FIREWALL

Now computers in the world has connect to others so we have to prevent how to make safe to our data. lets go

FIREWALL
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.

Many personal computer operating systems include software-based firewalls to protect against threats from the public Internet. Many routers that pass data between networks contain firewall components and, conversely, many firewalls can perform basic


History

The term firewall originally referred to a wall intended to confine a fire or potential fire within a building. Later uses refer to similar structures, such as the metal sheet separating the engine compartment of a vehicle or aircraft from the passenger compartment.

Firewall technology emerged in the late 1980s when the Internet was a fairly new technology in terms of its global use and connectivity. The predecessors to firewalls for network security were the routers used in the late 1980s:[2]

Clifford Stoll's discovery of German spies tampering with his system[2]
Bill Cheswick's "Evening with Berferd" 1992 in which he set up a simple electronic to observe an attacker[2]
In 1988, an employee at the NASA Ames Research Center in California sent a memo by email to his colleagues [3] that read, "We are currently under attack from an Internet VIRUS! It has hit Berkeley, UC San Diego, Lawrence Livermore, Stanford, and NASA Ames."
The Morris Worm spread itself through multiple vulnerabilities in the machines of the time. Although it was not malicious in intent, the Morris Worm was the first large scale attack on Internet security; the online community was neither expecting an attack nor prepared to deal with one.[4]
First generation: packet filters

The first paper published on firewall technology was in 1988, when engineers from Digital Equipment Corporation (DEC) developed filter systems known as packet filter firewalls. This fairly basic system was the first generation of what became a highly involved and technical internet security feature. At AT&T Bell Labs, Bill Cheswick and Steve Bellovin were continuing their research in packet filtering and developed a working model for their own company based on their original first generation architecture.[5]

Packet filters act by inspecting the "packets" which transfer between computers on the Internet. If a packet matches the packet filter's set of rules, the packet filter will drop (silently discard) the packet, or reject it (discard it, and send "error responses" to the source).

This type of packet filtering pays no attention to whether a packet is part of an existing stream of traffic (i.e. it stores no information on connection "state"). Instead, it filters each packet based only on information contained in the packet itself (most commonly using a combination of the packet's source and destination address, its protocol, and, for TCP and UDP traffic, the port number).[6]

TCP and UDP protocols constitute most communication over the Internet, and because TCP and UDP traffic by convention uses well known ports for particular types of traffic, a "stateless" packet filter can distinguish between, and thus control, those types of traffic (such as web browsing, remote printing, email transmission, file transfer), unless the machines on each side of the packet filter are both using the same non-standard ports.[7]

Packet filtering firewalls work mainly on the first three layers of the OSI reference model, which means most of the work is done between the network and physical layers, with a little bit of peeking into the transport layer to figure out source and destination port numbers.[8] When a packet originates from the sender and filters through a firewall, the device checks for matches to any of the packet filtering rules that are configured in the firewall and drops or rejects the packet accordingly. When the packet passes through the firewall, it filters the packet on a protocol/port number basis (GSS). For example, if a rule in the firewall exists to block telnet access, then the firewall will block the TCP protocol for port number 23. [9]
[edit] Second generation: "stateful" filters
Main article: Stateful firewall

From 1989-1990 three colleagues from AT&T Bell Laboratories, Dave Presetto, Janardan Sharma, and Kshitij Nigam, developed the second generation of firewalls, calling them circuit level firewalls.

Second-generation firewalls, in addition to what first-generation look for, work up to layer 4 (transport layer) of the OSI model. Therefore they regard placement of each individual packet within the packet series. This technology is generally referred to as a stateful packet inspection as it maintains records of all connections passing through the firewall and is able to determine whether a packet is the start of a new connection, a part of an existing connection, or is an invalid packet. Though there is still a set of static rules in such a firewall, the state of a connection can itself be one of the criteria which trigger specific rules.

This type of firewall can actually be exploited by certain Denial-of-service attacks which can fill the connection tables with illegitimate connections.
[edit] Third generation: application layer
Main article: Application layer firewall

The key benefit of application layer filtering is that it can "understand" certain applications and protocols (such as File Transfer Protocol, DNS, or web browsing), and it can detect if an unwanted protocol is sneaking through on a non-standard port or if a protocol is being abused in any harmful way.

An application firewall is much more secure and reliable compared to packet filter firewalls because it works on all seven layers of the OSI model, from the application down to the physical Layer. This is similar to a packet filter firewall but here we can also filter information on the basis of content. Good examples of application firewalls are MS-ISA (Internet Security and Acceleration) server, McAfee Firewall Enterprise & Palo Alto PS Series firewalls. An application firewall can filter higher-layer protocols such as FTP, Telnet, DNS, DHCP, HTTP, TCP, UDP and TFTP (GSS). For example, if an organization wants to block, all the information related to "foo" then content filtering can be enabled on the firewall to block that particular word. Software-based firewalls (MS-ISA) are much slower than hardware based stateful firewalls but dedicated appliances (McAfee & Palo Alto) provide much higher performance levels for Application Inspection.

In 2009/2010 the focus of the most comprehensive firewall security vendors turned to expanding the list of applications such firewalls are aware of now covering hundreds and in some cases thousands of applications which can be identified automatically. Many of these applications can not only be blocked or allowed but manipulated by the more advanced firewall products to allow only certain functionality enabling network security administrations to give users functionality without enabling unnecessary vulnerabilities. As a consequence these advanced version of the "Third Generation" firewalls are being referred to as "Next Generation" and surpass the "Second Generation" firewall. It is expected that due to the nature of malicious communications this trend will have to continue to enable organizations to be truly secure.
[edit] Subsequent developments

In 1992, Bob Braden and Annette DeSchon at the University of Southern California (USC) were refining the concept of a firewall. The product known as "Visas" was the first system to have a visual integration interface with colors and icons, which could be easily implemented and accessed on a computer operating system such as Microsoft's Windows or Apple's MacOS. In 1994 an Israeli company called Check Point Software Technologies built this into readily available software known as FireWall-1.

The existing deep packet inspection functionality of modern firewalls can be shared by Intrusion-prevention systems (IPS).

Currently, the Middlebox Communication Working Group of the Internet Engineering Task Force (IETF) is working on standardizing protocols for managing firewalls and other middleboxes.

Another axis of development is about integrating identity of users into Firewall rules. Many firewalls provide such features by binding user identities to IP or MAC addresses, which is very approximate and can be easily turned around. The NuFW firewall provides real identity-based firewalling, by requesting the user's signature for each connection. authpf on BSD systems loads firewall rules dynamically per user, after authentication via SSH.
*http://technogeektips.wordpress.com/2011/03/29/is-your-password-hacked-protect-your-computer-from-hackers/
*http://en.wikipedia.org/wiki/Firewall_%28computing%29