Firewalls,how the work Firewalls

Firewalls,how the work Firewalls,Firewalls,how the work Firewalls,

Today computing, a firewall is a piece of hardware and/or software which functions in a networked environment to prevent some communications forbidden by the security policy, analogous to the function of firewalls in building construction.A firewall has the basic task of controlling traffic between different zones of trust. Typical zones of trust include the Internet (a zone with no trust) and an internal network (a zone with high trust). The ultimate goal is to provide controlled connectivity between zones of differing trust levels through the enforcement of a security policy and connectivity model based on the least privilege principle.

There are three basic types of firewalls depending on.whether the cation is being done between a single node and the network, or between two or more networkswhether the communication is intercepted at the network layer, or at the application layerwhether the communication state is being tracked at the firewall or notWith regard to the scope of filtered communication these firewalls are existPersonal firewalls, a software application which normally filters traffic entering or leaving a single computer through the Internet.Network firewalls, normally running on a dedicated network device or computer positioned on the boundary of two or more networks or DMZs (demilitarized zones). Such a firewall filters all traffic entering or leaving the connected networks.In reference to the layers where the traffic can be intercepted, three main categories of firewalls exist:network layer firewalls An example would be iptables.application layer firewalls An example would be TCP Wrapper.application firewalls An example would be restricting ftp services through /etc/ftpaccess fileThese network-layer and application-layer types of firewall may overlap, even though the personal firewall does not serve a network; indeed, single systems have implemented both together.There's also the notion of application firewalls which are sometimes used during wide area network (WAN) networking on the world-wide web and govern the system software. An extended description would place them lower than application layer firewalls, indeed at the Operating System layer, and could alternately be called operating system firewalls.Lastly, depending on whether the firewalls track packet states, two additional categories of firewalls exist:stateful firewallsstateless ewallsNetwork layer firewallsNetwork layer firewalls operate at a (relatively low) level of the TCP/IP protocol stack as IP-packet filters, not allowing packets to pass through the firewall unless they match the rules. The firewall administrator may define the rules; or default built-in rules may apply (as in some inflexible firewall systems).A more permissive setup could allow any packet to pass the filter as long as it does not match one or more "negative-rules", or "deny rules". Today network firewalls are built into most computer operating system and network appliances.Modern firewalls can filter traffic based on many packet attributes like source IP address, source port, destination IP address or port, destination service like WWW or FTP. They can filter based on protocols, TTL values, netblock of originator, domain name of the source, and many other attributes.Application-layer firewallsApplication-layer firewalls work on the application level of the TCP/IP stack (i.e., all browser traffic, or all telnet or ftp traffic), and may intercept all packets traveling to or from an application. They block other packets (usually dropping them without acknowledgement to the sender). In principle, application firewalls can prevent all unwanted outside traffic from reaching protected machines.By inspecting all packets for improper content, firewalls can even prevent the spread of the likes of viruses. In practice, however, this becomes so complex and so difficult to attempt (given the variety of applications and the diversity of content ach allow in its packet traffic) that comprehensive firewall design does not generally attempt this approach.