: What is firewalls ? Explain types of firewall

: What is firewalls ? Explain types of firewall.

 

Defn:

          To protect private networks and individual machines from the dangers of the greater Internet, a firewall can be employed to filter incoming or outgoing traffic based on a predefined set of rules called firewall policies.

OR

 Acting as a barrier between a trusted network and other untrusted networks -- such as the Internet -- or less-trusted networks -- such as a retail merchant's network outside of a cardholder data environment -- a firewall controls access to the resources of a network through a positive control model. This means that the only traffic allowed onto the network defined in the firewall policy is; all other traffic is denied.

***  Types of Firewalls ***

      *  Packet Filtering Firewall   :

On the Internet, packet filtering is the process of passing or blocking packets at a network interface based on source and destination addresses, ports, or protocols. The process is used in conjunction with packet mangling and Network Address Translation (NAT). Packet filtering is often part of a firewall program for protecting a local network from unwanted intrusion.

 ** Stateful Inspection Firewalls  

 

    

      Stateful inspection, also known as dynamic packet filtering, is a firewall technology that monitors the state of active connections and uses this information to determine which network packets to allow through the firewall.

***  Application-Level Firewall

 

     

  Application gateways provide high-level secure network system communication. For example, when      a client requests access to server resources such as files, Web pages and databases, the client first connects with the proxy server, which then establishes a connection with the main server.  

   The application gateway resides on the client and server firewall. The proxy server hides Internet Protocol (IP) addresses and other secure information on the client’s behalf. A computer’s internal system may communicate with an external computer using firewall protection. The application gateway and external computer function without client information or knowledge of the proxy server IP address.  

** Circuit-Level Gateway Firewall :

 

   

      A proxy server is a security barrier between internal and external computers, while a circuit-level gateway is a virtual circuit between the proxy server and internal client.

For example, when a user Web page access request passes through the circuit gateway, basic internal user information, such as IP address, is exchanged for proper feedback. Then, the proxy server forwards the request to the Web server. Upon receiving the request, the external server sees the proxy server’s IP address but does not receive any internal user information. The Web or real server sends the proxy server a proper response, which is forwarded to the client or end user via the circuit-level gateway.