Firewall

Firewall, important thing that you have to know 
if you want safe even surfing in the Internet.

A firewall is a system or group of systems running the access control security between a secure internal network and an untrusted network such as internet.Firewall designed to permit the trusted data or data via a trusted, easy to refuse service attack, preventing internal network from outside attacks that couldpenetrate the firewall every time.

Generally also used to control access to anyone who has access to a private network from outside parties. Today, the term firewall became prevalent that the term refers to systems that manage communication between two different networks.Given today many companies that have access to the Internet and also of course the network incorporated in it, then the protection of digital capital of the company from attacks by hackers (hackers, pemata-eye, or other data thieves) becomes mandatory.

Firewall System Components

Firewalls can be either PCs, routers, midrange, mainframe, UNIX workstation, or a combination of these. Firewall which may consist of one or more functional components as follows:

• Packet-filtering router
• Application level gateway (proxy)
• Circuit-level gateway

Example Types of Firewall 

A firewall consists of one or more elements of software that runs on one or more hosts.These types of firewalls are as follows:

•  Packet-filtering firewall
• Dual-homed Gateway Firewall
• Screened Host Firewall
• Screened subnet firewall

Packet-filtering firewall

• Consists of a router is placed between the external network and internal network secure.
• Packet Filtering Rule is defined to allow or deny traffic.

Dual-homed Gateway Firewall

• Dual-homed host has at least two network interfaces and two IP addresses.
• IP forwarding is disabled on the firewall, consequently IP traffic on both interfaces are chaotic in the firewall because there is no other way for the IP through the firewall except through a proxy or SOCKS.
• The attack is coming from an unknown service will be blocked.

Screened Host Firewall

• Consists of a packet-filtering routers and application level gateway.
• Host the form of application level gateways, known as the "bastion host".
• Consists of two packet filtering routers and a bastion host.

Screened subnet firewall

• Provide a high level of security than other firewall type• Creating a DMZ (Demilitarized Zone) between internal and external network, so the router only allow access from outside the outer bastion host to the information servers and routers within only allow access from internal network to the bastion host
• The router is configured to forward all untrusted traffic to the bastion host and the same case also to the information server.

*source: http://belajarit.um.ac.id/index.php/jaringan/18-pengenalan-jaringan-komputer/65-firewall.html