Subnetting Tutorial

Subnetting Tutorial

The Basics: If Internet addressing remained as it was originally designed, it is likely that the number of hosts today would far exceed the available IP addresses. The problem with the standard classed addressing scheme is that the network ID length is predetermined by the class of the IP address. This also predetermines the number of hosts on each network. Below is a table of the standard classed IP address scheme:

Class From IP To IP Maximum Networks Maximum Hosts
A 1.0.0.0 126.255.255.255 126 1,677,216
B 128.0.0.0 191.255.255.255 16,384 65,536
C 192.0.0.0 223.255.255.255 2,097,152 256

It is obvious that a Class A IP range is unrealistic in its number of hosts. A network with this much traffic on the wire would crawl to a halt. This system does not allow more than a two tiered structure for IP addressing, this does not really match the actual layout of the Internet. Subnetting allows for differing lengths of network IDs. This means that Any IP class range can be divided up into multiple network IDs. The subnet mask essentially tells the router what part of the IP address to use as a network ID, as demonstrated in the following table using binary:

IP Address 10000000 00000001 0001 0001 00000001
Mask 11111111 11111111 1111 0000 00000000
Result 10000000 00000001 0001 N/A
Logical Address 128 1 1 N/A

The logical address is exactly what the router sees and it uses this to determine where to send the packet. This enables the CMC network to divide the Class B IP address range into class C subnets. This means that at a maximum there is only 253 hosts on one line. This subdivision enables added security within the network and organization of the network structure.

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