Firewalls are basically a barrier between your computer (or a network) and the Internet (outside world). A firewall can be simply compared to a security guard who stands at the entrance of your house and filters the visitors coming to your place. He may allow some visitors to enter while denying others whom he suspects of being intruders. Similarly a firewall is a software program or a hardware device that filters the information (packets) coming through the Internet to your personal computer or a computer network.

Firewalls may decide to allow or block network traffic between devices based on the rules that are pre-configured or set by the firewall administrator. Most personal firewalls such as Windows firewall operate on a set of pre-configured rules that are most suitable under normal circumstances so that, the user need not worry much about configuring the firewall.

Personal firewalls are easy to install and use and hence preferred by end-users for use on their personal computers.  However, large networks and companies prefer those firewalls that have plenty of options to configure so as to meet their customized needs.

For example, a company may set up different firewall rules for FTP servers, Telnet servers and Web servers. In addition, the company can even control how the employees connect to the Internet by blocking access to certain websites or restricting the transfer of files to other networks. Thus, in addition to security, a firewall can give the company a tremendous control over how people use the network.

Firewalls use one or more of the following methods to control the incoming and outgoing traffic in a network:

Packet Filtering: In this method, packets (small chunks of data) are analyzed against a set of filters. Packet filters has a set of rules that come with accept and deny actions which are pre-configured or can be configured manually by the firewall administrator. If the packet manages to make it through these filters then it is allowed to reach the destination; otherwise it is discarded.

Stateful Inspection: This is a newer method that doesn’t analyze the contents of the packets. Instead, it compares certain key aspects of each packet to a database of trusted source. Both incoming and outgoing packets are compared against this database and if the comparison yields a reasonable match, then the packets are allowed to travel further. Otherwise they are discarded.

Firewall Configuration:

Firewalls can be configured by adding one or more filters based on several conditions as mentioned below:

IP addresses: In any case, if an IP address outside the network is said to be unfavorable, then it is possible to set  filter to block all the traffic to and from that IP address. For example, if a certain IP address is found to be making too many connections to a server, the administrator may decide to block traffic from this IP using the firewall.

Domain names: Since it is difficult to remember the IP addresses, it is an easier and smarter way to configure the firewalls by adding filters based on domain names. By setting up a domain filter, a company may decide to block all access to certain domain names, or may provide access only to a list of selected domain names.

Ports/Protocols: Every service running on a server is made available to the Internet using numbered ports, one for each service. In simple words, ports can be compared to virtual doors of the server through which services are made available.

For example, if a server is running a Web (HTTP) service then it will be typically available on port 80. In order to avail this service, the client needs to connect to the server via port 80. Similarly, different services such as Telnet (Port 23), FTP (port 21) and SMTP (port 25) services may be running on the server.

If the services are intended for the public, they are usually kept open. Otherwise they are blocked using the firewall so as to prevent intruders from using the open ports for making unauthorized connections.

Specific words or phrases: A firewall can be configured to filter one or more specific words or phrases so that, both the incoming and outgoing packets are scanned for the words in the filter.

For example, you may set up a firewall rule to filter any packet that contains an offensive term or a phrase that you may decide to block from entering or leaving your network.

Hardware vs. Software Firewall:

Hardware firewalls provide higher level of security and hence preferred for servers where security has the top most priority. The software firewalls on the other hand are less expensive and hence preferred in home computers and laptops.

Hardware firewalls usually come as an in-built unit of a router and provide maximum security as it filters each packet in the hardware level itself even before it manages to enter your computer. A good example is the Linksys Cable/DSL router.

Why Firewall?

Firewalls provide security over a number of online threats such as Remote login, Trojan backdoors, Session hijacking, DOS & DDOS attacks, viruses, cookie stealing and many more. The effectiveness of the security depends on the way you configure the firewall and how you set up the filter rules.

However, major threats such as DOS and DDOS attacks may sometimes manage to bypass the firewalls and do the damage to the server. Even though firewall is not a complete answer to online threats, it can most effectively handle the attacks and provide security to the computer up to the maximum possible extent.

If you are working in the field of computer networks or an enthusiast in the field of network security, you are sure to have come across the term “Denial of Service attack” which is simply referred to as “DoS attack”. Today, this is one of the most common types of network attacks carried out on the Internet. In this post, I will try to explain DoS attack, its variants and methods involved to carry out the same in an easily understandable manner.

What is a DOS Attack?

Denial of Service or DoS attack is a type of network attack designed to flood the target network or machine with a large amount of useless traffic so as to overload it and eventually bring it down to its knees. The main intention behind DoS attack is to make the services running on the target machine (such as a website) temporarily unavailable to its intended users. DoS attacks are usually carried out on web servers that host vital services such as banking, e-commerce or credit card processing.

A common variant of DOS attack known as DDoS (Distributed Denial of Service) attack has become quite popular in the recent days as it is more powerful and hard to detect. A typical DoS attack has a single place of origin while a DDoS attack originates from multiple IP addresses distributed across two or more different network. The working of a DDoS attack is shown in the following diagram:

DoS attacks can easily be handled by blacklisting the target IP (or range of IPs) that are found to be making too many requests/connections (in an unnatural way) to the server. However, DDoS attacks are complicated as the incoming requests seem more natural and distributed. In this case it is hard to find the difference between the genuine and malicious traffic. Taking an action at the firewall level to blacklist suspected IPs may result in false positives and therefore may affect the genuine traffic as well.

Methods Involved in DoS Attack:

The following are some of the commonly employed methods in carrying out a DoS attack:

Nowadays many android phone users use the inbuilt “pattern locks” as a security to their phones. But the main problem with it is that, if you forget the pattern you used and you try out many wrong attempts, it gets locked permanently. So, just follow these simple steps to unlock pattern locks on your android device and use it again free of cost.

Unlock using Google Account :

If you don’t have data connection or internet access or if you don’t have your google account linked to your phone, then, you can skip this step and refer the Additional TRICK.

When you try different patterns and unable to unlock your phone in five attempts. Then a message pop-up and shows two buttons “next” and “try again”. Now click on “next” button and you see two options for unlocking phone. One is answer the security question and the second option is to provide Google account details.

Mostly people don’t set a security question. But if you set it then simply answer the question and unlock your device quickly. Otherwise check the Google account option and click “next”.Now provide your Google account username and password attached with your device and click on “sign in”. After that you are directed to choose new pattern and now you can unlock with this pattern.

2) Now hold these buttons all together at the same time

“Volume up + Home Key + Power Button”

until the phone boots (if you device doesn’t have a home button just hold together volume up key   and power key)

3) Now a screen like DOS will come up with different options

4) Use the volume key to move up and down then scroll down to “Restore Factory Defaults” or “Delete all User Data” depending on which is on your device. Select this factory reset option and then press power button to let the action begin.

Now it asks you for confirmation, select “yes”.

5) After clicking on the settings above, now scroll down to “Reboot System Now” and wait for your phone to reboot (restart).