The present system of IP network numbers,
established in 1981, uses a 32 bit number to identify computers on the internet. These
numbers are represented as a sequence of four 8 bit numbers (octets), each of which
can therefore vary between 0 and 255. The first part of each 32 bit number represents
the network, and the remaining part refers to the individual
computer.
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To accommodate different network sizes,
IP address space was originally divided into three sections; Class A (0.x.x.x to 127.x.x.x) - 8 bit network prefix,
Class B (128.0.x.x to 191.255.x.x) - 16 bit network prefix and Class C (192.0.0.x to 223.255.255.x) - 24 bit network prefix.
These classes remain generally applicable, but the introduction of Classless Inter-Domain Routing (CIDR) has allowed
for the more efficient division of address space to create arbitrary sized networks.
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