Packet Filtering

In firewall applications, packet filtering is handled by utilities known as packet filters. The packet filter evaluates the header of incoming packets based on a specific criteria. On that basis, it decides whether to prevent the packet from passing or to accept it. Once the criteria for filtering rules have been set, a packet filter can be configured in three ways. First, the filter can be configured to only accept packets that are deemed as safe and automatically drop others. While this is the most secure method, it can also be an inconvenience when genuine packets are wrongfully blocked. The second configuration can be set to drop only the packets that the filter determines as unsafe while accepting all others. This method is less secure but reduces the level of inconvenience in web browsing. In the third configuration, a packet will be quarantined when the filter encounters a packet that doesn’t adhere to the rules provided. From there a user can determine what should be done with it. Packet filters were originally developed on OpenBSD, but have since been ported to many other operating systems.