites
to dynamically find your IP address in real time:
As described in the pages on confidentiality
Internet sites can and do track your IP address and other information.
If you want to block or disguise
can use an
The sections below provide more information about the
IP address format, allocations, lookup
databases, and references to more
Format. An IP address is made up of
four bytes of information (totaling 32 bits) expressed as four
numbers between 0 and 255 shown separated by periods. For example,
your computer's IP address might be 184.108.40.206, which is shown
below in human-readable decimal form and in the binary form used
on the Internet.
. 17 . 159 . 4
11101110 00010001 10011111 00000100
Each of the four numbers uses eight bits of storage, and so can
represent any of the 256 numbers in the range between zero (binary
00000000) and 255 (binary 11111111). Therefore, there are more
than 4 billion
possible different IP addresses in all:
4,294,967,296 = 256
* 256 * 256 * 256
Allocations. The Internet
Assigned Numbers Authority manages the allocation of
IP addresses to different organizations in various sized blocks.
The IANA IP
Address Allocations page provides a focal point for this
world wide IP address management. An official list of the allocations
of IP address blocks can be found at the Internet
Protocol Address Space site, and related information can
be found at the IP
Most of the address blocks have been allocated to research, education,
government, corporations, and Internet Service Providers, who in
turn assign them to the individual computers under their control.
A few addresses are reserved for future or special use. The historical
top-level allocations of these blocks of IP addresses are described
For Comments 1466.
If you connect to the Internet over a phone line, then your IP
address is probably assigned dynamically
by your Internet service provider from an available pool of addresses
each time you log on. If your computer is permanently connected
as at the office or on a high speed home connection, then your
IP address could be permanently assigned, or could be reassigned
each time you reboot your computer.
Lookup databases. You can find out more information
on any particular IP number by searching one of the following databases. Since
each address is generally kept in only one database, you might have to try
more than one to find the database that has the information on any particular
You can also search the web for information about an IP address;
for example, is there any information about address 220.127.116.11?
Resources. The following resources provide
J. Postel; Address Mappings; Sep 1981.
1518; An Architecture for IP Address Allocation with
CIDR; Y. Rekhter, T. Li; September 1993.
1918; Address Allocation for Private Internets;
Y. Rekhter, B. Moskowitz, D. Karrenberg, G. J. de Groot, E.
Lear; February 1996.
2050; Internet Registry IP Allocation Guidelines;
K. Hubbard, M. Kosters, D. Conrad, D. Karrenberg, J. Postel;