What is firewall ?
A firewall is a network security system that monitors and controls the incoming and outgoing network traffic based on predetermined security rules.
  • A firewall typically establishes a barrier between a trusted network and an untrusted network.
  • A firewall can be hardware, software, or both.
The primary goal of a firewall is to block malicious traffic requests and data packets while allowing legitimate traffic through.

Four general techniques of the firewall to control access
1.Service control:-Determines the types of Internet service that can be accessed, inbound or outbound
2.Direction Control:-Determines the direction in which particular service requests may be initiated and allowed to flow through the firewall.
3.User Control:-User control manages or authorizes admission to a service according to which entity is trying to access that specified service.
4.Behaviour Control:-It controls how particular services are used.

How does a Firewall work?
A firewalled system analyzes network traffic based on rules. A firewall only accepts those incoming connections that it has been configured to accept. It does this by allowing or blocking specific data packets units of communication you send over digital networks based on pre-established security rules. A firewall works like a traffic guard at your computer's entry point or port. Only trusted sources or IP addresses are allowed in.

Types of Firewall
  • Packet filtering firewall
  • circuit-level gateway
  • application-level gateway (Proxy firewall)
  • stateful inspection firewall
  • next-generation firewall
why do we need Firewall ?
Firewalls focus on blocking malware and application-layer attacks. Firewalls can act on previously set policies to better protect your network and can carry out quick assessments to detect invasive or suspicious activity, such as malware. Especially Next-Generation Firewalls along with an integrated intrusion prevention system are able to react quickly and seamlessly to detect and combat attacks across the whole network.

Advantages of Firewall
  • A firewall blocks harmful packets.
  • A firewall monitors Network Traffic.
  • Firewalls serve as an important blockage against these malicious programs.
  • Centralized and simplified network management. 
  • It prevents hacking.
  • It promotes privacy.    
Disadvantages of Firewall
  • They often cannot protect against an insider attack. 
  • Firewall cannot protect a network or pc from viruses, Trojans, Worms and spyware which spread through flash drives, portable hard disk etc. 
  • They may restrict authorized users from accessing valuable services.
  • In general hardware firewalls are more expensive than the software firewalls & hardware firewall require installation and maintenance which can be costly.
  • when the software firewalls constantly run on the background they consume more processing power and RAM resources. This can lead to diminished system performance.
  • cannot protect against the transfer of all virus-infected programs or files.   


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