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IP V5 Addressing
IP Addresses.
IP (Internet Protocol) addresses are numbers that identify Internet hosts. They
provide universal addressing across all the networks of the Internet.
IP addresses are placed in the IP packet header and are used to route packets to
their destinations. An IP address is a 32-bit value split into four 8-bit pieces
(octets) that are separated by dots. An example of an IP address is
206.98.23.16. Each of the 4 numbers within the IP address can be between 1 and
255.
IP addresses are prefix based. The initial prefixes of the IP address can be
used for generalized routing decisions. For example, the first 16 bits of an
address might identify a corporation, the next 4 bits may identify a branch of
that corporation, the following 6 bits may identify a particular LAN in that
corporate branch, and the entire 32-bit address might identify a specific host
within that LAN.
To simplify packet routing, Internet addresses are divided into five classes:
Class A, Class B, Class C, Class D, and Class E. Very large corporations and
entities receive Class A addresses, mid-sized companies and universities usually
have Class B addresses, and most smaller companies and ISPs have Class C
addresses. Class D is a multicast address and Class E is reserved.
InterNIC, a cooperative effort of Network Solutions, Inc. (NSI) and the U.S.
Department of Commerce, allocates classes, which include the network part of an
IP address, to organizations. The individual organizations then assign the host
portions of the IP address to individual hosts.
Class A addresses are given to very large organizations such as the defense
department, major universities, and very large corporations such as IBM® and
Hewlett Packard®.
Class A addresses begin with a number between 1 and 126 (127 is reserved) in the
first octet, leaving the 3 other octets open
to split into local addresses. Although there are only 126 Class A codes, there
are more than 16 million individual IP addresses within each Class A. Needless
to say, it’s almost impossible to get a Class A.
Class B addresses are claimed by mid-sized companies, universities, and other
entities that need thousands of IP addresses. Class B IP addresses begin with
numbers between 128 and 191 in the first octet and have numbers from 1 through
255 in the second octet, leaving the last 2 octets open to denote local
addresses. There are 16,384 Class B addresses with 65,536 individual IP
addresses each. These are also very difficult to get.
Class C addresses—the most common—are used by most companies and ISPs. A Class C
address has a number from 192 through 223 in the first octet and a number from 1
through 255 in the second and third octets, leaving only the fourth octet free
for local addresses. There are more than two million Class C addresses and each
contains 255 IP addresses.
Subnetting enables a network administrator to further divide the host
part of the address into two or more subnets to make them easier to manage. A
filter called a subnet mask is used to determine the subnet to which an IP
address belongs.
Because IP addresses are difficult to remember, many also have text equivalents
such as whitehouse.gov or blackbox.com. These text-based addresses are called
domain names and can be obtained from Network Solutions (networksolutions.com).
A database program called Domain
Name Service (DNS) keeps track of the names and translates them into
their numeric equivalents.
The Internet is expected to outgrow the number of available IP addresses soon. A
new system of IP addresses called Internet Protocol Next Generation (IPng or
IPv6) is being designed to extend the capacity of the Internet.
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