The ever-popular Slashdot was unreachable for over an hour last evening due to massive amounts of traffic hitting its network. Normally Slashdot is known for bringing other sites down with the traffic it generates (the so-called Slashdot effect, or slashdotting).
Slashdot being Slashdot, they have been very transparent about it (which is a Good Thing) and they have posted an explanation on their website.
What is interesting is that the traffic wasn’t from an external source; it was generated by their own network equipment. Two switches had gone haywire and flooded their network with traffic (40 Gbit/s was going through their core switches), essentially creating an internal DoS attack.
Here is an explanation from Sourceforge’s chief network engineer (Sourceforge owns Slashdot):
Through the process of elimination I was finally able to isolate the problem down to a pair of switches… After shutting the downlink ports to those switches off, the network recovered and everything came back. I fully believe the switches in that cabinet are still sitting there attempting to send 20Gbit/sec of traffic out trying to do something — I just don’t know what yet. Luckily we don’t have any machines deployed on [that row in that cabinet] yet so no machines are offline. The network came back up around 10:10 PM EST.
A more detailed description of what happened is available over at Slashdot. It’s an interesting read.