FIREWALL

What Is Firewall?

We can use a firewall to protect our home network and family from offensive web sites and potential hackers.Basically,a firewall is barrier to keep destructive forces away from our property.In fact,that is why its called a firewall.Its job is similar to a physical firewall that keeps a fire from spreading from one area to the next.
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Firewall may be classified into three different ways:-

• By their processing type
• By their evolutionary generation
• By the way they are implemented

Firewall by processing type:-

1. Packet-filtering firewall:-

Packet filtering firewall come in three types:

1. Traffic on a network is broken into packets,smaller message units.Each packet must hold at least two address.that of the sender and that of the recipient.A packet-filtering firewall will hold a database of rules that tells it what to do with packets.often the rules are based on the address mentioned above and the protocol the packet is being sent under.The rules may include all three ideas,

• The first rule says if packet is from any address on the 172.16.0.0 network(172.16.x.x) and being sent to any address on the 10.10.0.0 network,using any protocol,drop the packet.The X character are used as WILDCARD on some firewall,as the text mention later.Other firewall might use zeros instead,so we need to know the syntax for the fire we are configuring.
• The second rule says if the packet is from any address on the 192.168.0.0 network(192.168.x.x) and being sent to the specific address 10.10.10.25 (10.10.1.25),using the HTTP protocol,let that packet through.This tells me that 10.10.10.25 is the address of a web server on that network,because HTTP is a web pages.
• The third rule says if the source address is specially 192.168.0.1 and the destination address is specially 10.10.10.10,and the protocol is FTP, then let the packet through

• Static-a system administrator sets the rules for the firewall
• Dynamic-The firewall sets some rules for itself,such as dropping packets from an address that is sending many bad packets
• Stateful-Packets sent by an attacker often are sent to a port that the attacker has guessed is open; a stateful firewall denies packet sent to any por unless a connection to that port has already been negotiated; this kind of checking puts more processing overhead on the firewall.

2. Application gateway firewall: The ISO-Open system interconnect networking model has seven layers that describe what happen to a packet as it prepared to be sent out on network,and what happen when that packet is received by the machine that is meant to act on it.