PPT Slide
[13 pts] Why is classful addressing inefficient ? Explain how subnet masks and VLSMs help to address this problem. Assume that you are given the class B address space 128.113.0.0 and you had to configure 250 subnets with 120 hosts each, and 1000 networks with 30 hosts each. What subnet masks will you use to accomplish this task ?
Classful addressing is inefficient in two ways:
Internal fragmentation: An enterprise will not be able to use all the class B address space because no single network is that large leading to several host numbers being unused
External fragmentation: everyone wants class B addresses, and hence the class C and class A network numbers are unused.
Subnet masks allow sub-division of a class into sub-networks so that each subnet will have fewer host numbers to represent a single broadcast domain.
VLSMs allow a single class to have multiple lengths of subnet masks. This allows each subnet to have exactly the number of bits necessary to number all its hosts.