1. A firewall is a part of computer system or network that is designed to block unauthorized access while permitting authorized communications. 2. It is a device or set of devices configured to permit, deny, encrypt, decrypt, or proxy all (in and out) computer traffic between different security domain based upon a set rules and other criteria. 3. Firewalls can be implemented in either hardware or software, or a combination of both. Firewalls are frequently used to prevent unauthorized internet users from accessing private networks connected to the internet, especially intranets. 4. All messages entering or leaving the intranet pass through the firewall, which examines each messages and block those that do not meet the specified security criteria. 5. A firewall blocks unauthorized connections being made to your computer or LAN,, normal data is allowed through the firewall but all other data is blocked.
There are several types of firewall techniques:
i. Packet filter
ii. Proxy server
iii. Circuit-level Gateway
iv. Application Gateway