Firewall - FAQ

[Fatal1ty]

What is Firewall?

How it works?

How my Firewall can be defeated?

My Firewall works?

Useful links

References

Last word

What is a Firewall?

A firewall is something like a security guard that guards your

computers from intruders from the internet. It only allows selected

packets to pass through to the Internet from your computer. There are two types of firewall, software and hardware firewalls.

For Examples

software firewalls are Sygate Personal Firewall, ZoneAlarm, Norton

Firewall, etc... and hardware firewalls are Netgear, D-Link, TRENDware, etc... It is possible two install both firewalls but it is not sure that you have protection from both of them.

How a Firewall works?

To know how firewall works, you need a basic concept on how data is being transfered accross the Internet. This explanation only gives you general ideas of the whole data transmission process so that you can understand firewalls. To really understand this process you need to read TCP/IP (Transmission Control Protocol/Internet Protocol) documents.

The proccess begin with when you start up an Internet application for example internet browser, FTP(File Transfer Protocol) or email client. When you send an email, the email client will transfer the email to the TCP. Then, TCP will break this email data into smaller piece of data which we called it as packets and send it to IP. IP will add a header which contains some info to each of the packets to make sure that they know where they come from, where to go and what port they are using. So, the packets will not lost while they are accross the internet. So, that is how data been transfered.

Firewalls work in 3 ways, packet filter, application filter and port

filter. When firewall receive packets, it will compares the header

information. If the information corrects, the firewall will allow the

packets to pass through it. If not, the firewall will discard the

packets and leave it.

Firewall also can block certain application to pass through it. Its

only allow applications that have grant permission to connect to the internet. This permission is set by you. Usually, the permission will set to allow for applications that you always use i.e Internet browser, FTP, AIM, etc. If an application have no permission but want to connect to the internet, the firewall will ask you either to allow it or not.

If you set to allow, the firewall will allow to pass through it else

the firewall will block it.

Beside than that, the firewall also can block or close certain ports.

Only certain ports will be open to connect to the internet. For example, port 80 (used for browsing web page), port 25 (used for sending and receiving emails) and port 21 (used for transfer files between your computer and the server) will be open. Other ports will be closed. By shutting unused ports, your computer is safe from intruders from internet because there is no where to break in to your computer.

How my Firewall can be defeated?

Sometimes, a firewall also can be defeated. This usually cause by

misconfigure or manage it incorrectly such as accidently allow an

application that should not have an access to the internet or leave

unused ports open. Besides than that, a firewall also can be fooled. This tricks called as IP Spoofing. This trick can be done by changing the packets header. So, the firewall thinks that the packets come from trusted system. Another technique is Firewall Tunneling. Firewall Tunneling is dangerous because it uses any ports or protocols that have allows permission to sneak into your computer.

Does my firewall work?

To make sure that your firewall works, there are many security websites that can run test on your firewall. My suggestion is try to make as many test as you can find in the internet. This is because different website run different test. I had included some links that can help you in Useful Links section.

Useful Links

More about firewall

Code:

http://www.howstuffworks.com/firewall.htm

http://www.firewall-net.com

http://www.firewallguide.com

Software firewall

Code:

http://soho.sygate.com

http://www.zonelabs.com

http://www.www.symantec.com

Hardware firewall

Code:

http://www.dlink.com

http://www.trendware.com

http://www.netgear.com

Firewall testing

Code:

http://scan.sygate.com/

http://www.pcflank.com

http://www.auditmypc.com

References

Some texts about firewall

Steal This Computer Book 3

Sam's Teach Yourself TCP/IP in 21 days

How Stuff Works

Last Word

Thanks for reading. I hope my grammar is clear and easy to understand. I also had make tutorial about "NetBIOS Based Hacking". I will post it if you want. Feel free to give ideas, suggestions or comments about this text.

Thanks for reading!