# IP Addresses - Indirizzi IP

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Every computer must have a unique number in order to work properly in a network or on the Internet. This number is called address because it makes possible for a computer to be found by other computers - ( something like the human addresses! ) -and to establish a communication with them.

So we have IP address: Internet Protocol address. This number is in the form of XXX . XXX . XXX . XXX where XXX is an integer number between 0 and 255. ( DOTTED QUAD: four group of decimal numbers separated by a dot ). Computers don't understand our decimal system but only electrical signals like on - off, so we must use the binary system (base 2 not base 10) where a number is composed by a series of 0 and 1. Example: 7 is represented by 00000111. Every binary cypher, that is 1 or 0, is a bit and 8 bits makes one byte. So 255 is, in binary,11111111. Since every group of the IP address is formed by 8 bits and there are four groups (or four bytes ), we say that an IP address is 32 bits long ( 8 x 4 = 32 ). Example 192.0.2.79 , in binary, looks like this: 11000000000000000000001001001111 Since there are 2 cyphers - 0 and 1 - it is possible to have 4.294.967.296 ( 2^32 ) of different combinations of addresses.

Every IP addresses shows two things: the network to which the computer belongs and the host, that is the number of the computers. There are private IP addresses ( computers NOT connected to the Internet) and public IP addresses ( computers CONNECTED to the Internet ).

IP addresses are divided in classes: A - B - C - D - E

Class A: IP addresses between 1.0.0.0 and 127.255.255.255. The first byte identifies the networks, the next 3 bytes the host. We have 127 networks and 16.777.216 hosts.

Class B: IP addresses between 128.0.0.0 and 191.255.255.255. The first 2 bytes identify the networks, the next 2 bytes the hosts. The first byte is limited to 128 - 191, so we have 16384 networks and 65536 hosts.

Class C: IP addresses between 192.0.0.0 and 223.255.255.255. The first 3 bytes identify the networks, the last byte the hosts. The first byte is limited to 192 - 223, so we have 2.097.152 networks and 256 hosts

Class D: it is used for multicast, that is when just one host is broadcasting and all the others are receiving.

Class E: for future use

From 10.000 to 10.254.254.254
From 172.16.0.0 to 172.31.254.254
From 192.168.0.0 to 192.168.254.254
IP addresses may be dynamic or static.
Dynamic when the addresses changes every time that a computer or network is connected to the Internet - the ISP gives a different address at every connection.

Static when the address is still the same.

There will be a new kind of IP addresses, IPV6 ( base 16 ) which will allow to have more addresses.

Renato Piccini - Florence - Italy
Computers Networks technician
http://www.softgrafic.com

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