In 2003 University of Wisconsin Madison ("UoWM") began to suffer a massive influx of NTP traffic directed at its NTP server. This was not an intentional attack. I think it's interesting.


On 14th May 2003 UoWM's network started receiving a rapidly escalating deluge of IP traffic of the order initially 40,000 packets per second. The University staff responded pretty rapidly and identified sufficient characteristics in the traffic to block it in their ISP's border routers (1). It's characteristics were:

This looks very much like a distributed denial of service attack, for example implemented by a virus.

Traffic continued to escalate to the point that it exceeded 250,000 packets per second consistently dropped by WiscNet's border router. (1) explains the procedure that UoWM staff employed to determine the source, which makes good reading in itself. The outcome was that the packets came exclusively from certain models of Netgear domestic router. The router polls the hard coded address of UoWM's NTP server once every second until it gets a response. Since at least 250,000 other guys are doing the same thing, it has little chance of getting such a response. Thus the behaviour builds up into a massive deluge of NTP traffic, with little prospect of ever declining.


Initially UoWM's ISP, WiscNet filtered out the traffic. So the Internet core has been carrying all this stuff, but generally it never got answered. Netgear ultimately produced firmware patches which fixed the problem. However, the consumers who bought the items have to do this upgrade on their own initiative.


Netgear estimated around 700,000 affected devices were sold and this is consistent with the measurements taken by WiscNet and UoWM; UoWM estimate the half-life of these devices in the problematic state as five years (1). Is this the longest and most comprehensive denial of service attack the world has ever seen? Even Windows and Outlook viruses have shorter half lives than this - the average consumer is surely more likely to run Windows Update than to do something obscure like download firmware onto a router.

Bugs in passive-looking routers have historically been produced in business quantities, and given to enterprise IT staff, ISPs and telcos. Retail leverages massive economy of scale to produce huge numbers of units and give them at low cost to people who don't understand them at all. This means bugs get distributed much more widely and more rapidly, and are far less likely to get fixed in a hurry.


I own one of the affected routers and it works just fine for me. Needless to say I upgraded the flash and reconfigured the NTP server address in it at an early stage. I don't personally have a problem with Netgear or Nortel.

(1) is the definitive write up on this topic, but is much too long and graphical for e2.


1. "Flawed Routers Flood University of Wisconsin Internet Time Server", Dave Plonka, August 21, 2003 - University of Wisconsin-Madison

2. RFC 1305 "Network Time Protocol Version 3 - Specification, Implementation and Analysis" David L. Mills, March 1992

3. RFC 2030 "Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI" D. Mills, October 1996

4. Internet Assigned Numbers Authority (IANA) TCP and UDP Port Numbers registry

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