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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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