20-08-2012, 11:07 AM
FIREWALLS
FIREWALL.RTF (Size: 73.38 KB / Downloads: 55)
1.INTRODUCTION :
Basically a firewall is a barrier to keep destructive forces away from our property. Its job is similar to a physical firewall that keeps a fire from spreading from one area to the next.
All of us are well aware of the Internet browsing. For example, the employees of a larger company while browse the web they probably obstruct with the firewall to access certain sites.
If we have a fast Internet connection in our home we might have faced the firewalls for our home networks as well. It turns that a small home network has also many of the same security issues that of larger carporate network does. We can use firewall to protect your home network and family from offensive web sites and potential hackers.
2.ABOUT FIREWALLS
What are Firewalls ?
A fire wall is a piece of software or hardware, which stands between two entities can be private network on one side and a public network like the Internet, on the other side. They can control what kind of traffic flow across and protect the network from hackers.
What it does ?
Lets say that a company is running with 500 employees. So the company will have hundreds of computers that all have network cards connecting them together. In addition, the company will have one or more connections to the Internet connections. Without firewall in place all of those hundreds of computers are directly accessible to anyone on the Internet. A person who knows what he or she is doing can probe those computers, try to make FTP connections to them, try to make Telnet connections to them and so on. If one employee makes a mistake and leaves a security hole, hackers can get to the machine and exploit and hole.
With a firewall in place, the landscape is much different. A company will place a firewall at every connection to the Internet. The firewall can implement security rules. For example one of the security rules inside the company might be
Out of the 500 computers inside this company only 1 of them is permitted to receive public FTP traffic. Allow FTP connections only to that one computer and prevent them on all others.
A company can set rules like this for FTP servers, Web servers, Telnet servers and so on. In addition the company can control how employees connect to Web sites, whether files are allowed to leave the company over the network and so on. A firewall gives a company tremendous control over how people use the network.
Who needs a Firewall ?
We need a firewall if we have a network (called a trusted network), which is connected to nay other network (called untrusted network), which does not belong to our network (like the Internet). We need a firewall to setup controlled access between two or more networks owned by us. If we have a large WAN which used the Internet as its backbone, we want to protect networks with firewalls.
We need a firewall even though we browse the Internet from a single desktop computer at home. This computer is considered as a gateway because it provides the only point of access between the home network and the Internet. If we use Internet applications like ICQ, having some bugs, an anonymous person can exploit this to bring our computer down or breaking our privacy. If we blindly accept files from anonymous people ( this generally happen when chatting ), we may unknowingly accept a file that can be an installer of a service that may continuously run on a port, and through which the sender can connect to our computer and issue commands to do whatever he wants to on our machine. This is a popular Trojan called Back Orifice works. Examples of personal firewall software’s for home computers are Norton Personal firewall, BlackIce, Zonealarm, VirusMD and Conseal PC Firewall. These can be configured to deny any foreign connection to our desktop computer.
3.TYPES OF FIREWALLS:
Firewalls use one or more of three methods to control traffic flowing in and out of the network. They are
i. Application-filtering Firewall
ii. Packet-filtering Firewall
iii. Stateful Inspection
i. Application-filtering Firewall :
An application-proxy firewall is implemented in proxy servers. Any one wants to access anything outside the trusted network must go through the proxy server. This proxy firewall will grant or block access depending on a set of rules. The rules can be based on the user login name, source, and destination machines IP addresses, protocol in use like TCP, UDP, ICMP, Port address etc. An application proxy can block or allow access to application-specific data. For example, you can block MP3 and video files.
ii. Packet-filtering Firewall:
A packet-filtering firewall controls access based on information in the packet header. As we all know, data that has to be transmitted across the network is broken into small chunks of data called packets. Each packet has header and a part of the original data, called its content. The header consists of information like source, destination, port, and number of the packet in the sequence. Packets that are analyzed against a set of filters are sent to the requesting system and all others discarded.