Packet-filtering is an intuitive concept for a firewall. In this case there could be two approaches: the firewall will either by default accept the packet or reject the packets. There is certainly the possibility that a packet does not match any of the rules. When it checks that a packet does not have the destination address, it will reject the packet. Thus, for instance, such a firewall may have a rule that only the packets having a specific destination address will go through.

Source and destination transport-level address.The rules could be based on the following parameters: It checks each packet against these rules and decides whether they can go through. It is typically set up as a list of rules based on matches of fields in the IP or TCP header.Ī packet-filtering router has a set of rules. An application level gateway works as a proxy server and examines the traffic at the application layer.Ī circuit level gateway simply establish two different connections, one with the server, and one with the client outside the network, and forward TCP packets.Ī packet filter Firewall blocks or forwards packets based on the transport and network layer addresses and protocols. There are three common types of firewalls, the packet-filtering router, the Application- Level Gateway, and the Circuit-Level Gateway.Ī packet-filtering router examines the packets and decides whether they could flow through.

Application level gateway