Increasing web traffic to their site is considered a good thing by most web site owners most of the time. However, this is not always the case. An overload of web traffic to a site can slow it down or cause it to become inaccessible. The reason for this is that a web server can handle only so much web traffic at a time. Too much traffic and the server becomes overloaded. This is a particular problem for small-scale websites, as their servers are generally not as powerful as those of larger sites. Larger sites generally use more than one server to handle the extra web traffic.
Causes of server overload vary. They may be caused by nothing more than the fact that a web site has suddenly become very popular, and there has not been enough time to update the server to deal with the extra web traffic. Advertisements for a site, the sites mention in the media, or widespread emails that link to or mention the site may all cause an upsurge in a site's popularity. These are sometimes referred to as the Slashdot effect, the Digg effect or the Reddit effect.
In some cases, server overload may not be so innocently caused. Sometimes outside persons use specific tactics to overload a server and make it unavailable to web users. This is known as a denial-of-service attack. Frequent targets for this type of attack include banks and credit card companies. One way of perpetrating a denial-of-service attack involves flooding the targeted web server with communication requests from outside. This malicious web traffic is sent in such volume that web traffic from legitimate users is effectively blocked as the server becomes overloaded. Denial-of-service attacks frequently force web servers to reset themselves, or take up so much computing power that the server is rendered ineffective.
The Internet Architecture Board (IAB) is the oversight committee in charge of Internet development. The Internet Architecture Board classifies a denial-of-service attack as a violation of their Internet proper use policy. Denial-of-service attacks are also considered illegal under many different national and international laws. The earliest known denial-of-service attack happened in January of 2001. The website Register.com was targeted, and the attack lasted for roughly one week before it was traced to its source and stopped. Other targets have included game servers, DNS root servers, social networking sites, P2P torrent sites, and Iranian, Georgian, and Irish government web servers.
Methods for preventing denial-of-service attacks include many of the technologies used already to monitor and regulate web traffic. These include firewalls, routers, switches, intrusion-prevention systems (IPS), and proactive testing. However, particularly powerful or complex denial-of-service attacks can overwhelm most firewalls and routers. In addition, if the denial-of-service attack lacks an associated signature, most intrusion-prevention systems will be rendered useless to stop the attack. Sometimes front-end hardware (which is intelligent hardware that takes effect before web traffic reaches the web server) can be useful for preventing denial-of-service attacks.