The Internet is a global network of computers. Any computer connected to the Internet can communicate with any other computer connected to the Internet. It can make analogy with road network that allows a car to starting a village to reach any other village. There are smaller or larger streets, and the route used is not necessarily straightforward.
The Internet is a decentralized network, meaning that there is no institution or a state that ail his own or govern the operation. Financial and logistics support is carried out by companies whose accesses and management is overseen by a committee called ICANN (Internet Corporation For Assigned Names and Numbers).
Because everyone in the world can connect to the Internet without restrictions, it is considered as public. Like any entity open to the public, Internet presence involves a considerable risk, both for people and especially for companies. Being an open space, the Internet allows individuals or organizations to cause malicious damage other members more than any other network.
Given that information has become very valuable, fraud temptations for containing systems became increasingly larger. Given that reason either financial interests, or simply entertainment, crime found a good place in computer networks.
To enable companies to protect themselves from threats from the Internet, and also to be able to use the advantages that make it so popular, it is using an architecture that is called Intranet. The intranet is a private network (as opposed to Internet which is public) within a company or institution. Intranet computers inside are not accessible from the outside, but can access both internal resources and resources from Internet servers. This is possible using a device called firewall. It is basically a filter which allows only connections in a single direction inside to the outside. A pretty good analogy foe firewall is a private PBX, found in most companies with more than two offices. A firewall does not close completely access from the outside, only if programmed to do so; firewall connections are bidirectional. A firewall does not block, currently, only those unauthorized connections from the outside, leaving the intranet users to access resources from both the Intranet and the Internet. Users outside the Intranet can access only that information that the firewall allows access and is configured to provide them.
Like phones, computers use numbers to be identified. These are organized into four groups of numbers separated by the character “. “(Point), called IP addresses. Computers in a network are assigned consecutive groups of 256, 128, 64, 32, 16, 8 or 4 addresses based on the number of devices to be connected. A special type of IP address is the private addresses. These are similar numbers inside the PBX I mentioned above.
Private addresses are easily recognized because they have a standard form, as 10.xxx.xxx.xxx, 172.16.xxx.xxx, ie 192.168.xx These addresses are used only to computers intranets.
The connection between two networks is done using a router. It has one connection for each network to which it belongs. In general, the router may be a dedicated equipment, itself an ordinary PC can serve this role.
The router acts as a dispatcher, which decides which network is intended for information it receives, often with the added role of firewall. It is the most widespread of Internet equipment, after PC, the point of entry and output of information between networks. It is a common fact that between two computers on the Internet to be used several routers (may be even a few tens) in transit.
Because of the important role it has, the router is the most delicate networks equipment. Being the equipment through which transit so much information, his compromise is equivalent to the access, usually unauthorized, to all this information. When controlling access to the router that connects to the router through which a companz connects to Internet, not only that zou have access to all the messages that the company submit its partners, but also get an open door to the inside protected network.