A Firewall is a structure aimed to avoid unapproved access to or from a network that is private. The Internet is a volatile and unsafe environment when viewed from a computer-security perspective, therefore "firewall" is an excellent metaphor for network security. They can be implemented in both hardware and software. Firewalls are normally used to avoid un-approved internet users from accessing private networks that are connected to the Internet, for example intranets. The firewall examines all the incoming and outgoing data and it is able to block messages that do not meet the security conditions.
Below are types of firewall techniques:
Is at the entry point of the network it protects, it looks at every single packet that is entering or leaving the network and it is the one that accepts or rejects based on the user’s outlined rules. This simply means that the firewall is the first program that receives and handles incoming network traffic, and it is the last to handle outgoing traffic.
It is a second type of firewall that provides security to specific applications like the FTP and Telnet servers. Effective but can enforce performance degradation.
Seizes each and every message that will be entering or leaving the network. The Proxy server then conceals the original network addresses.
Also known as the “Circuit Level Gateway”, it authorizes connections before permitting the data to be swapped. This means that the Firewall will not basically permit or prohibit packets, but it also regulates if the connection between both ends is valid according to configurable rules, it then allows traffic from other sources for a limited time to see if a connection is valid based on destination IP address and or port, user password, source IP address and or port etc. All sessions of data exchange are authorised and all traffic is prohibited, except when a session is opened. A circuit Level filtering controls for an advanced period of time than a Packet Filter, an advantage is that it is able to make up for the faults of the ultra-simple and utilisable UDP procedure where the source address is never validated as a utility of procedure. IP spoofing can be a bit difficult for it will be reduced. But the one of the disadvantages is that the Circuit Level functions at the Transport Layer and might need considerable alterations of the programming which usually provides transport functions.
In this method the firewall goes more in its guideline of traffic. They are commonly regarded as being the most secure kind of firewall and they surely have the most sophisticated abilities. One of its disadvantages is that the setup is complicated, it needs thorough care in the different applications that use the gateway. Application gateway is usually applied on a detached computer on the network with a main purpose of providing proxy service.
All firewalls irrespective of type have one very significant thing in common which is they; receive, review and make choices of the incoming data before it get to the other parts of the system or network. That means they handle packets and they are strategically placed at the entry point of the system or network, the firewall is intended to protect.