This means that each packet passing through the firewall, regardless of whether it is a new or existing connection, is evaluated by rules set by the administrator.

Stateless filtering provides an independent packet evaluation feature, where the connection is unknown. Packet forwarding is the fundamental routing feature, a function also performed by a firewall. Once the packet passes through the firewall (and only in this way can it reach the final destination), it has the power to define whether or not this should be forwarded. This is the basic concept of understanding a packet-control structure, and it is only possible because firewalls are strategically placed in a network topology where inter-network traffic is tapered or strangled. Packet filtering is nothing more than a mechanism capable of parsing headers in certain layers of the TCP/IP suite and, based on a pre-set rule pattern, forward the packet to the next step, or disregard it. In every layer, there is header information useful for processing, besides the data part (payload) where information is actually transported. Packet filteringĪll communication in a computer network is segmented into small packets according to the maximum transfer unit between the networks (MTU), usually 1500 bytes. We will cover the topic in an introductory way to ensure that you can benefit from understanding both the concepts that were (and are) so important to firewalls. Understanding the functioning of these mechanisms facilitates the understanding of new technologies, besides helping in a substantial way in defining the best application, according to the needs of the environment.Įven with the complexity behind security and firewall solutions, stateful filters are often used nowadays, however, usually in a transparent way, not being manageable or visible by administrators and security analysts.

In spite of the advanced age, when dealing with technological aspects, stateless and stateful filtering respectively formed the basis for the construction and evolution of firewall solutions used nowadays. Two of the first and main filtering mechanisms, present in firewalls, were created between 19, initially by Digital Equipments and later by the AT&T Bell Labs.

This post is also available in: Português English Español

Stateful vs stateless firewall