Firewall

In computing, 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, secure internal network and another outside network, such as the Internet, that is assumed to not be secure or trusted. Firewalls are often categorized as either network firewalls or host-based firewalls. Network firewalls are a software appliance running on general purpose hardware or hardware-based firewall computer appliances that filter traffic between two or more networks.

 

Host-based firewalls provide a layer of software on one host that controls network traffic in and out of that single machine. Routers that pass data between networks contain firewall components and can often perform basic routing functions as well, Firewall appliances may also offer other functionality to the internal network they protect such as acting as a DHCP or VPN server for that network.

 

Filter Mechanisms

 

Firewalls use 3 types of filtering mechanisms:

• Packet filtering or packet purity
  Data flow consists of packets of information and firewalls analyze these packets to sniff out offensive or unwanted packets depending on what you have defined as unwanted packets.
• Proxy
  Firewalls in this case assume the role of a recipient & in turn sends it to the node that has requested the information & vice versa.
  
• Inspection
  In this case Firewalls instead of sifting through all of the information in the packets, mark key features in all outgoing requests & check for the same matching characteristics in the inflow to decide if it relevant information that is coming through.

Types of Firewall

• Software firewalls
  New generation Operating systems come with built in firewalls or you can buy a firewall software for the computer that accesses the internet or acts as the gateway to your home network.
• Hardware firewalls
  Hardware firewalls are usually routers with a built in Ethernet card and hub. Your computer or computers on your network connect to this router & access the web.