FIRE WALL

      FIRE WALL 



Definition of FIRE WALL  :  A Firewall is a system which limits network access between two or more networks. 




---->  Firewall is deployed between a trusted, protected private network and  an untrusted public network. 




----> For example, the trusted network might be a corporate network, and the public network might be the Internet.




----> A Firewall might grant or revoke access based on user Authentication, source and destination network addresses, network protocol,  network service or any combination of these. It might be implemented as an Application Level Firewall or a Packet Level Firewall.




---> Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.



There are several types of firewall techniques:



1) Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.



2) Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.



3) Circuit-level gateway: Applies security mechanisms when a TCP(TRANSMISSION CONTROL PROTOCOL) or UDP(USER DATA PROTOCOL) connection is established. Once the connection has been  made, packets can flow between the hosts without further checking.


4) Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.