IP ADDRESSING SYSTEM

The IP addressing system is a systematic way of assigning Internet protocol numbers to all the system on a particular network for easy carriage of data and for identification purpose

The Internet continues to grow at a phenomenal rate. This is reflected in the tremendous popularity of the World Wide Web (WWW), the opportunities that businesses see in reaching customers from virtual storefronts, and the emergence of new ways of doing business. It is clear that expanding business and public awareness will continue to increase demand for access to resources on the Internet.

Issues with Internet Protocol

Over the past few years, the Internet has experienced two major scaling issues as it has struggled to provide continuous and uninterrupted growth:

• The eventual exhaustion of IP version 4 (IPv4) address space


• The need to route traffic between the ever increasing number of networks that comprise the Internet

The first problem is concerned with the eventual depletion of the IP address space. IPv4 defines a 32-bit address which means that there are only 232 (4,294,967,296) IPv4 addresses available. As the Internet continues to grow, this finite number of IP addresses will eventually be exhausted.

The second problem is caused by the rapid growth in the size of the Internet routing tables. Internet backbone routers are required to maintain complete routing information for the Internet

Unfortunately, the routing problem cannot be solved by simply installing more router memory and increasing the size of the routing

Other factors related to the capacity problem include the growing demand for CPU horsepower to compute routing table/topology changes, the increasingly dynamic nature of WWW connections and their effect on router forwarding caches, and the sheer volume of information that needs to be managed by people and machines.

Proposed solutions

The long-term solution to these problems can be found in the widespread deployment of IP Next Generation (IPng or IPv6). Currently, IPv6 is being tested and implemented on the 6Bone network, which is an informal collaborative project covering North America, Europe, and Japan. 6Bone supports the routing of IPv6 packets, since that function has not yet been integrated into many production routers.

Concept of Classful IP Addressing

A classful network is a network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing in 1993. The method divides the IP address space for Internet Protocol version 4 (IPv4) into five address classes based on the leading four address bits.

When IP was first standardized in September 1981, the specification required that each system attached to an IP-based Internet be assigned a unique, 32-bit Internet address value. Systems that have interfaces to more than one network require a unique IP address for each network interface. The first part of an Internet address identifies the network on which the host resides, while the second part identifies the particular host on the given network.

In recent years, the network number field has been referred to as the network prefix because the leading portion of each IP address identifies the network number. All hosts on a given network share the same network prefix but must have a unique host number. Similarly, any two hosts on different networks must have different network prefixes but may have the same host number.

Primary Address Classes

To provide the flexibility required to support networks of varying sizes, the Internet designers decided that the IP address space should be divided into three address classes-Class A, Class B, and Class C.

Class A Networks (/8 Prefixes)

Each Class A network address has an 8-bit network prefix, with the highest order bit set to 0 (zero) and a 7-bit network number, followed by a 24-bit host number. Today, Class A networks are referred to as “/8s” (pronounced “slash eight” or just “eights”) since they have an 8- bit network prefix.

Class B Networks (/16 Prefixes)

Each Class B network address has a 16-bit network prefix, with the two highest order bits set to 1-0 and a 14-bit network number, followed by a 16-bit host number. Class B networks are now referred to as “/16s” since they have a 16-bit network prefix.

Class C Networks (/24 Prefixes)

Each Class C network address has a 24-bit network prefix, with the three highest order bits set to 1-1-0 and a 21-bit network number, followed by an 8-bit host number. Class C networks are now referred to as “/24s” since they have a 24-bit network prefix.

Other Classes

In addition to the three most popular classes, there are two additional classes. Class D addresses have their leading four bits set to 1-1-1-0 and are used to support IP Multicasting. Class E addresses have their leading four bits set to 1-1-1-1 and are reserved for experimental use.

Unforeseen Limitations to Classful Addressing

The original Internet designers never envisioned that the Internet would grow into what it has become today. Many of the problems that the Internet is facing today can be traced back to the early decisions that were made during its formative years.

• During the early days of the Internet, the seemingly unlimited address space allowed IP addresses to be allocated to an organization based on its request rather than its actual need. As a result, addresses were freely assigned to those who asked for them without concerns about the eventual depletion of the IP address space


• The decision to standardize on a 32-bit address space meant that there were only 232 (4,294,967,296) IPv4 addresses available. A decision to support a slightly larger address space would have exponentially increased the number of addresses thus eliminating the current address shortage problem.


• The classful A, B, and C octet boundaries were easy to understand and implement, but they did not foster the efficient allocation of a finite address space. Problems resulted from the lack of a network class that was designed to support medium-sized organizations. For example, a /24, which supports 254 hosts, is too small while a /16, which supports 65,534 hosts, is too large. In the past, sites with several hundred hosts were assigned a single /16 address instead of two/24 addresses. This resulted in a premature depletion of the /16 network address space. Now the only readily available addresses for medium-sized organizations are /24s, which have the potentially negative impact of increasing the size of the global Internet’s routing table.

Concept of Subnetting

A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.

In 1985, RFC 950 defined a standard procedure to support the subnetting, or division, of a single Class A, B, or C network number into smaller pieces. Subnetting was introduced to overcome some of the problems that parts of the Internet were beginning to experience with the classful two-level addressing hierarchy, such as:

• Internet routing tables were beginning to grow


• Local administrators had to request another network number from the Internet before a new network could be installed at their site.

Both of these problems were attacked by adding another level of hierarchy to the IP addressing structure. Instead of the classful two-level hierarchy, subnetting supports a three-level hierarchy.

Subnetting attacked the expanding routing table problem by ensuring that the subnet structure of a network is never visible outside of the organization’s private network. The route from the Internet to any subnet of a given IP address is the same, no matter which subnet the destination host is on. This is because all subnets of a given network number use the same network prefix but different subnet numbers. The routers within the private organization need to differentiate between the individual subnets, but as far as the Internet routers are concerned, all of the subnets in the organization are collected into a single routing table entry. This allows the local administrator to introduce arbitrary complexity into the private network without affecting the size of the Internet’s routing tables.

Subnetting overcame the registered number issue by assigning each organization one (or at most a few) network numbers from the IPv4 address space. The organization was then free to assign a distinct subnetwork number for each of its internal networks. This allowed the organization to deploy additional subnets without obtaining a new network number from the Internet.

In summary, an IP address is an address used in order to uniquely identify a device on an IP network. The address is made up of 32 binary bits, which can be divisible into a network portion and host portion with the help of a subnet mask. The 32 binary bits are broken into four octets (1 octet = 8 bits). Each octet is converted to decimal and separated by a period (dot). For this reason, an IP address is said to be expressed in dotted decimal format (for example, 172.16.81.100). The value in each octet ranges from 0 to 255 decimal, or 00000000 - 11111111 binary.