The issue of subnetting has long been a mystery to many system
administrators. It seems that there are just too many bits, bytes, and masks
involved to make it worthwhile. Besides, who needs all that trouble when it's
all you can do to just maintain the network as it is? You can certainly find
sympathy, but if your network plans call for Internet access then IP (Internet
Protocol) addressing and possibly subnet masking are topics that you s hould be
familiar with.
As networks grow to increasing numbers of segments, more network address
numbers will be needed as each segment requires an individual number. The
InterNIC (whose name signifies cooperation of Network Information Centers or
NICs), however, is not eager to hand out unlimited network addresses because
they are quickly running out of them. The Internet community is generally taking
a firm stand on limiting address availability, due to the accelerated growth
demand for Internet access. Network administrators will have to work with what
they have to better accommodate network requirements and the shrinking supply of
address numbers.
One way of accomplishing this address conservation is to take the address
that is assigned to your network and expand the capacity with subnets.
Subnetting allows you to increase the number of networks available to you
without applying for another IP address number.
IP Addressing
The IP addressing framework allows one to address about 16,000,000 unique
hosts for a Class A address, around 65,000 hosts for a Class B address, but only
254 hosts for a Class C address. However, there are no more Class A addresses
available, and the InterNIC has stopped assigning Class B addresses. Class C
addresses are the most numerous, but their limitation is that each can identify
only 254 unique hosts.
The IP address is composed of 32 bits, which consist of two parts: the most
significant bits (MSBs) identify a particular network and the remaining bits
specify a host on that network. The most significant bits of the network portion
actually determine the address class as shown in this table:
Address MSB
Class Pattern
Class A 0
Class B 10
Class C 110
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