pers never imagined the kind of growth it has witnessed. 32-bit IP addressing puts a limit of 2 to the power of 32 addresses, i.e. 4 294 967 296. With the way the Internet is growing, this will soon deplete. If more bits had been used for addressing, the availability of IP addresses would have increased exponentially. IP 6 addressing uses 128 bits, which is virtually limitless, IP Addressing Network Prefix Subnet Number Host Number Figure 4.44 Example of subnetting but implementing IPv6 would require organisations worldwide to patch their systems and modify existing IP addresses. As of now, organisations are simply delaying this due to the enormity of the task. 4.9.3 Subnetting This is a technique that allows three-level hierarchies in addressing rather than two-level hierarchies, which was used in classful addressing. The network prefix remains the same but the host number is further subdivided into a subnet number and a host number (Figure 4.44). When faced with the requirement of installing a new network in an organisation, instead of applying to the Internet authority for yet another network, an administrator can instead divide the present network into various subnetworks or subnets. These subnets are internal to the organisation. Hence there can be as many nodes as required behind only a few Internet visible public IP addresses. Private subnetting has several advantages. Firstly, an administrator no longer has to make a request for a network number from the Internet before a new network is installed. This also accomplishes a more efficient use of the scarce IP address space. Secondly, since the subnets are not Internet visible, Internet routing tables would not grow with increasing numbers of subnets. Just one route from the Internet to the network is good enough to take care of all the machines belonging to different subnets inside it. Thirdly, every time there is a change in routing in an organisation's private network, routing tables of Internet routers need not be updated. The last but most important adv