View source for Firewall (computing)

==Physical and Virtual==
Firewalls can be either physical devices which sit on the network between the Internet and the internal client, or software systems which are installed onto the client's device.

===Hardware===
[[File:Firewall with DMZ.jpg|thumbnail|Conceptual network with one firewall and a DMZ]]
Hardware firewalls are generally considered the best front-line of defense. When an incoming connection reaches the protected network, the connection must first go through this hardware firewall.  If the connection is unwanted, it will generally be ignored.  In this case, the entity attempting to connect will simply have their request time out.  Some firewalls will outright reject the request, however, which is a less effective defense method. (If rejected outright, a potential attacker will know he has found an active device, whereas if the request is ignored, it will be more difficult to know if there is even a device to connect to.)<br />
To the outside world, there is only one device (the firewall) on the protected network. Even when a connection is permitted, the communication still passes through the firewall using a specified port.  Therefore, even active connections do not reveal the internal [[IP address]] of devices.<ref name="WhatIsMyIPAddress.com">“What is a Firewall?” WhatIsMyIPAddress.com, http://whatismyipaddress.com/firewall. Accessed 7 Sept. 2017.</ref><br />
However, many hardware firewalls (all but the newest types) often do not know what connections are being used for.  Most do not collect the packets and reassemble messages, so connections can be abused without the firewall knowing.  Even the ones which do attempt to analyze traffic can have difficulty understanding what is going on.<ref name="WhatIsMyIPAddress.com"/>
Some firewall configurations also offer what is called a "DMZ." This is a separate section of the network which is protected from the outside, but also cannot communicate directly with the inside network—it must go through another firewall (or the same one again) first. Sometimes certain servers and honeypots are placed here.

===Software===
Software firewalls are not typically considered a good first line of defense, but a good addition to a tiered defense system.  They digitally intercept and attempt to analyze traffic on the client's system. Since this kind of firewall operates on the [[OSI model]]'s application layer, it has an easier time of understanding what the communication link is being used for. Additionally, this host firewall filters traffic within the [[local area network]], meaning that unwanted traffic from other hosts behind the perimeter firewall can still be blocked.<ref>“Firewall Types.” TechNet, Microsoft, http://technet.microsoft.com/en-us/library/ff602917(v=ws.10).aspx. Accessed 7 Sept. 2017.</ref><br />
Host firewalls rely on the operating system in order to operate properly. This means that if the host system is infected or otherwise compromised, the software firewall can be prevented from blocking unwanted traffic.<ref name="WhatIsMyIPAddress.com"/>
<!--A disadvantage of software firewalls is that unwanted communication coming from the internet must in this case be blocked at the computer (or mobile device), so by this time, the communication has already gotten through the hardware firewall (assuming there is one). Although the attempt was still ignored, the external entity now knows there is at least one active device at that IP address.<ref name="WhatIsMyIPAddress.com">“What is a Firewall?” WhatIsMyIPAddress.com, whatismyipaddress.com/firewall. Accessed 7 Sept. 2017.</ref>-->