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CIDR Addresses
A CIDR address has some of the characteristics of a subnetted Class
A, B or C address, see earlier. They are
written as aa.bb.cc.dd/x. The new
/x specifier indicates how many bits of the
address, starting from the MSB, are to be interpreted as the
"network" part, leaving the remainder to be interpreted as "host"
part.
For example, suppose an organisation needed about 1000 IP
addresses for its Internet-connected hosts. A suitable CIDR
allocation would be (eg)203.100.100.0/22. This
means that the address part is 22 bits, and the host part is 10
bits, giving 1024 host IDs. As usual, we write all zeros in the
host part of the address when referring to the "network"
itself.
An additional characteristic of CIDR is that IP address blocks are
now allocated on a geographic basis, or more
correctly, on the basis of domain names. So, for example, virtually
all IP addresses recently allocated in Australia now have
203 as their first byte. This is done to
simplify routing, see later
The tutorial for this lecture is Tutorial
#10.
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Copyright © 2001 by
Philip Scott, La Trobe
University.
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