Firewall Explained

In this article, I will teach you how a firewall acts and what it guards within the network environment. So let's get started...

What is a Firewall?
A firewall governs the traffic between at least two networks. Firewalls are commonly altered using UNIX systems but even on Windows platforms, MAC and OS/2 OS's all function well. A well known firewall known as Checkpoint Firewall-1 is a highly secured commercial product and CISCO pix are currently keeping in touch with it.

A Packet Filtering Firewall asks as a filter and not allowing every packet being passed from it without certain settings being set beforehand. A Packet can get accepted, dropped or rejected. When a packet gets accepted, that's not a problem at all. If a packet gets dropped it will take more time to scan for open ports and rejected means it does not accept the packet but sends an ackowledgement back to the sender. The Packet Filtering Firewall oversees five chracteristics in order to accept a packet frame from thr sender which are:

IP of the Destination
Port of the Destination
IP of the Source
Port of the Source
IP Protocol (TCP/UDP)

We can say that a router can act as a firewall and is found at the third Layer of the OSI model which is the Network Layer. Also, certain rules are applied to the firewall to prevent the network from malicious attacks and Denial of Service attacks (DoS attacks).

As an enhancement over the common firewall a newer firewall came to hand called "stateful inspection engine". Basically, it remembers the connection of a conversation between two hosts and only examines the first packet of it.

What is an Application Proxy Firewall?
A packet is sent to the firewall and stopped to be examined and compared to the rules of the router. If they match, the packet is destroyed and re-created into a new data frame. This will make the TCP/IP Protocol Suite much more secured then the Packet Filtering Firewall. The disadvantage is that a Proxy-Application has to be coded for each program. For instance, a Web Application Proxy needs to have a HTTP Proxy, an FTP Application needs to have an FTP Proxy, a Gopher Proxy needs to have a Gopher Proxy etc. The Application Proxy Firewall operates at the seventh Layer of the OSI Model, which is the Applcation Layer.

What is an Application Gateway Firewall?
An Application Gateway Firewall also operates at the seventh Layer and is used to connect to a server from a server before it. Therefore, to telnet to a server and then telnet again from it to another server that is located outside the network.

What is a SOCKS Firewall?
Socks Firewall makes part of the Application Proxy Firewall mentioned earlier. These types of firewalls differ by modified every system in your internal network to communicate with external networks. On Windows or an OS/2 system this can be easily done by swapping some DDL files.

Until next time,
DarkSolo