A firewall is a network security system that monitors the incoming and outgoing traffic of a host or a network and filters the traffic based on some pre-defined rules. In other words, it monitors each packet and matches it with some pre-defined rules. And, based on the rules, it decides whether the packet should be allowed.
Now, there can be different types of firewalls, such as packet filters, stateful filters, web application firewalls, etc. A stateless filter is a packet filter. It monitors each packet and filters them based on some information on the packet header, such as the source address, the destination address, port number, or specific protocols like TCP and UDP. The problem with this type of firewall is while monitoring a packet, it cannot understand whether the packet belongs to some existing connection.
So, to address the problem, stateful filters are developed. A stateful filter is a type of firewall that, much like a stateless filter, can filter traffic based on source IP address, destination IP address, port number, and specific protocols like TCP and UDP. But, along with that, it maintains the connection state of a packet. So, while monitoring a packet, it can understand whether the packet belongs to some existing connection or belongs to a new connection. And, based on the connection state, it can filter the traffic.
For example, we may want to allow packets from an existing connection to a specific port number and block new connections. With a stateful filter, we can easily make a firewall rule and block unwanted traffic. With a stateless filter, it is not possible as a stateless filter has no idea about the connection state of the packet.
Loading...
