Packet filtering works at the network layer of the OSI model and makes the logical decisions based on the IP addresses of the source and destination. In the client/server network model proxy server provides the indirect access to the internet because all the incoming and outgoing traffic is monitored and filtered at the proxy server. 

In this system, detailed information about the two way traffic can be gathered.  Application gateway provides the highest level of security, performance and scalability.

How Firewall Works

The firewall stays in the background and monitors incoming and outgoing traffic. It stays between the junction points between the two networks usually a private and public network. 

Firewall works on the access and denial methods.  It may allow all traffic if it meets the criteria or it denies all traffic if it doesn’t meet the criteria set in the firewall applications or hardware appliances.  Firewall criteria is concerned with the source of the traffic, IP addresses, ports no and the type of traffic. 

There are certain rules that can be implemented to put security check on the traffic. By implementing firewall on your home or network computer you can protect yourself potential security threats on the internet such as identity theft, privacy lost, data lost and attacks from hackers.  Firewall can hide your internet-connected computers and block ports.

Implementation Requirements

There are many important components and configurations are involved in the firewall implementations.  Many network administrators configure rules and filters without testing them.  The best practice is to install the firewall solution in a test environment.  Testing may involve scanning all the open ports from internal trusted and outer untrusted network. 

Closely check the log files and ensure that the firewall is tracking the things that were specified. Run each test again and again.