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More On Address Classes
The Internet address format can be described graphically:
- Example 1:
- in a class A network, only values from
00000000 to
01111111 are possible. Of these 128 combinations, 126
are permitted (networks 0 and 127 are reserved for other purposes).
Hence there can only ever be 126 class A networks, each of which
can have a huge number of hosts.
- Example 2:
- ironbark's IP address is
149.144.21.60 This is a
class B network (149.144.0.0), and ironbark's host ID
within this network is 21.60. Note that when we write
an IP address with all-zeroes in the host part, we are referring to
the "network number" itself.
- Example 3:
203.17.3.5 is a class C address. The network
number is 203.17.3.0, and the host number is
5.
Network numbers above 223 are also reserved for special purposes,
outside the scope of this subject.
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