From previous articles have discussed about EXPLAIN THE UNDERSTANDING AND TYPE OF FIREWALL, and the previous article incomplete explanation of the type of firewall. In this explain about the type of firewall.

Packet Filtering Gateways
Packet filtering gateways can be interpreted as a firewall in charge of filtering the packets coming from outside jarigan protects. Filterirasi this package is limited to the packet source, destination packages, and attributes of the package, for example, the package aims to our server that uses the IP address to port 80. Port 80 is the attributes of the package. As seen in Figure 11.4, the firewall will skip packets with a destination to the Web server that uses port 80 and rejected the package to the Web server to port 23. When we see the architecture of TCP/IP, this firewall will work on the internet layer. Firewall is usually part of a router firewall. Software that can be used for packet filtering implementations including the iptables and ipfw.

Application Layer Gateway
Models can also be called a firewall Proxy Firewall. The mechanism is not only based on the source, the other mechanism that occurs is the package will not directly get to the destination server, but only up to a firewall alone. The rest of this firewall will open a new connection to the destination server and package attributes, but can reach the content (content) package. purpose after the package is checked by the applicable rules. If we look from the side of the TCP/IP, this type of firewall will perform filtering at the application layer (Application Layer).

Circuit Level Gateway
Model circuit level gateway firewall works on the Transport Layer reference model TCP/IP. This firewall will oversee the initial TCP connection is commonly referred to as TCP Handshaking, which is a process to determine whether the connection session is allowed or not. The shape is almost the same as the Application Layer Gateway, it's just part of the filtered there is no distinct layers, which is located at the Transport layer.

Statefull Multilayer Inspection Firewall
Model firewall is a combination of the three previous firewall. Firewalls of this type will work at the Application layer, Transport and the Internet. With the incorporation of the three models, namely firewall Packet Filtering Gateway, Application Layer Gateway and Circuit Level Gateway, one could say this type of firewall is a firewall, providing the most features and provides the highest level of security.

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