Efficient Addressing

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How to Make Routing Scale



Flat (Ethernet) versus Hierarchical (Internet) Addresses
-All hosts attached to same network have same network address
Problem: inefficient use of Hierarchical Address Space
-class C with 2 hosts (2/255 = 0.78% efficient)
- class B with 256 hosts (256/65535 = 0.39% efficient)
Problem: still Too Many Networks
- routing tables do not scale
-Big tables make routers expensive
-route propagation protocols do not scale


Subnets contd.


Subnetting is not the only way to solve scalability problems

Additional router support is necessary to include netmask and forwarding functionality

Non-contiguous netmask numbers can be used
-They make administration more difficult
Multiple subnets can reside on a single network
-Requires routers within the network
Subnets help solve scalability problems
- Do not require us to use class B or C address for each physical network
-Help us to aggrigate information

Chief advantage of IP addresses: routers could keep one entry per network instead of one per destination host