Who does not know the story of the indestructible Internet that survived even a nuclear attack. It is not wrong, because the network was developed to be as fail-safe as possible.

Nevertheless, it happened to the day exactly 40 years to the big crash. At the 27. October 1980 the Internet forerunner Arpanet had to be switched off and restarted, for the first time after 11 Years of operation. The research network of the US Department of Defense was idle for four long hours because a technical defect had triggered a “Denial of Service” (DoS). 50 network nodes were affected by the failure.

In this section we always present astonishing, impressive, informative and funny figures from the fields of IT, science, art, business, politics and of course mathematics on Tuesdays.

The extreme requirements for survivability The on 29. Arpanet, launched in October 1969, handled the communication using special computers manufactured by Bolt, Beranek and Newman (BBN). These communication computers were called Interface Message Processors (IMP) when they connected host computers or Terminal Interface Message Processors (TIP) when only terminals were connected to them. For the transmission of data packets, these computers stored routing tables, which recorded how the host computers could be reached via which IMPs.

The routing of the data packets was carried out according to the principle of hot potato routing, which Paul Baran wrote in the year 1960 in his text “Reliable Digital Communication Systems Using Unrealiable Repeater Nodes. ”With this hot potato routing, the data packets were transmitted to the next node, determined from the response times of the individual nodes Network node the traffic could be rerouted immediately.

With regard to his idea, Baran noted that such a flexible network of connected computers is reasonably fail-safe against an enemy attack: “But a real-life system is a collection of compromises, and this system is no exception. The author believes, though, that it represents an acceptable price to have to pay for a national communication system able to meet the extreme demands of survivability in the face of a determined enemy. ” ( “But in real life a system is a collection of compromises and this is no exception. However, the author believes that it is an acceptable price to be paid for a national communication system that has to meet the extreme demands of survivability in the face of a determined enemy. “)

Restart of all communication computers required On 27 October the network failed. This was first noticed at the IMP 50, who sent a faulty routing table to other IMPs, which saved it and then failed for their part without forwarding the table Try single I. Restarting MPs failed because the actual error was initially not recognized: IMP 29 had a hardware -Defect that caused a bit to “slip”, as BBN engineer Eric C. Rosen wrote in his detailed analysis of the incident. As a result, the routing table contained incorrect entries for the most recent saved data of the available nodes. The solution to this resulting “Denial of Service” was to restart all communication computers and repair IMP 29 had to. After four hours, the Arpanet was able to resume operations. For Rosen it was “endless minutes” during which there was hectic phone calls, as the BBN company chronicle says.

The Arpanet in Ok