Arunachalam’s Weblog

DISTRIBUTED DENIAL OF SERVICE (DDOS)

Short for denial-of-service attack, a type of attack on a network that is designed to bring the network to its knees by flooding it with useless traffic. Many DoS attacks, such as the Ping of Death and Teardrop attacks, exploit limitations in the TCP/IP protocols. For all known DoS attacks, there are software fixes that system administrators can install to limit the damage caused by the attacks. But, like viruses, new DoS attacks are constantly being dreamed up by hackers.

What is a Distributed Denial of Service (DDoS) attack?

Have you ever tried to make a telephone call but couldn’t because all the telephone circuits were busy? This may happen on a major holiday and often happens on Mother’s Day. In fact, in the United States, telephone companies used to air commercials on television and radio that suggested you avoid peak calling times by making your calls early or late in the day.

The reason you couldn’t get through is because the telephone system is designed to handle a limited number of calls at a time. That limit was determined by weighing the cost of having all calls get through all the time with the amount of traffic the system receives. If the total number of calls is always high, it makes economic sense for the telephone company to provide more capacity to match that demand. However, if the number of calls is low compared to the holiday peaks, then the telephone company will build networks that accommodate only the lower off-peak number of callers and advise their customers to avoid peak calling times. It’s a basic matter of supply and demand.

Imagine that an intruder wanted to attack the telephone system and make the system unusable by telephone customers. How would they do this? One way would be to make call after call in an attempt to make all circuits busy. This type of attack is called a denial of service, or DoS, attack. In essence, the intruder has caused the telephone system to deny service to its customers. It is not likely that one caller working alone can tie up all telephone circuits. To do that would require making as many calls as possible from as many telephones as possible.