Firewalls Essay

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FIREWALLS Firewalls are software or hardware devices which are used to control the network traffic between networks or hosts to protect them from malicious attacks. By using firewalls in host system we can prevent unauthorised access to that system. So inclusion of firewall gives the additional layer of security. Firewalls can be placed at the two places which are perimeter of a network (at the router) and at the host. These are also called as external and internal firewalls respectively. If firewall at router only used, then there is a chances of occurrence of attack on hosts from internal systems. If firewall at host only used this might be not sufficient to protect it from attack. So we have to use both type of firewalls to increase security. Basic firewall is packet filtering. It is also called ‘stateless inspection firewall’. This routing device gives access control to source address and destination address. In packet filtering firewalls they do not take care of state flow of packets coming from it. The basic form of packet filter is operates at network layer, and it consists of source IP address and destination IP address. This stateless inspection firewall is vulnerable to attack. In this packet filtering they do not detect if destination address of any packet is spoofed. So by changing the destination address of a packet an attacker can attack the system. In state full inspection firewall unlike stateless packet filtering it keeps the track of packet from source to destination. If at any place packet deviates from its expected path this firewall blocks that packet. It follows the state table. State table consist of source and destination IP addresses, port number, and connection information. In state full packet filtering firewall checks the packet with state table at every state, because an attacker could change the header of a packet in the

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