You can set the fire walls using two basic ways. First, you can purchase a firewall appliance, which is basically a self contained router with built in fire wall features. Most fire wall appliances include web-based interface that enable you to connect to the firewall from any computer on your network using a browser. Second way is to set up a server computer to function as a firewall computer. The server can just run about any network operating system.

There are several types of firewall techniques:

• Packet filter:

Packet filters work by inspecting the source and destination IP and port addresses contained in each TCP/IP packet. TCP/IP ports are numbered that are assigned to specific services that help to identify for which service each packet is planned.

• Application gateway:

The application gateway knows the details about the applications that generate the packets that pass through the firewall. The Proxy server examine the packet and decide to pass it to the real server. Application gate ways are aware of the details of how various types of TCP/IP server handie sequences of TCP/IP packets, so they can make more intelligent decisions about whether an incoming packet is valid or is part of an attack.

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• Circuit-level gateway:

It applies security mechanisms when a TCP or UDP connection is established because it manages connections between client and servers based on TCP/IP addresses and port numbers. Once the connection has been made. packets can flow between the hosts without further checking.

• Stateful packet inspection (SPI):

A firewall with state full packet inspection looks at packet in groups rather then individually. It keeps track of which packets have pass to through the firewall and can detect patterns that indicate unauthorized access.