A firewall [I1] [I2] [I3] [I4] [I5] [F1] [S1] [S2] [S3] [S4] [S5] [E1] [E2] is basically a structure, a computer equipment, a software normally placed between Internet (or among Intranet) and the company local network in order to filter all packages and let enter only those that according to a certain security requirement are suitable to pass from the external net (thought to be less safe) and the internal net (thought to be safer).
As you can see a firewall allows to link different net portions to different security levels. Therefore it can also be used inside a local net to make safe parts of local nets on which it is required a higher level of security.
But how does a firewall work? A firewall is a calculator with its own software. This calculator is linked from one side to a part of the net not very safe and from the other side on the net which needs to be made safe.
All packages pass through this software that has decisional processes. The processes follow strict rules previous decided, for example “ to reject all packages coming from a particular IP address (remember that inside an IP package there is always the origin address). Or I can decide to accept only some services like e-mail but to discard server web. The firewall is basically an intelligent element which divides one area from the other of the network.
It has some limits though:
- It does not protect from internal menaces and sabotage
- It does not protect from transmitting infected files or e-mail with infected attachments
