Firewall is an electronic network security system designed to forestall unauthorized access to or from a non-public network. It is implemented as hardware, software, or a mix of both. Firewalls are accustomed to prevent unauthorized Internet users from accessing private networks connected to the net. All messages are entering or leaving the intranet submit to the firewall. The firewall examines each message and blocks those who don't meet the required security criteria.
The four techniques used by firewalls to control access and enforce a security policy are:
Service control regulates the types of Internet services that can be accessed inbound or outbound which can be done by funnelling traffic on the basis of an IP address, protocol or port numbers. The can be done by making use of proxy software or host server software.
Direction control regulates the direction in which particular service requests may be initialized and are allowed to flow via through the firewall. A User control manages or authorizes admission to a service according to which entity is trying to access that specified service.
A User control typically applied to access inside a perimeter but also can be applied to incoming external traffic.
Behaviour control which manages how specific services are used such as filtering of emails.
Functions of Firewall
The most important function of a firewall is that it creates a border between an external network and the guarded network where the firewall inspects all packets (pieces of data for internet transfer) entering and leaving the guarded network. Once the inspection is completed, a firewall can differentiate between benign and malicious packets with the help of a set of pre-configured rules.
The firewall abides such packets, whether they come in a rule set or not, so that they should not enter into the guarded network.
This packet form information includes the information source, its destination, and the content. These might differ at every level of the network, and so do the rule sets. Firewalls read these packets and reform them concerning rules to tell the protocol where to send them.
