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4.2.2 Address assignment in IP networks
Any IP-network device is characterized by the addresses of three groups:
Physical address. It is a hexadecimal MAC address of the network adapter or port. The MAC
address is unique and is 6-byte long: the first 3 bytes are the manufacturer’s identifier and the
other 3 bytes are uniquely assigned by the manufacturer itself. For example, 18-B7-34-39-AA-FC.
Network address (IP address). It is assigned during the configuring of network devices by the
administrator and does not depend on the physical address. The address has a decimal
representation and its length is 4 bytes. It consists of two parts: network number and node
number. Depending on the class of the network, different quantity of bytes is assigned to the
network number..
IP address classes
The network address consists of two logical parts: network and node number. The values of the
first address bits mean what part of the address refers to the network number and what to the
node number:
• Class A networks. The network number takes one byte, the other three show the node number
in the network. Class A networks can only have numbers in the 1.0.0.0–126.0.0.0 range.
Networks with number are not used, and number 127 is reserved. The node count must be more
than 126 but less than 224. The first bit of the network address of Class A must start with 0.
• Class B networks. The network and node numbers take two bytes each. Class B networks can
have numbers in the 128.0.0.0–191.255.0.0 range. The node count must be more than 28 but
less than 216. The network address of Class B must have the first two bits equal to 10.
• Class C networks. The network number takes three bytes. Class C networks can have numbers
in the 192.0.1.0–223.255.225.0 range. The node count must no be more than 28. The network
address of Class C must have the first three bits equal to 110.
• Class D networks. The networks of this class have a special multicast address. Class D
networks can have numbers in the 224.0.0.0–239.255.225.225 range. All nodes that have this
address will receive a packet with an address that belongs to Class D network. The network
address of Class D must begin with a sequence of 1110.
• Class E networks. The networks of this class are not used and they are reserved for future
(experimental) usage. Class E networks can have numbers in the 240.0.1.0–247.255.225.225
range. The network address of Class E must begin with a sequence of 11110.
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