Can you imagine having a set of computers connected in a network without a firewall? No one would dare to do so nowadays. So what is this firewall? It is a set of related programs located at a network gateway. This is used to ward off unauthorized access to the network and allow only authorized access.
There could be different types of firewall - it could be a hardware firewall or a software firewall. A hardware firewall is usually a router device, whereas a software firewall is listed software used to provide security to the network.
A firewall can be used only if there are at least two network interfaces – one for the network it is intended to protect, and one for the network it is exposed to.
So how does it work? A firewall checks all traffic routed between the two networks to find out if it meets certain criteria or not. If the criteria are met, it’ll be allowed to go ahead, else it will be blocked. A firewall checks every traffic, whether it is inbound or outbound. A firewall filters every traffic coming in and out of the network. It can filter based on source and destination, which is known as address filtering.
Now, there are certain techniques for the firewall to work properly.
1. Packet filter: Here, each packet coming in or leaving out of the network is looked into. This is based on user defined rules and on the basis of that, it accepts or rejects traffic. It is effective but tough to configure.
2. Application gateway: In this, it looks after certain applications like FTP or telnet or http. This has been found to be very effective but sometimes causes performance degradation. You can get some gateway technical support to learn more about it.
3. Circuit-level gateway: Here, it applies security when a TCP/UDP connection is established. But once the connection is made and secured, further checking is not done.
4. Proxy server: In this, it intercepts all messages entering in and leaving out of the network.
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