The IP Address consists of 32 bits (4 8-bit bytes) They are shown with each byte represented by it's decimal value (0 - 255 (28) separated by decimal points =(e.g., 128.96.96.14)
An IP address consists of two parts, one identifying the network and one identifying the node, or host. The Class of the address determines which part belongs to the network address and which part belongs to the node/host address.
e.g. Class A networks assign the first octet to the network and the rest to the hosts. IBM has network number 9.0.0.0, MIT has network 18.0.0.0 Address Range Num. of Default Type Lowest Highest Networks Mask (1) ________________________________________________________________________ Class A 0.1.0.0 126.0.0.0 126 255.0.0.0 Class B 128.1.0.0 191.254.0.0 16 K 255.255.0.0 Class C 192.0.1.0 223.255.254.0 2 M 255.255.255.0 Class D 224.0.0.0 239.255.255.255 Used to support multicasting. Class E 240.0.0.0 247.255.255.255 Used for experimentation. Reserved 248.0.0.0 255 1. Reserved Addresses: 0 (default route), 127 (loopback address) and 224-255 are reserved. Networks 128.0.0.0, 191.255.0.0, 192.0.0.0, and 223.255.255.0 also are reserved. 255.255.255.255 Broadcast (2) The standard structure can be modified by using a Subnet Mask to use Host Address bits as network addresses locally. Bellcore uses a Subnet Mask of 255.255.255.0 which allocates the 3rd byte to a subnet number and leaves the 4th byte for the host name. This provides more efficient routing of network traffic.As of May of 1995 the Address space was allocated as follows: (2^32 = 4 Billion potential addresses) used as follows: Class A: 38% allocated the remainder is reserved. Class B: 80% in 1993 dropped to 62% in 1995 by reassignment. Class C: 28% allocated.
The weighted total shows that 65.74% (34.74% actually allocated to organizations and 31% reserved for future growth) of the total IPv4 address space has been allocated. It should be noted that careful extrapolations of the current trends suggest that the address space will be exhausted early in the next century. However, the situation is already serious.
Classless Inter-Domain Routing (CIDR) is removing the distinction between classes above. It was introduced in 1993 when the exponential growth if IP address assignment indicated Class B addresses would shortly be depleted. With CIDR, addresses are increasingly thought of as bitwise contiguous blocks of the entire address space.
This scheme allows "supernetting" of addresses together into a blocks which can be advertised as a single routing entry. The practical purpose of this effort is to allow service providers and address registries to delegate realistic address spaces to organizations and be unfettered by the traditional network classes, which were usually inappropriately sized for most organizations. For example the block of 2048 class C network numbers beginning with 192.24.0.0 and ending with 192.31.255.0 can be referenced as 192.24/19, or 192.24.0.0 with a mask of 255.248.0.0 (ie 2^19 in dotted decimal notation). This is referred to as a network with a /19 (19 bit) prefix.
The New Internet Routing and Addressing Architecture (NIMROD) working group of the IETF is working on TCP/IP Version 6 which among other things will make more addresses available.
See IP number assignment statistics, and See appeal to return unused IP numbers.
Example assignments: 0.0.0.0 Internet Assigned Numbers Authority 1.0.0.0 IANA (RESERVED-9) 2.0.0.0 IANA (RESERVED) 3.0.0.0 General Electric Company 4.0.0.0 BBN Planet 5.0.0.0 IANA (RESERVED) 6.0.0.0 Army Information Systems Center 7.0.0.0 IANA (RESERVED-11) 8.0.0.0 Bolt Beranek and Newman Inc. 9.0.0.0 IBM Corporation 10.0.0.0 IANA (RESERVED-6) 11.0.0.0 DoD Intel Information Systems 12.0.0.0 AT&T ITS 13.0.0.0 Xerox Palo Alto Research Center 14.0.0.0 Public Data Network 15.0.0.0 Hewlett-Packard Company 16.0.0.0 Digital Equipment Corporation 17.0.0.0 Apple Computer, Inc. 18.0.0.0 Massachusetts Institute of Technology 19.0.0.0 Ford Motor Company 20.0.0.0 Computer Sciences Corporation Return to Internet History5/4/95. Send comments and updates to webmaster@cc.bellcore.com
