A firewall is an application that serves as a security guard between your organization’s internal network and the outside network. As most of us are already aware, firewalls protect and filter out unauthorized traffic, data, and information that might compromise the integrity of the company; this traffic can be incoming or outgoing.
They are usually installed between the internal and external network by a professional system administrator. Essentially, there are 4 different types of firewalls implemented by businesses and organizations worldwide. Each one has certain advantages and disadvantages over the other.
1. Network Level Firewall
These firewalls operate on the network layer of the OSI and TCP/IP models and hence, they filter incoming and outgoing traffic based on packet headers, IP addresses, service requested, and the port utilized for forwarding the data packet.
Network firewalls have been used since a long time; they can also filter unauthorized traffic based on other factors like specific domain names and different protocols. Routers usually come built-in with such firewalls. However, these firewalls cannot understand XML and HTML.
2. Circuit Level Firewall
One of the most inexpensive among the other three types of firewalls, circuit level firewalls operates at the transport layer of TCP/IP model and the session layer of the OSI model. It determines the authenticity of the session that is requested by monitoring and inspecting the handshake between data packets.
The handshake process is simple and can easily be manipulated by hackers. When one device sends data segments in packet form, the other device responds with its own data packet. As a result, the first device acknowledges the sent packets and validates their receipt as well. Hackers can modify this process to overload the destination, causing a denial of service or DDoS.
Internal networks can be hidden on such firewalls from the outside world and session rules can also be changed or restricted.
3. Application Level Firewall
Also known as proxy servers or proxies, application level firewalls are quite similar to circuit level firewalls. The difference is that they work on particular applications only. Their main function is to protect the internal network of an organization from trojans, malware, viruses, keyloggers, and other types of malicious programs.
When they are setup as a web proxy, various functionalities like gopher, telnet, ftp, torrent, etc. are not allowed through the firewall. They can also be used to block a website based on the content. The downside of application level firewalls is that they are slow because they examine each data packet in a thorough manner; hence, it takes more time for the data to be filtered.
They have no transparency for the end user and usually require manual configurations on systems.
4. Stateful Multilayer Firewall
These types of firewalls are the most expensive compared to the other three, but they offer all the combined benefits of the other three firewalls. On the network layer, SML firewalls filter unauthorized data packets, check for session authenticity, and inspect the content of the data packets.
The advantages of using SML firewalls are that they establish a direct connection between the client and host, thus offering transparency, and they are much faster as no proxies are involved.
