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Communication
Class A
0
Computer
Network
Class B
1
0
Network
Class C
1
1
Computer
0
Network
Computer
Figure 10-2 Classes of addressing
The classes are distinguished between by their initial bits. A class-A network only
uses the first seven bits to distinguish between the networks (i.e., only 126 class-A
networks exist worldwide but these can contain all 224 computers). Class-B networks can still address 65,536 different computers. A total of 16,384 class-B networks are possible. Class-C networks are the smallest networks. They can contain a maximum of 256 computers but can be addressed in very great numbers
(i.e., 221).
In addition, special Multicast addresses are reserved. These are identified by the
first bits 1110. Addresses with the bit sequence 1111 are reserved for future applications.
Originally, it was assumed that a 32-bit address area would be sufficient. However,
the enormous popularity of the Internet caught everyone by surprise. Already now,
class-A addresses are no longer available. Class-B addresses are only assigned
after rigorous examination. However, class-C addresses are easy to obtain. Currently, strong initiatives to expand this address area are making the rounds. The
draft with the greatest chance of success is called IPng (i.e., IP next generation).
It defines an address area of 16 octets.
IP addresses are noted in decimal format in groups of four. For example, a valid
IP address is 201.1.212.1. This is a class-C address. The initial number indicates
this since C-class networks are located in the area from 192 to 223. The last number specifies the computer in the network. In our example, this is the computer
with the address 1. The numbers 0 and 255 should not be used in the address
since they have special functions (e.g., zero is used for network addresses).
The ARP (i.e., Address Resolution Protocol) is used to announce IP addresses on
the Internet. This protocol can be used to assign a hardware address (MAC,
Ethernet address) to a known IP address and vice versa. A diskless client can use
a Broadcast message announcing its MAC address to fetch its IP address from
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SICOMP IMC – System Manual
J31069-D2001-U001-A0-7618