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Internet Protocol - IP is a service used for data transmission without permanent connection. This identifies each logic interface of connected equipments using a number called IP address. The more used standard is IPv4. In IPv4 the current standard is Internet communication, the IP address being represented on 32 bits (for example: IP address assignation it's not realized randomly but by organizations that distribute addresses space.

IPv4 addresses have a length of 32 bits (4 bytes). Each address identify a network and a work station inside the network. Usual notation is obtained by writing each byte in decimal form, separated by full stops. For example is the notation used for the address: 11000000.10101000.00000000.00000001

Addresses class

IP address in decimal and binary format

At the beginnings of the Internet, IPv4 addresses were divided in 5 addresses class marked from A to E. The division was made according to the binary configuration of the first byte of the address, thus:


First byte in binary

First address

Last address




uses 8 bits for the network and 24 for the work station



uses 16 bits for the network and 16 for the work station



uses 24 bits for the network and 8 for the work station



used for multicast addresses



used for experimental

  • Source: Wikipedia

To identify stations are used only addresses from classes A to C. There are 2 addresses of class A unused on the Internet:

  • Interval - is not used so to not be confused with the implied route;
  • Interval - is used only to diagnose the local node (this will always be the one responding to the call of an address from this class).

Sadly this method wasted too many IP addresses and with Internet spread there were the danger to run out of address space. To solve this problem in early 90s were designed several solutions.

  • Private addresses - addresses for devices not connected to Internet. There are three intervals reserved for private addresses:
  1. Addresses reserved for class A: -;
  2. Addresses reserved for class B: -;
  3. Addresses reserved for class C: -
  • CIDR - Classless InterDomain Routing - refers to the way IP addresses are represented in the routing table and the way update messages are sent. In CIDR notation the IP address is always written with the network mask. For example an address: with mask would be written in CIDR notation as, because first 24 bits from the IP address indentify the subnet.
  • VLSM - Variable Length Subnet Mask - is a process which involves specifying a network mask for each address associated to an interface. This allows dividing an address class in several networks of various dimension minimizing wastage of IP addresses.
  • IPv6 - is a protocol developed to replace IPv4 in Internet. Addresses have a length of 128 bits (16 bytes), considered to be enough for a long period of time. In theory there are 2128 or about 3403 x 1038 unique addresses.

External links

RIPE - organization for Europe, Middle East parts from Africa and Asia

This term is in development.
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