A denial-of-service (DoS) attack involves an attempt to disrupt the normal functioning of a website or web service. In a typical DoS attack, the attacker will overload a site’s server with requests for access far above the capacity of the site, meaning that legitimate requests cannot be processed. Other examples include: disrupting service to a specific person or system, flooding a network with traffic to prevent legitimate traffic from flowing, preventing a person from accessing a particular service and disrupting the connection between two specific machines, thereby interrupting a service. An e-mail bomb is another type of DoS attack wherein a large number of spam emails are sent in order to disable a mail server. In a distributed denial of service attack, the attacker uses several host computers to attack another computer or network.
Preventative measures against denial of service attacks include: maintaining a firewall, utilizing router filters, disabling unused networks, having a switch with automatic monitoring for DoS attacks and observing regular system performance to get a baseline and use it to gauge unusual activity. DoS attacks violate the rules set forth by internet service providers as well as the Internet Architecture Board’s (IAB) internet proper use policy. DoS attacks can disable single machines or whole networks and can cost an organization much time and money dealing with them.