The Internet Protocol: IPV4 Address Allocation

We ended the last lesson with a discussion on variable-length subnets. Let's discuss how blocks of addresses are allocated to organizations, in this lesson.

Allocating Blocks of Addresses to Organizations

A second issue concerning the addresses of the network layer is how to allocate blocks of addresses to organizations.

  • The first allocation scheme was to allocate class address blocks on a first come, first served basis.

  • Large organizations such as IBM, BBN, as well as Stanford or MIT were able to obtain one class A address block each.

  • However, most organizations requested class B address blocks consisting of 65,53665,536 addresses, which was suitable for their size. Unfortunately, there were only 16,384 different class B address blocks. This address space was being consumed quickly. Since a disproportionate number of class B address blocks were being used, the number of entries for class B blocks increased. So the routing tables maintained by the routers were also growing quickly, and some routers had difficulties maintaining all these routes in their limited memory. Hence, the purpose of address space classes was being defeated.

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