Firewalls and network security:

The most commonly accepted network protection is a barrier, a firewall between the corporate network and outside world. The term firewall can mean many things to many people but basically it is a method of placing device-a computer or a router between the network and the Internet, to control and monitor all traffic between the outside world and the local network.

Typically the device allows insiders to have full access to service on the outside while granting access from the outside only selectively, based on log-on names, password, IP address or other identifiers. Generally speaking, a firewall is a protection device to shield vulnerable area from some form of danger. In the contact of the Internet, a firewall is a system-a-router, a personal computer, a host, or a collection of hosts set up specifically to shield a site or sub-net from protocols and services that can be…. from hosts on the outside of the sub-net.

A firewall system is usually located at a gateway point, such as a site’s connection to the Internet, but can be located at internet gateways to provide protection for smaller collection of hosts or sub-nets. Firewall come in several types and offers various levels of security. Generally firewalls operate by screening packets and/or the applications that pass through them, provide controllable filtering of network traffic, allow restricted access to certain applications and block access to everything else.

The actual mechanism that accomplishes filtering varies widely, but in principle the firewall can be through of as a pair of mechanisms, one to block incoming traffic and the other to permit out going traffic. Some firewalls place a great emphasis on blocking traffic and others emphasize permitting traffic. In short, the general reasoning behind the firewall usage is that without a firewall usage, network security is a function of each host on the network and all host must cooperate to achieve a uniformly high level of security.

The larger the sub-net the less manageable it is to maintain all hosts at the same level of security. As mistakes and and lapses in security become more common, break-ins can occur not as the result of complex attacks but because of simple error configuration and inadequate passwords.

Firewalls in practice:

Firewalls range from simple traffic logging systems that record all network traffic flowing throughout firewall in a file or database for auditing purposes to more complex methods such as IP packet screening routers, hardened firewall hosts and proxy applications gateways. The simplest firewall is a packet filtering gateway or screening router. Configured with filter to restrict packet traffic to designated addresses. Screening routers also limit the types of services that can pass through them.

More complex and secure are application gateways. They are essentially PCs or Unix boxes that size between the Internet and a company’s internal network to provide proxy services to users on either side.

For eg. a user who wants to FTP in or out through the gateway would connects to ftp software running on the firewall, which then connects to machines on the other side of the gateway. Screening routers and application gateways, firewalls are frequently used in combination when security concerns are very high. In cases of heavy traffic, sub networks or hardened firewall machines are set up between the Internet and a company’s private network.

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