Stateful inspection firewall works at the network layer in the OSI model. You can use this configuration if you need higher network speed and do need limited login and authentication capacity. They also fail to fight against spoofing attacks. Since a router cannot check packet in the application layer, this type of firewall cannot defend attacks that use application layers vulnerabilities.
Normally, the IP address of the source and destination, port number and type of traffic are taken into account when the router processes each data packet. Based on access control list, the router either forward or drop packets. A router functions as a firewall by examining every packet passing through the network. This type of firewall is the most common and easy to deploy in a small-sized network. In a typical case, both the Internet and the internal users have access to the screened subnet, but the traffic flow between the two subnets (one is from bastion host to the internal network and the other is the sub-network between the two routers) is blocked. In this configuration, two packet filtering routers are used and the bastion host is positioned in between the two routers. This is one of the most secured firewall configurations. In this case, even if, the router got compromised, the internal network will remain unaffected since it is in the separate network zone. To eliminate this drawback we can use the dual homed bastion host firewall system, where a bastion host has two network cards- one is used for internal connection and the second one is used for connection with the router. The main problem with the single homed bastion host is that if the packet filter route gets compromised then the entire network will be compromised. This type of configuration can have a web server placed in between the router and the bastion host in order to allow the public to access the server from the Internet. No traffic from the internal network can go to the Internet. Traffic having the IP address of the bastion host can only go to the Internet.Traffic from the Internet can only reach the bastion host they cannot reach the internal network.A bastion host is basically a single computer with high security configuration, which has the following characteristics:
In case of single homed bastion host the firewall system consists of a packet filtering router and a bastion host. There are two types of screened host-one is single homed bastion host and the other one is dual homed bastion host. The following are the list of seven different types firewalls that are widely used for network security. Depending on the kind of service and security you need for your network, you need to choose the right type of firewall. There are several types of firewalls that work on different layers of the OSI model.
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