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The key to understanding IP is knowing what a routing table looks
like.
IP addresses are 32 bit numbers and are represented in a dotted
decimal notation:
XXX.XXX.XXX.XXX
Each decimal number represents eight bits of binary data, and
therefore can have a decimal value between 0 and 255:
0.0.0.0 to
255.255.255.255
It is the value of the first number of the IP address that determines
the class to which a given IP address belongs. IP addresses most
commonly are class A, B, or C.
| Class |
Range |
Allocation |
| A |
1-126 |
N.H.H.H |
| (A) |
127 |
(loopback) |
| B |
128-191 |
N.N.H.H |
| C |
192-223 |
N.N.N.H |
| D |
224-239 |
(multi-cast) |
| E |
240-248 |
reserved |
| |
249-255 |
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N=Network
H=Host
Notes:
127.0.0.0 is a class A network, but is reserved for use as a
loopback address (typically 127.0.0.1).
The 0.0.0.0 network is reserved for use as the default route.
Class D addresses are used by groups of hosts or routers that
share common characteristics.
Class D addresses are used for multi-cast applications.
Class E addresses exist (240-248) but are reserved for future
use.
RFC 790 - Assigned numbers
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