Friday, August 26, 2011


According to Wikipedia 
"A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass. "

Firewall acts as a filter between the Home /private network and the Internet allowing only specified packets to enter into or exit the private/home network.

There are basically two types of firewalls :

1 : Hardware firewalls.
2 : Software firewalls.

Hardware firewalls are physical devices with ports. These devices are extensively used in Large and medium sized IT firms to control the traffic flow.The device is configured to allow/deny only certain packets to enter or exit through certain ports.

Ex :Cisco ASA 5500 series etc.

Software firewall is a software which is used to configure the rules of the firewall. It is configured to allow/deny the traffic only through certain pre-configured ports.

Ex : Antivirus programs,UFW in Ubuntu, SuSEfirewall2 in OpenSuSE etc.

Usually Servers in a firm are configured with firewalls to prevent access to the server by any anonymous user on the internet. Instead they allow users on the internet to access their server only through some of the standard ports such as 80 (HTTP). All the packets are dropped by the firewall except packets to port no 80.In this way,the packet traffic is filtered.
In a similar way,we can restrict access to some of the websites on the internet using firewalls.Thus firewall can act as a parental control system not letting access to some websites on the internet.
UFW firewall Configuration on Ubuntu :

UFW is a software firewall in Ubuntu which is used to configure the packet flow.

$ sudo ufw status 

Shows the current status of the firewall,displays all the rules already laid.

$sudo ufw default allow

By default allows all the traffic through all the ports

$sudo ufw default deny

By default blocks all the traffic through all the ports coming in or going out of the private/home network.

$ufw enable             

Loads all the rules laid and configured.

$ufw disable

Unload all the rules configured.

$ufw allow 80

Allow traffic through port no 80.

$ufw deny 80

Disable packet flow through port no 80. 

$ufw delete allow 80

Deleting the rule set.

$ufw allow from

Allow person with IP address to connect to the server and block all others.

$ufw deny from

Deny this IP address to connect to server.

Similarly on OpenSuSE we have tool called SuSEfirewall2 which is used to configure firewall on OpenSuSE Linux.

For any queries or clarifications , Leave a comment.
Suggestions for Topics to be included for future posts are welcome.

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1 comment:

Anonymous said...

cool bro..keep comin